Motorcycle Repair: Yamaha 400 Seca 1982, yamaha seca, combustion chamber

Question
Chris, First of all WOW for all your work.

Here's my problem, my Yamaha Seca 1982 bike starts fine, I run it for about 15 minutes till she's nice and warm, then when I stop at a light she only runs on the left cilynder... and then rpms drop and she stops if I try to give it a little gas to keep the RPMs up she don't like it and it sounds like I'm flooding it. I wait ten minutes and she starts up again... The bike also bogs and stutters at 3-4 thousand RPMs and as soon as I hit 4000 she kicks in hard and runs great. I took it out on the highway and if I run it at 4500 or more I can go for ever, as long as I don't stop to smell the roses... otherwise i have to sit for ten or fifteen and start over again. I can stop at lights if she's still cold but if she's hot, no go. I would apreciate any help.

previously the bikes been sitting for 2 years, the owner started it every couple of weeks and ran it up and down the street... it had carb done, plugs, wires and cleaned combustion chamber...

Thanks in advance for your help.
Pat

Answer
Hi Pat.

You could have a few things wrong.

1)  Possible problem with the mixture in one or more carbs.  When the bike acts up, stop it and pull the plugs.  See if they are fouled.  If all of them are fouled, you could have an issue with the air filter (if it's dirty, replace it) or the mixture in the carbs could all be maladjusted.

2)  The carbs could still be fouled with varnish.  This could be the case if the tank was not either cleaned or resealed when the carbs were cleaned.

3)  The float seals in the carbs could be bad or the floats could be set wrong.

4)  Make sure that all of the coils are working.  Test them as per the repair manual and replace if needed.

Start with those and see what you find.
Good luck and ride safe.
FALCON