backfire thru carb at 3000 RPM

[Jenz38]

Your gas is absolutley fresh ?

The wire wetween coin and points have no short cuircuit to the dist housing or is broken from inside ?

By the way,I have answered you the quest with rev out ? yes my engine runs up to limit without problems in standing.

[tiltbilt]

Your gas is absolutley fresh ?

The wire wetween coin and points have no short cuircuit to the dist housing or is broken from inside ?

By the way,I have answered you the quest with rev out ? yes my engine runs up to limit without problems in standing.

I am glad to get the answer to my question on if anyone has run their straight 8 to 3000rpm with no load.
Entire new wiring harness installed from vendor YNZ. No shorts inside or out of the distributor.

Thanks again for any and all ideas.

[Jenz38]

one thing i have yet , your inner valvesprings are installed ?

because what you cant see,you cant missing ,you understand ..

[tiltbilt]

one thing i have yet , your inner valvesprings are installed ?

because what you cant see,you cant missing ,you understand ..

Yes, I checked for inner valve springs yesterday when I checked for the valve spring shims/washers.

[Jenz38]

Puh .... at this moment im here at my end ... I think you/we must have a break .
I would then start completly new ,beginning with disassembling the cam and maybe the head for check it all...

please let me hear your thougts and ideas

[tiltbilt]

Puh .... at this moment im here at my end ... I think you/we must have a break .
I would then start completly new ,beginning with disassembling the cam and maybe the head for check it all...

please let me hear your thougts and ideas

I also don't know. The plan right now is to finish assembly of the rest of the car, then take it into my

mechanical shop for wheel alignment and new exhaust system. While it is in there, I can put it on the scope to see if I can spot something in the primary or secondary ignition and get some exh gas readings with the exh analyzer. Will keep you posted. Hope to do this around end of this month.

[telekenfun]

I also don't know. The plan right now is to finish assembly of the rest of the car, then take it into my

mechanical shop for wheel alignment and new exhaust system. While it is in there, I can put it on the scope to see if I can spot something in the primary or secondary ignition and get some exh gas readings with the exh analyzer. Will keep you posted. Hope to do this around end of this month.

After reading this thread that had only a mention of distributor timing, I suggest looking more in-depth into distributor function.
To start lets look at the advance characteristics of your Buick distributor. As I recall the vacuum advance starts with only a couple of inches of vacuum and the centrifugal advance starts somewhere between 600-1000 RPM. Each of these advance systems contributes about 10 degrees of spark advance.
Lets assume that everything is now mechanically operating perfectly. When this engine is running at 3000 RPM we can expect the centrifugal advance to be fully in. Also the vacuum generated by the engine's part throttle position in a steady state no-load condition will be significant. This may still create as much as 10 inches of vacuum and an additional 10 degrees of advance.
Under these operating conditions it is likely the engine has too much spark advance. The real time occurrence is that the cylinders are being sparked off while the intake valves are still open.
The simple means of checking if this circumstance exists is to disconnect and plug the vacuum advance line to the intake. The backfiring should stop occurring. If the backfiring moves up to a higher RPM it just indicates there is too much initial advance.
None of the backfire problems the engine now exhibits may not occur if the vehicle was under normal load conditions as the throttle opening would be larger, generating less vacuum and thus vacuum advance timing would not be in play.
These are my general thoughts on your situation.
Best Regards and Good Luck in all your endeavors, KB.

[tiltbilt]

After reading this thread that had only a mention of distributor timing, I suggest looking more in-depth into distributor function.
To start lets look at the advance characteristics of your Buick distributor. As I recall the vacuum advance starts with only a couple of inches of vacuum and the centrifugal advance starts somewhere between 600-1000 RPM. Each of these advance systems contributes about 10 degrees of spark advance.
Lets assume that everything is now mechanically operating perfectly. When this engine is running at 3000 RPM we can expect the centrifugal advance to be fully in. Also the vacuum generated by the engine's part throttle position in a steady state no-load condition will be significant. This may still create as much as 10 inches of vacuum and an additional 10 degrees of advance.
Under these operating conditions it is likely the engine has too much spark advance. The real time occurrence is that the cylinders are being sparked off while the intake valves are still open.
The simple means of checking if this circumstance exists is to disconnect and plug the vacuum advance line to the intake. The backfiring should stop occurring. If the backfiring moves up to a higher RPM it just indicates there is too much initial advance.
None of the backfire problems the engine now exhibits may not occur if the vehicle was under normal load conditions as the throttle opening would be larger, generating less vacuum and thus vacuum advance timing would not be in play.
These are my general thoughts on your situation.
Best Regards and Good Luck in all your endeavors, KB.

I very much appreciate your comments!
I have tried disconnecting the vacuum advance and playing around with moving the dist. both advanced and retarded. No change in backfire.
Hope to put it on the scope Next week to check primary and secondary ignition patterns along with hc and co readings.
Trying to get this car to interior shop so he can take it to the Buick Nationals in Portland July 23rd.

[tiltbilt]

Hi,
Wanted to thank all who replied to this thread !
Today, I put the air cleaner on, then warmed up the engine, then brought it up to 3000 rpm and guess what! NO BACKFIRE/POP Thru carb!!!
I believe there never was an issue ?
Will see how it drives out soon.

[TexasJohn55]

Or................It is still doing it but the air cleaner is muffling the noise.........?