Evinrude WOT/RPM Problems

[jherlyn]

Ok. I have been running a thread with Daviet and Levi_tsk helping me for a while now, but I feel I need to open a new thread for this one.

I have a 1975 Evinrude Hustler 75 HP. Now, she starts and idles ok, will shift and run in gear OK. However, when I open the throttle the motor climbs slowly to higher RPMs but it revs up and slows down in RPMs as it climbs. It peaks, but not at optimum WOT, and then it does the rev up/recede in RPMs again.

Now, I have changed the prop to a 15" pitch. And it helped.....A little, but the motor is still not running right. I am going to check the spark gap tester, but I am sure it will pass just fine. Fuel is good, have basically rebuilt it from the ground up.

My question is could it be exhaust. When I run it in the tank, there is an awwful lot of "soot" and it seems to be......inhibited. If it is exhaust, am I damaging the engine running it like that, and how hard is it to open the manifold and check for blockage/buildup. Are there flapper valves that could be stuck open? What kind of parts will I need? I have heard about exhaust could be the problem in a scenarion like this. Please help.

 

[jherlyn]

Re: Evinrude WOT/RPM Problems

Okay, so I got a repair manual....finally, and It is telling me some interesting stuff. I ran a spark gap test and she does fine, but the interesting aspect is in the ohm readings.

My repair manual says that when I test from the primary on the coil to the high tension output (the spark plug) I should be between 225 and 325 ohms with my meter on the highest setting. Well On the top I read right around 199, the second I read 197, and the third I read 194. Testing from the primary to the ground the book says I should test .1 ohms on the lowest meter setting. All three of my coils jump sporadically between .1 and .4, and sometimes even over to like 1.1. I'm thinking the coils are all just...weak, and because of that I'm not getting a hot enough spark for the open throttle to do what it needs done.

I'm going to go get the 2 coils that I can find in town tomorrow, seeing how I messed one up trying to get a good read on it. I will replace that one to begin with and see what my readings say. If they are completely different than I will know that this was at least A problem if not THE problem.

On the exhaust note, I looked at the breakdown and don't see anything that could cause a blockage. I think its either exhaust or spark because when idleing it smells gassy and produces alot of soot. Seeing how nobody replied to the exhaust thing my guess is with that idea I'm looking for zebras at a rodeo, so I'll start with the spark.

Final note, I wish I knew how to test the power pack without the "light tester" the book talks about that I'm sure I won't be able to find.

 

[Monte1961]

Re: Evinrude WOT/RPM Problems

well if the the spark is not hot enough, it wont ignite the fuel properly thus what is left unburned is coming out through the exhaust. I am sure if you look or have looked at the spark plugs lately, you will probably see that there very black in color and possibly have heavy soot on them. I am not sure what the exact ohms is for this application, but I sure would be interested! Good luck and post back!

 

[jherlyn]

Re: Evinrude WOT/RPM Problems

You know, the spark plug comment is true. I pulled them out a couple weeks ago, and they are awful black. The spark plugs are only about a month old, and they are too black in my opinion.

So, I'm now fairly confident spark is the culprit. I'm actually on my way in about 20 minutes to pick up the new coils. Does the power pack weaken like the coils did, or does it just quit when its toast? Anyone know? I'm asking because the marina in town actually has the power pack in stock and I'm wondering if I should buy it too, just to put everything in new.

 

[Monte1961]

Re: Evinrude WOT/RPM Problems

you can try it. but whats the worst that could happen? better to have it and not need it than to need it and not have it!

 

[jherlyn]

Re: Evinrude WOT/RPM Problems

Ok, so I replaced all of the coils on the motor, even though they didn't ohm test much different than the older ones. I took it to the lake, and I have good news and bad news.

First off the coils weren't my lack of power problem, it still exists. However, the engine now HARDLY smokes while idleing, she doesn't stink anywhere near as bad while running, and there is NO black soot floating on the water. So.....the coil packs WERE bad, and would have EVENTUALLY needed replacing, because the motor was not burning all the fuel provided to it.

But, I got daring with my father, and I took the cowel off the engine while in the lake. Then I had him gun it and I played with the advanced timing arm, and sure as hell I knew when I found the right spot. The boat JUST.......FLAT.......RAN! I mean, I damn near fell out. So, my timing is off.

Now, whether its the timing altogether or just the advanced timing is something I'm still working on. But early signs point to the advanced timing.

In conclusion, I'm excited yet nervous all at the same time. Because now I know what my final problem is to a fully functioning motor, but it has to do with the timing, which seems to be the hardest thing to dial in. and btw, the J. Reeves method is NOT recommended by the repair manual and according to the manual you WILL NOT get the right timing using it.