My '92 with 40/127.5 jets runs 99% perfectly.
That 1% is a very slight, occasional sort of stumble or hesitation that happens when going from throttle closed to throttle tip-in, particularly around 2-4K rpm. I can get it to sustain the odd running under like 1/10 throttle at parking lot speeds just holding like 8mph in 1st gear. But it'll also happen (like for 1/10 second) when rolling along in any gear on the road if I go from decel (throttle closed) to accelerate (throttle 1/4 or so) within that 2-4K rpm range. It just kind of burbles for a tenth of a second before it begins to accelerate as usual. Doesn't happen at all above maybe 4K rpm. Since I do a lot of my riding on low-speed neighborhood streets, I wind up in this 2-4K rpm cruise range (like 35mph in 4th gear) quite frequently so it becomes noticeable like when a car in front is turning right, you slow under engine braking just a smidge then roll back on to go back from 28 to 35 mph, right at that transition for 1/10 second it kind of burbles before accelerating.
My initial guess is it is lean at the transition off pilot. It feels like this is a condition that happens *just* as the slide begins to come up. I have sort of ignored this thus far because my gut tells me this may be just a side effect of a 2-circuit carb which is improved with the later-model 3-circuit carbs. But maybe it's something I can fix?
So, is this something that could be fixed by shimming the needle with a washer? If I did that would it be beneficial to switch to 125 mains? I have a pair of 125s and a pair of original 122.5s as well.
My other guess is that setting the idle higher would also sort of help with this issue but then I would be running into the dreaded "hanging idle", which I think actually covers this particular problem because in those conditions where you decelerate, it stays on main longer.
My other guess beyond that is that it's perhaps either a vacuum leak, or just worn/wrong springs in the slides or old diaphragms or maybe even a pinhole in a diaphragm.
I guess it's also possible it's carb balance.
Just don't want to take this apart more than once.
Looking for input here before I pull the tank off.
on my 05 carbs right now, I'm having the same issue. along with a hanging idle. [somewhat fixed the hanging idle. I think it's a vacuum leak..] but I also have larger main jets [possibly too large] causing a rich condition. [even when I pull my plugs they ARENT black at all, running in circles here] actually about to go play with my float height a little.. along with bleeding my brakes. - I've gone through 3 sets of brake pads on the same fluid. :laugh:
Quote from: J_Walker on December 21, 2017, 08:01:44 AM
on my 05 carbs right now, I'm having the same issue. along with a hanging idle.
Well I guess that cures me of my suspicion this problem would go away with Mk2 carbs.
BTW hanging idle is almost definitely the idle speed set too high (too much throttle plate bypass). Now you might have done that to compensate for other issues (frequently too-lean idle mixture, or as you suggest, vacuum leak).
Just my $0.02 on that issue which I have grappled with a ton, and my obsessive technical curiosity led me to find a solution that made logical sense.