'79 80HP Merc Stalling at ~2000 RPM

[jasunderland]

I have a '79 80HP Merc that wants to stall at about 1900-2200 rpm's. If it is warm and i throttle down slow, it will feel like it wants to puke but as a push the throttle down more and it gets past that 2300-2500 rpm mark, it will then rev up to 3000+...

if it is cold, i have to hammer it all the down for it to power through that dead spot and then back it off. If i try to go to slow through the throttle, it will just die. Makes it a big PITA trying to pull someone.

I took it to a marina and they said it was losing votage so I changed the stator, but it did not help.

This boat sat for about 9 years and when I got it out, the wireing was in pretty bad shape (the worst of it being the stator wires). The stator is the only wire I have replaced. I repaired the rest as best as I could.

I have not done anything with the carbs on it.

Any thoughts?

 

[jasunderland]

Re: '79 80HP Merc Stalling at ~2000 RPM

bump??

 

[Texasmark]

Re: '79 80HP Merc Stalling at ~2000 RPM

Keep bumping. One of the professional mechanics (big guns) on here will see it and surely come to your rescue. I am a shade tree guy and never was exposed to that particular problem.

Mark

 

[jasunderland]

Re: '79 80HP Merc Stalling at ~2000 RPM

Thanks Mark.

I didn't want to seem pushy, but am at my witts end!

 

[mr 88]

Re: '79 80HP Merc Stalling at ~2000 RPM

Besides the obvious,which is to rebuild the carbs it sounds like your mid range throttle linkage needs to be adjusted.Take the hat off and just ABOVE the distributor cap is a stop bolt with 7/16ths lock nut.That would be where you adjust the mid range. Sometimes the stop bracket has to be shifted a bit,counterclockwise,has two 5/16ths bolts,might have to take off the pointer plate to get the front bolt loose.The space between the stop on the adjustment plate should be around 3/16th so if you adjust the stop plate adjust the gap accordingly.As you give it gas the distributor advances if this is not in sync you get that dead spot.Get a manual...

 

[jasunderland]

Re: '79 80HP Merc Stalling at ~2000 RPM

Any specific brand of Manual better then the next? I have never really tore into carbs before... will the manual help with that also?

 

[mr 88]

Re: '79 80HP Merc Stalling at ~2000 RPM

Seloc #1408 if you cannot find a factory one, on Ebay,yes they are very detailed,so it would help. I would go with the mid-range adj as I described before tearing down the carbs. Run some sea foam with your next tank to help clean out the carbs.I really think your not sync'd up. Take the top off the motor and look at what I am talking about, then if you have questions ,fire away.Should be able to do this without a manual.I just rebuilt a 1978'ish 1400/1500 and what your describing is exactly what happened after the rebuild,would die out at 1200 rpms ,sometimes it would "catch" and zoom zoom ,once I got past that dead zone you could throttle down to 2700 rpm and give it gas,no hesitation,took awhile to adjust correctly but that was the problem. As far as the local marina, in most cases they would rather sell you a newer motor than fix it.They are not trained or could not be bothered by the vintage Mercs. Thats probably why they rattled of electrical,figuring you would give up and buy a motor from them.I have faith in you to fix this with out spending any money.

 

[jasunderland]

Re: '79 80HP Merc Stalling at ~2000 RPM

Great.

I will try the seafoam and see if it helps.

Also, here is a Pic I took last winter of that side of the motor. I see what looks like 3 adjustment screws (2 with what looks like red caps on the back sides). One looks like it has a Stainless Steel head and the other looks like it is black. Are these what you are talking about to be adjusted?


Thanks again for your help.

 

[mr 88]

Re: '79 80HP Merc Stalling at ~2000 RPM

Your set up is different than the 1500.I am guessing that the 3rd one is linked up to the carb as it is pressed against a rod mechanism and that may be the bolt that needs to be adjusted.Maybe it's not kicking in quick enough and that bolt has to be screwed in a bit.Again I am not 100% sure and that is where the manual comes in handy.The top two are probably the timing and slow speed adj, do not adjust them unless you have a timing light.Advance throttle and see what stops do what ,motor not running.The 4th one on the very bottom may be slow speed as well,not sure. I am somewhat surprised that no one else has chimed in on this.

 

[OldMercsRule]

Re: '79 80HP Merc Stalling at ~2000 RPM

I'm not very experienced with the stator fired inlines, (I have two parts engines that are stator fired, one an 1981 inline6 and a 1978 800 inlne4).

I do know that you don't have a distributor on that engine and stator/switchbox issues can cause similar rpm/power range problems like you now have.

CDI has a great trouble shooting stator/switch box site that has a section on yer engine at page 81.

You mentioned wiring issues which can cause problems, and nine years sitting could cause fuel system issues with leaking gas lines/dirty carbs/fuel pumps et al. It is a process of elimination. Good luck.

http://issuu.com/cdielectronics/doc...t.xml&backgroundColor=000000&showFlipBtn=true