carb modification question

[The Lorax]

Eric, your issue sounds more like mid-range, could be needle height; doon't know much about carbs, but I got the impression somewhere that (in the case of your vintage of carbs) you might shim the needle up a bit and see how it runs, the carbs may be having a time during that transitional phase between pilot circuit and main circuit. just a thought, have a nice day and ride safe

[DGXSER]

Finally found it!!

OHHH YEAAHHH!!!! Matt you are a genious and don't even know it my brother!!!

As some of you may know, I cleaned and rebuilt my carbs in December. Ever since then I have been fighting with my no 1 plug fouling up horribly if I idle to much or ran under about 3K rpm. Well, tonight, thanks to Matts suggestion to Eric, I finally honed in on it.

I realized that while cleaning I took one of my needles out to see what needed cleaning in there. Turned out nothing was there to clean, so I never took the other three apart. So, tonight I pulled out the no 1 slide and no 4 slide (so I did not have to pull them off the bike). I noticed the no 4 needle would move or spin freely and no 1 would not. So I pulled no 1 out and then checked the fiche and found I had the stupid thing assembled in the wrong order . I was putting the spring in first then the needle and then the plate and it goes needle, spring, plate. That subtle change moved the needle enough to make it rich!

Reassembled in the correct order and she is running all the way through the rpms without a stumble or a skip of any kind!!

Matt, I owe you a beer and a steak!!

[dbeardslee]

Don - glad you found the gremlin - good catch, Matt. Might be a good place for Eric to check also, with his machine exhibiting the same behavior. What does the #1 plug look like now? Just wondering if #1 might need colortuned again. Shouldn't bother the synch, but you never know. Easy enough to check. If you want to double check I promise I won't try to stick the boroscope in your ear again .

[The Lorax]

Glad I could be of some assistance have a nice day and ride safe

[Ken Talbot]

Personally, I've never been much of a believer in the idea that coils make much of a difference. I'm sure they might in some cases, but there are just so many other things that can go wrong. Things like poorly connected sparkplug caps, dirty electrical connections, partly broken/corroded pick coil wires, weak batteries, etc. All of these can contribute, but I could never fathom how they would ever cause a problem at a specific, fairly narrow RPM range.

An engine needs fuel, air, compression, and spark to run. When I hear of a problem in a narrow range, or with just one cylinder, I lean towards fuel and air, which usually means carbs and air filters. Chances are usually good that someone has done something with both of these. Chances are usually good that nobody has messed with the coils.

YMMV, TMSAISTI, JAT, etc, etc

Hmm, four replies since I started typing mine. I gotta learn to type way faster....

[DGXSER]

Ken, thanks for your wisdom, I do agree that my issue was not going to be coil driven as it only effected one cylinder. Even if only one coil was weak, it would get both cylinders it feeds.

As it turned out, my stumble was the one plug getting so carboned up it would barely fire until I ran it hard at high RPM to clean it off. I had noticed it even idled higher after I got off the highway before. Then after a little driving on city streets or stop and go, it would idle down and even develop a bit of a miss or stumble at idle if I did not get it up over 3k soon.

[dbeardslee]

Ken - thanks for the response. I was thinking more the wires coming from the coils rather than the coils themselves - thought one might be shorting against the frame or something as they're 30 year old wires. I didn't know, but I figured you would.

So Don's problem has been identified - turns out it was Don . Sorry Don, couldn't resist. It's just that you don't make many mistakes, so I have to take advantage when I can . But we're still left with Eric's problem, which is incredibly similar to Don's - a stumble between 4500 and 5000. Haven't heard a report yet on his plug condition. Mixture and synch were set identically to Don's. Could float height also cause that condition, or in that rpm range are we better off looking at the needles?

[egleaves]

For the record, when I re-jeted my carbs last week I decided I was in a hurry to get them back on the bike and I did not check or adjust the float height. A mistake, I'm sure.

I should probably start there, then repair/replace some electrical components, and then think about shimming up the needles as suggested by The Lorax.