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Moto Guzzi V700, V7 Special, Ambassador, 850 GT, Eldorado, 850 California - Carburetion
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Table of contents
- Accelerator pump check valve/ball
- Air box
- Air filters
- Amal carburetor information
- Carburetor balancing/synchronizing
- Carburetor balancing/synchronizing without carb sticks
- Carburetor float bowls - checking for leaks
- Carburetor rebuild - Dell'Orto VHB
- Carburetor - setting them up
- Carburetor - single manifold
- Intake manifolds
- O-ring for sealing the carburetor enricher cable holder to the carburetor body
- Pinging
Accelerator pump check valve/ball
Updated: Prior to 2007 Dec 11
There is a little ball inside the accelerator pump that serves as a check valve. The ball is solid and made out of some sort of plastic that is very resistant to nasty chemicals. I've even accidentally let them soak in carb cleaner only to find no damage. They seem to last forever, but if you need to check yours to see if it has worn, the size should be 3.175 mm or 0.125" or 1/8".
Air box
Updated: Prior to 2007 Dec 11
The stock air box could have been designed better than it was. Although a little inconvenient from a maintenance perspective, the real problem is non-filtered air leaks. The rubber boot that connects each carburetor to the airbox deteriorates over time and does not create a tight seal, thus allowing dirt into the engine.
Greg Field provided these instructions to me:
I just silicone the boot to the box. Silicone it, weight the boot with something heavy enough to smoosh the boot's rim to the airbox, and leave the weight in place for 24 hour until the silicone is dry.
These boxes are [very difficult] to install if you don't do it right. The trick is to detach the left carb by undoing the three screws holding the manifold to the head. Put the box in place, worming the right boot spigot over the right carb's inlet. Then worm the left carb's intake into the boot, and tighten down the three manifold screws to affix the carb. Then "wiggle" everything to its best alignment and so there is minimal twisting and puckering of the rubber of the boot. Insert and tighten the three airbox screws. Tighten the hose clamps to the carbs. Also, you may want to mess with the jetting some. I found that 40 pilots and 140 mains worked better than the stock jets. Better gas mileage, too, and no fouled plugs.
I do not like k&ns because I do not believe they filter air very well. They do flow air very well and strain out the big stuff, though. The stock air filter is probably not much if any better at catching grit than the k&n individual elements or single element for the airbox would be. If you hold either up to the light, you can see right through. And the stock element doesn't even get oil to help catch stuff. Unfortunately, there really isn't a better option for the loops (a paper element for the stock box would be ideal), so I ran a k&n element in the stock airbox.
Why the box? It keeps the k&ns out of the sun, so they stay oily longer (really, they do not filter at all if not wet, and 80 percent of the individual pods I see on bikes are dry as a desert) and clean longer because dust and dirt settles on the box rather than the exposed filter. Also, it significantly reduces intake noise. This was important to me.
The airbox may also reduce performance on some bikes. On mine, it seems not to have, though I never did any dyno runs to confirm that. My bike acquired a reputation for going faster than most people really wanted to go, so I'm pretty sure the airbox wasn't hurting me much.
Greg Field's instructions were very helpful when I first installed the stock air box on my Ambassador. Here are a few additional notes from my experience:
- When I first siliconed the boot in place, I weighed it down, but not enough. Only the edge got "glued" to the airbox plate and it broke off when I first tried to insert the velocity stack into it. The second time I really weighed it down so that the boot lip was flattened against the plate. I haven't had any trouble yet.
- I've found that I can remove either carb without disturbing the airbox (and leaving the boot in place) simply by removing the three bolts that secure the intake manifold to the head.
- I've not noticed any performance decrease on my Ambo. On the contrary, I'm quite certain it runs stronger with the velocity stacks than without. I don't believe my air intake is restricted any more with the UFI than with the K&N pods. No data here, just my opinion.
- The box does make things quieter…and let's me hear other sounds the bike is making…I like that.
Air filters
Updated: 2009 Sep 22
There really aren't very many choices when it comes to air filters for the V700, Ambassador, and Eldorado motorcycles. As far as I know, we are limited to the following:
- Air filters for the stock air box:
- UFI part number MG# 12113600
- K&N part number MG-0100
- Air filters that replace the stock air box:
- K&N part number R-0642 - This filter must be clamped directly to the carburetor body…with the stock velocity stacks removed.
- K&N part number RU-2450 - This filter may be clamped directly to the velocity stacks that originally came on the Moto Guzzi Convert, SP1000, G5, and T3 models. Alternatively, the stock velocity stacks may be turned down on a lathe and made to work (I've not done this, but I've heard it will work). If using pod filters, this set up (with the later model velocity stacks that screw right into the VHB carbs) is my favorite. The fit is good, the clamp is secure, the important velocity stack is kept, and the slightly smaller physical size of the filter allows it to fit better in the available space.
- K&N part number MG-2640 - This is a single filter that is clamped directly to both velocity stacks that originally came on the Moto Guzzi Convert, SP1000, G5, and T3 models. Alternatively, the stock velocity stacks may be turned down on a lathe and made to work (I've not done this, but I've heard it will work). K&N lists this filter as a suitable replacement for the 1000 cc G5, SP, and Convert. Thanks to Paul Linn for bringing this alternative to my attention.
- UNI MG-1 - This filter can be clamped directly to the stock velocity stacks.
There is nothing wrong with the stock UFI filter, but it would be nice if a quality generic replacement were available. The "performance" choice alternatives are pretty disappointing as K&N and UNI filters - although highly touted by their respective marketing departments - flow very slightly better but filter out less than paper filters. For interesting reading, check out:
If you are aware of any additional air filters that fit (especially filters that will fit the stock air box), please let me know by sending an email to greg>at<thisoldtractor.com
Amal carburetor information
Updated: Prior to 2007 Dec 11
Contributed by Joe Jump on the Yahoo! Loopframe_Guzzi news group.
Joe describes the Amal carburetors used on the late Eldorado models.
Those Amals are 930's - same stuff used on Nortons, BSAs and Triumphs post 1967-68. The numbers following the dash (after 930) defines the specifics with respect to main/idle jets, slide cut-away and needle taper/position. Don't worry about that - just replace hat you remove with the same parts which have individual IDs. The nylon screw that broke off in your hand is a bowl drain/main jet access screw. Parts for these are plentiful. There is a shop somewhere in Florida (Tampa area) called MAP (Made Across the Pond). They will have everything you would need. Do a Google search. And I'm sure you could find the parts in Daytona if you looked in the Yellow Pages.
I run 930s on my Norton. I had the carbs done by AMR in Arizona. Instead of sleeving the slide, they bored the body to accept Mikuni slides which are hard chrome plated brass. You loose the choke but I've found them to be unnecessary with the ticklers. I've put 20k miles on them and they still work great. Amal needle jets and needles are known to wear kinda fast - recommended replacement every 10k miles for precise metering.
One other thing to watch - the float hinge pin can vibrate (British twin) and actually wear an indentation into the bowl gasket. When this happens, the float can buzz around a bit more than normal and cause the fuel in the bowl to splash out through the tickler button and perhaps affect mixture too (too high of a fuel level in the bowl). I had this problem and resolved it by slightly pinching the tabs in the bowl adjacent to the float hinge pin to keep it captive in it's slot.
Lots of people curse Amals. They are simple units and once they are sorted with dissimilar metals between the body and the slide, updated with viton tipped float needles, and the idle jet is opened up/cleaned (bread wrapper twist tie and Gummout spray works great for this), they work good and last a long time. Just my opinion.
Carburetor balancing/synchronizing
Updated: Prior to 2007 Dec 11
Contributed by Patrick Hayes on the Yahoo! Loopframe_Guzzi news group.
I presume you have the more common Dell’Orto square slide carbs. There are some early loops with round slide Amal carbs and these comments will be all wrong for them.
I presume you have plenty of slack in the "choke" cables so that they close fully and are NOT hanging off the end of the taut cables.
I presume you have vacuum tap ports on your intake manifolds. Again, early loops did not have these ports. They can be added easily. Later loops all had them.
I sure hope you have some form of vacuum measuring tool. Forget about doing it by ear, or feel, or counting rotations before stall, or sticking toothpicks in the carb throats. Those techniques are all horribly crude as related to vacuum measurement.
I hope you do not try to do this with analog gauges. It is impossible. It is far easier to read and far more intuitive if you use vertical column manometer vacuum measuring devices.
I like CarbStix the best, but they do have the danger of spilling toxic mercury. Mine are 25 years old and intact (tap wood). There are modern copies which use steel rods instead of mercury. That would be my choice if I were starting anew. There is an electronic TwinMax. Not as intuitive. But very small and portable as long as you learn how to read it. For about $2 you can make a tool out of fish tank air hose and ATF oil.
Get the bike running and warm and hook up the vacuum.
Begin by setting the idle speed. This is the big, exposed, knurled screw. DO NOT TURN THE SCREW!!! When the slides rest on the pointed tips of these screws there is a lot of contact load. You can damage the screw or the slide. Even for slight adjustments, always crack the throttle ever-so-slightly as you turn this screw so that it is not loaded while turning.
You probably will not have equal idle vacuum readings. They certainly won't be steady as they pulse up and down with each cylinder suction. You can visually and mentally average out where there center positions are. Whichever column is averaging lower, that side is open too far in relation to the other and that cylinder is working harder than the other. Depending on your idle speed, you can choose to slow down the harder working side (and its mercury column will now rise slightly on average) or you can open and accelerate the non working side. It doesn't matter if you choose to open one or close the other, you need to get them pulsing in average parallel. Remember to crack the throttle as you adjust this screw. Counterclockwise drops the slide, slows the cylinder, and raises the mercury column. Clockwise is opposite.
Once you have the idle speeds equal (showing equal pulsing vacuum) you can adjust the mixture. This is the smaller, recessed screw. Turn it inwards clockwise until you hear the motor stumble. Turn it outward counterclockwise until the stumble eases. Back out at least an additional 1/4 turn and maybe even 1/2 turn from this non-stumble point. You want the idles a little bit rich.
Go back and look at your idle speed balance as it may have been altered. Repeat the above two paragraphs.
Now to acceleration balance. Many will write to you about mid-range and high range balance. Hooey!! At big throttle openings and higher rpms, your engine cannot possibly detect minor vacuum imbalances. The place where it is CRITICALLY important is at a stop light or traffic light when you are feathering the clutch and adding throttle to accelerate away. Cylinder imbalance is one of the biggest aggravators of the famous loopframe grabby clutch. It doesn't grab at 75mph, it grabs at 3mph when you are pulling away from a light.
If you did the above idle work accurately, the two carbs are drawing equally at idle and the two cylinders are producing equal power pulses. Now, when you open the throttle it becomes critically important that BOTH sides open and draw simultaneously and both cylinders increase their power output equally. Crack the throttle open. Not a WFO twist, just a 10% crack. Look at the vacuum columns. Just as you crack the throttle, one side suddenly drops or loses vacuum before the other. That side has a tighter cable and is starting to work harder first. Again, you can either loosen that cable or tighten the other.
The effect you want is two equally pulsing vacuum columns at idle and then they both drop simultaneously and equally as you begin to open the throttle. Everything else is superfluous.
You will never get perfection. You are talking lots of sliding parts in the carburetor and the cables and the throttle handle. Its all sloppy stuff and it will look a little different each time you blip the throttle. You will be amazed at how nicely the motor runs when it is in sync and how easily or quickly it goes out of sync. You will soon learn what it looks like to have these columns perfect and also what it looks like to have these columns close enough for everyday smooth operation without being fanatic about it.
Carburetor balancing/synchronizing without carb sticks
Updated: Prior to 2007 Dec 11
Even if you don't have mercury carb sticks, you can still do a pretty good job of synchronizing the carbs by hand (both of the following methods are performed with the engine off). And, since the factory didn't include bosses in the intake manifolds to which mercury carb stick could be attached, they expected (and provided explicit instructions in the manual) the carbs to be synced without them.
One method (recommended by the factory) is to put a thumb and a finger into each air inlet and feel when each slider starts to move when you very slowly open the throttle. The goal is to make both sliders open at exactly the same time.
An easier and more sensitive method is to create two 6 inch straight pieces of wire. Place each wire in the air inlet with the end under the slider. The other end of each wire should come pretty close to meeting in the middle. Now, when you open the slider very slowly, you can simply view which wire moves first. Thanks to John Schwartz for this tip.
Regardless of which method you choose, use the throttle cable adjustment screw to synchronize the movement.
Carburetor float bowls - checking for leaks
Updated: 2008 Apr 25
Contributed by John Prusnek on the Yahoo! Loopframe_Guzzi news group. In John's own words:
Another way to test floats for leaks is to put them in the freezer overnight, then submerge them in a cup of hot water, look for bubbles as the air inside expands.
Carburetor rebuild - Dell'Orto VHB
Updated: 2008 Nov 10
This is a series of photos I took during the assembly of the carburetors on my I-Convert project bike. These are Dell'Orto VHB 30 carburetors. But, the procedure is 100% identical for Dell'Orto VHB 29 carburetors. Thanks to Charlie Mullendore, Robert Hawkes, Steve Farris, and Adam S. for making helpful suggestions for improvement.
It is a very good idea to work on one carburetor at a time. That way, you can refer to the assembled carburetor as a pattern.
Parts needed
Consumable parts I always replace:
Consumable parts I replace depending on condition:
- (2) Choke (enricher) plungers (these are cheap enough that I always have them on hand)
- (2) Float needles (these are cheap enough that I always have them on hand)
- (2) Floats (I order these if I need them. I do not replace unless I detect leaks in the originals.)
Disassembly
Disassembly is pretty much the reversal of assembly. So, just start from the last photo, and work your way up to the top.
Cleaning
Prior to these photos being taken, I had completely disassembled both carburetors and soaked all of the metal parts in a bucket of carb cleaner. With the parts out of the carb cleaner, I thoroughly rinsed them in a bucket of rubbing alcohol. Rubbing alcohol dries very quickly, leaves no residue, and - in my experience - does a good job of neutralizing the carb cleaner (though I'm not a chemist and haven't a clue whether or not alcohol neutralizes the carb cleaner, or simply dilutes it to a point where it doesn't matter). Use gasoline if you like, but I prefer rubbing alcohol. Even after cleaning, some of the brass parts appear discolored. Not to worry, they are clean and the discoloration really doesn't matter, as they will discolor again soon enough. But, if you like, a quick turn at a fine wire wheel (not coarse or heavy) will polish them up nicely. Just be cautious around the openings so that they are not enlarged and DO NOT WIRE WHEEL THE TAPERED NEEDLE AT ALL.
As an alternative, after soaking the parts in carburetor cleaner, Charlie Mullendore rinses them thoroughly in cold water, then hot water, and finally sprays through all of the passages with Berkebile 2+2 Gum Cutter.
Assembly
A bunch of carburetor parts!
Clean the jets
Here is a strand of wire I've pulled from a wire brush. The wire is stiff and strong, yet small enough to easily fit through the smallest passageways.
The strand of wire next to a jet.
Insert the wire through the jet and spin the jet around a few times with your finger. Repeat with all the holes in all the jets: both main jets, both idle jets, both choke (enricher) jets, and both atomizers. Quick, simple, done. I learned this tip from my Dad, Tom Bender.
Clean the passageways
Blowing compressed air through the idle jet passage…
…you should feel air escaping from (a) the mixture screw hole, (b) two tiny holes in the throat of the carb (you've shown one - there's another closer to the atomizer hole IIRC) and (c) a small port at the inlet near the threads for the 'velocity stack' (thanks to Charlie Mullendore for assisting in identifying air escape locations).
Blowing compressed air through the main jet passage…
…you should feel air escaping from this location.
Blowing compressed air through the mixture screw location.
Blowing air through the vent…
…you should feel air escaping from this location AND…
…you should feel air escaping from this location.
Blowing air through the choke (enricher) jet passage…
…you should feel air escaping from this location AND…
…you should feel air escaping from this location.
Blowing air through the vent…
…you should feel air escaping from this location.
Blowing air through the choke (enricher) jet passageway in the float bowl…
…you should feel air escaping from this location.
Accelerator pump, atomizer, main jet
Note: Some prefer not to disassemble the accelerator pump piston; choosing instead to consider it perfectly functional if they hear the plastic ball bearing rattle inside the accelerator pump piston.
This is the small plastic ball bearing.
Place it inside the accelerator pump piston.
Screw the spring holder into the pump piston.
I keep the pump piston from rotating with a pair of snap ring pliers.
Then I give the spring holder a bit of a snug with a screwdriver. It doesn't need much, just a wee little bit.
Now insert the assembled pump piston into the accelerator pump body.
Place the spring on the end of the spring holder.
Slide it into place and screw on the main jet holder.
Tighten the main jet holder to the accelerator pump body with a pair of wrenches. Just a light snug. There is no need for much torque at all here.
Now place the main jet into the main jet holder.
Secure the main jet in place with a wrench and a screwdriver. Just a light snug. Don't get carried away and strip the threads, etc.
Place the atomizer into the main jet passageway.
Set the carburetor on end and let the atomizer fall to the bottom.
Use a wooden popsicle stick to push the atomizer into place. The wood is soft and you will avoid damaging the atomizer. I learned this tip from Charlie Mullendore.
You'll know it is seated properly when you can see it protruding here. Note: I am using the ice pick as a pointer, I am not poking anything.
Insert the accelerator pump assembly into the main jet passageway.
And tighten with a wrench. Just a light snug. There is no need to start weight lifting just to assemble Dell'Orto carburetors.
Idle jet
Insert the idle jet into its passageway.
And tighten with a screwdriver. Just a light snug. You should be getting a very clear picture by now that nothing on the carburetor requires much torque.
Choke (enricher) jet
Here is the contents of the carburetor kit. Notice that there are 3 small o-rings. The middle sized one is used for the choke (enricher) jet.
I position the o-ring like this, and then push it over the top. I've found this method easier than trying to bring it up from the other end. Charlie Mullendore prefers to slip it up over the threaded end first, then work it over the larger end into the groove. Either way works fine. Charlie recommends using silicone spray on the o-ring to help it slip on easier.
Here the o-ring is in place on the choke (enricher) jet.
Insert the choke (enricher) jet into the body of the carburetor.
And tighten with a screwdriver. Just a light snug.
Float, float needle, float pivot pin
This is the float, float pivot pin, and float needle.
Place the float needle into the clip on the float.
Insert the float needle into the carburetor body and position the float between the hinges.
Insert the float pivot pin.
And push it through to the other side. USE YOUR FINGERS ONLY! There is no need whatsoever for the float pivot pin to be hammered or wedged into place. If the splined end gets stuck too far in, the pin is very difficult to remove. The float bowl will prevent the pin from falling out, anyway.
Float bowl, float bowl nut
Now it is time to fit the large o-ring to the float bowl. It is easier to do if the o-ring and float bowl are warm. So, if you are working in the winter months, just take it inside the house and let it warm up.
Start in this corner.
Then do this corner.
Then do this corner.
Up to now, fitting the o-ring has been easy. Now comes the tricky corner. If you roll the o-ring into place, it will immediately try to roll back out. You can fight it for eternity (or until the o-ring breaks) and it'll still want to roll out. The trick is to roll it in the opposite direction just a bit using your thumb and forefinger, and then roll it into place. This 'neutralizes' any roll and the o-ring will stay nicely in place.
Fit the float bowl to the carb. You may need to wiggle it in place a bit as you seat the o-ring on the choke (enricher) jet.
The float bowl nut and gasket.
Fit the gasket to the float bowl nut. Charlie Mullendore uses a little dielectric grease on the gasket to help it tighten down easier.
Screw the float bowl nut in place.
And tighten with a wrench. A heavy snug is good here. You want the float bowl tight. But again, we are dealing with soft metals, so take it easy.
Idle speed screw
The idle speed screw and spring.
Place the spring on the idle speed screw.
Insert the idle speed screw and spring into the body of the carburetor. Tighten it down a bit.
You can see the end of the idle speed screw protruding through to the inside.
Mixture screw
The mixture screw and spring.
Place the spring on the mixture screw.
Insert the mixture speed screw and spring into the body of the carburetor. Screw it in until it bottoms out. DO NOT OVERTIGHTEN! Just bottom it out gently. Then, back it out the number of turns specified by the workshop manual (generally 1 1/2 - 2 turns for the left carburetor and 1 3/4 - 2 1/4 turns for the right carb).
Slide and tapered needle
The slide and tapered needle.
Insert the top of the tapered needle into the bottom of the slide and push it through. I do it this way so that I avoid any potential damage to the tapered needle.
Place the needle clip in the position specified by the workshop manual (generally the middle).
Insert the slide complete with tapered needle into the body of the carburetor. Notice that the large flat area of the slide must face the intake manifold, not the air filter.
Carburetor top and throttle return spring
The carburetor top and gasket.
Fit the gasket to the carburetor top.
I like to slather on some grease in a hopeless attempt to keep the gaskets from shrinking.
Insert the bolts complete with wave washers.
Insert the cable adjuster complete with jam nut.
Here is the throttle return spring. Notice that one end has the wire bent in toward the middle.
Insert the bent end into the carburetor top. This holds the spring in place.
Now place the carburetor top complete with spring onto the top of the carburetor. Note that the cable adjuster is positioned nearest the intake manifold, not the air filter.
Hold the top down on top of the carburetor body and screw the top in place. DO NOT OVERTIGHTEN THESE BOLTS! They only take a light snug and are far too easy to strip. Be careful. I will also reemphasize, hold the top in its finished position and then screw the bolts in place. That is, don't use the bolts to pull the top into position.
Choke (enricher) assembly
Here is the choke (enricher) assembly.
This is the sealing surface of the choke (enricher) plungers. New plungers have a flat sealing surface that has not been indented by years of constant spring pressure. While these may function fine, I will not reuse them. New ones are inexpensive and easily replaced. Adam S. recommends the following technique to extend the life of the plungers: One trick that I use, and it works fine, is to remove the rubber plug from the choke plunger, using a small dental pick. Flip the rubber piece over and you'll have a nice new sealing surface.
The body uses the largest of the small o-rings.
And fits in place like so.
Insert the assembly like this.
And secure in place with the screw.
Insert the cable adjuster.
Place a rubber dust cap on the cable adjuster for the choke (enricher).
And place the other rubber dust cap on the cable adjuster for the throttle.
Banjo fitting and filter
Fit a new plastic fuel filter to the carburetor fuel inlet. Note: the filters do not come with the carburetor kit and must be ordered separately.
Here it is in place. The center of the filter usually needs to be pushed in place over the protrusion in the carburetor inlet.
Fit the banjo in place.
Select the smallest of the fiber washers.
Place it on the bolt.
Insert the bolt into the carburetor body.
And tighten to secure. You'll want to snug the bolt, but not over tighten. If fuel leaks from this location when you hook up the tank, check a couple things. (1) Did you fit a new plastic filter? If not fit one. (2) Is the banjo fitting bottoming out before it makes sealing contact with the plastic filter? I had one that did this. Drove me crazy until I figured it out. I fit a new banjo and it sealed immediately. Do be careful not to over tighten these bolts. The threads are somewhat easily striped. It is much easier (and cheaper) to replace the plastic filter and banjo than to deal with buggered threads. JUST ANOTHER QUARTER TURN IS NOT YOUR FRIEND!
Carburetor - setting them up
Updated: 2008 Apr 25
Thanks to Charlie Mullendore of Antietam Classic Cycle for providing the following information on the Yahoo! Loopframe_Guzzi news group. In Charlie's own words:
I don't use the old "pull the plug wire off" method to set the carbs. Here's the (likely a bit backasswards) way I do it instead:
If you don't have vacuum ports to hook some sort of balancing device to, you'll need to remove the airbox and sync. the carbs by measuring the height of the slides (from the bottom of the slide to the base of the carb throat). You can use drill bits or other similar objects as measuring tools.
As a "base setting", I usually adjust the throttle stop screws (on the square area of the carb body) until there's an approx. 10mm wide (semi-circular) opening showing at the front (towards the engine) of the slide when I look into the carb throat. Measure the slide height at the back (towards the filter) with a drill bit and set both carbs the same.
Make sure you have a little (3 mm or so) slack in the throttle cables where they go into the carb. top. If your throttle twistgrip has a "friction screw" that you can turn in to hold the throttle open, turn it in to do just that. Or if not, figure some other means of holding the throttle open (assistant, duct tape, etc.). Open the throttle slightly and acting on the cable adjusters on the carbs tops, set both slides to the same height. Make sure you still have slack afterwards.
Turn the idle mixture screw (small screw, recessed into the carb body, near the float bowl)in until it seats lightly and then back the left one out 1 1/2 turns and the right one out 1 3/4 turns.
Release the throttle holding device, start the engine and let it warm up. If it's idling too high, turn each throttle stop screw out an eighth of a turn. If too low, turn them in an eighth of a turn each. Try to turn them in or out precisely the same amount to avoid disturbing the balance you set earlier. Next turn each idle mixture screw in until the engine speed drops (listen carefully as it can sometimes be difficult to tell) and then back it out 1/2 turn. If necessary, adjust the throttle stop screws again to achieve the desired idle speed.
Alrighty then. Clear as mud? Best job I can do right now with only 5 hours of sleep last night and after doing some sort of weird triathlon today (ride 4.5 hrs./200 miles to lunch in Keysville, VA, ride 5 hrs./210 miles home, push mow grass for an hour!).
Carburetor - single manifold
Updated: 2010 Aug 01
Sonny Angel setup
Single carburetor manifold for a round fin Moto Guzzi. Photo courtesy of John Boettcher
Max setup
Thanks to John Engle for sending me these photos and information in a private email.
Single carburetor setup on a Moto Guzzi Ambassador. Work done by Max, a machinist from Clever, MO. Ace Mallot knows Max and reports that the single carburetor setup works well. A standard Dell’Orto VHB 29 carburetor is used. Photo courtesy of John Engle.
Max's Moto Guzzi (also with a single carburetor). Photo courtesy of John Engle.
Unknown setup
Thanks to Tom Short for provided these pictures.
Single carburetor setup on a Moto Guzzi Ambassador. Photo courtesy of Tom Short.
Single carburetor setup on a Moto Guzzi Ambassador. Photo courtesy of Tom Short.
Single carburetor setup on a Moto Guzzi Ambassador. Photo courtesy of Tom Short.
Single carburetor setup on a Moto Guzzi Ambassador. Photo courtesy of Tom Short.
Single carburetor setup on a Moto Guzzi Ambassador. Photo courtesy of Tom Short.
Intake manifolds
Updated: 2010 Feb 10
VHB Carburetors
The intake manifolds are not the same for each side. Since the cylinders are in different positions on the crankshaft, the intake manifolds are slightly different in order to partially compensate for this positioning difference (the rubber boot that connects the velocity stacks to the air box take up the remaining difference). These photos should make it pretty clear which side is which. "S" markings mount on the left side of the motorcycle, "D" markings mount on the right side of the motorcycle.
S on left, D on right
Close up view of markings
S on left, D on right
D is taller than S
S near, D far
D near, S far
Adorning a toothpick cactus
O-ring for sealing the carburetor enricher cable holder to the carburetor body
Updated: 2009 Jul 20
On some VHB carbs (certainly not all), the aluminum holders for the enricher cables have a groove to accept a small o-ring. The purpose of this o-ring is to prevent foreign material (e.g., rain) from entering the carburetor. This size of this o-ring is 1 mm thick with an inside diameter of 8 mm and an outside diameter of 10 mm. Thanks to Jon Sefcek for sending me this information in a private communication.
Pinging
Updated: Prior to 2007 Dec 11
Contributed by Patrick Hayes on the Yahoo! Loopframe_Guzzi news group.
First lets understand what a "ping" is. The compressed air/fuel mixture in your cylinder does not "explode". Rather, it burns at a very fast rate. The flame starts at the tip of the spark plug and progresses outward, like ripples in a pond, until it reaches the cylinder walls and consumes all of the mixture. This progressive flame can be measured and seen. A famous Dr. Diesel put glass windows into cylinder heads about 110 years ago to confirm this. The ripples of pressure ahead of the flame wave cause the mixture to get a little more compressed than just the cylinder compression. Increase it enough, and the remaining mixture spontaneously and completely 'explodes' by adiabatic pressure, ahead of the intended flame front. This can be heard as a 'ping'. Generates lots of instant heat and can melt aluminum. Any of that in your motor? It creates a snowball effect. The pinging makes the engine hotter. The engine pre-heats the air/fuel mixture a little more before it is sparked. Once sparked, the the pre-heated mixture burns more rapidly than the engineer intended it to. It pings and generates more heat again.
The ignition timing curve is designed to allow the flame front to propagate smoothly so that the piston is already starting down and relieving pressure as the flame reaches maximum internal pressure. That's fine on the drawing board. You can do a lot of things to screw up the design.
The progress of the flame is also partially controlled by the nature of the fuel. Premium or Hi Test fuel is designed to burn more slowly so that the flame front is not effected quite so much by high compression motors. Contrary to popular opinion, regular fuel burns faster than premium fuel.
Are you burning 'regular' fuel? Don't do it.
Realize that the ignition timing was designed in the 60's when we could buy 96 octane fuel. Now the best we have is 91. So, the designed ignition timing is too far advanced for the modern fuel. Try backing off the timing by 1° or 2°. You may sacrifice a little performance, but you have to adapt your old motor to the modern fuel reality.
Probably the worst condition for pinging is to contaminate the air/fuel mixture with oil. Minuscule amounts of oil. Far less than you could measure or see burn as smoke. Guzzis have no seals on the valve guides. After a period of wear, they start to bleed some oil past the intake valve stem on suction. Suddenly, your expensive 91 Premium fuel is probably burning at an equivalent of 84 cheapo regular. Ping. When was the last time you did a complete valve job and exchanged the guides and/or valves. My bet is that 40K miles is about the life limit with about the last half of that life passing excess oil.