1981 2pg blown crankcase seal

[sbklf]

After rebuild (piston, cylinder and crank kit) it had an occasional backfire that would blow the fuel pump diaphragm. After about 4 of those it quit pumping fuel and I found the clutch side crankcase seal blown (literally nothing left of the rubber seal lips).

-If timing, which blows the fuel pump, too far advanced or retarded?
-Is it likely that the backfiring blew the crank seal?
-What else causes backfiring?

[cart around]

The backfire is absolutely what blew out the seal, and diaphragm. It's caused by not having a spring on the end of your throttle cable.

The spring makes sure that the throttle plate stays closed until the pedal switch makes contact. It will also smooth out your throttle response so you can putt around the yard real slow. I suspect that right now, your throttle is very touchy.

Look at my two pictures in this thread. http://www.buggiesgonewild.com/gas-e...djustment.html

Find an ink pen, and rob the spring from it.

[Dabble Inn]

I installed a spring on mine after the fresh rebuild last year and it cured the backfire issue (Thanks to Cart Around), But now lately it's backfiring again....

Looking into it I've discovered that not all pen springs are created equal, The one I used was able to work itself about halfway through the cable hole in the throttle lever ffs. I've got an APB out for a bigger one, Yep it's not easy being me. Ughhh!!

[cart around]

Try a small washer that just fits over the cable, and is bigger than your spring.

[Dabble Inn]

Yep thought about that, might have to make one. I really do need to fix it as soon as I can before it blows a seal.

For now I have discovered that when stopping if I leave the peddle down just far enough for the ignition to remain hot (engine idle for a few seconds) it doesn't backfire when starting again

[cart around]

This is the exact problem that you had 3 years ago. http://www.buggiesgonewild.com/gas-e...backwards.html

Was it ever fixed? Did you keep running it, and replace diaphragms, or has it been sitting since then?

You are building up a lot of back pressure. Have you ever cleaned the exhaust?

I really don't think it's timing. That should be set in the center so it will run in either direction. Moving the timing will just make it run better in one direction.

[sbklf]

I understand and know the importance of the throttle/ignition coordination, have the spring (a found that pen springs are too weak for my carb) and am pretty sure it is set correctly but will check it again thanks for the reminder. Yes same problem from 3yrs ago, the piston is in correctly and the muffler is new. I also converted it to HEI ignition and installed a new pulse coil and it did not make a difference. Regarding your timing comment, since it runs both directions is it correct that if I retard the timing for forward direction it will then be more advanced in reverse?

[cart around]

Originally Posted by sbklf

Regarding your timing comment, since it runs both directions is it correct that if I retard the timing for forward direction it will then be more advanced in reverse?

As far as I know, there is only one trigger point on the crankshaft. Giving one takes from the other.

Pages L-13 through L-18 give very good instructions, and the timing curve.

[Dabble Inn]

Originally Posted by cart around

Try a small washer that just fits over the cable, and is bigger than your spring.

Originally Posted by Dabble Inn

Yep thought about that, might have to make one. I really do need to fix it as soon as I can before it blows a seal.

For now I have discovered that when stopping if I leave the peddle down just far enough for the ignition to remain hot (engine idle for a few seconds) it doesn't backfire when starting again

Follow up;

Ok I couldn't find a bigger spring so I made a washer tonight, My buddies don't call me Mcguyver for nothing. I couldn't get a decent pic of the finished product but here's the materials I used, Success!!!!