[mnm99]

I came home from the car show and noticed more than before popping sound through the exhaust. I believe my timing has something to do with it, what do you think?
(Vac disconnected) Initial timing set at 15* total 36* all in at 2800rpm ----NO POPPING
(Vac connected) Initial timing at 15* mechanical to 36*, with vac 52* all in 2800rpm----POPPING Starts popping around 2500 rpm.

Does it sound like a lean pop? I didn't hook up my LM1 yet to check. What do you think?
__________________

 

[figbash]

Check for an air leak in the exhaust, it doesn't take much to cause popping. The manifold gasket is a good place to start.

Tom

 

[Dave427]

How old are the plugs, wires etc? I would check tune up stuff first.

Dave

 

[mnm99]

I talked about this a while ago with this engine. It's always been there. I hear it more I guess because I went with electric fans and got rid of the noisy flex fan. Things I did before were...New wires, ohm wire, plugs, cap rotor, timeing in every way possible, new manifold gaskets, new exhaust gaskets, Checking A/F with my LM1 got 15.1 at 3000rpm, adjuster rockers 3x, new carb, got carb worked on at local shop, rejetted, power valve, carb gasket, and on and on. I got this motor last year and have been having a problem since. I already had to bring it back for crushed valve seals....

Back to what I found. With only 34* of timing it seems almost gone. As soon as the Vac is hooked up it starts. I know many people that run that much timing with the vac and don't have problems. What do you think is up?

The exhaust gaskets are new and so are the intake.

 

[Dave427]

What carb are you running do you know your jet sizes?

Dave

 

[chevguy65]

fatigued valve spring?

I have heard if it sat through winter the springs can become weak and can cause a popping.

No builder here, just passing along information.

 

[mnm99]

What carb are you running do you know your jet sizes?

Dave

Holley 670 avanger. I don't remember the jets. I may have changed them from 65 to 68's in the primary and left the secondary 68's

Still has the Warentee. I afraid to bring it back though. The first time I had to TELL them the valve seals were bad after seeing little orange particals under the valve covers in the heads.. They said it could be the intake gasket I INSTALLED. They charge $85 an hour if the problem isn't theirs. I feel they try to find a problems we do. They told me the idle quality was the carb last time and recommended a Qjet that would fix the problem, bull. I really think it's something with the drive train, cam, lifters ect... I did everything I and we can think of to try to fix it. It's a GM350 290hp engine. Here's the specs. Should it have a slight lope idle?


290HP / 350 Long Block GM Crate Engine Specifications:
Horsepower: 290 @ 5100 RPM
Torque: 326 @ 3750 RPM
Compression Ratio: 8.5:1
Block: Cast Iron 4-Bolt Main
Crankshaft: Nodular Iron
Heads, Chamber Size: Cast Iron, 76cc
Valves (I/E): 1.94"/1.50"
Camshaft, Lift (I/E): .450"/.460"
Camshaft Duration @ 0.050" I/E: 222°/222°
Intake Manifold: Not Included

I'm thinking of a set of 64cc AFR heads and a nice Roller cam this winter. Think it will wake it up? Think the bottom end can handle it?

 

[mnm99]

Holley 670 avanger. I don't remember the jets. I may have changed them from 65 to 68's in the primary and left the secondary 68's

Still has the Warentee. I afraid to bring it back though. The first time I had to TELL them the valve seals were bad after seeing little orange particals under the valve covers in the heads.. They said it could be the intake gasket I INSTALLED. They charge $85 an hour if the problem isn't theirs. I feel they try to find a problems we do. They told me the idle quality was the carb last time and recommended a Qjet that would fix the problem, bull. I really think it's something with the drive train, cam, lifters ect... I did everything I and we can think of to try to fix it. It's a GM350 290hp engine. Here's the specs. Should it have a slight lope idle?


290HP / 350 Long Block GM Crate Engine Specifications:
Horsepower: 290 @ 5100 RPM
Torque: 326 @ 3750 RPM
Compression Ratio: 8.5:1
Block: Cast Iron 4-Bolt Main
Crankshaft: Nodular Iron
Heads, Chamber Size: Cast Iron, 76cc
Valves (I/E): 1.94"/1.50"
Camshaft, Lift (I/E): .450"/.460"
Camshaft Duration @ 0.050" I/E: 222°/222°
Intake Manifold: Not Included

I'm thinking of a set of 64cc AFR heads and a nice Roller cam this winter. Think it will wake it up? Think the bottom end can handle it?

??

 

[bones454]

I'd say you're getting too much timing (vacuum advance )

does this happen at a cruise (hi vacuum) condition and while you have your foot stuffed into it (lower vacuum) or only at a cruise ? if only at a cruise, I try to take a few degrees away from the vacuum advance if it is adjustable

 

[csmnlm]

A worn exhaust cam lobe can cause a back fire through the exhaust. I had a bad exhaust valve lobe that would back fire under decel.