Motor jerking at mid throttle

[wilson973]

Took my 89 Johnson 70 hp out on the river yesterday for the very 1st time. Starts up just fine, Runs really good at idle to almost half throttle, then its starts jerking and I cant get it to stop or go any faster. I have to run it at less than half throttle. I just had the 3 carbs rebuilt, and took the off and checked again. Checked for full leaks or kinks. None. A freind said it sounds like it is going into SLOW MO. Says it probaly has a bad sensor on it. I disconnected all my tan wires including the one coming from the power pack. Still only can run at half throttle. Can anyone please lead me in the right direction. Really wanna pull the kids this weekend on Big Bertha.

 

[countvlad]

Re: Motor jerking at mid throttle

Took my 89 Johnson 70 hp out on the river yesterday for the very 1st time. Starts up just fine, Runs really good at idle to almost half throttle, then its starts jerking and I cant get it to stop or go any faster. I have to run it at less than half throttle. I just had the 3 carbs rebuilt, and took the off and checked again. Checked for full leaks or kinks. None. A freind said it sounds like it is going into SLOW MO. Says it probaly has a bad sensor on it. I disconnected all my tan wires including the one coming from the power pack. Still only can run at half throttle. Can anyone please lead me in the right direction. Really wanna pull the kids this weekend on Big Bertha.

sounds like you have fuel and spark.... have you checked the timing at WOT? i would also check the spark with a GAP tester to make sure you have good spark...

 

[tashasdaddy]

Re: Motor jerking at mid throttle

i first suggest check spark and compression, on all cylinders. could be closed fuel tank vent, weak fuel pump, water in fuel. carbs not completely cleaned, you have 3 jets in each carb, that have to be remove and cleaned. running motor without all carbs working together, you have a very high chance of BLOWING the motor.

 

[wilson973]

Re: Motor jerking at mid throttle

My compression is 105, 105, 112. That is good. I have really good spark. Sharp crisp blue spark. I also tried unventing the gas. Run a while with vent open and run a while with vent closed. Neither way did any good. What should my spark gap be. It is at .25 now.