No fuel to bottom cylinder

[MeHoBy]

I have a 1974 Merc 500, 50hp, ser#3482234. Have had a real running and stalling problem this year. Did a link & sync, helped a little. Compression 125# on all 4 cyl. Good spark. Pulled the plugs, #1-3 all showed normal wear. #4 was dry and shiny as the day installed. Could it be a reed problem? Bottom carb feeds bottom cylders, right? #3 is firing. Any ideas would be appreciated.

 

[Moody Blue]

Re: No fuel to bottom cylinder

Sounds to me like you have water getting into the #4 cyl. The water steam cleans the plug and cyl. Lower crankseal failure or leaking exhaust cover permits water into the lower cyl's.

The bottom carb fees the #3 and #4 cyl so if #3 is getting fuel then #4 most likely is as well. Your motor has a distributor so most likely if one plug has spark, then they all will.

I've just pulled the powerhead on my 1971 Merc 800 for the same reason.

 

[MeHoBy]

Re: No fuel to bottom cylinder

Thanks Moody Blue. I'll check those 2 items

 

[pinboy122]

Re: No fuel to bottom cylinder

Possible stuck float or inlet needle or screen?

 

[Laddies]

Re: No fuel to bottom cylinder

A bad lower crank seal will effect #4 cyl, does it run on all 4 out of the water if so it's sucking exhaust by the seal.

 

[MeHoBy]

Re: No fuel to bottom cylinder

Possible stuck float or inlet needle or screen?

The carbs come off next forr cleaning. I'll be sure to look at them closely

 

[MeHoBy]

Re: No fuel to bottom cylinder

A bad lower crank seal will effect #4 cyl, does it run on all 4 out of the water if so it's sucking exhaust by the seal.

I never checked it on the muffs to see if it is affected. I'll change the seal anyway since I'm in this far