Bad intake manifold gasket

[lkmurraylvr]

Hi all,

I've got a bastardized 94 mercury blackmax 150 carbed outboard that's been having some issues. Main problem is it seems a cylinder is sometimes not firing. Sometimes it'll come right up on plane and other times I have to play with it and choke it to get it up. Sometimes my top speed is only 35 or so and then it'll feel like another cylinder kicks in and my speed will pick up by 7-8 mph then the power drops off again. It'll come and go quickly sometimes. The only thing I've found in my limited testing is that the intake manifold gasket is pretty much gone. Large areas are blown out on each side. I know this is causing the spitting and sputtering when I give it gas and on idle, but could it cause my erratic power delivery? And if not, could anyone give me any pointers where else to look? I checked the plugs and they're fine....I'll be checking the ignition in the a.m. Any other pointers would be much appreciated.

Thanks,
Jason

 

[hkeiner]

Re: Bad intake manifold gasket

If it were my motor, I would immediately fix the manifold gasket before running the motor any more at higher speeds. A leaking gasket could cause a too lean fuel/air mixture resulting in overheating and damage to the pistons. After doing this repair, I would then re-evaluate where to go from there depending on how the motor runs after this fix.

Having said that, the erratic power situation sounds more like intermittant ignition failure rather than a gasket/carb/fuel related failure. However, cleaning the carbs and rebuilding the fuel pump is a good thing to do if you have not already done that lately. Squeezing the fuel bulb during engine bog to see if it improves performance of the motor would provide a clue that the fuel pump is weak or the carbs are gummed up.

 

[lkmurraylvr]

Re: Bad intake manifold gasket

Thanks for the response. Carbs are brand new, but not sure about the fuel pump. I'll try pumping the bulb next time I'm out. I'm thinking its ignition related too. I tested all the plugs today while cranking and they all have spark, but I don't know if that means anything.