spark and compression yes, but no power on bottom cyl on 1985 125 Force

[trikefloats]

Hi folks,
I have some experience with Rotax ultralight engines, and when I had these symptoms and I know it is not a fuel problem, because I have two cylinders getting fuel from single carb,and the other is running fine, that usually means crank seal leak. But with outboard engines a friend of mine told me that he has heard, that the cooling water may do these problems on the bottom cyl if the gasket is leaking. I will inspect the reed valves today.
Any ideas before I remove the power head to change the seal? Any tests that I can do? THANKS IN ADVANCE.

 

[Barnacle_Bill]

Re: spark and compression yes, but no power on bottom cyl on 1985 125 Force

Do you have a strong spark? i.e. will it jump a 7/16 gap with a blue snap? Its possible to have spark but not strong enough to fire under compression.

 

[john from md]

Re: spark and compression yes, but no power on bottom cyl on 1985 125 Force

If you have spark and you have compression all you need is fuel and air.

If you have a water leak, you will have water in the engine. Do you?

If you have a head gasket leak, you will not get compression.

If you have a carb gasket leak, your engine will run lean. But it will run.

If you have a bad reed valve it will run but with power loss.

Don't jump to conclusions, it can get expensive. You will do better if you take a methodical approach towards eliminating the variables.

Oh and BTW, search the past threads for problems. We have fixed a hell of a lot of them.


John

 

[GrindKore]

Re: spark and compression yes, but no power on bottom cyl on 1985 125 Force

If you have spark and you have compression all you need is fuel and air.

If you have a water leak, you will have water in the engine. Do you?

If you have a head gasket leak, you will not get compression.

If you have a carb gasket leak, your engine will run lean. But it will run.

If you have a bad reed valve it will run but with power loss.

Don't jump to conclusions, it can get expensive. You will do better if you take a methodical approach towards eliminating the variables.

Oh and BTW, search the past threads for problems. We have fixed a hell of a lot of them.


John

100% agree here, start with easy things like condition of the spark plug. Does it have fuel/oil coating, is it dry, or does it appear wet?