Mercury 25 Hp approx 1999 model......one cyl at low rpm

[dthx]

2 Stroke Mercury 25
top cyl compression is 120
bottom cyl compression is 115
getting great spark to both plugs...long and bright
both plugs new
The coils are applying voltage to both spark plugs per my meter but I have no way of knowing how much is correct.
tiiming is correct
carbuerator is clean
The motor starts up fine but runs only on the top cylinder untill the RPM is jacked up to almost max or 3/4 max .....then the bottom cyl kicks in...
Anybody have an idea what might be wrong....?

 

[flyingscott]

Did you replace any parts on the carb? How did you check the spark?

 

[racerone]

Does spark jump a gap of 5/16" or more ?------------What happens when you swap coils ?

 

[dthx]

Dont know about the coils.....will do...
Yes...the spark jumps at least 5/16

 

[flyingscott]

If you have spark that jumps 5/16" your coils are probably good. What about the carb? What was done to that? I had a similar problem with my 1987 25 hp Merc and it was the carb.

 

[dthx]

well,...the carb feeds both cylinders by way of the same throat, doesnt it?
So if the top cyl is getting enough fuel wouldnt the bottom one get enough fuel too?

 

[flyingscott]

I asked you 2 times what you did to the carb and you still have not answered me. It is either the carb or the lower crank seal if everything else is correct.

 

[dthx]

Sorry for not answering earlier....I didnt do anything to the carburetor.
The motor HAS been sitting for about a year.....but started right up.
I was talked out of taking the carb apart because of the reasoning above (March 17th post).

 

[flyingscott]

I can only give you advice whether you take it or not is you choice. Good luck with your motor

 

[MH Hawker]

one other thing my 1996 15 hp motor has a 2 stage ING it switches from 300 volts to 600 around 2500 rpm, my high rpm ing went out and needed anew CDI box

 

[dthx]

Dont write me off, flyingscott....I'll take your advice and get into the carburetor.....I know I should...
Thanks for the CDI comment, Hawker.....

 

[flyingscott]

Dont write me off, flyingscott....I'll take your advice and get into the carburetor.....I know I should...
Thanks for the CDI comment, Hawker.....

You need the complete kit for the carb. Make sure you get the primer and the fuel pump diaphragms.

 

[dthx]

Will do
Thanks