[theendisgone]

i have a yamaha 55 been laid up for a few months but was serviced prior to that took it out and it went fine on full revs for about 10 miles then it stopped reving and would only run at a tick over speed on full throttle when in gear and would not rev but when put into nuetral it revs goodi am guessing that it has dropped fire to one cylinder would this be due to something as simple as the plug or is it likely to be something else i have changed the plugs but have not had a tide to test it in yet thank you in advance for any advice

[jim dozier]

Verify that you have spark on all cylinders, it could be something simple like a spark plug. It may also be that one of your carbs has sucked some crud into the main jet and it will only run off the idle jets. If it has good spark try choking the engine some and see if it picks up a little or try spraying a little premix from a a squirt bottle into the carb throat. If it picks up you need to look at the fuel system and probably do a thorough carb cleaning/rebuild.

[rodbolt]

hello basics baby basics test spark and compression if both are good look into the carbs and fuel pump. good luck and keep posting