No fuel to bottom cylinder

M

MeHoBy

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Jul 15, 2008
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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.
 
M

Moody Blue

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May 24, 2004
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3,136
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.
 
M

MeHoBy

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Re: No fuel to bottom cylinder

Thanks Moody Blue. I'll check those 2 items
 
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Laddies

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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.
 
M

MeHoBy

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Re: No fuel to bottom cylinder

Laddies said:
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.
Click to expand...

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
 
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