won't exceed 3000 RPMs

[Trophy owner 1234]

I have a 2002 Mercury 125EXLPTO that suddenly will not exceed 3000 RPMs in WOT. I can get the revs higher in nuetral and reverse, but not in forward. I have replaced the plugs and the fuel filter, but that did not help. The engine seems to run fine in all speeds. Also, there used to be a point around 2300 RPMS where the engine really began to move out, that no longer exists.<br /><br />I have now determined that the lower two cylinders are not firing. What controls these two cylinders to kick in once the engine hits a certain RPM?<br /><br />Can you point me in the right direction?

 

[Coolmaker]

Re: won't exceed 3000 RPMs

Is the bottom clean? Is the boat trailered or at a slip at a marina? Is the gas line bulb tight? Is it firing on all cyls?

 

[Trophy owner 1234]

Re: won't exceed 3000 RPMs

The boat is trailered and the bottom is clean. The gas bulb is firm. I just checked the plugs (replaced them yesterday) and found that the bottom two are clean, like they haven't fired. I am thinking it has to do with the engine not engaging all cylinders at a certain speed. I understand at slow speeds this engine just runs on two cylinders. Can someone explain what controls the cut in of all four cylinders for this engine?

 

[bshores]

Re: won't exceed 3000 RPMs

I had a similar problem on a 1989 175 hp merc and the mechanic said it needed new cylinder heads. Shouldn't be your problem but I wasn't able to troubleshoot my problem and thought I would offer my 2 cents. Good luck.

 

[Trophy owner 1234]

Re: won't exceed 3000 RPMs

After doing some searching on this site, there is alot of information but takes some time to hunt it down, I am thinking this may be a stator problem. Am I jumping to conclusions here or what? I can't get the fly wheel off right now so it may be a few days before I can rule this in or out

 

[Laotzu]

Re: won't exceed 3000 RPMs

You may be able to test stator output without removing from the motor. You'll need a DVA meter to do properly. I suggest you get a manual. A good investment.<br /><br />However, when my 50hp had this problem, it was varnish flakes in one of the carberators causing it to run on 2 instead of 3 cyl.<br /><br />Jerry

 

[jesse321]

Re: won't exceed 3000 RPMs

I had the same problem with my 90 ELPTO only 3200 rpm. I cleaned out the cylinders with mercury cylinder cleaner to get the carbon out. Now I am topping 5500 rpm like it should.

 

[Trophy owner 1234]

Re: won't exceed 3000 RPMs

The problem is solved. I started with the basics after getting a bit overwhelmed at first. I found I wasn't getting a spark in number 3 cylinder. Swapped out the coil with another cylinder and got what I was looking for. Bought a new coil (CDM) and she is runnig like a charm. The lesson here is to do the research, start with the basics and begin elimination the problem areas in a sytematic way. I am thankful I didn't act on my hunces, but worked it out logically. Thanks everyone.