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2002 25hp yamaha mid range rpms problem

J

jblanton

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I work on motors for other people as a side job. Not a professional. My motor sat up for about 8 months and accidentally ran bad gas through it. After replacing fuel filter and cleaning carburetor THOROUGHLY. The engine runs and idles fine. The problem is after about mid range rpms it will begin to studder and bog down and if not held wide open or backed off it will shut down completely. but if you put your hand over the intake while it is studdering it will work fine. I've checked the fuel pump and made sure its working properly and checked to see if the motor wasn't pulling air in the carburetor. Not entirely sure if the timing is correct. I don't have the money to take it to the shop. Need help.
 
What kind of Yamaha is this? 2stroke, 4stroke? How do you test the fuel pump? Sounds like air mixture adjustment problem. It could be the jet issue. 20 years of experience with these and I at times have to take the carbs out the 2nd time to recheck. Did you have to adjust the floater? If you're positive of its compression, spark and fuel flow, you must have missed something in the carb.
 
Its a four stroke the carburetor is clean as far as I can tell. I've blown it out cleaned by poking with a needle. the only thing I haven't tried is an acid soak for monetary reasons. Someone told me it is pulling air; but I can't find a place. I try spraying the outside with carb cleaner while its running and water but nothing changes. The jets are fine but i did find out that my accelerator pump kept hanging up yesterday I have been running ethanol gas through it which can't help but the tank is now clean and zero ethanol running in it now have yet to test.
 
I have been having similar problems with my 2002 25hp 4 stroke. I got a gallon can of Berry's Carb Dip for about $30and also ordered a kit for about the same amount. Everybody told me that the passages were so small that chances are that the carb is clogged slightly somewhere. I'm waiting on the kit to come in the mail but tearing down that carb is not too bad so you might want to take it apart and soak it.

My accelerator pump was hanging up too.... I cleaned it up real good and it ran better...but then a few days later something went wrong and it wouldn't start. I expect something got sucked up after I put it back together so I took it back off and soaked it for 24 hours... like I said I'm still waiting on the kit.
 
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You still have bad gas in the line somewhere. Make sure you clean everything out starting at the fuel filter/water separator all the way to the carbs. I've made short cuts before sucking water into the carbs and the problems just kept coming back. I eventually clean out the gas tank, replace the fuel filter/water separator, clean out the fuel filter at the motor, clean out all the carbs to eliminate the problem. GL
 
I ran the test on the water hose and it ran fine like a champ. Then the real test in the river. Now the motor won't hold prime it will just run the bowl out of gas and not pump in much. I took the hose off the outgoing side of the pump, while it was running and very little fuel comes out just little squirts. So now I have to figure out what is stopping fuel flow in the pump.
 
After a good soaking and a carb kit my motor is running pretty good, still bogs a little if I slam it wide open but I haven't put it in the water yet. I ran it on the hose it it seems okay..still might have a slight hiccup but acceptable. Seems the more I run it the better it runs(on the hose anyway). I'm not sure how fast that plunger should go down but when I open the throttle up it has a lag, I still think it may need replacement.
 
If it lags the spring in on the throttle is wearing out or the throttle is out of adjustment. You need to make sure you get that right before putting it in the water because I had the same problem and when I put it in the water the lag increases and the motor will sometimes backfire. CAREFUL!
 
jblanton said:
If it lags the spring in on the throttle is wearing out or the throttle is out of adjustment. You need to make sure you get that right before putting it in the water because I had the same problem and when I put it in the water the lag increases and the motor will sometimes backfire. CAREFUL!
Click to expand...

I think the throttle spring is good...It seems like it is just compression pressure under the plunger maybe..not sure yet.
 
Jblanton,
How did you check your fuel pump? I bet you your fuel pump is bad. The fuel pump diaphram is bad that's why when the motor is running it's not pumping fuel out. Unless it is clogged somewhere along the inlet side. GL
 
Success!!!

Put it in the river today and it ran perfect! I think think when it's in the water and I slam open the throttle the load on it from being in the water prevents it from turning up faster than it can get fuel unlike when I tried it on the hose.

Bottom line is. Removed and soaked in Berryman's Carb Dip for 24+ hours, installed a kit (float, o-rings, float valve etc). RAN GREAT! Problem solved!

The kit was about $35, Berryman's $20 at Wal-Mart (although I spent $30 at Autozone:mad:) and a little effort.

Shop woulda charge between $100 and $150.

Also installed a 10 micron fuel/water separator filter, and will only be running NO ETHANOL gas in the future!
 
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I the fuel pump is bad. it needs a new diaphram and the carb dip Im definitely trying out new kits for each and maybe the problem is solved.
 
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