I have a 1971 Johnson 100 that just recently has been sputtering at full throttle, then seems to lose power. At first I thought it was bad gas so I changed out the gas then ran some Sta-bil with the new gas. Then after consulting my manual, I thought it may be a fuel pump, so I changed that out as well. It fires right up, and will run solid at full throttle for about 10 minutes before it will start to sputter, then it will throttle down to about 3/4. Anyone have this happen or have any advice on this? Thank you!
You might want to start with some basic checks, compression and spark tests. Does it help if you squeeze the primer bulb when it is acting up? You do have points under the flywheel as well as a dist cap and rotor. You have an amplifier for the ign system, and a lot of wiring in between.
How is the fuel delivery system, have you cleaned the lately?
For it to take that long to act up you would think it would be electrical rather than fuel, but could be either.
You might want to invest in an OEM manual to help you trouble shoot and repair your system.
I recently had all of the wiring replaced, including the amplifier. It had been running good since July 4, but last weekend is when the sputter started. I replaced the gas tank and the fuel line to the motor as well. I will check compression this week. Thank you for your quick response.
I checked compression 125 on all 4. Spark seemed good on land but I run into the problem after it warms up. Could it be the coil, points? Anything else? Also, if points where do I find for this motor? I have no luck so far. They are the clip type.
Thank you in advance.