1979 Mercury 140 Outboard won't rev under load

[cbaillie]

I have a 1979 mercury 140 outboard I just bought. I went thru the fuel system, carbs, 125psi compression...etc. Hooked up the muffs, fired it up... ran fine....was peeing water and would rev up so I thought I was all good. Took it out on the river... fired it up... soon as I tried to throttle up... blah.. would not rev past about 2200. Had to throttle down and idle back. Checked spark and all 6 have a nice spark. I was told the ignition boxes can cause this.
Anyone else run into this? Can I test the boxes myself? How about the stator?
Thanks a lot!

 

[emckelvy]

Re: 1979 Mercury 140 Outboard won't rev under load

Definitely check the stator, failure to rev up is a common symptom for stator issues. A CDI-brand replacement will fix that for good!

Resistance checks alone might tell you but you may have to check voltages while it's running. For that you'll need to purchase or make an adapter for your voltmeter. Do a search on "DVA" for much info on that topic.

Here's a few helpful links:

http://www.boatpartstore.com/mercreadings.asp

http://forums.iboats.com/showthread.php?t=371144

http://www.boatfix.com/bykeywordnew2cdi.asp?textfield=511-9773&texttype=2&submit=Search

HTH & G'luck..........ed

 

[cbaillie]

Re: 1979 Mercury 140 Outboard won't rev under load

Thanks. I was thinking that would be my next step before throwing new parts at it. Needed another opinion.
Appreciate it!

 

[cbaillie]

Re: 1979 Mercury 140 Outboard won't rev under load

Hello,
I replaced the stator with a CDI brand and that did not help. I'm assuming it's either the boxes or trigger. By the way... whats that trigger do anyway? Does that turn the high voltage on to the coils or something?
Still a newbie and trying to learn.
Thanks again!

 

[cbaillie]

Re: 1979 Mercury 140 Outboard won't rev under load

Does anyone think I should disconnect the 2 yellow wires to the rectifier and try it again?
Thanks again

 

[Faztbullet]

Re: 1979 Mercury 140 Outboard won't rev under load

Before buying anymore parts do the basic trobleshooting:
1) check compression
2) check fuel system(carbs & fuel pumps)
3) check ignition system (go to CDI web page and download troubleshooting guide) and use the proper testing equipment.

 

[cbaillie]

Re: 1979 Mercury 140 Outboard won't rev under load

Hello there,
The compression is between 125 and 115psi on all cylinders. The fuel system has been gone thru as in cleaning the tank, lines, filters, and carbs. The vent is also working on the tank as well.
I'm curious about the trigger and boxes. What happens in the ignition system when you give it a little gas under load, feathering the throttle not to kill it. It has never been on plane yet. Spoke to the previous owner and a shop told him one of the boxes are bad. The thing is, it has spark on all 6 cylinders. So my question is, what changes on the ignition under load?
Thanks again!

 

[JeffMarGA]

Re: 1979 Mercury 140 Outboard won't rev under load

I am having the same problem with the same motor. We have replaced packs, stator, trigger, cleaned carbs. Works well out of water, but once under load it will only rev a little past idle then chokes down also bogs down in reverse under load?? They are now considering timing advance or yet another stator.

 

[cbaillie]

Re: 1979 Mercury 140 Outboard won't rev under load

Hey... does the trigger move? Like slide around the crank to advance timing?

 

[JeffMarGA]

Re: 1979 Mercury 140 Outboard won't rev under load

I am going to pick it up today and put it in, just to see if it will come out of the hole or not under load. He did not tell me what he did over the phone, but he is not charging me either. Sounds like he must have missed something when he did the other work? I will find out and let you know something this afternoon.

 

[JeffMarGA]

Re: 1979 Mercury 140 Outboard won't rev under load

Got it out there before the rain, replaced the bulb primer (bad check valve) - could here it rattle in there when you shook it. then adjusted the carbs slightly with the new bulb - it gets up and runs like it should. did have to reprime the bulb a couple of times when we would stop for a bit. thats an easy fix. good luck - and yes i left the yellow wires out of stator connected to rectifier.

 

[cbaillie]

Re: 1979 Mercury 140 Outboard won't rev under load

Hey Jeff,
Glad yours is running good for ya now. I replaced the line with blub primer and its worse. ??? Did you also replace the fitting that connects to the engine? It looks like theres a check valve in there.
Thanks again!

 

[JeffMarGA]

Re: 1979 Mercury 140 Outboard won't rev under load

not yet but i am going to get one today - the rest of the fuel system is tight - that fitting going into the motor does not feel snug and i feel that is what is causing it to leak back down. bulb will get hard but won't hold it. you said the fuel pump was working on the motor?

 

[cbaillie]

Re: 1979 Mercury 140 Outboard won't rev under load

Fuel pump is working good. Took it off again to check for any pinholes as well. Going to try taking the wires off the rectifier today. I'm still wondering if that trigger under the stator moves? Does anyone know if that thing spins to advance th timing.
Thanks again for your help!

 

[cbaillie]

Re: 1979 Mercury 140 Outboard won't rev under load

OK... I think I may have found something. The little black cup that goes together that advances the timing is very loose. I would assume that would mess with the advance if you are able to the move the throttle giving it gas and that thing doesn't advance the timing fast enough.
Thanks guys!
Well.. I was messing with the advance mechanism and busted the ear off the trigger. Guess I'm done playing boat mechanic. Ha.
I may order a trigger and rectifier tonight. Someone told me the boxes are probably bad. What do you guys think? It's sparking on all 6 wires.
Thanks again.