35HP Johnson idles rough

[Gewe1]

Re: 35HP Johnson idles rough

Sorry, I missed your compression test, but still feel you may have a blown head gasket, all of your symptons are the same that I had on a 25hp. At idle pull the bottom plug and engine stalls, but if I gave it gas it would fire about 80% of the time.Ran very ruff at idle.

 

[copus]

Re: 35HP Johnson idles rough

Update<br />I finally got the boat in the water to try it under load. Motor started after 3 pulls. If I slowly gave it gas it wanted to stall, so I shoved the throttle forward and it took off. Got the boat on plane but sounded like it was running on 1 cylinder. Top speed about 15 MPH. I ran it for about 10 minutes and then it overheated and died. Pulled the cover and block was too hot to touch. I let it sit for about half an hour till it cooled. Started up in a few pulls and we limped back to the ramp.<br />When I got home I took a compression test. Both cylinders 100 lbs.<br />I should add that I had already installed a new power pack. While running on muffs at a fast idle, I pulled the top plug wire and no change, but a nice fat spark.<br />Then pulled the bottom wire and the engine stalled. I'm stumped Should I pull the flywheel and do some checking or is it time to bring it to the shop?

 

[copus]

Re: 35HP Johnson idles rough

^

 

[G DANE]

Re: 35HP Johnson idles rough

Copus - if you got a flywheel puller - try to pull it and see if the upper cranckseal leaks fuel. Be sure you engage flywheel correct on key when reassembling. Tighten to right turque.<br /><br />Why did it heat up ? Do you get water from tell-tale when iddling ? Is the impeller and water pump OK ? Are you sure you havnt got fuel squirting out somewhere, it sounds like the upper cylinder gets too little fuel.<br /><br />By the way: if you get water from telltale when iddling, but overheats when running, either your thermostat is stuck, cooling circuit blocked, waterpump bad, or head gasket leaking air to cooling water when speeding. I know, many hints.<br /><br />Do a little checking and let us know more.

 

[oldboat1]

Re: 35HP Johnson idles rough

I think I would attack the overheating first. Make sure there is no blockage (suspect top cylinder). I would remove the head cover and inspect the water passages -- probably drop the lower unit again (unfortunately), and try to force water up through the intake tube. Actually, it would be good to do that before pulling the head cover. If you are not getting good flow, but are sure the passages in the head are clear, remove the exhaust cover and check the passages there. Blow air or water through at multiple points.<br /><br />If cooling is not the problem, and you remove the flywheel to check things out, I suggest you look first for wire abrasions -- possible a condensor wire is getting nicked by the spinning flywheel, and that is causing shorting.

 

[copus]

Re: 35HP Johnson idles rough

G Dane<br />Oldboat1 ...Pulled flywheel, no signs of leakage,just a little grease on the armature plate bearing.<br />Why did it heat up? Don't know. New water pump and we had water coming from the two axhaust ports,the telltale and the prop. New thermostat.<br />Pulled the head and the gasket was OK.<br />Another thing i found was when I put my finger over the sparkplug hole on the top cylinder, the compression was very low compared to the bottom cylinder. With the guage the lower cylinder pumps to 100 in a couple of pulls, but the upper takes 4 or 5 pulls to hit 100. I think the upper has stuck or worn rings.I'm soaking it with Merc Power tune.Piston to cylinder clearance is .012 upper and .010 lower. Does this sound like an overhaul is in my future? I've pretty much ruled out an electrical problem.

 

[DavidT]

Re: 35HP Johnson idles rough

If you guys don't mind, I'm having a similar problem with a 1977 Johnson 25. Unit runs and has a distint miss and coughing at idle and under load. Plugs are wet fouled after a few minutes of running. The unit requires a hell of a rich mixture to run in length of time. 4.5 to 5 turns backed out. Exhaust so rich it burns my eyes. I've changed two secondary coils. The original plugs that my father-in-law had were Champion J4C gapped at probably 0.020", I changed to 0.040" per the clymer manual (but wrong recommended plug) and the unit idled pretty good with an occasional miss that was regular under load. I put the Clymer recommended QL77RC4 gapped at 0.040" and NGK recommended (4122?) gapped at 0.030" and unit ran like crap, missing and coughing. I took carb apart and checked for wronk float level, pulled idle screw out and looked inside...carb is extremely clean with no apparent faults. No raise in engine rpm when sprayed with WD-40. Was thinking the CD2 Power pack bad but now I'm leaning towards air leak, but both plugs are wet when removed. Any thoughts greatly appreciated.<br /><br />Thanks,<br /><br />DavidT

 

[oldboat1]

Re: 35HP Johnson idles rough

copus -- It's a puzzler. You might try running without the thermostat and see if that makes any difference in the cooling. It does start to sound like a control module problem, but I don't have any additional ideas....<br /><br />DavidT -- Start with absolutely fresh fuel and oil, in the the right mix. (suggest you post a new thread to help insure additional responses).

 

[G DANE]

Re: 35HP Johnson idles rough

Copus - sorry for not being here for some time.<br /><br />Clearance is much bigger at piston head than skirt, as head expands much more, but according to manual skirt clearance should be aro 0.0088. I dont think 0.010 - 0.012 at head is any problem at all. Your compression seems a bit low, i had 120-135 on all mine, but meters are different. Compression should be OK if exceeding 100, and within 15.<br /><br />As your ignition is fine, somehow or other the top cylinder gets less gas/air mixture than the other. Try to Cranck very slow ( plugwires off and grounded to old plugs ) and listen around motor carefully. Any difference in sound when upper/lower inhails ?? Can you hear any leak, somewhere om motor outher surface.

 

[copus]

Re: 35HP Johnson idles rough

G DANE.... Tried your suggestion about listening for an air leak. I had a friend over with very good hearing and neither of us could hear any air escaping anywhere. I've decided to rebuild the block myself since the parts aren't to expensive. I rebuilt an old 1960 Johnson 75HP years ago and it came out pretty good. Thanks for all your suggestions and help.

 

[jasonmcrai]

Re: 35HP Johnson idles rough

have you checked all your vaccum lines i've had a motor that did a similar thing but it was the bottom cylinder

 

[copus]

Re: 35HP Johnson idles rough

Problem solved. A few days ago I removed the head to check for any leaks in the gasket. Gasket was OK, so I tilted motor up and sprayed Merc Power Tune into both cylinders. Did this for 3 days and let it sit.Cranked it over today and the differance was amazing.I can pull either plug wire and motor will run same on either cylinder.<br />Compression feels the same in both cylinders now.<br />So I guess it was a stuck ring. I have yet to try it under load, when the river goes down. Still not sure why it overheated last time.Will keep you posted.

 

[35hp Johnson]

How to set sync and link on 1982 35hp Johnson

 

[GA_Boater]

How to set sync and link on 1982 35hp Johnson

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