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1986 Johnson 140

S

ssf4444

New member
Hello,

I have the type of engine the title describes on the same year Diplomat.
The bought was bought last year and interior completely gutted and redone before having it one the water. Once complete I did get a chance to get it on the water and well the engine has issues now.
So I am posting on here to see if anyone has insight on what my problem is and how to fix it.

The the engine starts, idles, and runs fine, at low to mid rpms. (It has a 21 inch prop) but once it approaches higher rpms (another piece of info, the Tach does not work) it cuts out. If you leave the throttle forward when it cuts out, it will cut back in once the rpm and boat slows down then starts to accelerate again, (it cuts back in.) It will continue to do this...If you back the throttle of, it runs fine as long as the higher speed/rpm is not approached. Since the tach is not working..it does this around the low 40 MPH range.

Some diagnosis already does was the fuel system. Tried running it with a portable gas tank plugged into it, same thing happens. After trying that the fuel pump was replaced. That did not fix it either.

I am thinking it is either the carburetors or something ignition related.
I did take the front panel off the air intake to observe the jets shooting fuel while it was running. I didnt notice anything that was off or would seem to be cause of my problem.

Could the carburetors just need taken apart, cleaned and put back together with new gaskets and all or is my problem much deeper?

Any information would be very much appreciate.
Thanks in advance!
 
Welcome - SSF this might just be your lucky day and you could save 10 weeks of time that it cost me finding my exact same problem on a Merc 90hp powerhead. Here's a link to get you started.

http://checkmate-boats.com/forums/showthread.php?t=18589

Be sure to visit the entire link on Iboats (register so you can see pics)

http://forums.iboats.com/showthread.php?p=2923363&posted=1#post2923363

...but if you electrical voltage checks out at WOT (could also be a faulty voltage regulator since the tach is acting up), and your engine compression is even it sounds exactly like my carb float problem.

After reading the entire posts, ask questions, some very knowledgable folks here to help.
 
It does sound like low float level may be starving for fuel past a certain rpm., Or You need to test out all your electrical. Get a manual if you don't have one and a good OHM meter and go to work on it. The manual will tell you how to do it. Also CDI puts out a good manual how to test your electrical components.
I think they may be free from CDI,
 
Clean your main jets.. look at your plugs and see if you have a cylinder that is real lean .. with the tach giving you problems I would check the voltage regulater
 
Well how about a little more basics, you say the motor is cutting out? Like shutting off or seriously missing? Or is the tach just shutting off, if you think it is the tach circuit in the voltage regulator just by pass it, take the harness side gray wire off and just attach it to the yellow gray on the terminal board, if the charging system is good the tach will now work, if not the tach is bad.

As far as the running of the engine, if you rtach is not working and you are running wide open with a 21 you may be banging the 6000 rev limiter. If you think its fuel related and the carbs are cleab whats the fuel pressure?
 
It is cutting out as in its not burning any fuel, Im sure its still turning over and everything, just no propulsion, when the engine slows down enough, it fires right back up and takes off again.

It doesnt seem to be "missing."

The sometimes, the tach will start to move when first starting the motor, but has never gone above 500 rmp, except for once when the engine was started out of the water (with a boot and gardenhose) to where it his 2k rpm.

As soon as the lakes around here thaw, and we get at least a 50 degree day, I plan to put the boat in the water and disconnect or bypass the tach to try and see if that will fix it or at least rule that out and then continue from there if needed.
 
If it loses power enough to slow all they way down it is running out of fuel, or sticking, do a compression test and a fuel pressure test
 
Thank you to everyone who posted on this.
Today I installed a new voltage regulator. The Tachometer now works.

I hope to put it in the water this weekend to see if that also may have fixed the cutting out at high rpms problem (at the very I will be able to tell at what RPM it is cutting out at!)
 
Good to hear. I will be anxious to hear your results and see if electrical problems give the exact same symptoms as my carb float issue. Wow...that was a frustrating 10 weeks! :brickwall:
 
Hey 82, rumour has it that the Muskie Machine is up on plane and ready to strike, any truth to this?
 
Wow...word makes it to the west coast fast. First muskie tournament this weekend...ready with all new chartplotting/down imagining electronics...some new 10" lures...some new 18" lures....this is going to be fun. Boat is running great! :D. Glad to see you didn't get crunched at the dock!
 
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