upper 2 cyls no fuel

[les morgan]

I have a 1983 merc 50hp 4cyl motor and the upper 2 cylinders are not getting
fuel. It happened before and I could remove and clean the carb, then the
problem would go away for a few days. Now I have rebuilt the upper carb
again and tried a different carb from a spare engine and still have the same
problem. The main problem is that the upper carb does not seem to have
any vaccum to pull the fuel into the cyls. I can hold a clean rag over the
lower carb and the engine stumbles and dies, but when I do this to the
upper carb nothing happens---- also adjusting the upper idle control screw
it seems to make no difference. Does anyone have any suggestions before
I have to pull the powerhead to check the reeds?

Thanks
Oneoarinthewater

 

[CharlieB]

Re: upper 2 cyls no fuel

Before I touch the fuel system I test EVERY 2 stoke motor for spark AND compression. This way I KNOW that the engine is basically sound and that the ignition system is capable of running the engine.

Then I move on to the fuel system, pull the fuel line from the outlet side of the fuel pump and crank the motor, is there enough fuel flow and pressure to feed the motor?

The carbs are the LAST thing to look at, buy the time I get to the carbs the rest of the motor is ready to add fuel, water and stir.

 

[les morgan]

Re: upper 2 cyls no fuel

Thanks for the reply Charlie. But I have been off work for about 3 weeks
due to a heart attack (doing fine) And I have not had access to a compression gauge. I am a service manager for a Chevy dealership and will
be able to access a gauge next week.

Les

 

[CharlieB]

Re: upper 2 cyls no fuel

Ouch!

I had a triple 2 1/2 years ago.

I am VERY lucky to still be here.

Take your time, the boat will still be there when you are ready.

Go slow and steady, small steps, at your own pace.

Take Care,

Charlie B

 

[les morgan]

Re: upper 2 cyls no fuel

Here it is Monday and was able to borrow a compression gauge. From top
to bottom 122-125-120-123. I have not been able to find an adjustible spark
gap gauge at a auto parts store but I can hear the spark jumping when I
remove a plug wire and hold it next to the plug. My main concern is that I
cannot bog the engine down when I hold my hand or a rag over the upper
carb opening. (It is like the upper carb is not sucking in the fuel) I do not
see where spark could affect the suction. Anyone have any ideas?

Oneoarinthewater....

 

[CharlieB]

Re: upper 2 cyls no fuel

We are assuming that the upper carb is full of fuel.

Pull the fuel line and check fuel FLOW and pressure. Possibly the fuel pump is weak and not filling the upper carb?

To play devil's advocate, IF the upper main seal was leaking, the second cyl wold still be working, howeverr, if the crankseal BETWEEN the two cyl's was poor THEN you could get a power lose on both top cyl's, HOWEVER< I would think that they would idle and then lose power as rpm comes up.

Check the fuel pump and line to the upper carb first.

Stay with the KISS principle for now.

Are the upper plug wires in the right order, no wiring got switched anywhere?
(Clutching straws now).