Carb Gurus, ever see this B 4

[sixlow]

Bought a carb set from a Cali bike with over 100k miles, completely rebuilt them with redeye kit, new 38's and 100's, air valves checked, float levels good and new float valves. All Cali emission ports capped and glued. They sat for about 2 months after rebuild in a box, after install once I hooked up the throttle cables I realized the butterfly barrels were not returning and everything was stiff, removed the bank and was able to free up the butterflies with PB Blaster. Install bank with pilots 2 turns out, popping below 3k and on decel. Pilots 2 1/4 same thing, 2 1/2 same thing, take intakes off and check the brand new o rings, all is good, boots were tight, while intakes were off I reset pilots and went to 3 turns out, better, but now stinking up the joint, and still popping below 3k on light throttle. the whole time above 3k ran great, as well as WOT ran great. Belly tank with electric pump, and glass pack exhaust, about 200 miles total on this ultra sonic cleaned bank. At a loss I took them back out and rebuilt my old bank. Did some investigating and the only weird thing is this quick accumulation of crud between #4 and #6 carbs were the barrel passes thru the middle carb, I scratched a line in the crud. So I am concluding that the barrel pivot seal here is bad and sucking in air below 3k and spitting fuel out over 3k. Anybody ever see this before ? This is not a replaceable part, is it ? let me add the popping was left side only.

[Pappy!]

If you think it is sucking air at that point you can take a propane torch (without lighting it) and run the gas close to that point. If it is leaking the engine will immediately pick up RPM when the propane gets sucked in. Nicer on the paint than spraying gas or chemicals to check a vacuum leak.

[WintrSol]

I've seen something similar in old Keihin carbs on the CB450 from '65 to '75; on those, there is a felt seal around the throttle shaft on either side of the carb. The shaft seals are not on the parts diagrams. Over on a 450 forum, they have found a way to use hard felt to cut new felt seals; if I recall, some have used other materials. Getting a good seal without binding is the hard part.

I'm guessing here, but I think there are also hard felt seals on the Valkyrie carbs, and yours have started leaking for some reason. In any case, the symptoms are about the same.

[Thunderbolt]

Mike did you replace the small hoses about 1" long that go to the small decel valve or whatever it is called?  One on each carb.  That rubber sometimes will crack and suck air in and cause popping.

[sixlow]

Pappy, that is a great idea and will use it if I ever find myself searching for an air leak again.
Terry, I believe those lil rubber hoses were tested as well. I may be able to test them again without separating the carbs, but after 3 turns out the popping was only on light acceleration below 3k and the decel pop went away for the most part.
WintrSol, thanks for that insight and you say the symptoms are about the same do you mean low rpm pop and high throttle seemed fine, did others get this crud build up as well ?
Thanks guys

[WintrSol]

WintrSol, thanks for that insight and you say the symptoms are about the same do you mean low rpm pop and high throttle seemed fine, did others get this crud build up as well ?
Thanks guys

Yes, to all of that. The riders couldn't get the idle right, the idle would hang for a long time when revved, and some crud build-up on the throttle arms. The carb throttles aren't coupled, so the crud, when present, was less noticeable, and, of course, there are only two, but the similarities are there. If the other parts check out, but the propane still causes a change in the idle, it could be this. I don't know if the seal can be replaced on Valkyrie carbs, though. On the 450 carb, you could remove the throttle plate and a kind of clip on the shaft opposite the throttle arm, and slide the shaft out. That was the easy part - getting it back together with new felt, without tearing it up, was harder.

Some have had luck by impregnating the felt with grease, using a needle on a gun; mostly temporary, but repeatable. Again, no clue about this part of the Valkyrie carb, since I haven't had to take mine apart.