35HP Johnson idles rough

copus · May 20, 2002

1982 Johnson 35hp model J35RCND manual start. Engine idles rough when running in a barrel. So far I have changed water pump, removed carb and cleaned, replaced thermostat,checked and set sync and link,new sparkplugs. When running fuel bulb is hard (new tank, bulb and line).Compression is 100 lbs top cyl. and 95 bottom cyl. When running at idle, if I pull the top plug wire, there is no change. If I pull the bottom wire,engine stalls. If I increase slightly above idle speed and repeat this it will run on either cylinder. Seems to me the top cylinder is weaker for some reason. I replaced the coil on that cylinder, but no change. Could this be a bad powerpack?

G DANE · May 20, 2002

Re: 35HP Johnson idles rough

Hi copus I just had exactly same problem, same motor. I´d suggest to tests: Check if both plugs have spark, by grounding thread to block while helper crancks motor. If ok, produce a 1/2" gap for spark to jump to block. If both can, ignition is OK. In my coincidence a leaf in the reed valve set was broken. This can be observed when carbureator is off. Try to look at the two sets of reedvalves, in the intake housing. Are alle the leaflike valveblades there ? It can be a bit difficult to see, but can be done.

petryshyn · May 20, 2002

Re: 35HP Johnson idles rough

where you getting spark when you pulled the top wire?

copus · May 20, 2002

Re: 35HP Johnson idles rough

Schematic... Yes,I was getting spark to both cylinders and I also replaced the coil on the top cylinder.It will run on the weaker cylinder only, if I up the rpm's.

copus · May 20, 2002

Re: 35HP Johnson idles rough

G Dane... Thanks, I will take your advise and check the reeds tomorrow and let you know what I find.

DJ · May 20, 2002

Re: 35HP Johnson idles rough

Copus, You didn't by any chance cross the plug wires, did you? I just went through that experience myself. Boy did I feel like a dolt!!

ralph · May 20, 2002

Re: 35HP Johnson idles rough

Have the same motor. What are you setting the idle adjustment screw at? (on front of carb)

copus · May 21, 2002

Re: 35HP Johnson idles rough

D Johns.... Wires are on correctly,thanks. Ralph... Initial idle adjustment out about 1 1/2 to 2 turns. I slowly turn it in untill engine starts to run lean and then backout slightly for best idle with no coughing.

copus · May 21, 2002

Re: 35HP Johnson idles rough

G Dane...I removed the leaf assembly and everything looks good. No bent or missing reeds.

G DANE · May 21, 2002

Re: 35HP Johnson idles rough

Sorry Copus, i didnt read your post well. If you catch up the second cylinder by opening throttle it is not a reed issue. I would guess you have some airleak, perhaps at upper crankshaft seal. this will leanup the mixture for the upper cylinder. Do you have a flywheel puller ?

G DANE · May 21, 2002

Re: 35HP Johnson idles rough

Hey - if its the upper cylinder, the leak could be at the screw holding the bracket for the bar for the electric terminals. This screw passes through the intake manifold. If it is not tightened firm, it will cause airleak and affect iddle. Try to spary WD 40 on there and on the fuel pump when iddling. Does it change. BTW a bad cranckaxelseal is VERY rare.

copus · May 21, 2002

Re: 35HP Johnson idles rough

G Dane.... I tried spraying WD-40 around all gaskets but there was no change in rpm's. I noticed when I pulled the lower plug wire (the stronger cylinder), I could really hear the spark jumping. But when I pulled the topwire it was much softer. Also when the engine is running at idle I can hear clicking noises,such as a spark would make. I,m going to run it tonight when it's dark and check for spark leakage. As for the flywheel puller I might be able to scrounge something up. What would I look for once I get the flywheel off?

copus · May 21, 2002

Re: 35HP Johnson idles rough

Well, I ran the engine in the dark and I can hear what seems to be sparks but I see none. Could be under the flywheel.Engine would cough every so often. Adjusting low speed would not get rid of it. I guess i will pull the flywheel tomorrow and check there.

G DANE · May 21, 2002

Re: 35HP Johnson idles rough

Copus - The only wisible sight of a leaking upper cranck seal would be if fuel squirted out around cranck axel end ( messy with oil ) I dont think any spark would jump there, as all components under flywheel are common to both cylinders, and low voltage < 340 Volts at least. If you pull flywheel, be sure to use puller pulling on the three 1/4" threads around center and to engage wheel right to key and use correct torque when reattaching. When did this rough iddling start and how ? Maybe somone else could give you a good clue here.

G DANE · May 21, 2002

Re: 35HP Johnson idles rough

When this problem appears, how do the plugs look like ? very wet at upper ? If the fuel pump started leaking fuel through diaphrame, it would flood upper cylinder. Try to remove fuel pump by the two screws and prime bulb. Will it leak fuel through the little vacuum hole ?

fireman 757 · May 22, 2002

Re: 35HP Johnson idles rough

Haven't seen your engine but check your vacuum lines. Under the carb they make a sharp bend and sometimes they will crack and it's hard to see. How does it do at Wide open? Have you had it in the water to test it in gear? If it has sat it might just need a good running. Make sure you have fresh fuel. Also are you sure that your points are set correctly and your condensers are working?

copus · May 22, 2002

Re: 35HP Johnson idles rough

G Dane...Fireman Checked fuel pump like you suggested and found no leaks.I did notice that the spark was not retarding all the way at idle, so I had to put a small helper spring to pull the plate back all the way. This got rid of the coughing. I ran engine at a very fast idle and shut down. Pulled top plug which was wet and sooty.Bottom plug was much drier with a little soot. When I pull the top wire, rpm's stay the same. When I pull the bottom wire ,rpm,s drop drastically but it still keeps running. I bought this motor 2 years ago and it has been in the shed till last fall when I started it.Haven't had it on the water yet, so don't know how it will be under load. Using fuel from last fall but I,m going to get fresh fuel today. Fireman...No points, CD ignition

G DANE · May 22, 2002

Re: 35HP Johnson idles rough

Copus - did you try to make the spark jump from tip of an old plug to block, in exa 1/2" while someone else pulls cord. Will it produce 1/2" spark on both ? You have satisfactory compression, common carb to both, common drive coil, but each cylinder has its ignition coil and plug. Power pack distributes to relevant cylinder. The only diffenence can appear if: Airleak lets cylinder inhale air instead of air/gas mixture, spark is weak at one. I dont understand why ignition didnt return properly, tiller arm engages directly to stator plate before opening throttle ?

copus · May 22, 2002

Re: 35HP Johnson idles rough

G Dane... I tried the spark test. Both cylinders easily jump a 1/2" gap to block.The reason spark advance did not return all the way is that the vertical control lever with the slot in it is worn where the lower throttle control engages it. A good inch of slop.Going to replace that and the return spring that someone mangled.I guess I will try it in the water as soon as I register the boat and see how it goes.I can live with a slightly rough idle as long as it runs good under load. Thank you and everyone else for the help. I really learned a lot from this board and appreciate it. Copus

Gewe1 · May 23, 2002

Re: 35HP Johnson idles rough

Hi, I just recently had the same problem and went thru a lot of the same things you are doing. What I found was a blown head gasket between the cylinder and the water jacket. Have you check compression? May be worth a look. Good luck

35HP Johnson idles rough

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