Technical Holley backfiring, stumble

What is "fuel economy" lol

 

Bought gas recently?

 

For me I’ve always tried each way just to make sure.. I don’t know if the writer has but it should be in the line of the many checks.
One other thing is to check all the throttle shafts with a slight amount of starter fluid on an extension tube. You want no rpm increase if possible. I recently had to rebush 3 Holley 2 barrels to get idle repeatability. Nylon sleeves were also installed.

 

Every time I take this thing for a drive I do lol

 

I have a bunch of things to try and the aerosol is definitely quick easy and informative. I didn't think of the shafts at all.

 

Thanks

 

Based on info. you provided it sounds like your fuel level is too high in the float bowl. Fuel level should even with the bottom of the sight glass. Watch these videos:
How to Set and Fine Tune Holley Carburetor Float Level – RacingJunk News
If your fuel level is too high you first have to drain the fuel bowl to get rid of the excess volume of gas. Then adjust it as shown in the videos a little at a time.

How To Adjust Fuel And Float Level On Holley Carbs - Holley Motor Life
and this information on how to rebuild and adjust Holley Avenger carb.
199r10788.pdf (holley.com)

 

Your carb size is not really an issue , its a vacuum secondary carb & with the correct spring. Will only open as far as the engine calls for . You absolutely can lower & raise the float settings with the outside adjusters . You're off idle bog could simply be a too lean idle adjustment . The higher rpm problems , I'd be looking at ignition .

 

Like Joe sez BUT........I would go one step further
Buy a stick on timing tape for a SBC. (they're very cheap) Install it with the TDC /0 on your verified TDC mark on the balance.
Then.....when you check your timing you can see exactly what degree it is.
Big cams NEED LOTSA initial timing. !
While watching your newly installed timing tape.open carb up until it stops advancing the balancer. (Probably around 3000RPM...maybe more) Do it again and twist the distrib until it reads 36-38* at that RPM.
Forget about initial advance !! Just look at total.
Slow down your curb idle on carb because it will be idling faster.
Now adjust your vacuum with a gauge.
6sally6

 

Does it have a pcv valve ? Cap it off and check vacuum, then timing being off might have the vacuum low also, what about vacuum leaks?
Sounds lean off idle from your description I would experiment with increasing jet sizes. The WOT backfires do sound like ignition related

 

So, I'm making sure the advance weight are fully thrown out is what you're saying?

 

Indeed it does have PCV. Would originally have had road draft but...long gone

 

Thanks

 

Well I guess that's true. I'm thinking in terms of a different system

 

First step (well...first two steps!)
Lighter springs will get to total advance at a lower RPM.
You 'MAY' need to limit the total advance also. Limit it to 42* to prevent damage.
EZPZ with a Shivel-lay distrib. Not-so-much with a FoMoCo distrib.
Let us know..........
6sally6

 

Be sure and watch this video and pay special attention to the Holley secondary throttle plate screw adjustment.
(1) HEI Ignition and Holley Street Avenger Rebuild - YouTube
To make adjustment easy, replace the stock set screw with a small bolt. I think its 12-24 thds. That way you can make adjustments without removing the carb from the engine. Makes adjustment a lot easier.

 

Both of my SBC powered hotrods have less than 15" of vacuum at idle. Both are pretty healthy cams and are around 12"-13" vacuum, which is pretty normal for high performance cams.
The arm on the accelerator pump linkage should be just slight clearance to the linkage, but not so much as to cause a stumble when you press the gas pedal. But you might consider just installing a new accelerator pump diaphragm, and take a look inside the pump housing to make sure the little rubber back check is also good. If it doesn't sit flat and seal well, it can let some of the gas be pushed back into the bowl when you hit the throttle, resulting in less than 100% shot into the carb.

 

This has been mentioned but, How did the plugs look that you didn't remove and look at?

 

Check your PMs

 

There is a lot of misinformation regarding carb setup floating around. The .015" clearance on the accelerator pump is one of them. That is for WOT, not at idle as has been corrected above. As for the above mentioned float level, according the Holley, the fuel should be half way up on the site glass. If the bowl had a plug instead of a site glass, then the fuel level would be at the bottom of the hole with the plug removed- that is straight from Holley tech support two weeks ago. Backfiring (carb related) is typically a result of a lean condition. Is this a new issue or has it always done this? If it is new, I suggest checking the timng and for vacuum leaks. If all is well after that, you probably would be well off rebuilding the carb as something has clogged up a fuel passage somewhere most likely and is causing a lean condition. Also look at fuel pressure under load- I had a mechanical fuel pump slowly go bad that gave me grief as it slowly died. It could not supply the carb with enough fuel and caused the engine to run lean.

 

It's new.

I was just looking at the distributor, from the passenger side. The vacuum advance cannister will hit the manifold if I advance it any more, and it will hit the coil hold-down if I try to retard more than a few degrees.

My experience is all 400-430-455 Buicks, and this is never a problem on one of those. The can on this SBC is pointing at 7 o'clock. Did the previous owner's buddy stab this distributor in wrong I wonder.

 

If it keeps giving you problems think about looking at the cam you know fresh build by somebody else ,small block Chevy , flat tappet cam could be a flat cam lob or two just saying.

 

7-8 O’clock ish on the advance can

 

Not a fresh build at all. New to me isn't newly built. If it keeps giving me problems, why wouldn't seriously consider replacing an unknown mongrel engine "somebody's friend" built with one that I will build, and better?

Thanks. That makes me feel a bit better. But man there's no room for much adjustment here .

 

Re-stab it !? If it was easy women would be doing it !!

6sally6

 

I won't do that without verifying TDC.

First thing's first. I'll get it out of the garage so I can work and see what the dial-back light tells me as I give the distributor whatever tweak I can turn it to. With and without the can, if needs be. But oh right: The Pertronix module covers the screws fr the can. Of course.

 

Why would the vacuum advance mounting screws be a problem adjusting timing ?

 

No reason at all. I'll just push the can right through the coil and/or the manifold as I turn the distributor.

 

There should be .015 of available over-travel at WOT. That’s straight fro Holley. At idle, the cam should be touching the arm with no pressure on it.

I recently fought symptoms similar to what you’re describing. Mine seems to have been a failing power valve. A new one cured it.

Edit: thread link here

https://www.jalopyjournal.com/forum/threads/distributor-rotor-cap-causing-backfire.1293158/

 

I have a ten gallon tank. I don’t care as much about the price, filling it up isn’t much. But I do care about “can I make it to the next gas station?”