I'm hoping someone can help me troubleshoot the issue with my 1986 Johnson 4 HP Model No. J4BRHCDE. This is the issue:
Motor starts and idles fine. If throttle is increased while not in
gear, sounds like the
motor revs up fine, but don’t know actual RPMs so can’t know for sure if it is really at max
RPM. When in
gear, and throttle is increased (it is a slide on the front of the motor housing, not a twist on the tiller) the motor
rpm comes up, but does not increase as much as it should for where the throttle is. For example, when it is full throttle it is only about half the rpm used to run. Motor seems to run fine and I don’t notice any unusual vibration, it just runs at a lower rpm than it should. Then, from time to time, while I am running along at full throttle/half rpm, the motor will suddenly go to full rpm. It sounds to me like there is a “clunk” in the motor at the same time (and every time) it goes to full rpm. The motor will then run fine at full rpm until next time you throttle down. Then, you are back to full throttle/half rpm situation.
I suspected it was a throttle linkage problem. It has a cam/roller
wheel assembly, and when I pulled the cover and inspected it the roller
wheel is a little wobbly but it looks like it is always bringing the carb to full throttle, so now I’m wondering if it is a carb problem (something stuck in there is obstructing
fuel flow almost all of the time) or an ignition problem (only running on one cylinder most of the time, but occasionally the cylinder fires).
Anybody ever had this happen?