75 merc 40hp doesnt idle under 1400 rpm

[stevedon69]

1975 merc 40 hp will not idle under 1400 rpms.
took it to a shop and they did everything under the sun but rebuild the motor.
cleaned and rebuilt carb 4 times, has good spark.
he is thinking it has a vaccum leak at one of the seals on the crankshaft.
any help would be great!!!

 

[Texasmark]

Re: 75 merc 40hp doesnt idle under 1400 rpm

Keep harping on this but it will only cost you a few bucks to try. Doing a "decarb" with Sea Foam has done me a tremendous amount of good with ALL my engines of ALL types around the farm. I started with rough idle on my OB (which it cured) and went from there.

Do a search for the process on site.

Also, try squeezing the bulb when idling and see if it helps. If so, you have a fuel flow problem which could be caused by low vacuum caused by a crankshaft seal, or a bad fuel pump. Course on the fuel pump, if it were bad, or if the lines were clogged, it should hinder high speed operation.

Mark

 

[stevedon69]

Re: 75 merc 40hp doesnt idle under 1400 rpm

the guy that worked on my motor did all of the things you listed.
he de carboned the motor
rebuilt carb and feul pump
timing
check staters

are there any tricks to know about tearing the motor down? i have some exprience in working on motors but never a boat motor..

 

[stevedon69]

Re: 75 merc 40hp doesnt idle under 1400 rpm

took it to a diff mech, they did a leak down test in the crank case and it was good. they are going to look at some more stuff.

 

[AMD Rules]

Re: 75 merc 40hp doesnt idle under 1400 rpm

Have someone inspect the reeds. It doesn't happen to sneeze fuel out the front of the carb does it?

 

[stevedon69]

Re: 75 merc 40hp doesnt idle under 1400 rpm

havent seen any fuel come out of the carb. one of the mech said the reeds that he could see looked good.
where are the reeds on this motor??

 

[tashasdaddy]

Re: 75 merc 40hp doesnt idle under 1400 rpm

has anyone done a compression check. and a spark check?

 

[stevedon69]

Re: 75 merc 40hp doesnt idle under 1400 rpm

good spark and compression

anyone have any idea what a new carb would cost?