81 Gas Marathon barely runs pops/backfires

[jrw261]

I bought a pretty rough 1981 Marathon and have been nursing it back to health. I've had it running on jack stands many times pretty good and finally got enough repairs done to take it down the road. As a test ride I probably did 5 laps around the yard on three occasions and it did well. I spent a fair amount of time adjusting the throttle and throttle switch...I am not using a OEM throttle switch bit it seems to work as desired and appears to adjusted per all the other posts.

To the point...I pulled it out of the garage and through the gate...up on the road. It ran great then all of a suddenly it started backfiring and gradually died. It would not restart but it tried. I pushed it back and parked it out of frustration.

After dinner I went back out and checked some things. Got fuel, got spark, good air...cleaned the plug and tried to drive it. I got it running a little and made a half of a lap around the yard before it completely died and began popping and backfiring.

I'll swap the plug tomorrow but doubt that's the problem...I didn't do any engine repairs and compression seems good. What looks like a regulatory is pretty badly corroded but appears to be working fine.

Anyone have ideas? It ran fine for a few yard laps and a 200 ft dash down the road

[racin161]

Welcome to BGW Well my first guess is the crank seals are shot that's how they act when one or both have blown. You have to maintain crankcase pressure and if not your shot down. If you jack it up and on jack stands you can see the one behind the drive clutch look for oil or an exposed seal. You can also try spraying carb cleaner in that area while cranking and see if will fire if so then there lays your problem. Now the bad news the other one is behind the flywheel and the only way to check it is to remove the flywheel. In any case both should be replaced at the same time.


LOU

[birdleg1981]

Sounds like a dirty carb to me

[jrw261]

I finally got around to cleaning the carb and took it around the yard a few times. I have to modulate the choke to match various rpms. I have the same issue and will be checking seals tonight... I need to pickup some carb cleaner.

[rib33024]

WD 40 works to

[birdleg1981]

Rib thats all i use to clean my carbs. Any type of penetrant. I dont like the residue.left behind.with carb cleaner.

[jrw261]

I appears to be the crank seals. To pull the flywheel does the puller pull from the four screws or the should I use the finger style puller?

Are the seals installed from the inside of the case or externally?

[kyerik]

Seals go in from the outside.

You will use the screw holes nearest the center of the flywheel to pull it off with a puller (a cheap steering wheel puller is fine)- a wide jaw type puller would break the flywheel if you tried grabbing it and pulling from the outside edges.

I just pulled my flywheel off a few days ago to get to my crank seals- mine was on there really tight. You may not have enough room to get the flywheel off with the engine still in the cart.

[jrw261]

What crank freeplay should one see from these? I have more than I would expect to see..to the point I get seal separation. I'm tempted to put the new seals in it and run it for a while but I know better. It's a shame because it has good compression.

[islandguy]

hey there jrw261. I was wondering if you ever fixed your problem? If so was it seals ?