Mechanic Help Needed Please
Thread Starter
Melting Slicks
Joined: Mar 2008
Posts: 2,300
Likes: 1
From: Quincy IL
Mechanic Help Needed Please
1975 L48 Stock, Automatic. replaced push rods, and adjusted the valves, had carb professionally rebuilt. had a very rough idle... attempted to set timing... ran fine... drove about half an hour. Next time I went to driver was major rough... found out the valves were adjusted incorrectly. Re-adjusted valves... ran well... smooth idle. Next time I started it, rough again... very rough.... began to backfire through carb and popping out the mufflers.... pellets from catalatic converter were shooting out the mufflers. now the cat had no more pellets in it. car is still running very rough and popping badly through the tail pipes.......... where do I begin?? Very Discouraged...
Racer
Joined: May 2007
Posts: 370
Likes: 0
From: Cherry Hill N.J.
Help
Try checking lifters.....could be fouled with crud.......watch rockers to make sure oil is coming from push rods onto top of heads.
Look to see if all rockers are moving about equally.
Adjust valves properly....make sure they aren't to tight.
Just a few ideas to try to help solve your problem
Look to see if all rockers are moving about equally.
Adjust valves properly....make sure they aren't to tight.
Just a few ideas to try to help solve your problem
Drifting
Joined: May 2008
Posts: 1,462
Likes: 43
From: Choctaw Country
1975 L48 Stock, Automatic. replaced push rods, and adjusted the valves, had carb professionally rebuilt. had a very rough idle... attempted to set timing... ran fine... drove about half an hour. Next time I went to driver was major rough... found out the valves were adjusted incorrectly. Re-adjusted valves... ran well... smooth idle. Next time I started it, rough again... very rough.... began to backfire through carb and popping out the mufflers.... pellets from catalatic converter were shooting out the mufflers. now the cat had no more pellets in it. car is still running very rough and popping badly through the tail pipes.......... where do I begin?? Very Discouraged...
Valve train is straightforward,,,,
make sure you adjust it in sequence.
If you started off wrong you'll be messed up and it can be like having firing out of order.
It helps to make sure you are cold when you do it, temp can have affect.
Backfire
usually a timing issue so if you get the valve train back in order and all set you should be OK assuming nothing else is wrong.
Exhaust popping
usually a carb/air intake problem.
Check your carb and intake gaskets and vacum
Also, DB caught one the other day that was spot on... make sure your choke is set correctly or it'll run good at first (like you describe) and then go to pot.
there will be lots of other folks who will chip in and they all have good advice. Be patient and use your logic in order.
Intermediate
Joined: May 2003
Posts: 42
Likes: 0
From: pittsboro NC
I went through the same thing the other day. The car would run rough and pop. I changed the vacuum advance line from the line holley said to use to a full vacuum and it has ran great ever since. This may not be your problem, but don't give up...I was quite frustrated over a simple fix. Check your vacuum lines.
I ended up starting from scratch and checked everything...plugs, wires, timing, dwell, cap, valves.....everything. It sounds like you have already done this.
It could be that your lifters are not pumping up (like BHRIG said). Maybe that would explain why it runs good cold? Some say you can clean the lifters, but if they are that dirty inside.....
I ended up starting from scratch and checked everything...plugs, wires, timing, dwell, cap, valves.....everything. It sounds like you have already done this.
It could be that your lifters are not pumping up (like BHRIG said). Maybe that would explain why it runs good cold? Some say you can clean the lifters, but if they are that dirty inside.....
Le Mans Master
Joined: May 2006
Posts: 7,708
Likes: 266
From: indy indiana
I once had a problem with lifter backoff. The adjustment nut,or stud threads,was pretty worn,but not o much for visual inpection to reveal.I would adjut the valve,run great, then after a few days, the miss,clater,would return. Bought a plastic insert nut,fixed it.
Intermediate
Joined: Aug 2006
Posts: 44
Likes: 0
yeah - check valve train - you ran with the lifters adjusted wrong may have caused some to go bad or cam to wear down in places.
check your coil - a weak/on/off spark can cause all that too (backfire, too rich,...)
check your coil - a weak/on/off spark can cause all that too (backfire, too rich,...)
