1971 100hp johnson

[slim82]

this thing has officially ruined my weekend...I have a 71 100hp johnson that was running fine last week. took it out friday and it had a horrible missfire on cyls 3&4 so i rebuilt the carbs, replaced the plugs, gap on the points is .010. the amp box is less than 1yr old, and now it runs worse than before. it still misses and wont start without the throttle fully open. ive adjusted and re adjusted the slow idle screws about a dozen times. Can anyone help me out? im ready to turn this thing into an anchor!

also there is no water in the gas or in the cylinders and compression is around 120 per cyl.
thanks

 

[bigpoppakdog]

Re: 1971 100hp johnson

Well, I have a 70' 115 hp evinrude. This past week it seemed like mine was displaying symptoms of "bad fuel." It turned out my coil had come loose. One bolt fell off completely and the other was barely in. So when I was accelerating the vibration would cause the coil to loose ground and cause the motor to run rough.

That said, there could be many other issues. Fuel line, fuel filter, etc...Plus are you sure it was a misfire on the plugs? Does this have a clipper switch? I had symptoms like this a couple years ago when I got my motor. Turned out this clipper switch was bypassed by a jumper wire. It was this jumper wire that was bad. So I stuck in quite a bit of $$$ on a 5 cent wire problem.

If it is a misfire then you have to draw your attention to those components.

The recommended setting for the idle screws for my motor is 1 1/2 turns out and then adjust from there.

I'm sure others will ask you to do a checklist

1. Check for volts coming from battery to your terminals
2. Check ignition coil.
3. Check for spark in spark plugs
4. DVA meter to check for powerpack power
5. Check speed sensor
6. Check fuel lines
7. Set idle screws to 1 1/2 turns out to start
8. Carbs cleaned(you said you did)
9. new plugs(check)


If your electrical is showing up good then I would say check fuel delivery. But, electrical is often mistaken for fuel problems.

Not sure if this helps, but its my summary on my experience with my motor.