[69nomad350]

so I've finally been putting some break in miles on my wagon now that my brakes and suspension are up to snuff. The car was running really well all winter, and now that I'm driving it I notice that under higher loads, when I let off the gas it backfires a bit.....in the intake I believe?

What should I check to fix this issue. the carb was freshly rebuilt so I am still trying to dial that in but I am a newbie so any tips here would be appreciated.

under 30mph or so it doesn't seem to happen but above that when I accel it sounds good, then let off there is some popping.
I couldn't capture it very well but hopefully this helps.

 

[Lew540]

Is this a roller cam or a flat tappet? When you mean break in you mean a fresh motor? The reason I ask about type of cam is what you are describing could be a cam lobe going if flat tappet. You mention carb was freshly rebuilt by who and what did they fix, adjust or replace? Make sure your distributor/wires etc. arer in good shape too.

 

[Jasons 69 Chevelle]

Is it lean popping

 

[smitty454]

If you are a newbie, learn to read and set timing. Get a light and tell us what your timing is initial and total.

Could be a lean misfire.

Could be a bad plug wire.

And like Lew said, good chance a cam lobe is going flat too.

Check timing
Check plugs
Report back to us.

 

[69nomad350]

it is a flat tappet RV cam

engine was rebuilt by a guy I found locally near Chicago

the carb was rebuilt by me following guides online. and tuned by me who knows very little but reads a lot ( probably the issue). the carb was leaking gas so I figured try spending 30 before buying a new carb.

initial timing is around 12 degrees last time I checked. I was planning on putting timing tape on it so I can check my total timing. and have read a lot on the subject on this site. plug wires are all fine but should I pull a plug to see the condition of them?

 

[Bob Tiley]

I prefer a dial back timing light rather than a timing tape. You just turn back the dial on the light to get your timing mark back to zero and read the dial.

 

[smitty454]

Yeah its probably the carb. I dont know my way around an edelbrock carb but im sure someone who does will chime in soon.

 

[69nomad350]

I prefer a dial back timing light rather than a timing tape. You just turn back the dial on the light to get your timing mark back to zero and read the dial.

it's a holley 4160 (edited because dyslexia)

 

[MikeN]

On my old truck with a mild 350, the distributor/timing had moved, and caused backfiring as you describe.

 

[RAMBO]

Have you retorqued your intake and carb bolts since you put it in the car?
Vacuum leaks on a fresh motor are very common after a few months due to everything heat cycling. Retorque everything on the top end and it may just resolve itself.

A few years back i had a brand new crate motor, ran good for a month or two then started having issues backfiring, idle issues... The intake bolts needed retightening, but it didn't even occur to me since it came out of the crate fully assembled.

A friend sprayed some starting fluid around the base of the carb and intake edges to check for leaks while it was running and those RPMS instantly shot up.. Nearly all the bolts were loose. Retorqued and was good to go again.

 

[hydro462]

Pull the vacuum advance, plug the vacuum line and add 4 or 5 degrees more initial.

 

[Chebell]

Mine wiped out two new flat tappet cams right off the bat. I’d change the oil and look for any evidence. If it has any kind of metal in it it will be pretty obvious and an oil change never hurts at any mileage. Flat tappet cams these days are absolute junk compared to twenty/thirty years ago, what you describe concerns me. If it is a lobe it will junk the entire engine in no time!

 

[69nomad350]

im getting close to my first 500 miles so was planning an oil change soon but should I just do it early? I think I'm around 350 miles now. would it hurt to check timing and carb first to see if it gets better or worse