Miss fire on a Johnson 1990 140

I get high rpms on nutral, but once I put it into drive my engine doesn't even plain, seems like it boggs out, what u guys think it can be, gas tank was flushed ,gas lines flushed, carbs redone, spark plugs new, please may I get some info just bought and haven't been able to run on it, also compression is at 145 almost 150

Re: Miss fire on a Johnson 1990 140

well you have 3 jets in each carb. did you remove and clean all 12?

Re: Miss fire on a Johnson 1990 140

Mako77 said:

I get high rpms on nutral,

Click to expand...

Keep doing that and you may not have a motor to worry about.

Re: Miss fire on a Johnson 1990 140

I was going thru the factory service manual, and came across an interesting trouble shoot trick/tip. Find top dead center (TDC) of cylinder 1 mark the flywheel at the pointer, do it for each cylinder 1, 2 ,3 and 4, you should have marks around the flywheel now. Start the motor in test tank or in water(not muffs) and hook a induction timing light to each cylinder 1 at a time and run it at the rpms that is having issue. The timing light will highlight its corresponding mark, and the mark thats way off, or not showing is the cylinder with issue. It could be fuel or spark, at least you narrow it down.

running on muffs doesn't provide enough back pressure and the idle and rpms will be higher then normal. If you thought it was carbs, pop the airbox off, and drain each carb, note how much fuel comes out. 1 with less fuel could be a stuck close float, or clogged, narrows down the problem.

Let us know what you find

Re: Miss fire on a Johnson 1990 140

So basically ,paw, you telling me it's the timing might be off??
I will try it on water and post once I try and find the solution. Thanks for your suggestion. It would not be incorrect fuel mixture???, would that be cause of bogging

Re: Miss fire on a Johnson 1990 140

You have QuikStart on your engine, which advances the timing whenever you start the engine. Be sure that you are following the factory service manual for your specific engine if you decide to do anything with the timing.

Re: Miss fire on a Johnson 1990 140

I greatly Appreciate ur post, and will keep it in mind once I mess with timing , but do u think it's a timming issue??????

Re: Miss fire on a Johnson 1990 140

No. It could easily be ignition though. If you get an inductive timing light, you can "read" the spark while the engine is running through the RPM range and see if it is breaking down. You will need someone to drive while you watch.

Another thing that you can do is to remove the air silencer and use a couple of fingers to block the carbs one at a time so that you can isolate the problem cylinder by seeing which one does not change.

Don't pull plug wires on the 90 degree looper to check spark; you will damage the powerpack and have to replace it. (Sure, ask me how I know that.)

QuikStart is supposed to disengage when the engine reaches 96 degrees or 1100 RPM, whichever occurs first. If you don't hear and feel nthe engine slowing down at that time, check the temperature switch.