30 hp Merc problems

[Robj]

I have a 1994 30 hp, 2 cylinder Merc outboard. The problem is the bottom cylinder. At idle the only way I can get the bottom cylinder to fire is by turning out the mixture screw 5 turns. Normally it should be about 1.5 turns, but at that mixture the bottom cylinder does not fire, it is dead. Anyone have any ideas as to what may be causing this problem?

Thanx for your help and have a great day,

Rob.

 

[JB]

Re: 30 hp Merc problems

Sound like a sealing problem in #2, Rob. Look for leaks at gaskets, reeds or crank seals.

 

[Robj]

Re: 30 hp Merc problems

Thanx for your reply JB. My guess was an air leak at the bottom crank seals. Does that sound reasonable? The bottom would be affected by leaking lower seal while the top cylinder would not, and by adding more fuel it richens the mixture and the cylinder fires. I don't think it could be the reeds because it only has one carb and a leak at the reeds would affect the top cylinder as well?

Thanx again and have a great day,

Rob.

 

[JB]

Re: 30 hp Merc problems

I doubt that a crank seal would leak enough air to cause your problem, Rob. A bad gasket at the reed block or a bypass cover is more likely. Try squirting some fuel premix around these areas and see if the jug starts to fire.

Though you have only one carb, the reeds for the two cylinders are completely isolated from each other.

 

[Robj]

Re: 30 hp Merc problems

Thank you JB.

That is why I was asking because I was unsure. I was ready to pull the engine and replace the bottom seal. But if you don't think that is the problem I will leave it. It is far easier to pull the reed assembly and reseal it.

Have a great day,

Rob.

 

[Robj]

Re: 30 hp Merc problems

Hello,

I am going to start working on this next week. Anyone have any other ideas where I could be getting this air leak from? Should I be looking at the fuel pump or oil injection pump as possible causes to this air leak? I know they run of from crankcase vacuum. Want to try and get as much information as possible before I start taking things apart. I know if I run it like it is doing so will only make the repair much more expensive.

Thanx and have a great day,

Rob.

 

[Robj]

Re: 30 hp Merc problems

I think I figured it out. i checked all the hoses and there weren't any leaks. I removed the carb and checked the reeds, they all looked fine. In the intake of the bottom cylinder, there is a check valve, it sits in a rubber housing, has a nylon ball with a brass insert. Guess what, the nylon ball is missing, allowing air to flow freely. This caused the air leak into the bottom crankcase and my lean misfire. Will buy a new checkvalve tommorrow and see what happens, but I am quite certain that this is my problem. Need to get ready for the 30 million salmon that will be swimming past my house!!

Have a great day

Rob.

 

[Robj]

Re: 30 hp Merc problems

I removed the reed block, reeds look great, flat. Replaced the check valve, new gaskets and put it back together. Bad News, still doing the same thing. So the reeds and intake are all OK. Any other suggestions? Should I pull the powerhead to check the crank seals? Getting desperate, out of ideas. Any suggestions are greatly appreciated.

Thanx and have a great day

Rob.