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Yamaha 25hp 2 Stroke 2003- revving up and cutting out

IrishBoat

New member
Hi, long time reader and first-time poster....

I just got an engine which had been seized up but had some work done on it to get it going again. I can start it now with a few pulls, but once it starts and the throttle is opened a bit, the engine revs up too much, returns down after a while. It sometimes cuts out, but sometimes stays running, but when I put it in gear it cuts out after a few seconds. It is then much harder to start.

Any ideas as to the problem? I got this engine for free, so I would like to be able to get it running!

Thanks in advance for any help!!
 
Seized up and some work was done to it.... What work was done??
I seized engine should be completely disassembled, checked and put back together...

Were new gaskets used on reassembly? Possible air leak causing it to rev up.

What is the compression of this motor?
 
Thanks for your reply Tony,

I'll be honest- I don't know what work was done but remember my friend saying that they used hydraulic pressure to free the pistons. I don't know much about the inner workings of an engine- I suppose my question should be should I bring it to another repair shop or should I think about letting her go?
 
I think you should get another opinion on it.
If you feel you can tinker, a service manual and some basic tools can get you a long way.
Otherwise, maybe get a repair shop to check it out for you. If it has good compression, it may be a cheap fix, but using hydraulic pressure to free an engine, should only be followed by a tear down and close inspection.
 
UPDATE:

I've got the engine working by stripping down the carbs and giving them a good cleaning. Reassembled, brought her out for a spin, and now have a new problem! The engine runs fine up to 1/3 throttle, but if I give it anymore the engine bogs down and to avoid stalling I have to reduce throttle again. I removed the carbs again, and when I did I noticed that only the upper carb float bowl had fuel in it. I suspected a bad fuel supply, so I replaced the hose from the tank to the engine and checked the internal fuel lines, no problems. Put it together again, same problem. I removed one of the spark plug leads (the upper one) and the engine starts no problem, but then stalls when put in gear. the opposite lead doesn't stall.

I'm thinking that the fuel is not getting to the lower carb- any ideas? Could it be the gasket on the side of the carb needs replacing?

Thanks in advance for any help!

P.S: Just looking at the diagrams for the carbs and it seems that I didn't remove the nozzles and jets in the carb while cleaning. Could this be my problem? I unscrewed the top part of this section, but the rest didnt come out.
 
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