engine revs up and down!

[Becauseican]

I have a 1985 40 hp johnson.model number J40ELCO.It set up for a few years and i've been trying to get it lined back out. i put new carb kits in and was having serious problems with it bogging down and dying then realized i failed to put 2 of the gaskets in each carb. now runs alot better but at high speed it slows down and speeds up repeatadly. not really bogging down. just loses speed then regains it immeditly. if its sucking air somewhere would that do it or does it sound like a high speed jet? i baught a can of sea foam and will run it in tank this weekend. bottle says put the pint in 8-25 gallons. i have a 6 gallon tank. would it hurt anything to put the pint to the 6 gallons? 1 more question. i have noticed most of the linkage as pretty wore out. should the advanced timing start moving forward at the same rate as the carbs are being opened? any response would be greatly appreciated THANKS!

 

[levi_tsk]

Re: engine revs up and down!

i wouldnt -
sounds like your floats are slighly off kilter or something
yes they should up to an extent then the timing arm should hit a stop and the throttle should move a little further

 

[Becauseican]

Re: engine revs up and down!

you think its the float? think its not letting enough gas in carbs? should be bent down a hair? at high speed i would think the float would be down constantly letting fuel flow in? but im by no means an expert.

 

[DJ]

Re: engine revs up and down!

Floats should be adjusted to sit level with the carb. body help upside down.

Surging usually indicates an air leak.

Your linkage is very important. If it is not adjusted correctly (synch/link), or worn out, the engine will not accelerate and run correctly.

 

[Becauseican]

Re: engine revs up and down!

How can you make sure its in synch? as soon as the the throtle arm starts moving the carbs should the advance timming arm start moving forward?

 

[Monte1961]

Re: engine revs up and down!

The turn plate should start to move before carb/s open. Should be two marks where the throttle cam lines up. Make sure the cam wheel is between those marks.

 

[Becauseican]

Re: engine revs up and down!

ok i checked throtle cam and its between the 2 lines but the theottle cam is going forward before the turn plate ever moves. maybe that explains why engine sounds so bad at high speed..i need to find a way to adjust it so the plate moves just a little before the throttle cam starts moving right? hopefully linkage is not to worn out.

 

[Monte1961]

Re: engine revs up and down!

To even make you more confused, the throttle is moved by the turn plate. As long as it doent open before or after the two notches, then you are good to go. If not the do a link and sync.

 

[Becauseican]

Re: engine revs up and down!

Ok..your right. lol that did confuss me. the only thing moving the carbs is the roller thats against the throttle cam. your saying something else is working the carbs to?

 

[Monte1961]

Re: engine revs up and down!

Nope thats it!