wow another carb question SHOCKING

OK here it is-popping while idling, popped on deceleration, while idling it feels like it's running on 3 cylinders, acceleration is very good, when cruising it feels like it's missing or running on 3 cylinders. 107.5 mains, stock air box and oem filter, open exhaust. plugs look fine. Bigger mains or move the needles a clip or two or both?

Have you check your valve clearance latley? Roy

This is what I've been taught and have learned from my two friends/mentors...

"popping while idling, popped on deceleration"...
Are both conditions of running too lean...

popping while idling:
In reviewing my project, to get through emissions, I had tweaked my slow jets (Keihin for pilots) to far out for lean operations at idle...

Once in the bay, I couldn't get it to start or idle at all with out being on the throttle... Spit, back fire you name it... Not allowed in the test, she has to be able to idle during the test...

So rolled the old girl out of the bay, tweaked the slow jets 1/4 turn in for richer operations, went back in line and passed with flying colors. After the test, tweaked them back in 1/2 turn (richer) for normal driving...

popped on deceleration:
Sure could be an exhaust leak in the system or vacuum leak for that matter but if carb related, get your mains corrected first... Meaning if no falling on it's face in WOT response then mains most likely on or at least close to on the spot.

While driving 1/2 to 3/4 rpm range, let the throttle snap back to close, if pops or pop-=pop-pop during decelerations, then most likely still a little lean on the clip position... Change one position for richer operations and test ride her again.

Set jets to normal manual specs... Start with mains first, then needle jet clip position then go after your pilots... Only do one at a time in this sequence otherwise you'll be chasing this for a really long time.

Hope this helps, worked for me in learning the fine art of carb tuning...

OMR

roy-b-boy-b wrote:

Have you check your valve clearance latley? Roy

Maybe three hundred miles since I did them.

Old Man Rock wrote:

This is what I've been taught and have learned from my two friends/mentors...

"popping while idling, popped on deceleration"...
Are both conditions of running too lean...

popping while idling:
In reviewing my project, to get through emissions, I had tweaked my slow jets (Keihin for pilots) to far out for lean operations at idle...

Once in the bay, I couldn't get it to start or idle at all with out being on the throttle... Spit, back fire you name it... Not allowed in the test, she has to be able to idle during the test...

So rolled the old girl out of the bay, tweaked the slow jets 1/4 turn in for richer operations, went back in line and passed with flying colors. After the test, tweaked them back in 1/2 turn (richer) for normal driving...

popped on deceleration:
Sure could be an exhaust leak in the system or vacuum leak for that matter but if carb related, get your mains corrected first... Meaning if no falling on it's face in WOT response then mains most likely on or at least close to on the spot.

While driving 1/2 to 3/4 rpm range, let the throttle snap back to close, if pops or pop-=pop-pop during decelerations, then most likely still a little lean on the clip position... Change one position for richer operations and test ride her again.

Set jets to normal manual specs... Start with mains first, then needle jet clip position then go after your pilots... Only do one at a time in this sequence otherwise you'll be chasing this for a really long time.

Hope this helps, worked for me in learning the fine art of carb tuning...

OMR

I'll have to print this out for sure. With the bike going like a raped ape when I open the throttle and the good plug condition I'm thinking I'll leave the mains alone. I was a little surprised to find 107.5's in there but that's the stock size. The more I look at the rubber bits all over the bike the more I find to replace so I'm going to order a new set of manifolds and boots. I'll also try moving the needles one clip. I don't want to mess with it too much because I'm getting a new exhaust this winter and might have to go through it all again.

Almost forgot... You'll still be required to sync the carbs...

A little tip I learned from Larry.... Set the idle as low as possible 500-800rpm... Then sync for the +/-2cmHg...
After completing, then adjust back up to normal operations 800-1000rpm... Possibly higher....

Note: Depending on your engine builds (as in my case) my motor doesn't like the idle specification range 800-1000rpm. Both Plummen and Larry stated this to me where that range was intended for stock motors, not modified performance engines where you have head over sizes valves, port & polished intakes, performance cams and increased compressions etc....

Ahhhhhhhhhhhhhh, makes sense;) ....
My engine idles @ 1100-1200 nicely, just where she wants to be....

OMR