'85 Johnson 150hp Throttle Gives Out

[tlynch]

Hello,<br /><br />I Have a 1985 Johnson 150hp Engine and when I am running at high rpms, 4500 or above the enigne sometimes loses throttle and it drops down to around 2000 (not always exactly but around) RPMs. If I keep the throttle open and wait it kicks back in. Usually within 15 secs or so, sometimes when is comes back in it goes in and out a couple of times. Someimes I thnk it helps to back off to idle and slowly accelerate again, it sometimes gets back up to high rpms and sometimes stops off at around 2000 rpms. The engine never dies and never seems like it is going to stall. It is so similiar each time I would think that it would either be an electrical promblem of some sort or a jet in the carb that clogs or something. It does not seem like there is a clog in the fuel line as it seems to repeatitive an exact.<br /><br />Thank you for your help in advance, I do not even know which direction to head in so any help would be greatly appreciated.<br /><br />Todd Lynch<br />Stonington, CT<br /><br />todd@shifteight.com

 

[12Footer]

Re: '85 Johnson 150hp Throttle Gives Out

What you have described is a fuel delivery problem. To confirm this, have someone reach back and squeeze the primer bulb a few times. If the primer ball has collapesed, the tank is not venting, or the pickup tube in the tank is clogged.Make sure the gas tank is venting (getting air to replace the fuel the engine is burning). It can be anything from the vent screw on the tank,all the way to the back side of the carb. Air leaks in a fuel hose, bad primer ball,anti-syphon valve inside the tank,fuel pump check valve or diaphram, clogged jets in carb,or fuel filter.<br />If the fuel is over 3 months old, it is varnish.<br />I'm sorry i can't be more specific, but really, any one or more of the above will cause the symptoms. It could be elctrical, but it would have a noticeable miss usually.

 

[keiser]

Re: '85 Johnson 150hp Throttle Gives Out

Could be the ground on a coil? A fouling plug? A bad plug wire? Sounds like to me it is losing spark to one cylinder and then getting it back. A bad connection somewhere along the line from the coil to the spark plug, if I am right. <br />The reason I believe this is the problem is because it seems to be cutting power very close to half. Had the same problem. A friend of mine had a set of coil's. One with a bad connection, the wire was almost fully frayed. I cut it, stripped it enough to put a new connector on it and pulled the bolt it was grounded to and used it to reground the coil. It ran better than it ever had since he got it Four years before. Something to look for.<br />Good luck,<br />keiser

 

[clanton]

Re: '85 Johnson 150hp Throttle Gives Out

Check magnets in flywheel, then ignition system check with peak reading meter. If you can get it up to 5000 rpm in water in gear running smooth, trim up and watch the tach. If the tach drops 300/400 rpms the stator is bad.

 

[Beernutz]

Re: '85 Johnson 150hp Throttle Gives Out

A lotta good suggestions.<br /><br />Try running it at night, and look for arcing around the coils. Barely visible cracks in the coil casings can cause your problem.

 

[tlynch]

Re: '85 Johnson 150hp Throttle Gives Out

Well, I bought a timing light and a peak reading volt meter and when I went out to see what the problem was with the engine only acted up once again for less than a second, so I have had no chance to test it.<br /><br />D**N intermitant problems!<br /><br />I have used it a lot since then and the problem has not come back. Oh well, if I could fix every problem simply by buying the tools to diagnose it I would be a happy man!<br /><br />Could this have been caused by poorly mixed gas/oil (injection was removed) and the spark plugs fowling up?<br /><br />Thanks for all of your help,<br />Todd Lynch