1990 carb linkage

[dan161]

I have a 90 marathon with a 3pg motor in it. The problem I I am having is that it is backfiring through exhaust fairly frequently. What I have found is that the carb butterfly isn't closing all the way. I'm not sure how the linkage is supposed to be hooked up, but I have found some discussion on here that maybe it needs to have a return spring on it. I tried to add a fairly lightweight spring to help close the butterfly but then it won't open. It just pulls the cable and governor spring, but butterfly won't open. So I am at a loss to figure out how to get the carb to close, while at the same time not having to much pressure so that it causes it not to open. Any advice would be great. I don't want to blow out my crank seals with the backfiring. Thanks

[1989Marathon]

Pop the linkage off between the governor arm and carb. Loosen the jam nuts and turn the plastic piece to shorten the linkage slightly until it is enough to close the butterfly.

[dan161]

I will mess with that to see if it will work. I had to extend it previously because it wasn't opening the carb all the way with the pedal to the floor. Thanks

[dan161]

Ok, so I shortened the linkage and was able to get the carb to close all the way, which did stop the backfiring but now the carb doesn't open all the way. Its close but not quite all the way. If I try to lengthen the linkage any more then it is then it won't close all the way again. I'm not sure what else to do about it, if anything....I don't want the backfiring so maybe I just need to live with almost open all the way. Thanks for advice.

[1989Marathon]

Are you saying it doesn't open all the way because you can still pull it open more, or have you actually looked at the butterfly to see where it is when open. Some butterflies can be opened a little past 90°. You want them to be at 90° when fully open. Anything past that, and you are essentially closing it back up.

[dan161]

Good point. I haven't taken air intake hose off to actually look at butterfly, just the top of the carb where linkage bolts on. I'm not to concerned about it anymore tho. I drove it quite a bit tonight and it seems to be running pretty good right. I may have to tighten up the linkage another turn as still getting some backfiring. But that may be cause I have the governor tightened up pretty tight also. I've heard that will cause backfiring also.