johnson 25hp

good afternoon i recently bought a 14' Mirrocraft with a Johnson J25RCIM it runs good always starts right up the issue i have is trolling at a idle it never dies but it shakes really bad and wants to die have put new plugs in in rebuilt the carb and checked the compression both where 120 psi any thoughts to make it idle better

thanks for reading
Paul

I would bet that you didn't get some of the small passages cleaned out completely. Did you use a factory kit and do a "complete" rebuild or did you just clean the carb?

It's a twin cylinder big bore engine.. if it doesn't actually die while trolling it's probably as good as it's going to get.
I recommend trolling with a drift sock or bucket so you can throttle up a bit, or invest in an electric trolling motor.

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I did buy a kit and disassemble it completely soaked it in cleaner the used a blow gun on all of the passages wasn't very sorry ?

Pappy said:

How about we start with the simple things first??

Right off the bat the engine was designed around and loves Champion plugs. Use them.
Secondly, from the sound of it the engine may be running rich. Try leaning it down a bit at a time until it sneezes lean then fatten it back up a bit. The leaner you can run the smoother the engine will be.
Third, Is the engine coming up to temperature? Was designed with a thermostat. The thermostat is there to warm the engine at idle and help provide a smooth idle. Many folks remove the thermostats because some boat ramp guru told them it was not needed.

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^^ pappy is right ( of course!)
Often when I'm doing a rough running/ won't idle repair on a motor, I quote for new plugs and a thermostat... it's hard to set the carb up if the engine temp is not consistent.

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I really appreciate all the good info i will be ordering a new thermostat and plugs and will update with how it goes
thank you

so i replaced the thermostat along with new champion spark plugs defiantly needed the thermostat i can lean it out or make it rich to burn your eyes but still is idling ruff but doesn't die ?

An induction tach can help diagnose a lot of problems like this.

I have a rough idle @ the mfg recommended rpm of 600-700rpm.

If I cant get it straightened out I might go back to a higher idle.

My 30hp merchatsu 2 stroke can idle at 750rpm all day.. but doesn't smooth out until about 900rpm.. nature of the beast when dealing with a larger twin cyl motor.

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Don't forget that ignition lead (timing) can affect idle quality too--dramatically in some cases. The way I do it (or did it earlier) is to reduce the throttle opening, then retard the timing, reduce throttle a little more, repeat. On that particular motor, 7° ATDC is spec and ideally you have to kinda sneak up on it. There are 3 major timing events. Idle, pickup, and max. pickup timing is where the ignition timing is at the exact time where the throttle roller hits the advance. Max is just that, maximum advance.

Been a minute or two since I've done a Johnnyrude, but on the stuff I'm used to, all 3 have to be checked any time the carb is off.

Where would I find the procedures on adjusting the timing ?

xforce said:

Where would I find the procedures on adjusting the timing ?

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At the top of this section in the stickies.

Iirc it is in section 2-64 in the manual.