1982 90 hp Merc rev limited at 3000 rpm

[flyrods4fun]

I have an inline 6 merc that used to run like a banshee. A few weeks ago we were running the boat and began to loose power at full throttle. Motor will not run past 3500 rpms under load but will run up in neutral. We have rebuilt the carbs and fuel pump and changed the filter but did not help. We even changed the fuel tank. Squeezing the ball in the fuel line under way does not help. At idle, we verified spark in every cylinder with a spark tester and checked compression, also fine. Now I am leaning towards an electrical problem but don't know where to begin. How can I troubleshoot the power packs, coils, stator, etc to find the bad component? Any help would be appreciated.

 

[flyrods4fun]

Re: 1982 90 hp Merc rev limited at 3000 rpm

OK, looked at the motor last night and measured the resistances on the Stator and the pickup and all measure fine according to the manual. I have seen many posts on this site with the same or similar problem but have not seen anyone that has successfully resolved it. I will figure this out and post what finally corrects it. Tonight will check timing and do a Linc and Synch. Any other advice?

 

[Chris1956]

Re: 1982 90 hp Merc rev limited at 3000 rpm

Check compression and spark on all cylinders. Look at the color of the spark plugs. Post results. Perhaps you have bad coils, low compression or water infiltration.

 

[Jonezin]

Re: 1982 90 hp Merc rev limited at 3000 rpm

mine did that then just started,
Hey Chris did you forget about me?, check your mail.

 

[flyrods4fun]

Re: 1982 90 hp Merc rev limited at 3000 rpm

Already checked compression, but thanks. 130 psi in each cyl. No water intrusion, checked that. Checked timing last night and it was spot on, 6 deg ATDC at idle and 20 deg BTDC at WOT. Losing spark on Cyl. 2,4 and 6 at higher RPMS. Cyl. 2 is intermittant at High RPMs and 4 and 6 almost completely drop out. Plugs on those come out oily, others look clean. Going to change the Stator today if I can find a Merc. flywheel puller. One question, when measuring the Coil voltage (the Blue and Red wires from the Stator) with a DVA, should the wires be connected to the switch box or removed? Also, don't have a DVA, can the voltage measurement be done with a DVM and load resistor? This was the only thing I was not able to check, but since I am loosing spark on the second bank and only at higher RPMs, I am assuming its the Stator.

 

[Chris1956]

Re: 1982 90 hp Merc rev limited at 3000 rpm

I recommend you consult the troubleshooting guide on the CDI Electronics web site. You may have a bad switchbox, instead of a bad stator.

 

[flyrods4fun]

Re: 1982 90 hp Merc rev limited at 3000 rpm

Thanks chris, I think you may be right. We pulled the flywheel today and removed the stator. The two yellow wires that go to the rectifier had insulation missing and most likely were shorting together. I fixed that problem by shortening the wires and crimping on new eyes. The used Stator that I found locally was no good :-( open coil winding. Luckily we were able to check that before the install and return the item for our money back. We re-assembled the motor with the now fixed Stator and still have the same problem. Our next move is to switch the two switch boxes to see if the problem moves to cyl. 1,3,5. I'll consult the CDI website first and keep you posted.

 

[CharlieB]

Re: 1982 90 hp Merc rev limited at 3000 rpm

You may switch the stator leads on the switchboxes, less wires to move.

 

[flyrods4fun]

Re: 1982 90 hp Merc rev limited at 3000 rpm

Thanks Charlie, but too late. We switched the boxes and no change in results. Still loosing spark on Cyls 2,4 and 6 at higher RPMs. So I'm still leaning towards the Stator or the trigger. Unfortunately I don't have a DVA to check the voltages to be sure what is bad. But considering the yellow wires were shorting together at the rectifier, I'm going to go with the Stator first, if that doesn't work then I'll change out the trigger.

 

[cannonford57]

Re: 1982 90 hp Merc rev limited at 3000 rpm

before ya go spending a lot of money,with a timing light check and if the fire goes away between 1800 and 2100 rpms its stator time most likely.theres way too much knowledge here(no i'm not one of them) to guess ,good luck with it...

 

[flyrods4fun]

Re: 1982 90 hp Merc rev limited at 3000 rpm

Sorry, forgot to mention, we are using a timing light to verify our loss of spark, and yes it drops out when the RPMs go above 1800 RPM.

 

[flyrods4fun]

Re: 1982 90 hp Merc rev limited at 3000 rpm

Success!!!! It was the Stator. Put in a new one and she runs like a charm. Spark in every Cyl and at high RPMs. Going to put her in the water tonight and see how she does.