75 horse Merc Running Poorly - New to me boat

Hello, All. Thanks for adding me to this group.

I have been searching for things on the thread relating to spark, stator, etc... so as to not have to create a new thread with information already posted. In searching I have only created more questions for myself, so I appreciate your having a look at this pos.

Early in May I purchased a 1986 Lund Tyee 4.9. It has a 1997 Mercury 75 on it. Engine Model # 75ELPTO.

I purchased the boat from a guy who said "there is something minor wrong with the top end", which was what the guy who sold it to him told him. He had purchased it in September but got transferred with his work and never got it to a shop before the snow flew last fall. So, once he got transferred he needed to sell. I took the risk because I got the boat for a good price.

When I got it home I pulled the cowl off and really looked the engine over closely. It is immaculate and was obviously well cared for. I checked out the spark plugs and all of them were loose. I thought "oh, crap. Somebody was in there and realized the engine is gone and didn't even bother tightening up the plugs. I did a compression test to rule out the biggest problem and got some good news. 120 in all three. Next I wondered if the problem with the top end could have been somebody not tightening the plugs. I started it in the driveway with muffs and it started right up and ran pretty well.

This past weekend we finally had weather good enough to enjoy some boating. I got to the lake and put the boat in the water. Off we went. It ran ok, but had a miss at higher revs and had no real punch out of the whole. The engine seemed like it was bouncing around running on different cylinders, or at least not running on all three. It moves along at lower RPMs ok, but again it was almost like it was dogging there as well. Same problem as at higher revs, but just not as pronounced.

While on the water I wondered if it was fuel related, so I had my son drive it and I pumped up the fuel line and really tried to make sure there was a ton of pressure in the bulb. No improvement.

As the day went along the problem got even worse.

I got it home and checked the spark. It does have spark on all three cylinders (holding the plug against the block), but I would not call the spark "strong." The plugs are NGK BUHW-2 which have an element in the center but are not your traditional plug with the tab that comes down for the spark to arc against. In the glove box were about a dozen other NGK plugs that are the traditional type. As I put this together, it would seem there has been a spark issue for a while. Now I got on the www. and started searching. As I did some reading it sounds like the stator could be the issue. Does that sound right? If so, I should replace that and the trigger at the same time, correct? I am mechanically inclined, but when it comes to testing ohms and resistance my head starts wanting to explode.

I appreciate any feedback/thoughts. I am willing to buy the right parts, I just don't want to buy parts I don't actually need.

Thanks in advance.

A bad stator can be tested with a DVA meter. If you can't locate one, and have an ohm meter, you can buy an attachment from Amazon (about 30 bucks). Great tool! Simply crank the motor over and take readings. If anything is off, you'll soon know.

Jeff

Thanks, Jeff. I will do some research and figure out where to start on the testing. I do have a good ohm meter. I just went back out and looked. it appears the voltage regulator has been replaced with a CDI unit and the trigger has been replaced with a CDI unit (tags on both). The stator does appear to be older (tan/maroon in color) and does not look as new as the regulator and trigger.

I ended up pulling the flywheel and replacing the stator. It seemed like it was just about the only thing in the system that hadnt been replaced and it was giving some funny numbers. Immediately after I put it on and got everything back together I started it up and it ran more smootly than before. Much better. I went out for a ride and then things started to act up again. I came back and pulled the CDM modules and started doing resistance tests on those. I dont understand why my multi meter when set on auto puts K's and M's behind the numbers, but this is what I got. Does anything look way out of whack? Two of them are black OEM style and one is a CDI replacement. on the plug side, they all seem to be in spec. The spec for the CDI unit is higher than that of the OEM.

Can't help you much with the Merc, but you definitely need to read up on using a multi meter.
Which actually may indirectly help you with the Merc..

Thank you for the constructive criticism. As said above, I am working through my issues with trying to figure out electrical things and ohms, etc... Thought the auto setting was the best option, but now understand why it wasn't

I did have a different look at the settings on my meter (taking it off auto) and got some different results and perhaps one that is telling?

Thanks again.

Sorry I wasn't trying to be an a hole by any means. The k,m,M, etc differ by a very significant value.
I will however step aside and let the pros pick this back up.