plug gap 1981 7.5 merc

[nickb911]

Got my motor running (almost) right finally. Started and ran fine until it died at WOT and seemed to be slightly surging before that. Primer bulb is still firm and fires right back up with choke ~1/2 out. Only died on me once today! That's a record for this season for me. My main question is:

What should my plugs be gapped at, and how do I gap them properly? Could this cause bogging at WOT?

This forum has been my saving grace BTW!

 

[Laddies]

Re: plug gap 1981 7.5 merc

.040-- plugged high speed jet.

 

[nickb911]

Re: plug gap 1981 7.5 merc

If the high speed jet is the one that sticks down into the float bowl, I have definitely cleaned that out. I'll check again, but I did notice that the opening where the screwdriver slot is isn't perfect, it looks to have been scraped? or something. Should I replace if in doubt?
If it's not that, could an air leak between the fuel tank and the carb be causing this engine to die at WOT maybe?

 

[Laddies]

Re: plug gap 1981 7.5 merc

A distorted jet could cause a problem, if you pump the bulb while it's acting up and it runs alright then you have a vacuum leak of a bad fuel pump.

 

[nickb911]

Re: plug gap 1981 7.5 merc

I have actually tried that, (pumping the bulb). It had no effect, I think. It's hard to catch it because I'm going along at speed and it just dies as if I hit the kill switch. I will try again though to be sure. While it is slightly surging, squeezing the primer bulb has no effect. That I'm sure of.
I removed my spark plugs today and one of them appeared very clean and new still, (they have only a couple hours on them if that) the other one was black and looked like it had been coated in fuel/oil. Could that be from flooding?

 

[86RajunCajun]

Re: plug gap 1981 7.5 merc

I have actually tried that, (pumping the bulb). It had no effect, I think. It's hard to catch it because I'm going along at speed and it just dies as if I hit the kill switch. I will try again though to be sure. While it is slightly surging, squeezing the primer bulb has no effect. That I'm sure of.
I removed my spark plugs today and one of them appeared very clean and new still, (they have only a couple hours on them if that) the other one was black and looked like it had been coated in fuel/oil. Could that be from flooding?

Clean plug with no signs of combustion mean no spark there.

I always say this, but its worked for me a lot of times. Start with the very basic beginning troubleshooting steps and look everything over real good for loose wires, burnt or chipped wires, etc etc. It has happened more than once a simple wire loose or a ground has ended a great day only to be fixed in 5 mins in my garage later after i scratched my head 5 or 10 times.

GL

RC

 

[nickb911]

Re: plug gap 1981 7.5 merc

So it seems that if I catch it in time squeezing the primer bulb can save it from dying. Does anyone know where to start diagnosing this? Also, where is the fuel pump in this motor?

 

[86RajunCajun]

Re: plug gap 1981 7.5 merc

So it seems that if I catch it in time squeezing the primer bulb can save it from dying. Does anyone know where to start diagnosing this? Also, where is the fuel pump in this motor?

Surely the fuel pump diaphragm if you can rule out the primer bulb by getting a new one.

It likely has a square shaped fuel pump. Follow the fuel lines from the carb to where ever it ends and you should be at the fuel pump housing.

The diaphragm isnt creating the suction the it should to draw enough fuel to the carb. This is why helping it by pumping the primer bulb improves the condition.

This would also explain why it appears you plug isnt firing fuel because your pump is only barely feeding enough fuel to the carb for 1 cylinder.

GL

RC