Calling all Triumph gurus

[mrt202]

I'll try make a long story short. My '02 America has an intermittent "skip" and poor idle. It has about 20'000 miles on it since the 904 install (and British Customs cams), 45,000 total miles. I've been fighting this problem for about the last 5,000 miles. I have tried (over the last month) new irridium plugs, rejetting, replaced the carburetors, swapped the CDI and coils and plug wires from a friends bike that runs flawlessly, all to no avail. I checked the valve clearances (all within spec), and checked compression last night. Compression is dead even side to side. The problem seems to remain on the left cylinder only. The only thing i haven't checked is the air gap for the igniter pickup. I can't imagine that would cause an issue on only one cylinder, but haven't ruled it out. It is only a problem at idle. It runs like a banshee otherwise. I'm hoping that somebody out there can help shed some light on this.

 

[Carnation]

vacuum leak? like on the inlet rubber or the vacuum port caps. maybe at the airbox to carb boot.

 

[mrt202]

vacuum leak? like on the inlet rubber or the vacuum port caps. maybe at the airbox to carb boot.

Forgot to mention, ichecked for vaccuum leaks too, both with a smoke machine AND a flammable aerosol. None found.

 

[Texas94fs]

Gas tank venting properly?

 

[mrt202]

Gas tank venting properly?

Yep.

 

[Fast Freddy]

try one clip richer on the needle,carbs may not be sinked. FREDDY

 

[Fast Freddy]

also check to see if carb slide rubber may have a crack.

 

[mrt202]

try one clip richer on the needle,carbs may not be sinked. FREDDY

Carbs synched with a Morgan Carbtune- spot on. Running Thrux needles with one shim. Tried 48 pilots and 160 mains... too rich. Backed down to 45 pilots and 155 mains. Plug color looks good there. I checked the diaphragms in the replacement carbs and they looked good. I guess i could've pinched one going back together. I'll recheck that.

 

[mrt202]

Also;
I don't think this has anything to do with it, but... I removed the headers to wrap them. While they were off, i cut out the crossover and welded in freeze plugs. Used Ultra Copper on the slip ons and torqued headers to the head good and snug. No exhaust leaks.
I ran a piece of hose across the front vac. nipples and the caps are in good shape on the rears.

 

[Fast Freddy]

I would still try one more step richer on the needle.

 

[mrt202]

I would still try one more step richer on the needle.

So another shim, totalling 1.0mm ?

 

[mrt202]

As for the jetting, i've tried EVERY size from 130-160 mains, and 42,45 and 48 pilots. Also trying stock and thruxton needles with different combinations of shims. I don't know of a dyno anywhere near me, but my butt dyno and plug coloration says it's really close. I could be wrong, it has happened before.
I have completely gutted, debaffled and drilled my airbox, and use a Uni filter. 904, BC cams, ported intake and polished exhaust runners, and Sceptre pipes.
Using Pat's jetting calculator left me running extremely lean. Carb farting at and just off idle, midrange pop/stumble etc. That was with 150/42s. Fattening it up fixed that. I'm concerned that running it lean for so long may have damaged a valve/seat . I don't pamper it by any stretch of the imagination. 20,000 hard miles since Nov. 07(BB job) I have never seen the temp gauge exceed 180-190 degrees. Usually stays between 150-170.

 

[Fast Freddy]

is one of the carbs popping out of the filter?

 

[mrt202]

is one of the carbs popping out of the filter?

it was popping back through the carbs (both sides, sporadically) with the smaller jets.

 

[Fast Freddy]

That is a lean pop, just go richer on the needle should take care of that for you.

 

[tattooedcouple]

A long shot..but a friend of mind had a bad idle and slight hesitation when he first hit the throttle,then the bike would run great.It was a week battery..was not getting enough juice at idle to run good,started fine didn't act like a battery problem

 

[mrt202]

Update

Turns out it was a bad coil. Swapped coils with a buddy of mine and now mine's running like a raped ape again... :rock:...and his runs like shit... with a bad miss on one cylinder...
Now i've gotta come up with a good stock coil. Anybody got a spare?