XS650+Mikuni VM34's - Fuel not getting into cylinder?

[Sami Laakso]

Hey guys, having a strange carb problem which I thought I might find help here

So: Got 70's XS650, late 70's if I remember correctly. Two Mikuni VM34's as carbs and pods. It ran nicely last summer until rev gauge assembly got loose inside the right crankcase cover, and the bike was going to get some major cosmetical modifications as well so I put it aside waiting for winter. Fixed the rev assembly, changed bike from flat tracker to a scrambler look, rewired the whole bike, DIDN'T touch the engine (valves, ignition, anything, didn't even open valve covers) or carbs (just let them sit on intake flanges).

Put everything back, checked for spark, it was ok so started kicking. Nada. After sweating for a while checked spark again, still fine. But plugs were bone dry. After some fiddling I came to conclusion that no gas is getting to plugs. So, must be some last summer's crappy fuel in carbs blocking them. Pulled carbs, cleaned them quickly, put them back. Still acting same. Pulled carbs again and cleaned them VERY thoroughly with carb cleaner and running wire through passages. Put them back, still the same. Plugs bone dry. Now I don't know what to do next, clearly something is still blocking but where?

I'm using external gas supply for carbs, using T-junction to flow it from one pipe to both carbs. Fuel enters float bowls nicely and quickly but seems to stay there.

 

[TwoManyXS1Bs]

Welcome to the forum, Sami Laakso.

First thing I'd try is remove the pods, block off a carb with my hand, and kick thru a couple times. Same on other carb. That should get some fuel in there, maybe get it to fire. See if it keeps running...

 

[Sami Laakso]

Welcome to the forum, Sami Laakso.

First thing I'd try is remove the pods, block off a carb with my hand, and kick thru a couple times. Same on other carb. That should get some fuel in there, maybe get it to fire. See if it keeps running...

Thank you Ah yeah , I didn't try to block the carb although I've had pods off all the time now. I should mention that it doesn't even try to fire, doesn't even promise. It's like nothing is going into those cylinders. But i'll try with the intake blocked too! Thanks!

 

[Sami Laakso]

Okay! Third time is the charm i see. Blocking carb with hand didn't help so I pulled carbs third time and paid extra extra attention to the choke assembly and needle valve circuit. Didn't take too many kicks to start! So that's good, but now I have another problem: immediately I start her the revs shoot up skyhigh! Doesn't matter is the choke on or not, immediately when she starts the revs go up and stay there until I cut the power. What the hell? Air leak? Throttle cable looked ok, both slides hit nicely on the bottom and the idle screw.