Hesitation When Accelerating

[Moriarty]

Originally Posted by eschaider

Out of the box, Holleys will almost always come with a 6.5 power valve. That means the power valve opens at 6.5 inches of idle vacuum. If your car idles at 6 or 7 inches of vacuum that means your power valve is open at idle creating a rich idle. You want your power valve to open at roughly ½ your idle vacuum. An engine with 6 inches of idle vacuum wants a pwervalve with a 3 inch opening value.

This was exactly the info I needed for the similar issue I had been chasing. Switched out the 6.5 for a 4.5, readjusted the transfer slot square and viola!

Thanks,
Aaron

[eschaider]

If you are supplying an adequate volume of fuel, you should be able to immediately open all four throttle blades w/o any stumble. That is exactly what a carburetor with mechanical linkage does.

When you slow down secondary opening to match an anemic fuel deliver curve you are reducing engine power and throttle response. That is a left handed solution to a simple fuel delivery problem.


Ed

[eschaider]

Duplicate post

[zzmac]

Sorry Patrick but I'm not a carb guy and you've got me a little confused. You said to zip tie the secondaries shut and now you're showing me it rotating and the secondaries opening up. Do I shut them with a zip tie or do it like in your pic above?

[patrickt]

Originally Posted by zzmac

Sorry Patrick but I'm not a carb guy and you've got me a little confused. You said to zip tie the secondaries shut and now you're showing me it rotating and the secondaries opening up. Do I shut them with a zip tie or do it like in your pic above?

Sorry I confused you. The two zip tie posts by me have nothing in common with one another. They are entirely different subjects and you can completely ignore, for now, my second post showing you how to tell when the secondaries open by putting a zip tie around the shaft. For now, just wire/tape/even clog the top with towels so the secondaries can't open, then take her for a spin. We're just trying to figure out, for right now, if the secondaries kicking in are causing the bog. Nothing more. If you come back and say "wow, with the secondaries wired shut, the car runs beautifully. A little slower, but beautifully" then that tells us where to start looking.

[zzmac]

Okay, so I closed down the secondaries and took it for a test drive. No bog.

One step closer. :-)

[patrickt]

Originally Posted by zzmac

Okay, so I closed down the secondaries and took it for a test drive. No bog.

One step closer. :-)

That presumably tells you that the problem is on the secondary side. It doesn't tell you exactly what the problem is, just what side it's on. Now, you might want to go back to the carb place and tell them "you know, when I lock out the secondaries the problem goes away. What do you make of that?" And see if they say, "O.K., let us take a look at it one more time." They will then check the air flow through the secondary bleeds, the fuel flow, the fuel level in the bowl and, of course, the operation of the vacuum canister and springs that act to open the secondaries. On the other hand, they might just want to be rid of you since they should have done it right the first time.... Out of curiosity, how much slower was your car running on only half a carburetor?

[zzmac]

It was still pretty quick.

[patrickt]

Originally Posted by zzmac

It was still pretty quick.

OK, if the guys in the shop are receptive to listening, you might throw in as you're leaving, "some guy on the internet thought the vacuum secondary spring could use some tweaking. Ya think that might be it?" But they still need to walk through the protocol, so maybe just shutting up is a better idea.

[zzmac]

Originally Posted by patrickt

OK, if the guys in the shop are receptive to listening, you might throw in as you're leaving, "some guy on the internet thought the vacuum secondary spring could use some tweaking. Ya think that might be it?" But they still need to walk through the protocol, so maybe just shutting up is a better idea.

They're great guys at the shop.

[zzmac]

Originally Posted by patrickt

OK, if the guys in the shop are receptive to listening, you might throw in as you're leaving, "some guy on the internet thought the vacuum secondary spring could use some tweaking. Ya think that might be it?" But they still need to walk through the protocol, so maybe just shutting up is a better idea.

If the vacuum secondary spring is seated properly would this more than likely mean it needs a stronger spring (if it's the spring)?

[patrickt]

Originally Posted by zzmac

If the vacuum secondary spring is seated properly would this more than likely mean it needs a stronger spring (if it's the spring)?

That's one possibility, and that's the easiest answer (might not be the right one, but it's the easiest). There also could be a sticky mechanism involved, so that the vacuum mounts up and "pops" the secondaries open instead of smoothly and gradually opening them. It could also be a clog on the air bleeds over on the secondary side or any other transitioning orifice that's involved. I always instantly suspect a Holley has a clog even if the Holley just came out of the factory box because I've seen so many clogs and they can be caused by pretty small pieces of crap. It's probably not a clog, but I always suspect them nonetheless and clean them out good with the poisonous carb cleaner that works, not the watered down crap they sell in CA. Then I blow out the air bleeds, transition slots, idle mixture holes, all of that with about 30 psi of air from my compressor. Only then do I start thinking that it might be something else. The chart below is the spring rate for Holley vacuum secondaries. If you put the black spring in there, that's pretty much like having your secondaries tied down shut, so I bet the black spring would stop your bog. But you'd only have half a carb again. If you then walk up the chain until you find the spring that opens the secondaries the fastest, but without creating a bog, then that's the winner. BUT, if the problem is something else, like a sticky mechanism, then you're going to have to fix that to get everything to work just right.

[patrickt]

Out of curiosity I pulled the spring specs for your 770 just to see what it originally came with out of the box (knowing that the carb guys have probably monkeyed with it). Of course Holley would list a stock spring color that is different than every other color in its rainbow of choices in the vacuum secondary spring collection.

[patrickt]

Originally Posted by patrickt

It could also be a clog on the air bleeds over on the secondary side or any other transitioning orifice that's involved.

John, are you reading these posts carefully?

[zzmac]

Near the end of my short test drive once again the RPMs stayed at about 3000 for a very short time with my foot off the pedal. Can that have anything at all to do with the carb or would it strictly be linkage?

[patrickt]

Originally Posted by zzmac

Near the end of my short test drive once again the RPMs stayed at about 3000 for a very short time with my foot off the pedal. Can that have anything at all to do with the carb or would it strictly be linkage?

Could be the linkage between your foot and the carb, and it could be the linkage that's actually in the carb itself making it stick a little bit. Lubricate everything that moves and see if doing that improves the "stuck" symptom. I know the last time I lubricated the linkage in the carb alone, I was struck at how much crisper and cleaner the throttle felt and said to myself "damn, I should have done this a while ago considering it only took about thirty seconds."

[NROTOXIN]

Still haven't determined a sticking carb linkage/pedal.......if that is eventually determined not the case, maybe the distributor advance is sticking. Divide and conquer.

[zzmac]

Thanks I'll keep that in mind NROTOXIN.

[saki302]

One idea- if you have a cheap go-pro camera, tape a mount in the engine bay, and take video of it during a drive- keep the time on it accurate, and you can sync it with what's going on during the drive.

I have a crappy go pro 1 I can use for stuff like this.

-Dave

[zzmac]

Thanks Patrick!