Please Help merc refuse to idle!

Erik

Cadet
Joined
Jun 18, 2001
Messages
7
I have a 15hp merc that backfires smokes bad and will not idle. I have keep giving it gas for it to run. I have cleaned every port on the carb,install new switch box and cleaned the plugs over a dozen times. It seems to be running a rich mixture but i dount no how to adjust it. Its not the screw above the intake cause that screw doesnt seem to do anything at low speed. What am i not doing. Help! Erik
 

petryshyn

Commander
Joined
Oct 3, 2001
Messages
2,851
Re: Please Help merc refuse to idle!

'backfire' is quite a subjective word. Best describe it in detail to help determine cause. Also....what color smoke?? Do both plugs look the same when cleaning them? What tests have you performed?<br />Many conditions can cause a backfire. <br />-Carbon build-up<br />-Bad ignition, timing or synch.<br />-wrong plug heat range<br />-Leaking reed<br />-wrong headgasket (protruding)<br />-low octane fuel<br />-lean mixtures (more so on 4-strokes)<br />I'm sure there's many more!!! Thats why a discription is very valuable.<br /> :confused:
 

Erik

Cadet
Joined
Jun 18, 2001
Messages
7
Re: Please Help merc refuse to idle!

Yes the engine backfires. It sounds more like a dog snezzing. Then the plugs get dirty there is some serious carbon buildup on them looks more like rust, sometimes oil drips from them not all the time. I cant really say anything else...the switch box i had before i installed the new one was no good, all the wires rusted inside the insulation and the ground wire had a cut in it and it threw out a blue spark while engine was running.-help!
 

petryshyn

Commander
Joined
Oct 3, 2001
Messages
2,851
Re: Please Help merc refuse to idle!

I don't know of a common problem on this engine. Maybe someone else does and can help!! <br />Only things that I could think of that would cause a genuine 'rich condition' would be a defective or mal-adjusted carb.(float level too high), leaking fuel pump diaphram, choke valve closed, or in some cases a leaking reed valve. <br />I don't like the word 'rust' on your plugs. That will send us down a whole different path.<br />- Is it rust or carbon? Gotta know.....<br />- Again, what color is the smoke? (blue or white)<br />- Does the primer bulb get hard and stay hard as you squeeze for 10 seconds, or does it bleed down?<br />- Is the idle mixture screw only out 1 1/2 turns or so?<br />- hand in front of carb...when it backfires, can you feel an outward pulse(puff) at the entrance of the carb.<br />- was this problem there when you attained this motor, if not, did it occur gradually or suddenly?<br />- Have you tried different fuel since this problem occured?<br />- while maintaining the lowest idle possible(nursing the throttle)squeeze the primer abruptly. Does it stall instantly?<br />- get an old spark plug (not perma-gap) open up the gap to approx. 1/4". <br />or get a spark tester..<br />click me<br />Pull off one plug wire from engine and install on old plug(or spark tester). Hold old plug metal body to block. Pull engine over and observe spark. Does it jump this gap? If so, what color is it?(bluish white, or reddish orangish)<br />- when idling at lowest possible speed, spray wd-40 into carb intake('1 second' wiff)Whats the effect?<br />- what kind and how much oil are you adding to how much fuel?<br />If you go through this procedure, it will probably steer us in the right direction. If someone else knows of a common failure to check first......it could save you a lot of work!!! (not saying that the experience wouldn't due one some good) Depends what kind of person you are. I'd be just as happy working on someones headache, as fishing for walleye(sad, I know..)<br /> :) :)
 
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