Strange ignition sounds

[Minkota]

I just purchased the truck and it is making some strange noises and I was hoping someone could help me diagnose them.

When I accelerate I hear a rattling noise coming from the engine.
When driving at a steady speed I can hear a popping sound in the exhaust (kinda sounds like popcorn popping inside the exhaust )

Someone suggested maybe try adding an octane booster to the fuel but that did not make any difference. After that fuel ran out I filled up with Non-Ethanol fuel and it still is no different.

The truck is currently set up with a small block Chevy (not sure if it is 305 or 350), it has a Carter AFB Competition Series Carb, and it has a MSD 6A Ignition Box, Powerglide Transmission

I Ordered a new set of Plugs, Wires, cap, and Rotor and they should be here in a few days.
Any suggestions would be greatly appreciated.

[geezer#99]

That rattling noise is pinging or detonation.
Check your timing.
The popping could be fouled plugs or burned valves or a flat cam.
Fix the timing first, do a general tune up and then see if the popping is still there.

Don’t drive it until you fix the timing, you could burn a hole in a piston.

[toolboxchev]

If you hear popping coming from the exhaust while going downhill and downshifting it would definitely from bad valves or a head in need hardened exhaust seats.

[Minkota]

Originally Posted by toolboxchev

If you hear popping coming from the exhaust while going downhill and downshifting it would definitely from bad valves or a head in need hardened exhaust seats.

It makes the noise while driving on flat road and in "Drive".
I am going to replace the Plugs, Wires, Cap and Rotor and I will update when that is done. Thanks

[toolboxchev]

Sounds more like carb or timing issue first. Do your best to time the engine after the new components then work on carb issues if any, this is important.

Keep us posted we like the updates!

[68 P.O.S.]

x3 on timing. I agree with Geezer, don't drive it until your timing is dialed in or you risk grenading the engine. Do you have the vacuum advance hooked up and where to? Your carb is gonna need goodies as well after you figure out the timing.

[Minkota]

Originally Posted by 68 P.O.S.

x3 on timing. I agree with Geezer, don't drive it until your timing is dialed in or you risk grenading the engine.

Agreed, I have driven it very little since the purchase; i have not even registered it yet, I am waiting until the drive train issues have been resolved.

Originally Posted by 68 P.O.S.

Do you have the vacuum advance hooked up and where to?

Yes, it is connected to the Idle circuit vacuum port on the Carb not the Manifold Vacuum port.

Originally Posted by 68 P.O.S.

Your carb is gonna need goodies as well after you figure out the timing.

I figured it would possible need a rebuild at the very least since the previous owner only drove it approx 100 miles in the last 4 years.....

[68 P.O.S.]

Originally Posted by Minkota

Agreed, I have driven it very little since the purchase; i have not even registered it yet, I am waiting until the drive train issues have been resolved.
Getting it setup and running right is the fun part



Yes, it is connected to the Idle circuit vacuum port on the Carb not the Manifold Vacuum port.
The ported, or timed, connections are meant for emissions equipment use. You want it on manifold vacuum so the vacuum advance will properly work at idle and cruise. Which distributor do you have, points or HEI?


I figured it would possible need a rebuild at the very least since the previous owner only drove it approx 100 miles in the last 4 years.....
I would rebuild it if it was sitting for that long with minimal use. Carter is gone now, but Edelbrock took over these carbs, so any parts you need will come from Edelbrock. They're great carbs, but finicky if not setup correctly. They're fuel pressure and heat sensitive. You'll need a fuel pressure regulator set to 5.5 psi and you'll need to adjust the floats to stock specs to keep it from flooding. You will also need a heat insulating gasket to stop the carb from percolating fuel, which causes hard starting/running issues.

I responded in your message above in blue

[Minkota]

Originally Posted by 68 P.O.S.

The ported, or timed, connections are meant for emissions equipment use. You want it on manifold vacuum so the vacuum advance will properly work at idle and cruise. Which distributor do you have, points or HEI?

It is connected to the port shown in the attached photo labeled "Timed Vacuum Port (Distributor Vacuum Advance) I will switch it to the Non Emission Vacuum advance port.

[68 P.O.S.]

There you go, perfect!

[Minkota]

OK, I replaced the Spark Plugs and it seems to be running better but still has the rattling. I am going to try and check the Timing and verify it is ok. and after that the Cab...

[68 P.O.S.]

Keep at it. Do you have a timing light? You want to set your total timing to 36 degrees btdc. Which distributor do you have, points or HEI? That needs to be setup correctly too.

[Minkota]

Originally Posted by 68 P.O.S.

Do you have a timing light?

Yes, but its a cheap Autozone light, hopefully it is accurate.

Originally Posted by 68 P.O.S.

Which distributor do you have, points or HEI? That needs to be setup correctly too.

Currently it has an MSD 6A Ignition on it with an external Coil ( I havent looked inside the Cap yet to see if it is points or Electronic. I have never used MSD before, HEI has always been enough for my needs...

[68 P.O.S.]

Is your cheap timing light adjustable or fixed? If fixed, you'll need to buy a timing tape to put on the balancer. When you figure out what your distributor is we can make suggestions on setting it up.

[Minkota]

Originally Posted by 68 P.O.S.

Is your cheap timing light adjustable or fixed?

Fixed...