TheSamba.com Forums
 
  View original topic: Scary Popping Sound Suddenly Happening
Rayfield Thu May 06, 2021 4:43 pm

So, trying to keep it concise...my project car's engine WAS running well, I was making test runs around the neighborhood successfully, but then on a recent loop around a neighborhood, it developed a nasty-sounding POPing sound, when I give it gas. It seems to do it now, once the engine is really warmed up, and the sound is coming out of the exhaust. Also, it seems like it doesn't idle or run or SOUND as smooth as it did, before.

I know that's vague, here's the background:
The car sat for a very long time, this engine came with it, a stock 1600DP. I wound up changing out most of the fuel system, including a tank, fuel pump and a Chinese-made 34 PICT clone that had good reviews. The ignition system is also new, plugs, wires, a Pertronix Flame-Thrower distro with Ignitor module and new coil. It is running an exhaust header, and a baffled stinger. I like stingers, and the original exhaust was a rusty mess.

Again, it was purring like a kitten, 2 weeks ago. Now, it will run, but there's this scary popping that happens, seems to come on particularly once the engine is warm. The car doesn't buck, it just makes the popping, and I go on.

Here's what I've tried:
I pulled the carb off, pulled it apart, jets, float, etc, cleaned it out thoroughly.
I checked timing, it's where I originally set it, ~7.5BTDC at idle, 30ish degrees when revving.

Could an exhaust leak cause it? I'll probably jack it up tomorrow to check for that. Sticky valve? More serious internal issues? I will also mention that I'm getting a flashing oil light, here and there, at idle, even though there's plenty of oil in the engine, so I'm wondering about the overall health of this motor.

Thanks for any help..

67rustavenger Thu May 06, 2021 6:30 pm

n exhaust leak will cause a popping (Backfire) out of the exhaust tips.
Even pea shooters will do it.

You can connect a clean shop vac in blow mode. To the exhaust tips. And pressurize the exhaust system
Then apply a water/dish soap solution to all the exhaust sealing joints.
Bubbles will appear where the leak exists. If there are any.

sgmalt46 Thu May 06, 2021 7:04 pm

have you checked valve adjustment? sounds like a tight exhaust valve.
that would make it pop out he exhaust. tight intake will pop through the carb.
give em a look. check with engine cold.

Rayfield Fri May 07, 2021 2:03 am

I set the valves a couple of months back, but this is certainly worth checking, thanks. Maybe I got something wrong, or something's changed..?

I'd love for it to be something as simple as an exhaust leak, but leaks I've had on my bugs in the past seemed to make little pops when letting off the gas. That's a little different from the big sounds I'm hearing while on the gas, in this case. But definitely going to check for leaks, as well!

goober Fri May 07, 2021 4:43 am

When you check the valves check for any brass particles in the residual oil under the rockers on the heads. Have the valve guides been replaced recently?

Also check for any cracked or weak springs or unusual stem height. Try wiggling/pushing the exhaust valves sideways.

"I'd love for it to be something as simple as an exhaust leak,"

It probably is but check it out.

Rayfield Fri May 07, 2021 4:53 am

Thanks, good stuff!
This engine is a mystery to me, it came with this basket-case car when I bought it last year, from a guy who never got around to trying to run it. I was pleased when I finally got it going. So I can't speak to the valve guide situation. I'll be replacing this engine sooner or later, but hoped to get some service out of it while I'm working on everything else that's wrong with the car, lol.

goober wrote: When you check the valves check for any brass particles in the residual oil under the rockers on the heads. Have the valve guides been replaced recently?

Also check for any cracked or weak springs or unusual stem height. Try wiggling/pushing the exhaust valves sideways.

"I'd love for it to be something as simple as an exhaust leak,"

It probably is but check it out.



Powered by phpBB © 2001, 2005 phpBB Group