1967 Merc 650 Thunderbolt skipping

[wprohonic]

My Mercury 650 motor was running good then started having trouble at idle. When I pull back neutral throttle, she dies. Finally got her into gear and running fast then the power cut by approximately 50%. Slowly feels like she wants to go faster but never regained full power back. Drove it once since then and had to adjust idle screw all the way in to keep her idleing without stalling. Still feel skipping at WOT and not full power. Replaced the fuel line and no difference. compression seems to be around 150 psi at each cylinder. Used spark checker and shes firing off good at the house. Did notice that while checking spark and compression on the lowest cylinder on the motor that she didn't wanna run at all. Plugs look a little oily to me but not sure what's normal there. Please help

*also notice small amount of fuel puddling inside motor housing directly below carb.

 

[wprohonic]

Re: 1967 Merc 650 Thunderbolt skipping

changed all plugs...same skipping....tightened up all fuel fittings...plz help!

 

[usskydvr]

Re: 1967 Merc 650 Thunderbolt skipping

If you squeeze the fuel line bulb does the 'skipping' go away? If so, bad fuel pump or clogged fuel filter or both.

 

[wprohonic]

Re: 1967 Merc 650 Thunderbolt skipping

squeezing bulb makes it cut out....found pinholes in intake manifold where fuel bubbles out...any idea what caused this? could this cause the skipping? can I repair this or do I need to hunt down a 1967 Merc 650 intake manifold?

 

[usskydvr]

Re: 1967 Merc 650 Thunderbolt skipping

Where are these pinholes? Since the carbs bolts directly to the manifold and since it is also the crank cover there really aren't any runners. Any pinholes
here could let in excess air which would lean out the engine eventually burning a piston. The bulb squeeze ( not like a gorilla, but just good hand pressure) should not cause the engine to stumble unless the float is not set correctly which would let fuel in past the inlet valve. No idea on what caused the pinholes, but they need to be repaired.

 

[wprohonic]

Re: 1967 Merc 650 Thunderbolt skipping

Very small bubbles come OUT where I marked with the black arrow The bulb tends to empty out a little after it runs for a minute or so...gentle squeeze has minimal effect except for refilling the bulb.

 

[coolguy147]

Re: 1967 Merc 650 Thunderbolt skipping

really? is it the bolt? or is it on a gasket? crack? maybe a jb weld would fix it but why would it leak there is the big question?

 

[wprohonic]

Re: 1967 Merc 650 Thunderbolt skipping

Small holes in the metal...not bolt or gasket.

 

[usskydvr]

Re: 1967 Merc 650 Thunderbolt skipping

Ok, so I re-read the post again. You originally said that to keep her running you put the idle screws 'IN' all the way. That is full lean. You also said that she died when you gave the bulb a squeeze. If she was sucking air in the pinholes she would also tend to run lean. This sounds like she is running way rich. That points to float adjustment. The pinholes probably aren't an issue, but I'd JB them any way. As to why did they happen, I'm guessing impurities
in the aluminum finally came through. (p.s. plugs should look a bit oily,but they should all look about the same, especially if you are used to looking at those from a car)

 

[wprohonic]

Re: 1967 Merc 650 Thunderbolt skipping

Awesome info. I got the carb rebuild kits today in the mail along with new floats and fuel pump rebuild kits. Also gonna do the water pump while shes outta the water. I wondered if I could put a new crank cover on this motor. I found one but the guy selling it says they are like bearing caps and are machined to each motor. Is this true?

Thanks again!!

 

[usskydvr]

Re: 1967 Merc 650 Thunderbolt skipping

No, there are bearing adjustment bolts on the cover. You could use the one he has, but that is a MAJOR amount of work (you have to pull the powerhead) for a couple of pinholes.