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Post (8042)

Yermo(https://miles-by-motorcycle.com/yermo) you are most welcome. I think I can boil down the issue (or what I believe it to have been) thus... It was a throttle position problem. The behavior with the choke was a Red Herring, making it seem like a potential choke or fuel deliver problem. What it seems to have been instead is an overall misalignment of the various throttle adjustment parameters. The more I thought about it the more it made sense, as there are several different adjustment points which control throttle position either in whole (all carbs) or in part (single carbs). Watching the vacuum gauges really solidified it for me as I could tell that the "high idle" was in fact not an idle at all but was happening from an open throttle (watching the transition from the idle jets and idle bypass to the mains and airflow through the throttle bodies). From there it was a question of determining where in the throttle travel that transition occurs, then adjusting everything back to the point where releasing the throttle closes the butterflies and drops vacuum. Once getting the carbs and throttle cables and actions synced up such that closing the throttle truly closed the throttle and brought the system reliably into idle (only using the idle bypass for air and idle jets for fuel), we then could simply adjust the idle speed back down to the desired level - which we set at about 1150-1200 rpm. The summary is that what was happening is that the throttle was actually partly open, potentially in one or more carbs, and the condition was exasperated by having the throttle pull and return cables improperly adjusted, which created weird tensions on the cams and likely was inducing the behavior in the center two carbs (probably num3 actually, based on what I saw with the vacuum gauges as we cycled them in operation from idle, to off idle, to part throttle, to WOT). See if it still behaves tomorrow, but from what I saw it should be fine. Once everything is back together you should be able to adjust idle speed with only the idle adjuster. It should be obvious if it transitions from high idle to on throttle, just back it back off if it does. Remember with the idle and throttle cable changes...small changes, then wait for it to settle before assessing.

6 years ago byrshaug
Yermo
6 years ago
Video (8037)

How Motorcycle Carburetors work and how to tune and clean them

Here's a link to the kind of carb cleaner I like best (it IS the best) http://www.amazon.com/gp/product/B002ERT666/ref=as_li_qf_sp_asin_il_tl?ie=UTF8&camp=17...

Post (8030)

I found this on Keihim carbs I don't know if it applies to the carbs on the bandit. "Fuel screw: With the carbs synched, the engine warmed up to operating temperature, and the idle speed set, adjust the fuel screws so that when you rev the bike in neutral and release the throttle, the revs quickly drop to exactly idle speed again. If, when you release the throttle, the revs hang up a few hundred rpm above idle speed, then drop to idle, the idle mixture is probably a bit too lean. Turn the fuel screws out. Use a minimum of half turn increments until you know you've just about nailed it. You'll drive yourself up the wall trying to tune the thing in eighth or quarter turn increments if you're a mile off. In extremely lean cases the idle will hunt between the proper speed and something above it. If, when you release the throttle, the revs drop below idle speed then pick up, the idle mixture is probably a little bit too rich. Turn the fuel screws in. In extremely rich cases the engine will die after revving the bike and releasing the throttle, unless you've turned the idle speed screw way in, in which case it may act like the idle mixture is a little bit too lean. In slightly rich cases, the engine will respond well to throttle blips when cold, but will die or dip slightly below idle speed when hot. While having an exhaust gas analyzer is almost mandatory during tuning of main and needle circuits, do not rely totally on them to set idle mixture. Use an accurate tachometer (like your ear) and adjust the fuel screws to find the highest vacuum for each cylinder or highest idle speed, which will often be the same setting." http://www.factorypro.com/tech/tech_tuning_procedures/tuning_FCR_Burns,Pat.html

6 years ago bymothman
Yermo
6 years ago
Video (7937)

Motorcycle Mikuni CV Carburetor Cleaning for Suzuki, Honda, Yamaha Tutorial

Links below. Step by step instruction on how to disassemble, clean and assemble Mikuni CV Carburetors for Suzuki, Honda, Yamaha motorcycles... I hope you fin...

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