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Carb guys, what causes the hanging slow return to idle o the vv carb on a quick blip

55K views 58 replies 13 participants last post by  SportsterDoc 
#1 · (Edited)
Subject says it. Is it the cv slide slow to drop back down that keeps the revs from dropping like I am used to on every other gasoline powered engine in the world. Just one of a few quirky things I do not like about this carb. Also the Racing high idle on full choke on a cold start seems excessive too. Is this normal. I should have my other bike running today and begin to compare.

EDIT: Sorry for the typos, I'm not worth a darn on my little screen phone and can't edit a subject.
 
#54 ·
Ha we got our bikes cheap too because of bad carb tuning but for DG pipes. Now you have spacers to try on the bike with the DG pipe, I think you’ll need them there. Glad it’s over. I am still trying to figure out high altitude tune.
 
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#55 ·
I still would like to know what the correlation between those shims and the hanging high idle ??? Still looking or some closure to why..

Tweaker I had already bought some good spacers for if I needed them for the DG on that 03. Gonna start on making it 100% perfect next. Might be a few days.
 
#57 · (Edited)
I still would like to know what the correlation between those shims and the hanging high idle ??? Still looking or some closure to why..
Doug
The two links in post 19 and the comment in post 48 may provide a clue.
Carburetor Troubleshooting Guide
The 6 reasons for poor idle involve either too much fuel or not enough fuel.
Reason 3 (loose pilot) and reason 5 (enrichener leaking) add more fuel.
How did your spark plug read before the shims were removed?

Even when the vacuum operated slide is at the bottom, the curve provides airflow.
If the needle is lifted so that the taper is exposed, it can affect the fuel mixture.

There is also a coaster circuit to consider. The coaster/de-cel circuit adds fuel at high vaccum with throttle closed. This reduces lean mixture backfiring and reduces emissions.

If high enough, the needle contributes to the extra fuel along with the coaster circuit. Also, if the slide spring is weak or any binding, the vacuum operated slide may not close quickly. If the needle is raised high enough to leave/almost leave the needle jet nozzle, it may be striking it on the return and the needle not dropping as it should. Carbs in sixties, seventies and eighties had a dashpot, which slowed down throttle closing, serving a similar purpose to the coaster circuit.

I do not have all the answers, but maybe this will help some.

Did you seen the carb photos posted by jbfla circa 12 Nov 2010?
Here are 2 of the photos that he posted
Auto part Photography Engine Machine

Auto part Carburetor Automotive engine part Engine
 
#56 ·
Congratulations!

Doug,

I knew you'd figure it out, but I didn't necessarily expect it to be the same day I "predicted" it! LOL

Well done! And, to echo Ken and others, thanks for sharing--we all learn from each other's "Logic Trees". :D

Certainly, it must be time for an adult beverage or 6--you've earned it!

TS185
 
#58 · (Edited)
SportsterDoc) With 400 miles on the plug i assumed it would not be a significant clue to an intermittent problem, I probably should have looked at it and grabbed a vacuum reading for free clues before doing anything else, I guess I am out of practice on my Diag. skills.

Both TW's bought not running right, one barely hit on full choke for 1 sec. and the other started like it was tuned by an EPA regulator plus the hanging high idle problem. Both got brought back to proper running and oil changed, rode a short run enough to get good and hot and drained the hot oil and oil changed again. Clutches and throttle cables adjusted to spec and now both start the same ride the same and run like a clock. Good day !!! I may tinker on the 03 in the future cause I'd like to try a 34 pilot jet and get the pilot screw back in a couple of turns. Not sure I like the aftermarket pipe on the 03, kinda loud. I think we closed the book on both of these carb problems after going for a ride on both bikes back to back this morning. Thanks for the input guys !!

Land vehicle Vehicle Motorcycle Car Automotive tire
 
#59 ·
...Both got brought back to proper running and oil changed, rode a short run enough to get good and hot and drained the hot oil and oil changed again. Clutches and throttle cables adjusted to spec and now both start the same ride the same and run like a clock...
Glad both are sorted. I only replied further due to your correlation inquiry.
 
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