Mecury 25 willnot run full throttle

[herveymac]

I have a 86 25 hp merc that will not run open throttle. It is not the gas .It will fire on both cylinders . It statts good ,and it has 130 lb. of compression.It is a miss like it is not receiving fire. It will run on either cylinder with the plug wire off, one at the time.Help I am at my wits end .null<br />[*]null

 

[Trent]

Re: Mecury 25 willnot run full throttle

Cant remember on that engine..But I would look to see if this engine goes into slow speed due to overheat. Some had a two stage stator one for high speed and one for low.

 

[12Footer]

Re: Mecury 25 willnot run full throttle

It sure sounds like fuel starvation<br />Those engines have a very nice fuel pump design on them.It's part of the carb, and these puppies are dang-niegh bulletproof.<br />But I'll bet 1 US dollar against 1 donut it has black stuff in the check valves of the fuel pump (two metal reed-like tabs).<br />The rebuild kit that includes the fuel pump diaphram costs 36buks! Not cheap,but that's all you will be out, if I'm not right,and you'll have a donut on me. How can you loose?><br />to verify this before buying that expensive bag-o-rubber, take the boat out, and see if performance improves even a little bit with the cap on the tank loose,and pump the primer by hand to see if it improves.<br />The one bad thing that happens to the carb happens to most, and that is contaminants from the fuel,or even the fuel line itself. But your engine has a very nice filter mounted on it.Remove the black fuel line from the fuel pump side to the carb. Replace it just because it s black rubber, and alcohol "enriched" fuels desolve them.It may even look ok,bt the fuel is not filtered after that piece of hose, and all the little pieces of hose go into the carb,if they get past the pump.

 

[herveymac]

Re: Mecury 25 willnot run full throttle

It is not fuel in any way. I borrowed a carb off of another one and it did the same thing.

 

[Stream_fisherKY]

Re: Mecury 25 willnot run full throttle

Don't overlook simple problems. It sounds to me like fuel starvation and although another carb performed the same way doesn't mean there's not a problem that's fuel related. Not saying your prob is definetely fuel related but it could be that either your fuel pump is not functioning properly or contaminents in your fuel. The problem could also be in the stator plate. Just ideas, nothing definite. Good luck, and remember, when a problem arises the last thing you think it could be is usually exactly what the problem is.

 

[Prism]

Re: Mecury 25 willnot run full throttle

Most engines the timing will advance when you open up the throttle. I bet you a wire to your points or pickup sensor is either opening up, ie... is broken internaly and as it bends the conductor in side doesn't make contact any more, or it is rubbing on somthing and is shorting to ground at full open throttle. Try checking that.