1957 johnson 75 Engine misfire at low spead

" I have big problem to make t

" I have big problem to make that old engine run good. The spark plug are new, the carburetor is clean, the gap on the points is good (.020"), I also polish them with a 600 grid paper ta see if the engine would run better. Actually what the engine does is that at high speed it is running perfectly, Then, when I slow down , it goes good till the handle is just pass the start mark and when i go on the oter side of the start mark, it goes good for a short period then it start to misfire and seems to run on one cylinder. If I put the engine at full speed, it will pick up and fire good on both cylinder. I would like to know if this could be due to the points, condenser or coil. Is there a way to test does systems. "

"Luc.... The markings on the t

"Luc.... The markings on the throttle handle are more or less simply for reference, such as which way do I turn this thing for fast or slow. I suspect that your carburetor is out of adjustment (assuming that the carburetor has been assembled corectly, and is in perfect condition).

For starters... gently close both of the carburetor adjustable jets (needle valves). Now, back out the top one (slow speed) 1 1/2 turns. Back out the bottom one (high speed) 1 turn. In the water, start the engine (yes it will run lousy with those initial settings), put it in forward gear, and apply full throttle. Slowly turn in the bottom (high speed) valve until you hit a point where the engine starts to die out. At that point, back out that valve approximately 1/4 turn. At some point in that 1/4 turn out, you will find the smoothest setting for full throttle.

Now, slow the engine down to a point where it will remain running and shift into neutral. Slowly, in segments of 1/8 turns, start turning that top valve in. Wait a few seconds between each turn for the engine to respond. As you turn that valve in, the engine rpms will increase. lower the rpms with the throttle handle just to a point where the engine will remain running. Continue this procedure until you hit a point whereas the engine will either spit back through the carburetor (sounds like a mild backfire) or it will start to die out. At this point, back out that valve approximately 1/4 turn. Again, at some point in that 1/4 turn out, you will find the smoothest idle setting.

Hopefully, that will cure your problem, and at the very least, now you know the correct procedure for adjusting the carburetor.<grin>

Joe "

" Joe ... I dont think that th

" Joe ... I dont think that the carburetor is at fault because i already did the ajustment on the carburetor. Even when the engine start to run on one cylinder it is preaty smooth running for an engine that is running on one cylinder. The problem i am experiencing now is always the problem i have with all of my engines (snowmobile, boat, etc..). They always start running on one cylinder at one point. I really believe that the problem is in the electrical system but i dont know what to do for testing. Knowing that at high speed the engine is running good, Do you think that by replacing the points and condensers i could solve the problem??? "

"Luc... I can't say that n

"Luc... I can't say that new points and condensers will cure your problem but if they're rather old or pitted etc, it certainly won't hurt to have them replaced. Check the armature plate that the points are attached to. If there's excessive play whereas it can rock quite a bit and/or move from side to side slightly, the point setting would change when the timing is advanced/retarded which would result in a ignition problem. I have encountered that problem a few times and found that the cure was to gently tap the support plate (the plate that the armature plate rides on) at four areas. Looking straight down at the support plate, the tapped areas would be at 12, 3, 6, and 9 O'clock. This eliminated the excessive play and kept the armature from rocking. Worth looking into. There could be many causes... chafed wires, etc. It's strange that all your engines do this. Let me know what you find.

Joe"

" Thank You Joe I mill certain

" Thank You Joe I mill certainly let you know as soon as i found something.
Regards,
Luc "