I recently rebuilt the carbutrator. It runs but there is an annoying backfire/misfire. It seems to improve as the engine warms up. I used an original service manual for guidance. Yesterday while looking at the manual I noticed an exploded diagram of the carb. On the slow speed needle valve assembly there is a small piece called a needle valve bushing. The manual said nothing about the bushing only the retainer. As far as I nknow I did not see the old one either. Could leaving that bushing out be the cause of the misfire? There is a small piece in the kit that looks like the bushing. I can't believe I missed that. What do you guys think?
You can't see it, but it should be in there. Use a home made hook to get it out. Some people use a drywall screw, I've never personally tried that, but it sounds reasonable.
Is your miss at idle or high speed or all speeds? The bushing will cause a lean sneeze at idle, won't make much difference at speeds above fast idle.
The miss is mostly at idle. It gets worse when you try to go from mid throttle to idle So the old one is probably srtill in there. Ill see if I can find it.Thanks
I should add this motor is new to me. It has not been run in years. So this is the first time I've had it running. I repulled the carb and recleaned the slow speed jet and reinstalled this time with the bushing that I forgot the first time. Same old story. Hard start with misfires, after about a five minute warm up the misfires goes away and I was able to get it to idle down nicely. I am running champion j4c's and I don't own a torque wrench but i plan on getting one. I dont know If you guys read my previous post but I had a problem wit the stop switch, which had cracked insulation I have a new one on order, and will replace soon. I personally don't think this has much to do with it because the trend is that the misfires seem to improve the more the motor runs. Thanks for all of your input so far any more thoughts are greatly appreciated, as I still consider myself ignorant on outboard repairs.
Here's a thought for you.
Since the engine is hard starting, misfires at mid throttle and then behaves nicely after warmed up, I think you should check for a vacuum leak or a poor fuel connection or gasket. As the engine warms up, it actually expands a little bit. Perhaps enough to swell and seal off a vacuum leak or a bad carb or intake gasket.
Gary
1973 evinrude 18 hp carb rebuild
Linear Mode
