Subject: Re:RE: Spark Plug Reading
Author: Darrell Dick
Date: Aug 5, 2002, 9:24 AM
Post ID: 1710738014
There is a big battle going on over at the Brit-Iron list right now on the subject of reading spark plugs. Some say that it can only be done properly at WFO, others say it's OK to check at partial throttle openings, others say that with modern fuels you can't tell anything anyway.
Here's my 2 cents (I've kept my mouth shut on Brit-Iron, too many experts already). The BP6ES seems to be the universally recommended plug for your application. The brown to tan coloration sounds pretty good to me. As long as you aren't seeing white deposits, I would say your choice is probably not too hot.
As far as jetting goes, I've had pretty good success just using the seat of my pants. First of all, how does it run at WFO? Does is surge? Does power and top speed seem reasonable. Does the motor pick-up when you close the throttle slightly? The full throttle condition defines your main jet selection. You need a pretty good selection of jets usually to hone in on the target.
The needle position is then determined by throttle response and general driveability at partial throttle openings. The idle jet also comes into play here too. Particularly, in terms of response off idle. Naturally the idle jet controls the mixture at idle also.
Today, the best (most expensive) way to tune is to rent some dyno time. I guess exhaust gas analyzers are pretty good too. I've always been able to get results that satisfy me with some time and a bag of jets.
Now in your case, If the bike is set up completely stock, it seems to run well, and your recommended plugs are tan to brown then be happy and ride.
Best Regards,
Darrell Dick
Imlay City, MI