Lost 400-500 RPM's at wot

[SML Boomer]

After 18 years of absolutely no problems with an 1988 Evinrude 100XP, problems are starting to arise. I had the engine rebuilt last year and it performed very well over the winter in Fla. I had some starting problems in April and mechanic replaced rectifier/regulator and highly recommended VRO be disconnected which he did. I dislike the mixing now and plan to upgrade to the new OMS. Since the starting problem I have not been able to get the normal 5400-5500 RPM's I was getting before. The motor feels smooth but sluggish and comes out of the hole slow. WOT is now about 4900. The plugs are black with some carbon residue. I put in new ql77jc4 gapped at .030, same as before. My oil mix is not too rich and I am careful to follow the 50/1 ratio. My old non screw in compression guage shows around 110/112 lbs. My mechanic checked the linkage again and said he rebuilt the carburators and thinks they are ok. He is unsure as to the problem. I replaced the power pack this week and it made no difference. I'm not much of a mechanic but I checked stator resistance from brown wire to brown/yellow and only got 450. The manual I saw said it should be 555-705. Could weak spark cause this problem or it it more likely carburation? Timing?
Thanks in advance

 

[Reggie08]

Re: Lost 400-500 RPM's at wot

When was the last time you did a link-n-sync?

 

[Joe Reeves]

Re: Lost 400-500 RPM's at wot

The loss of 400/500 rpms is equivalent to losing one cylinder if all else is as it should be.

With the spark plugs removed, the spark should jump a 7/16" gap on on all cylinders on that model with a strong blue lightning like flame.... a real SNAP! What does that engine have? (The 7/16" gap is important)

The stator under the flywheel is a two fold component, the beginning of both the battery charging system and the ignition system.

A weak or failing stator would result in weak ignition which could account for the "black" spark plugs. I don't have the manual in front of me, nor do I recall the required ohm readings, however, if those readings you mention above are correct, the stator is faulty. Visually inspect the stator to see if there are any cracks and/or a substance leaking from it that is dripping down on the powerhead. If this leakage is present, replace the stator regardless of the ohm readings.

I'd suggest that the following areas be looked at.

Check to see that the engine has the proper full spark advance setting. Unless the mechanic tinkered with the linkages, that should have remained the same.

Make sure that the carburetors are clean, and the high speed jets that are located in the center bottom portion of the carburetor float chambers are absolutely clean. Best to manually clean those jets with a piece of single strand wire.

Check to see if the timer base under the flywheel may be sticking at any position.

And of course, double check the stator.

Problems with the above areas could result in pre-ignition, leading to piston4 damage. Is there another mechanic whereas you could obtain a second opinion?

 

[SML Boomer]

Re: Lost 400-500 RPM's at wot

Thanks Joe. I spent the winter down your way on Crooked Lake and Istokpoga. I probably do need the services of another mechanic. I don't want to be a pain with the origional mechanic but he has a good bit of my money and I still have the problem. I was told of a reputable guy who has the equipment to test at wot under load. I don't mind spending a few dollars to get it right. This web site has been a blessing. It's obvious that several of you know your stuff. One thing that I've gleaned from reading the posts is to be systematic and start with the simple stuff. That said, you can't beat a guy at his own game and a good outboard mechanic is worth their money.