mercury bottom carb blowing out

sambrigman

Petty Officer 1st Class
Joined
Jan 29, 2010
Messages
210
1995 40hp 4cyl mercury running rough bottom carb is blowing out while motor is running I can cover carb with my hand and makes no difference in running. would it be compression blowing out? any suggestion or idea greatly appreciated. thanks
 

racerone

Supreme Mariner
Joined
Dec 28, 2013
Messages
36,047
On a 4 cylinder they are internal on the crankshaft I believe.-------Your serial # is ?-----Not easy for a novice.to fix-------But there are other checks to do first !!!------Compression first.----Then check for spark on each lead and see if it jumps a 3/8" gap.-------Sounds like the bottom carb is flooding.--------The reeds are very reliable but could be held open by seagull feathers I suppose.
 

DeepCMark58A

Commander
Joined
Aug 17, 2015
Messages
2,030
If compression is good pull the carb bowls and clean them out, clean the floats. I had the same issue and it was a chuck of junk in the bowl.
 

sambrigman

Petty Officer 1st Class
Joined
Jan 29, 2010
Messages
210
1995 40hp mercury 4 cyl fuel pump not pumping reed valves??

This motor is driving me crazy. Bottom carb blowing out. I can cover completely makes no difference .I have tried all suggestions except reed valves, and now I find that the fuel pump is not working. I replace the pump, still not working. So could the pump not pumping be a symptom of reed valves. Thank you guys for your tips and ideas I am at wits end
 

racerone

Supreme Mariner
Joined
Dec 28, 2013
Messages
36,047
I believe in inspection / trouble shooting.-----Did you take the old pump apart or did you just run out and spend $ and find that motor still does not work.----Sounds like you now have a good spare pump.-------With a bad reed valve you would not get crankcase compression, thus no pressure pulse to drive the pump.
 

sambrigman

Petty Officer 1st Class
Joined
Jan 29, 2010
Messages
210
I got a new pump, and had the old one inspected by a mechanic, the old pump was good too
 
Top