RPM drops off when rpm reaches 4200

[Gerryk]

Have a Yamaha 90, 1988 3 cyl outboard. <br /><br />Seems to run fine for at lower rpm for any lenght of time.<br /><br />However as the rpm hits 4200 the rpms drop right off to less than 3000. The motot tries to pick up but can not until I ease back on the throttle. As soon as I go back to 4200...same problem<br /><br />Given the outboard a full service ( plugs, oil, checked compression, etc ) Changes fuel tanks, checked the prmier bulb, tried to choke it with no joy.<br /><br />I suspect it is being starved of fuel somehow - but unsure where to go from here.

 

[Hooty]

Re: RPM drops off when rpm reaches 4200

If the choke had no effect, I'm not sure it's fuel related. What you can try is give the carbie (carbie, I got that from you guys down under) a shot or two of premix using a squirt bottle, and see if anything happens with that. If not, I think I would start looking at ignition stuff.<br /><br />g'luck & c/6<br /><br />Hooty

 

[Crazy]

Re: RPM drops off when rpm reaches 4200

If everything checked out on the motor .... Then the next time it does this .... Kill the motor with the thotle in the same place .... '' turn the key off '' This is a 2 stroke motor right ? if it is pull the plugs and check the colour ... your looking for a light tan colour ... A black colour is to rich of a fuel mix , and a gray to white is to lean ..... You fliped the choke when this happened and it didn't fix it Right ? ...... Pull the plugs ..... you could also have a broken reed . Good luck I have Snowmobiles and they are 2 strokes Hahaha !!!

 

[sharkcat]

Re: RPM drops off when rpm reaches 4200

had this happen on a merc60 sounds like you have an intermitent ignition fault on one cylinder.Check for corrosion where the leads plug into the coils...

 

[jim dozier]

Re: RPM drops off when rpm reaches 4200

Try unplugging 1 spark plug at a time and running it. If it runs the same as usual that cylinder is the culprit, if it runs worse than usual that cylinder is a good one. It does sound like you're dropping a cylinder for some reason.