85 Johnson 45hp, won't idle in gear

Bought the boat this summer Asked specifically if it idles and trolls well..... haha. Starts ok, idles ok, accelorates well, and criuses fine. but I like fishing. At idle, when you put it in gear, within 30 sec to 10 minutes the rpm starts to slow down and will stall, unless at this point you give it a quick shot with the primer. then it picks right back up and you're good for another 30 sec to 10 mins. makes for a long day on the lake.... I've cleaned the carbs perfectly, replaced the fuel pump, checked for fuel line leaks. All the linkages appear to be adjusted pretty close. Spark plugs are new. Tried a hotter set. The carbs are non adjustable (the are idle jets rather than mixture screws, which I've tried a larger set). The float bowls are full when running because it takes off great, without hesitation. Ran Sea Foam through. Tried octane booster. The only thing I thought made any difference was I raised the floats slightly. How big a difference does a good thermostat make in a 2 stroke outboard? The tell-tail warms up slightly after a mile or two of cruising, but isn't hot. What about the reed valves? I don't think there's any blow back through the carbs.... ANY advise?

Re: 85 Johnson 45hp, won't idle in gear

Sounds like after you dump fuel on the vacuum side of the throttle plates you see improvement. Are the throttle plates closed @ start & idle? I would suggest you perform a sync & link to ensure the timing is sync'ed to the carbs.

Re: 85 Johnson 45hp, won't idle in gear

The throttle plates are closed fully at this point. I've tried disconnecting the timing linkage and advancing it manually, without any results, except raising the idle slightly. But it still seems to need fuel.... Its like a cold 4 stroke needs more fuel to run. But bigger mixture jets didn't make any difference either. What do you think of the thermostat just being too cold? Didn't bother my old dirt bike not to have a thermostat haha.
There is also some play in the throttle plate shafts. I also tried advancing the timing on the linkage in comparison to when the linkage hits the throttle roller.









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Re: 85 Johnson 45hp, won't idle in gear

I'm not sure what temp the tstat should be for that motor, but doubt it being too cold. Typically you'll have them open at 143, 165, and around 185 depending on the motors requirements & spec, They are definatly needed. Tell tail should be warm to hot but not scalding.
How are you "priming" the motor to keep it going? Priming dumps or floods the engine with a high fuel content on the manifold side of the throttle plates - very little air is passing the plates when closed. If the plates aren't fully closed or loose, you'll experience hard cold starts and rough idle.
How much play are you seeing?

Re: 85 Johnson 45hp, won't idle in gear

The tell tail is barely warm to touch I'd say. Thats on my list anyways, but we're running out of water time. It'll be froze over before we know it.... grrrr. I've checked to make sure the plates are right closed, even tried an extra spring to make sure. I could put a dial indicater on the throttle shafts, but I don't think its a huge deal. Hmmm, 1/2 mm total play? Apparently the 45hp is a commercial breed, and has an actual primer that connects just behind the throttle plates on both carbs, so it actually sprays the fuel directly in through a very small port there. Ideally, I'd like to find a pair of carbs that had manual mixture screws. Any suggestions? Fixed jets are ok until the motor gets old if you know what I mean. I also found specs for doing a syn & link, but its gotta be very close anyways. It'll idle all day if you don't put it in gear.... Thanks for your input. I know I've got a decent motor if I can iron the kinks out. Compression is close to 150 in both, and it jumps right to plane.

Re: 85 Johnson 45hp, won't idle in gear

Large.r idle jets make it run leaner, to richen up the idle you need to go smaller. Did you remove the core plugs and clean the small orifice 's in there?

Re: 85 Johnson 45hp, won't idle in gear

Hmmmm. I've cleaned the carbs with a spray carb cleaner a couple times. Then I finally had the boat at home, so I soaked them for 2 days in real carb cleaner. I poked a wire through everwhere I could. They really appear spotless after all that, but didn't look bad initially. I'll admit I was thinking wrong with the size of the jet, but in my defence, I had talked to a boat mech when I bought a 2nd set of jets, and he didn't steer me right on that one. I did however, while we were out one day, bend a small wire so I could put each end into the jet holes. It didn't plug the hole, only gave some restriction. At the time it didn't make any difference, but I may not have tried this long enough or it may have been running too rough by that time to smooth out..... It seems like its just a little problem staring me in the face, and I can't get it. If the weather isn't too bad tomorrow, I'm goin to find some water close to home and try going smaller with those jets....

Re: 85 Johnson 45hp, won't idle in gear

Ok.... This is a lesson for everyone dealing with carb issues.... While performing a syn & link in the shop, I noticed that one coil would not fire as large a gap as the other. After narrowing the gap to about a 1/4 inch, the spark was strong and blue. I'm sure it got even weeker however under compression, even if it only had to jump a 40 thou gap on the spark plug. The clencher was that after a moment of cranking and firing, the spark dissapeared, or was interupted suddenly. My whole problem has really been two problems this whole time... So I replaced the coil and off to the lake. Now the other part of this is that I was wrong about which the size of the idle jet changed the mixture. I even had a boat mechanic of 40 + years tell me that the larger the jet, the more flow and the richer the mixture..... My motor ran pretty smooth with the new coil after a little run to warm things up, but then the idle slowed and it wanted to stall. So I switched jets from 40's to 30's, which did actually richen the mixture. It ran very rough trolling in gear, like it was flooding, but finally did not stall for a change. So I put the 40's back in and inserted a small wire into the holes of the jets, to restrict it slightly. For the first time, it ran almost perfect!!!! I've also figured out how to make these mixture jets adjustable. Thats tomorrows project. Wow... Finally... Don't give up, and consider multiple problems.

Re: 85 Johnson 45hp, won't idle in gear

Adjustable idle air jet modification complete thanks to a pair of old 4 barrel Rochester carb needles. Looks factory built. Anxious to try out, but we've got 45mph winds today....