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1985 Yamaha 115 V4 problems. Hail Mary!

B

Brauny

New member
OK Guys.. I am throwing a hail mary on this one. Hopefully someone can help. I am having a engine knock when the motor is under load. I can idle at 1000 to 2000 all day without a problem. I can get up on plane without a problem even run at higher RPM's fine. When I go to take a corner, I hear a loud knock. I was told so many things it could be. From "LEAN FUEL KNOCK?" to the engine is shot.. I did have the pump from the external oil tank replaced right before this started. One other point, I did have older fuel in the tank when this issue started....I look forward to hearing the comments on this.
Thanks.
 
If it only happens when you take corners, that doesn't seem like internal engine knocking. But typically, knocking occurs due to:

1. Bad fuel
2. Bad spark plugs
3. Carbon buildup

Considering the age of the engine, do a compression test on all cylinders. Takes 10 minutes and will confirm if your engine is still worth putting money into.

If compression is ok, I would replace the spark plugs (and get the OEM plugs, which are probably NGK) and do a spark plug wire test as well. Also take pictures of the old plugs before you throw them away. If the knocking is due to having spark plugs with an incorrect heat range, you'll know because the plug tips will be white and blistering.

If it still occurs after that, hooking up an auxiliary tank that has all fresh high-octane fuel in it. No need to treat it, just let the old fuel in the engine lines run out.. shouldn't take more than 20-30 minutes.

If it still occurs with high octane fuel, then I would clean/rebuild the carbs.
 
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