'89 yamaha 50 fades at full spead

[allanr]

This motor is new to me and may not have run this summer but at full rpms it sometimes dies back to half. I hit the throttle two or four times 'til it takes off to full again. Only thing I've checked so far is the gas cap valve. Any ideas?

 

[johnkc]

Re: '89 yamaha 50 fades at full spead

full tune up, start with compression test, then spark test, then condition overall condition under the cowl, wiring ,hoses etc, clean carbs, do timing and linkage synch.

 

[JB]

Re: '89 yamaha 50 fades at full spead

Hi, Newbe. Sounds like water in the fuel to me. Purge your tank, lines, etc. Then check for air leaks in the fuel lines. If you don't find any solution there, start on JohnKC's suggestions. Start with the carbs, you may have some loose crud intermittently plugging up a jet.<br /><br />As for the compression test, it's always worth while to know what you have, but compression problems are not intermittent.<br /><br />Red sky at night. . .<br />JB

 

[allanr]

Re: '89 yamaha 50 fades at full spead

Thanks so far guys. The engines fades slowly, not rough like water knocking out the occasional cylinder and all are 130lbs. Being a diehard doityurselfer I'm determined to keep looking and learning about these things to prevent future costs and maybe save myself when I'm stranded. What about a quick fuel pump test? Is there one?

 

[johnkc]

Re: '89 yamaha 50 fades at full spead

when running down lake ,if you or a passenger take the primer bulb and when the motor acts up, squeeze it ,and the engine runs better, you have a fuel problem,anywhere from the pick up in the tank to the carbs, double check hose connections, the bulb ,it has check valves in it.loose or cracked hose under the cowl? anti-siphon valve ,at tank connection ,could be giving you this problem i am assuming built in tank though, for anti siphon valve

 

[MURX]

Re: '89 yamaha 50 fades at full spead

As for the quick fuel pump test squeeze the bulb while it's lagging and see if the RPM'S come back up, if they do maybe you've found the problem, another often overlooked point is this, if one carb has a plugged main jet or other obstruction such as a needle that sticks whenever you have a loss of fuel you're also starving that cylinder of lubrication, sometimes it pays to not do it yourself, many a outboard could of been saved if the owners woulda just takin' em in when they were not hitting on all cylinders some guys run em' till they scar up the jugs and come to find out they had a simple carburator problem thats now cost them a bundle, all in the name of saving money by doing it yourself, Don

 

[allanr]

Re: '89 yamaha 50 fades at full spead

Thanks for the scare Mercx. I will be more causious now and make sure the problem is solved. Is above freezing in Canada today so I'll try another tank and squeeze technique. Its owtta the water for winter after that and I got a long time to play with the carbs.<br />I may have to go south to try it!!!. Snowbird

 

[allanr]

Re: '89 yamaha 50 fades at full spead

Your're right on J.B. But why didn't anybody tell me to check my filter first...a bunch of rusty water in it Cleaned out all the carb bowls and it ran like a charm. Thanks and Mercx, even if the fuel is starved to a carb doesn't oil still get injected in the cylinder or were you just talking about a premixed engine?

 

[johnkc]

Re: '89 yamaha 50 fades at full spead

newbe, some times we can't see the forest thru the trees ,and on your oil mix ,it mixes before it goes into the carb