I'm working on a 1973 F250 with a 390 that I'm trying to troubleshoot. My truck will not idle at all, only spits out fire ball.

I recently got some new heads from a local machine shop. I've now got them installed as well as a full set of gaskets and seals, spark plugs and wires and new distributor cap. I also took the time to rebuild my Autolite 2100 manual choke carb, which was my first carb rebuild.

I removed my distributor for this process and now I'm wondering if that is the reason for my backfiring. In order to reset my timing and reinstall my distributor I took out #1 spark plug and put my finger over it while I cranked the engine by hand. When I felt air blowing through the hole I kept rotating until I reached 10 (also tried 0) on the harmonic balancer timing indicator. I then installed my distributor cap to where my #1 spark plug wire landed right where the rotor was. Did I do this part wrong? Would I have felt air rushing through on the exhaust stroke as well?

So, I've triple checked my firing order (1-5-4-2-6-3-7-8) and made sure all the wires were plugged in correctly. Thats about all I've done, I just wanted to hop on here and ask some folks what they thought. I've searched through the forum and most people who are having trouble with carb backfire are actually able to idle. Mine, I hit my remote ignition button and get fire which is what makes me think I am 180 degrees off or something.

 

I think you may have it firing on #6 ,not #1 , 180 degrees off . When you felt the air pushing your finger out, you said you brought it on over to 0 , it needed to go on around again to 0 . Or you could have used a socket wrench and backed it back to 0 , right after the air came out. So,now just bring it up to 0 ,with the rotor pointing at #6, then lift the dist. enough to rotate the rotor to point at #1 with out turning the crank any. That should put it close enough to time it, unless I am miss understanding what you did to began with.

 

Well while rotating clockwise, when I first felt air blowing out I wasn't anywhere near 0 so I did keep on rotating clockwise until I was on 0. does that make sense?

If not 180 degrees off, what else could it be?

 

Following what you said in the first post i still believe it's off 180 degrees . Lift the dist. and rotate the rotor 180 degrees and it should be close enough to start, then set the timing. That's all i can offer so at least try it , if no start then ,we can look for something else.

You can do that in about the same amount of time it has taken me to type this.




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is it possible to have timing out 180 and it still run?

 

No it will not run 180 out of time.

 

Well I'd hardly say it was running... It literally only backfired when I turned the key. No idling what so ever.

Jim, thanks for your help and input. I did do as you said before my reply with no firing what so ever. But now that I think about it I may have done too much so I'm going to try it again. For some reason I thought that I needed to redo my firing order after that... I'm going to go try again!

 

Do like you said...get on the compression stroke...air coming out...slowly keep going to zero. once there... open the cap see where it is if its not on #1 its wrong.... Make sure your firing order goes the correct way for your engine...clockwise or counterclockwise...try starting once you have the firing order correct then adjust/advance to 10-12 with the vacuum advance off but plug the vacuum line.

 

The reason i thought it was off was ,last week i put a different dist. in mine and got it off 180 degrees. Did the same thing yours is until i clocked it right. I got in a hurry because it was freezing weather and i was trying to get it done. Ended up taking me twice as long after messing it up.