Triumphrat

parrycm

Some context first - I fitted a Dynojet kit a little while back to my '95 TB (Mikunis) and wasn't overwhelmed with the results - I followed what they said in the instructions for the main jets and needles. I also fitted new (stock) needle jets.

It ran very rich and chewed fuel but I ran it like that on my ride up to the mid-Ohio mini raid because there wasn't time to return it to stock. Halfway back to Texas, it started a misfire (like a stutter) on cylinder 1 especially around 4000 revs and on steady throttle. On acceleration it seemed to go away and lessened at higher revs.

So, if I caned it the problem wasn't too bad and since I was on Arkansas backroads, caning it was pretty much mandatory (My God they're wonderful). I stopped at a Vintage Car Workshop in the middle of nowhere and drilled some holes in the RH side of the airbox. That certainly reduced the richness as it wasn't blowing as much smoke now but it still misfired.

So I figured I'd fouled a plug and so when I got back I replaced them with iridium items but that didn't fix it. Nor did swapping coils and wires, nor cleaning the igniter contacts. I even swapped out the float assemblies and still no result. I then returned the carbs to stock although I did retain the new needle jets. Still misfiring on cyl 1 d*mmit.

I have a spare set of bone stock Mikunis and so finally I fitted those but only after replacing all the o-rings which had hardened up which caused them to leak like a sieve. Voila! Based on a test run, all is now OK.

I've looked over the offending nbr 1 carb and can find nothing obviously wrong - but I'm no expert. The main jet and needle jet seem to be unobstructed, the diaphragm seems to be OK - the slide is a bit worn but then so are 2 and 3.

My conclusions so far are that the Dynojet kit was not the cause, nor is the float assembly, since the problem still occurred when those items were swapped out. It isn't the inlet rubber since I haven't touched it and it's running OK now.

Any ideas?

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Chris

"Panniers can never hold everything you want, but they CAN hold everything you need."

jimmyj900

My best guess would be worn needle jets (if the Dynojet kit didn't require drilling the slides). The Mikuni design lets the needle and jet come in contact (especially with worn slides) and the needle jets tend to go out of round and 'leak' a bit too much fuel around 4000 rpm.

Some of the Dynojet kits require enlarging the vacuum port in the slides and that could cause the slide to rise too rapidly.

If you examine the needle jets and they're good (not oval or having a shiny stripe inside) AND you've drilled the slides, then try lowering the needle one notch to hold off the taper start on the needles.

Let us know what you find!

Jim

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parrycm

Jimmy....

I replaced the needle jets when the kit was fitted. Would it be possible for one to wear out of round in 2000 miles?

If I rebuild the carbs with new slides/diaphragms etc - where is the cheapest place to source Mikuni parts?

Thanks!
Chris

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Chris

"Panniers can never hold everything you want, but they CAN hold everything you need."

jimmyj900

It's not very probable that you'd wear out a needle jet in 2K miles.

The next things I'd look at would be to check for loose jets, for dirt in the float bowls and leaking/soggy floats. Loose jets cause rich running (until they fall out) as will grit in a needle valve seat or a 'heavy' float raising the fuel level too high.

Another possibility is that there's a piece of dirt in one of the air jets at the front of the carb. That will richen the mixture also.


I can't help you on the Mikuni parts, but perhaps if you start a new thread someone can provide that information.

Jim

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CAUTION: This post may have been altered and critical safety information deleted without the permission or knowledge of the author.