Carter AFB (300hp) issues

[Gerald C.]

[Duke W.]

Re: Carter AFB (300hp) issues

What year and what model AFB?

What RPM are you measuring idle vacuum?

If a manual trans idle vacuum should be measured in neutral, and Drive if PG.

I don't understand what you're trying to say here. How many turns out were the idle mixture screws before the rebuilt and where are they now.

"The gaskets are installed as follows:
Base gasket, Insulator, gasket to block off the holes on each side in the intake, and then the metal plate, then the carburetor."

Sounds like you've got an extra part there. From the bottom up it's gasket, insulator, baffle. See you AIM

Duke

[Gerald C.]

Re: Carter AFB (300hp) issues

Duke:
1963 3461S
600 RPM
1 1/2 turns out
I took off the top gasket. So now I have gasket, insulator and then baffle. I didn't see that sequence in the AIM. I did look at 4 different parts catalogues and they all agree with this sequence.

Thanks

[Mark E.]

Re: Carter AFB (300hp) issues

The problem happened after rebuilding the carburetor so the problem is most likely what was done to it.

I would start over with another kit and double check all the work and adjustment settings. Blow out all bleeds and passages with spray carb cleaner.

From your post it sounds like someone else did this work? If so, Maybe have them do the rework (if you still trust their work). Check that they returned the same carburetor and components you gave them.

[Gerald C.]

Re: Carter AFB (300hp) issues

Mark,

Yes, a local rebuilder did the work. He and his family have been rebuilding carburetors for years. He did a Holley for me years ago for my 67 SB and it worked fine. I do trust them and I did get my original carb back as I took all the information down before I dropped it off. The 15" of vacuum is correct per the owners manual and I'm going to reset the timing this morning to 8 degrees at 500 RPM per the owners manual as this is the original engine with the correct cam configuration. If this process doesn't settle the bucking issue, I'm going to bring the carb back and have it redone.

I'll keep everyone posted. Thanks for all of your comments.

[Harry S.]

Re: Carter AFB (300hp) issues

Jerry, ask the rebuilder if he replaced the primary and secondary jets and/or the metering rods. 3461S's are sensitive in this area.

https://www.forums.ncrs.org/showthre...light=metering

[Gerald C.]

Re: Carter AFB (300hp) issues

Harry,

Will do. Thanks

[Duke W.]

Re: Carter AFB (300hp) issues

Mark,

The 15" of vacuum is correct per the owners manual a

I don't recall ever seeing an idle vacuum spec in either any owner's manuals of service manuals, but in my experience idle behavior of a 327/300 with an OE or OE equivalent camshaft should be close to 18" at 500 in neutral. Idle vacuum is very sensitive to both valve overlap and idle speed.

I take it that the engine ran fine before the carb overhaul, but poorly afterwords. My my best guest is than an assembly error like missing installation of a gasket is causing a vacuum leak. Be aware that there is a tiny o-ring between the choke housing and main body that seals that joint in the choke hot air system. One should be included in typical zip kits, but it's easy to forget or not install properly.

I believe your best course of action is to return the carb to the rebuilder, explain the problem, and have him redo the job.

Duke

[Gerald C.]

Re: Carter AFB (300hp) issues

Will do. BTW, please check out Page 44 of the 63 owners manual that indicates 8 degrees BUDC????(Before Upper Dead Center)@ 500 rpm.

[Duke W.]

Re: Carter AFB (300hp) issues

The '63 300 HP spark advance map is less than ideal. Max centrifugal is only 24, so 8 initial yields only 32 deg. max WOT advance and this doesn't occur until 4600 RPM.

The Chevrolet Power Manuals from the seventies recommend 36-40 max WOT advance for best power.

The '64 and '65 maps are also less than ideal, but they finally got it right in '66. Max centifugal is 30 and initial is in the range of 6-10. Bingo! The only issue is that max centrifugal doesn't occur until a lazy 5000. The black springs in the Mr. Gasket 928G spring kit will bring it all in by 3500.

Duke

[Gerald C.]

Re: Carter AFB (300hp) issues

Duke,

I don't understand the topics you're using. Like "map" and "wot". I do have the Igniter electronic ignition set-up and I hope that part is irrelevant in my carburetor issue case. Are you suggesting that the timing aim should be 10 degrees advanced? Again, the car idles and accelerates fine, the problem exist in the deceleration scenario. I'm going to reach out to the rebuilder on Wednesday to get his thoughts. Would improper float levels cause this bucking and I will address the points made in this discussion thread with the builder also.

Thanks

[Paul Y.]

Re: Carter AFB (300hp) issues

Duke, are the black springs the best also for an HEI dist. in a crate ZZZ engine? Inquiring minds want to know. Thank you. Paul

The '63 300 HP spark advance map is less than ideal. Max centrifugal is only 24, so 8 initial yields only 32 deg. max WOT advance and this doesn't occur until 4600 RPM.

The Chevrolet Power Manuals from the seventies recommend 36-40 max WOT advance for best power.

The '64 and '65 maps are also less than ideal, but they finally got it right in '66. Max centifugal is 30 and initial is in the range of 6-10. Bingo! The only issue is that max centrifugal doesn't occur until a lazy 5000. The black springs in the Mr. Gasket 928G spring kit will bring it all in by 3500.

Duke

[Duke W.]

Re: Carter AFB (300hp) issues

Duke,

I don't understand the topics you're using. Like "map" and "wot". I do have the Igniter electronic ignition set-up and I hope that part is irrelevant in my carburetor issue case. Are you suggesting that the timing aim should be 10 degrees advanced? Again, the car idles and accelerates fine, the problem exist in the deceleration scenario. I'm going to reach out to the rebuilder on Wednesday to get his thoughts. Would improper float levels cause this bucking and I will address the points made in this discussion thread with the builder also.

Thanks

WOT = wide open throttle

"Spark advance map" is explained in my tuning seminar.

Advance the initial timing as far as you can. Up to 40 degrees total WOT advance detonation or low speed bucking may be limitations.

[Duke W.]

Re: Carter AFB (300hp) issues

Duke, are the black springs the best also for an HEI dist. in a crate ZZZ engine? Inquiring minds want to know. Thank you. Paul

I only have experience with the Mr. Gasket 928G kit that is meant for single point and TI distributors. I believe they offer a different kit foe HEI distributors, but I have no experience with it.

Duke

[Gerald C.]

Re: Carter AFB (300hp) issues

Update:

The driver's side idle mixture screw is ineffective. It doesn't matter how many turns, nothing happens to the engine. Calling the rebuilder when he gets back from vacation.