Bike has extremely low idle with choke on, otherwise dies.


XS400 New Member
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Kelowna, B.C, Canada
Hey guys so my bike runs fine once it has warmed up. But the problem seems to be getting it to start to warm it up. Chokes on all the way to the left, once i turn it over there's nothing but it trying to turn over. Until eventually I get a bit of a chug but dies once i release the electronic start. Do it one more time and the same thing. It seems the third time (Third times a charm right? lol) It finally starts but with a veeeery low RPM at about 900-1000 rpm. I have set my idle stop screw for about 1300ish when the bike is warm so it's based off that. Also the bike needs to sit on the choke for a while then it jumps up to 4,000. But it needs to stay on half choke for a very long time. If you drive it with the choke off and keep it alive by reviving it if you stop then it'll be good to go in about 5-10 minutes of driving. Now for some potentially relevant information. It's a 1982 yamaha maxim 400. Mixture screws are set at about 3 1/2 turns out. Carbs bench synched by myself with a 3/8 drill bit in the dominant butterfly valve and tightened the adjustable valve to have the same tension by feel of the same machined sized drill bit. Carburetors went through a Yamaha dealership for a deep clean and submerged in a subsonic tank. Any ideas on what to check for? Clogged petcock valve maybe? Too lean of a mixture? I'm lost. Thanks!
Timing check/set, new plugs, adjust valves, and the like, all of which will make engine demand more fuel while running like crap.

You don't sync with a large drill bit, rather, the smallest one you can find. The smaller the more accurate the job is.