Hey all, I'll apologise for the long thread in advance... I've been searching for quite a while now across various sites, through tonnes of threads for a solution to a low RPM stumble that has reared it's head on my '96 M600 with the stock Mikunis. Everything I can find gives only a partial solution. Problem: The bike will stumble (read: misfire and even backfire through the airbox) on light throttle from idle. Load is not a factor - this happens with constant light throttle with the bike running in neutral. The problem seems to coincide with a high idle that is reluctant to settle when coming to a stop. Both seem more obvious when the bike is hot. What I've done so far; I've stripped the carbs down to check for wear. Needles are fine, emulsion tubes don't appear worn at all, jets are all clear, vacuum diaphragms appear fine, as do the idle screws and their O-rings. There was a large deposit of black gunk under the vacuum diaphragms and a tiny amount of separated fuel in the bottom of the float bowls near each drain. This was all cleaned with the appropriate solvents. Notes from carb teardown: Some muppet had either installed a washer under the between the plastic washer (under the clip - thus effectively raising the needle) on the needle jet in one carb, or had forgotten to put one back in the other carb. The carb diagrams I can see online are a little sketchy - does anyone know whether they should have one on each side? Carbs have been balanced. Idle mixture set as per factory recommended. Choke was stuck partially open - now solved. I reset the float heights to the recommended 14mm while I was there. The bike runs Remus twin slip-ons. No other mechanical mods. As always, any help you guys can offer me is most appreciated. It's coming into summer here and I'm desperate to get back on the old girl! Thanks Alex
was the washer under the carb needle for the rear cylinder? as this was probably intentional as the rear runs hotter!! This would have enriched the rear cylinder. This is what a tuner would also do on a remap if it was efi. Just a thought.
Howdy Mentalist. Good call on the rear cyl - the washer was indeed on that side. I've since tracked most of my problem down to plugs fouling due to a broken vacuum petcock. Weird thing happened today... I installed the new fuel tap last night with the carbs still off the bike. This afternoon, the thing mysteriously starting shooting fuel out of the main fuel hose! Could be a coincidence, but it happened soon after the sun had been started heating the tank up. Could a blocked breather cause the tank to push fuel past the vacuum tap? Cheers, Alex
