Johnson 50hp neutral/idle issues

[camobass]

Hi all, new to the forum and could use some help in identifying possible causes for a recent problem. I'm running an '05 Johnson 50hp two-stroke with roughly 60 hours on it, which until recently was running great. I have no real problems from a cold start, using the fast-idle lever and choke to get it going. Lately, when I go to restart the motor on the water it will start but will stall out pretty quickly unless I use the fast-idle lever once running, which I never had to do before. Also, at low idle (1100-1200RPM) the RPMs will periodically fluctuate between 800 and 1400 without any throttle change. At the same idle speeds, it seems that the motor is running rougher than it was before (side to side vibration/shaking). The engine still runs like normal above 2000 RPM all the way to WOT at 5650.

My first inclination is that it's a fuel control issue due to the RPM fluctuations at idle, but I could be way off. I've read about replacing the standard Johnson fuel line ties with stainless clamps to prevent air leaks, however I'm not sure that's the problem since the bulb will harden up pretty quickly (should it stay firm once the engine is running?). Is that something worth doing anyway?

My outboard mechanical knowledge is pretty low, but I'd like to see if it's something I can handle before turning it over to the shop.

Thanks in advance

 

[rick_l]

Re: Johnson 50hp neutral/idle issues

Is it possible that you may have water in your fuel?

 

[fireman57]

Re: Johnson 50hp neutral/idle issues

It could be possible that you are losing spark at low idle. I don't know much about them past the late 80's but it sounds like a coil or plug not working correctly. When it does this check your spark with a timing light. Or if you are really brave get some insulated pliers and pull the plug wires one at at time and see if it makes any difference on the rough idle or shaking. BTW after the engine starts the bulb will not remain real solid, it softens quite a bit.

 

[camobass]

Re: Johnson 50hp neutral/idle issues

Rick l, I suppose it could be possible although I would doubt it. I use only busy gas stations, sta-bil and keep the tank topped off in cooler weather. Any way to check whether this is the culprit?

Or if you are really brave get some insulated pliers and pull the plug wires one at at time and see if it makes any difference on the rough idle or shaking.

"Or if you are really brave" sounds like a good disclaimer that I shouldn't be messing with that...thanks for the advice, I'll check the plugs and spark timing.

Any other thoughts?

 

[Silvertip]

Re: Johnson 50hp neutral/idle issues

Timing does not generally change and since you admittedly don't know much about outboards, I'd suggest you not mess with that. Too much timing will put holes in the pistons. An engine with 60 hours on it should not need carb rebuilding however it is possible there is a small bit of debris in one or both carbs. The most inexpensive thing to try is a can of SeaFoam. Add a double dose of this fuel system cleaner to the fuel and run a tank or two through it. SeaFoam is an excellent product and may clean things up. As for warm restarts, use of the fast idle lever is not uncommon. There is no fast idle capability on most carbed two strokes so just a tad bit of fast idle helps on those warm restarts. A fresh set of plugs is certainly in order and taking a look at the old ones can be an indication of what's wrong as well. Old plugs (after a long wide open throttle run) should have a nice chocolate/tan color to the normally white center electrode. Gunky, oily appearance indicates a rich condition with possible misfire, weak spark/no spark issue. At idle, if the engine is shaking more than normal, push the key in momentarily. If the engine smooths out you are in need of carb rebuilds. Another thing to try wold be to turn each idle mixture screw in until lightly seated while counting the number of turns -- EXACTLY. Then remove the screws and using a spray carb cleaner with a spray tube, squirt some cleaner in the mixture screw holes. Then turn the mixture screws back in until lightly seated and then back them out the number of turns you counted previously.

 

[camobass]

Re: Johnson 50hp neutral/idle issues

Thanks for the input, I think that gives me a good idea of where to start diagnosing, and if it comes to it, what seems reasonable when it ends up in the shop.

 

[BigNiner19]

Re: Johnson 50hp neutral/idle issues

go ahead and check the spark...plugs, maybe pump some new gas through it.

My problem was the exact same that you described and mine was timing. But my motor is much older and had been tampered with some before I got my hands on it. Probably not your case with such a new motor...

Cory

 

[fireman57]

Re: Johnson 50hp neutral/idle issues

recheck all your fuel line connections and maker sure that they are tight. You may have a small air leak that causes your rpm flucuations. When it is cold you are hammering a bunch of fuel at it so it can overcome the extra air. Check from your tank all the way to the fuel pump, to the carbs, and also the small lines on the carbs for vacuum.