Subject: Re: Help! Carb adjustments
Author: Patrick Hayes
Date: Jan 16, 2005, 11:37 AM
Post ID: 1718219567
Mike Walker wrote:
| The throttle cables are new and lubed and slippery and do not seem to be binding. There is just enough free play at the throttle grip to prevent the throttle cable sheath from slipping out of the little 'port' at the end of the little chain device that translates the rotational motion of the throttle grip into the back and forth motion of the cable. There is about 4mm of play there. |
That's fine at the upper end. But it sounds like you have a one-to-two
throttle setup. Under the tank is a splitting device. This takes the
one throttle cable from your hand and gives you two throttle cables at
the carbs. At idle, is there freeplay where the throttle cables enter
the carbs.
You have not mentioned "choke" or enrichener cables as yet. It is a
VERY common mistake for people to set these snug and prevent the
enricheners from sealing against their seats. Do you have several mm of
play in these cables at the carburetor.
Sometimes it is hard to see or feel on both sets of cables because the
little rubber boots mask the freepay effect. Slide the boots up the
cables so they are not participating and then check for freeplay on all
four cables at the carbs.
| restarted quickly enough. Fortunately, because I was surrounded by rich Harley bikers with fabulous paint jobs! |
F the paintjobs!
| I'm not quite sure how I should adjust the carbs once the digital balancer is hooked up. I suppose I should set the pilot screws to the factory setting and adjust the idle screw and the throttle slide adjustments to get the vaccuum even between the two carbs? |
You will get plenty of advice and debate. Here's my success for years.
Basically that's it. I will presume for now that you have square slide
Dell'Orto carbs. (some loops came with round Amals). Get the bike
running and warmed up. You will be running the motor for awhile without
driving, so set up a fan in front to keep the cylinders mildly cooled.
I don't know what "digital" balancer your friend has unless it may be a
Twin-Max. I have one, but for simplicity and ease I really prefer the
old mercury Carbstix manometer. You can make an almost free set from
fish tank hose and ATF, or Motion Pro has a set with stainless steel
slider display instead of mercury. Regardless of which you have:
First, get the bike running and warm and able to idle at least roughly.
Adjust the two IDLE SPEED, larger exposed, knurled screws to get the
vacuum approximately equal at idle. CAUTION: These screws have tender,
tapered tips and they are hitting against a ramp on the soft internal
lifting slide. If you just turn the screw you risk damage to one or the
other. Blip the throttle ever-so-slightly to suspend the slides on the
cable and take the load OFF of the screw tips before you turn them
either way.
Second, once you can maintain an idle, go at the smaller, recessed idle
mixture screws. Screw them in gently to lean the mixture until you
start to hear an rpm reduction and see a slight change in the vacuum.
Back out until it steadies and back an extra quarter to half after that.
Third, seeing that you are idling smoothly and equally on both sides,
just blip the throttle slightly. In theory, as the slide lifts, the
vacuum in each intake manifold will be reduced. If you have vertical
column manometer, both columns begin to drop quite dramatically.
Usually the DO NOT. One side drops before the other as its slide gets
lifted off idle first. When you see this disparity in column drop, you
adjust the throttle cable AT THE CARB so that the earlier opening side
gets slackened and retarded a bit or the later opening side gets
tightened or advanced a little bit. Keep blipping the throttle and
tinkering with the cables until BOTH sides lift off of their idle rests
simultaneously. If you have a Twin-Max, then you will see a lateral
deflection in pulsing of the display needle. You need to see that
needle remain pulsing in the center as you blip the throttle.
You really need to make or own your own, personal set of carb
synchronizers if you want to maintain the Guzzi properly. It can be
done nearly for free.
Some people will talk about balancing at higher rpms and steady, high
rpms. I personally believe that the bike doesn't care at higher rpms.
The biggest effect of IMBALANCE is MOST noticeable just as you start off
from a dead stop when your engine rpm is least and you are quickly
adding load to the system as you let out the clutch. A little imbalance
really messes up the first part of the acceleration. Accurate balance
makes these as smooth as silk (provided you have a clean clutch). You
need to insure equal intake manifold vacuum at idle and equal vacuum
degradation just as the slides lift off of idle.
Patrick Hayes
Fremont CA
BTW, you're only 100 miles away. Let me know if you need a visit on this.