Need 66' Carb Help

[Gary N.]

I need some help with the original carb on my 66' 327/350hp. I had the carb restored some years back (+/-15) and it has run pretty good until fairly recently. Here's the symptoms:
It runs real rich (burns your eyes ) at an idle and the rpm's will paulse up and down at about 800-900 rpms. If I turn up the idle adjustment to about 1300 rpms it seem to smooth out. I though it might have a sticking float or needle valve so I took them out and they seemed to be fine. I re-adjusted the floats and the problem remained. It will bog down when I begin to give it gas and has even had a slight backfire thru the exhaust. I checked to see if the accelerator pump was working and I was getting a good shoot out of both. I can close the idle air adjustments all the way and it has no effect. If I turn on the AC even with the rpms above 1100 it will stall. I'm wondering if it's a bad power valve? Anyone ever had this problem? Any suggestions? I run it pretty often and use a fuel stabilizer to keep the gas in good shape. Any help would be greatly appreciated.
Thanks

[John H.]

Re: Need 66' Carb Help

I need some help with the original carb on my 66' 327/350hp. I had the carb restored some years back (+/-15) and it has run pretty good until fairly recently. Here's the symptoms:
It runs real rich (burns your eyes ) at an idle and the rpm's will paulse up and down at about 800-900 rpms. If I turn up the idle adjustment to about 1300 rpms it seem to smooth out. I though it might have a sticking float or needle valve so I took them out and they seemed to be fine. I re-adjusted the floats and the problem remained. It will bog down when I begin to give it gas and has even had a slight backfire thru the exhaust. I checked to see if the accelerator pump was working and I was getting a good shoot out of both. I can close the idle air adjustments all the way and it has no effect. If I turn on the AC even with the rpms above 1100 it will stall. I'm wondering if it's a bad power valve? Anyone ever had this problem? Any suggestions? I run it pretty often and use a fuel stabilizer to keep the gas in good shape. Any help would be greatly appreciated.
Thanks

Gary -

Your throttle blades are too far open at idle (which is why the idle mixture screws have no effect), and it's idling way rich on the transfer slots instead of from the idle mixture orifices. Set the idle mixture screws out 1-1/2 turns from lightly seated, start it, close down the idle speed screw to close the throttle plates, and re-adjust the idle mixture screws, using a vacuum gauge, for highest steady vacuum. Verify that your vacuum advance is deployed/operating at idle, which will allow you to close down the throttle plates.

[Garry M.]

Re: Need 66' Carb Help

Hi Gary,

I had a similar problem with my '66, which required that I replace the 4743 metering body in order to correct the bulk of the problems (running rich and lack of idle adjustment), but still retained a problem of gas occasionally dribbling over the main throttle plates after shutting off the car (which then drained the front bowl and required a long crank the next time I started it).

I have yet to have the car re-examined by a long-time carb builder (living in AZ, he escapes for the winter), so I can't provide any guidance as to what the root problem was and what it took to correct it. Just thought I would share what happened to me. Hope John's recommendation solves your issue versus having to do down my route.

I now have a service replacement 3367 on the car until I can get the original back to full working order.

Garry

[Wayne W.]

Re: Need 66' Carb Help

Any Holley that has not been rebuilt in 15+ years, needs attention.

[Gary N.]

Re: Need 66' Carb Help

John - It ran good until recently so I don't think anything changed the throttle plates. If I had just had it rebuilt I would agree. Garry - I'm not seeing any gas on the throttle plates after I shut it off - it looks dry. I still have a feeling it the power valve? i just wanted to see if anyone ever had a bad power valve and what the symptoms were. If the valve was weak or leaking I could see the valve opening and closing and causing the rpm's to paulse. Also if it was letting in to much gas it would burn rich and the idle air screws would probably not function. Thanks for your replies. I'm sure it will have to come apart, but I just wanted to get some opinions.
Thanks,

[Clem Z.]

Re: Need 66' Carb Help

if it was rebuilt using the old style cork gaskets that could be your problem as they shrink up over time

[Larry M.]

Re: Need 66' Carb Help

Any Holley that has not been rebuilt in 15+ years, needs attention.

I can certainly agree with that. The carb on my 1967 327/350 HP is in this category. Hasn't been apart in 18 years. Parts are on-site, it's just a matter of doing it.

My carb behaves similar to that of Gary N, except in my case it appears that the secondary (and possible primary) needle valve is deteriorated and gas can occasionally be seen dribbling over the throttle plates.....especially just after engine shutdown. Car (and carb) runs well down the road, but runs very rich at idle. Sometimes it's better than others.

Always something to do or fix on these cars. But I guess that's the fun of it.

Larry



Gary N: There is s quick test for a blown power valve. I don't have it handy, but it should be discussed in the archives. Just do a search.

[Timothy B.]

Re: Need 66' Carb Help

Gary,

If the power valve is not ruptured, open or closed it should not effect the idle of your L-79. When the power valve opens it lets additional gas into the main well. This additional enrichment combined with the gasoline from the main jets changes the A/F ratio for power enrichment under load. That's the only time the P/V should come into play unless it's ruptured in which case the motor will flood and not want to run. It's a good idea to replace it with a Holley part when you take the carburetor apart, make sure you use the correct gasket on the power valve.

The idle circuit of your holley seems to be where the problem lies and I bet it's a dry gasket and vacuum is pulling gasoline from somewhere it's not supposed too. Sometimes this is caused by warping of the main body surfaces, (front, back and bottom so it's a good idea to check them when installing new gaskets.

Also, keep in mind the sandwich gasket arrangement on the secondary side of the 4160 leaks and all these parts should be checked for flatness. The metering plate on the secondary can be bent be overtightening so be careful as many carburetor overhaul kits use thicker gaskets than Holley and it's easy to overtighten.

[Joe L.]

Re: Need 66' Carb Help

I need some help with the original carb on my 66' 327/350hp. I had the carb restored some years back (+/-15) and it has run pretty good until fairly recently. Here's the symptoms:
It runs real rich (burns your eyes ) at an idle and the rpm's will paulse up and down at about 800-900 rpms. If I turn up the idle adjustment to about 1300 rpms it seem to smooth out. I though it might have a sticking float or needle valve so I took them out and they seemed to be fine. I re-adjusted the floats and the problem remained. It will bog down when I begin to give it gas and has even had a slight backfire thru the exhaust. I checked to see if the accelerator pump was working and I was getting a good shoot out of both. I can close the idle air adjustments all the way and it has no effect. If I turn on the AC even with the rpms above 1100 it will stall. I'm wondering if it's a bad power valve? Anyone ever had this problem? Any suggestions? I run it pretty often and use a fuel stabilizer to keep the gas in good shape. Any help would be greatly appreciated.
Thanks

Gary------

I'd check for a blown power valve.

[Clem Z.]

Re: Need 66' Carb Help

Gary------

I'd check for a blown power valve.

just put you finger over the primary bowl vent with the engine at idle. if it stall out right away it is the power valve and if it takes awhile the power valve is OK. if the power valve is bad putting your finger over the bowl vent will force fuel thru the ruptured power valve causing the engine to stall quickly. if the power valve is good the pressure will cause fuel to be forced out of the booster nozzles and this takes longer to happen

[Gary N.]

Re: Need 66' Carb Help

Clem,
I tried what you said about putting my finger over the primary bowl vent and it didn't stall. Actually had no effect at all. It is ideling very rich. If I put the AC on even with the idel set up to 1100, it will stall the engine out. Someone said I might have a vacuum leak, so I blocked all the vacuum ports off and it had no effect. I realize it could also be an intake manifold leak but I haven't checked that yet. I believe it carb related. I should be able to close the idle air adjustments and it should have some effect (it used to). I'll probably send it off to be rebuilt. Any suggestions? I'd like someone good but don't want to wait 6 months to get it back.

[Clem Z.]

Re: Need 66' Carb Help

Clem,
I tried what you said about putting my finger over the primary bowl vent and it didn't stall. Actually had no effect at all. It is ideling very rich. If I put the AC on even with the idel set up to 1100, it will stall the engine out. Someone said I might have a vacuum leak, so I blocked all the vacuum ports off and it had no effect. I realize it could also be an intake manifold leak but I haven't checked that yet. I believe it carb related. I should be able to close the idle air adjustments and it should have some effect (it used to). I'll probably send it off to be rebuilt. Any suggestions? I'd like someone good but don't want to wait 6 months to get it back.

does your carb have a external bowl vent that is activated by the carb throttle arm and if it does you have seal that also so pressure will build up in the float bowl

[Gary N.]

Re: Need 66' Carb Help

Well I found the problem. It was the power valve. When I pulled the front bowl and metering block off I noticed the the power valve was loose. It apparently worked it way loose I guess. I went ahead and replaced it with a new one just to be sure since I didn't want to have to redo it again. I works great again. Thanks for your responces and help.