Off Roading Forums banner
1 - 10 of 10 Posts
G

·
Discussion Starter · #1 ·
All the sudden while going down the road, my '76 CJ with a 304 started backfiring non-stop back up through the carburetor. I could hardly make it back home due to the loss of power. The funny thing is, it idles nice and smooth--seemingly. But as soon as you give it a little gas, look out. I checked a couple cylinders for compression and they were fine. The plugs are all firing and look clean and aren't fouling. This past spring I put a new timing chain and gears from 4WD Hardware. It had been running great since. The vacuum lines seem OK but will check further. The carb and distributor are only a couple years old so should be in good shape. The motor was rebuilt around 10,000 miles ago. Any ideas on what else to check would be helpful. I am really stumped.--Kevin

 
G

·
Discussion Starter · #2 ·
I see no other way but to get the timeing light out and check timeing.
Sounds like the chain has jump a tooth on your timeing chain.
Check to be sure your distributor is tight or some how has not been turned.

 
G

·
Discussion Starter · #3 ·
Another thing to take a peek at... If you still have an air-pump system, be sure that the vacuum line is still connected to the diverter valve. The symptom you described can be caused by the vacuum being disconnected, or... the diverter-valve itself 'going-south'. The symptoms here are actually 'explosions' in the exhaust, and not backfiring through the carb.
Just a thought...

bob
 
G

·
Discussion Starter · #5 ·
I have the same problem on my 304. I am still trying to figure out the source. Mine definetly does backfire up through the carb. Pull the air filter and watch, see if you get a backfire up the carb. I have a manual choke, and if I pull it slightly, the engine idles at 1000 rpms and then it won't backfire at all. Otherwise, it idles like a kitten, and backfires if you give it any gas or load. If you figure it out, let me know! Dean
[email protected]
 
G

·
Discussion Starter · #6 ·
My 360 was backfiring like that because i did the timing at 1000 rpm and didnt disconect the vacume advance. nobody told me about that!! so i learned and retimed it with the vacuum advance disconnected and PLUGGED (it wont run at all if you dont plug the hose comming from the carb, nobody told me that either) and the motor at 500rpm (this keeps the mechanical advance from .... advancing?). RESULT? it runs bitchin. when i started it up to time it the right way, i saw that i had previously set it at 5deg the Wrong way because of the vacuum and machanical advance (i dont remember now whether it was supposed to be 5deg adv, or 5deg ret....it was like.. days ago.) anyways, its worth a check, sometimes it is the simple things that are hard to figure out. good luck ...see you in GLAMIS!!!!

 
G

·
Discussion Starter · #7 ·
I know which hose you are talking about. When I set the timing, I unplug it at the distributor, and then plug the hose. Should I also plug the orifice on the distributor that it hooks up to?

 

·
Registered
Joined
·
6,394 Posts
/wwwthreads_images/icons/tongue.gif Nope. But remember to have the RPM low to cancel out the effect of the centrifugal advance weights./wwwthreads_images/icons/crazy.gif

CJDave
 
G

·
Discussion Starter · #9 ·
Re: 304 backfiring like CRAZY - wow!

I just read your post about what you found... the 'missing' pushrods. I never would have guessed. I'll be interested to hear if you are able to discover the cause of this, or if you are able to see anything else that would lead to this. The only experience I've had that is even remotely similar, is a case of 'first-start-up', on a fresh engine, where the lifters apparently were pumped too full (before running), and on start-up, the pushrods buckled and fell out. In your case, I don't see what could have caused it, unless it got out of time (but you said it idled ok), or somehow the valves and pistons got together. When you pull the head, I'd recommend you look good for evidence of contact, or valve-stems that have become bent. Please let us 'inquiring-minds' know. And, no, I am not aware of this being a 'common' problem. Best wishes.

bob
 
G

·
Discussion Starter · #10 ·
Mine was doing the same thing. I think that it has some thing to do with the vacuum advance, because when I disconnected the vacuum hose, It ran fine. Right now I am driving it with the vacuum advance disconnected, until I get a chance to pull it apart. It is real simple to check. Pull the vacuum line and plug. If that does not fix, it is something else. Good luck.

 
1 - 10 of 10 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top