Holley Carb Help

[1972BlueC20]

Ok so I've been having ongoing issues getting my truck running just right since I got a new engine installed. 350 / 330 HP Crate Part # 19210008.

The engine came with a Holley Street Avenger 670 CFM vacuum secondary, electric choke carb. The mechanic who did my engine install couldn't get it running right with the Holley so I got frustrated and had him put my old Edelbrock # 1406 on it so I could drive the truck.

Everything was ok with the Edelbrock at first, but shortly after getting the truck It developed a hesitation at cruise and from a dead stop. I had some ideas of things to try to remedy the problem but since I still had the brand new Holley sitting in my garage, I decided to give it a shot myself with the Holley before changing out the accelerator pump ect on the Edelbrock.

I'm having the following issues with the Holley :

Major hesitation when going from cruise to WOT (like a cut out almost chokes and dies)
Intermittent hesitation from dead stop
truck is dieseling sometimes

I've already done the following :

Verified proper float fuel levels. Front was correct, had to lower rear bowl a little as per Holley instructions.

Fuel Pressure is currently @ 5.5 PSI, I'm running a Holley fuel pressure regulator. Have tried numerous pressure settings within the exceptable range, none cure the hesitation.

Adjusted the accelerator pump, getting a good healthy squirt of fuel and there is no play in the accelerator pump arm, has proper .015 clearance.

Moved the stock accelerator pump camshaft to the # 2 position, no improvement...might of even got a little worse.

Choke is opening all the way once warm.

No vacuum leaks

Adjusted idle mixture screws while using a vacuum gauge, getting 20-21 reading on vacuum gauge in park, getting around 15 in drive.

Purchased the spring set for the vacuum secondary system. Tried all the springs from lightest to heaviest, none cure the problem.....just caused the secondaries to open at different times.

Pulled one plug on each side of engine to see if I had a obvious lean or rich condition. Below are pics, plug with a little brown was from drivers side, other plug is from passenger side.

Timing is 12 BTDC at idle, running with vac advance hooked up to timed / ported connection.


Here are my two suspicions of what could be going on, most likely one or the other probably not both :

1) carb is going too lean upon WOT and I need a bigger squirter
2) vac advance isn't working properly

Also I think the dieseling is being caused by my idle being too high. Only does it sometimes, had to increase my idle in drive because it was barely staying running at stop lights at first but then in park the idle seemed too high. Not sure of exact RPM because I don't have a tach.

If neither of these ideas fix the problem, then I'm going to pull all my hair out.
Haven't been able to get this damn truck running right since I got the new engine. It drives great when just cruising around normally, it even drives great when hauling butt except for when it hesitates during the transition from cruise to WOT. If I can just get the hesitation worked out I will be happy and quit bugging you guys for help LOL

I'm planning on getting an air / fuel mixture gauge and installing a wideband o2 eventually so I know exactly whats going on with my mixtures. However I can't do that for at least a few weeks or so.

Please let me know if you guys have any ideas or suggestions!

[Kenfuzed]

Have you tried to run with the vac advance plugged off to verify this is not the problem? According to the spec sheet for that engine it is run without using the vacuum advance. This is how I have mine set up (not same engine, but same HEI).
http://www.chevrolet.com/content/dam...e-19210008.pdf

In that spec sheet it says:

Set spark timing at 32º before top dead center (BTDC) at 4000 RPM with the vacuum advance line to the
distributor disconnected and plugged. This setting will produce 32º of total advance at wide open throttle
(WOT). The HEI vacuum advance canister should remain disconnected. This engine is designed to
operate using only the internal centrifugal advance to achieve the correct timing curve.

[1972BlueC20]

Originally Posted by Kenfuzed

Have you tried to run with the vac advance plugged off to verify this is not the problem? According to the spec sheet for that engine it is run without using the vacuum advance. This is how I have mine set up (not same engine, but same HEI).
http://www.chevrolet.com/content/dam...e-19210008.pdf

In that spec sheet it says:

Set spark timing at 32º before top dead center (BTDC) at 4000 RPM with the vacuum advance line to the
distributor disconnected and plugged. This setting will produce 32º of total advance at wide open throttle
(WOT). The HEI vacuum advance canister should remain disconnected. This engine is designed to
operate using only the internal centrifugal advance to achieve the correct timing curve.

yeah this is on my list of things to try....I had it originally set up without using the advance but several other board members told me there is never a reason to not run the vac advance on a street daily driven vehicle....I was getting bad MPG until I hooked up the advance....got an extra 2 mpg from hooking it up.

I will try to run it without tomorrow to see if it makes any difference.

[71 super]

Check for vac leak around intake, the first has good color , but second looks to be lean. If deiseling idle def. too high. Remove mixture screws and spray carb cleaner through the holes. If the bleeds are clogged this will clean them out and may improve signal. Did motor back fire through carb? Check while running and see if boosters are dripping, doubt this is happening based on color of plugs, sounds like vac. Leak of some form. are you pulling from constant vac port or timed port? What type of dist. Are you running? If you have a dial back light with tach bring rpm to 3000 and see what timing is totaling out at. With that motor total timing should be in by 3000, set it at 32-36 degrees all in by 3000 and see how it does. No vac advance hooked up. The curve in dist. May be too slow for engine. Do you have vortec type heads?

[geezer#99]

At what rpm are you checking your timing?

[1972BlueC20]

Originally Posted by 71 super

Check for vac leak around intake, the first has good color , but second looks to be lean. If deiseling idle def. too high. Remove mixture screws and spray carb cleaner through the holes. If the bleeds are clogged this will clean them out and may improve signal. Did motor back fire through carb? Check while running and see if boosters are dripping, doubt this is happening based on color of plugs, sounds like vac. Leak of some form. are you pulling from constant vac port or timed port? What type of dist. Are you running? If you have a dial back light with tach bring rpm to 3000 and see what timing is totaling out at. With that motor total timing should be in by 3000, set it at 32-36 degrees all in by 3000 and see how it does. No vac advance hooked up. The curve in dist. May be too slow for engine. Do you have vortec type heads?

The motor has never back fired on me. Not sure if it ever back fired on the mechanic when he was getting it running for the first time.

I have sprayed carb cleaner all around the base plate and anywhere I thought could potentially be leaking and never got any increase or change in idle.

To check the vacuum I am pulling from manifold vacuum on the carb.

I am running this distributor, GM part # 93440806. It came with this engine.

I have the stock heads that came on this engine. They are Vortec heads.

As for the timing. I have a crappy timing light and I checked it once only at idle with the vac advance plugged and it read 12. I didn't at the time understand how to check it at higher RPM so I don't know the total timing. I asked the mechanic to set it to what the instructions for the motor suggested which I think was 32 all in but then he bumped it up a little because it was a little sluggish and some forum members told me the bean counters at GM use overly safe timing which can result in poor performance.

I need to get a better light and recheck the timing asap.

[geezer#99]

But still the question remains!
What rpm did you check your timing at?
What rpm does your motor idle at when hot and in park?
The root of all your carb problems ( with either carb) is in your timing!

[1972BlueC20]

Originally Posted by geezer#99

But still the question remains!
What rpm did you check your timing at?
What rpm does your motor idle at when hot and in park?
The root of all your carb problems ( with either carb) is in your timing!

That's the thing, I don't know my RPM because I don't have a tachometer. I'd say 1,000 to 700 rpm if I had to guess but I really need to find out. How can you tell without installing a tachometer? Do any timing lights tell you? Be gentle, I'm learning lol

[69chevy lwb]

I'm having a similar problem with my carbed ls1 my Holley street avenger wasn't setup from the factory so I had to tune it myself which worked but it began to develop a huge hesitation any time the throttle was applied and it continued to get worse as time went on. I also had diesling issues. Mine seems to be a result of excessive fuel pressure and late timing. As my idle is around 500 rpm. Upping my timing fixed the diesling but it still has hesitation when applying throttle. So fuel pressure and a carb retune are next on my list

[geezer#99]

Originally Posted by 1972BlueC20

That's the thing, I don't know my RPM because I don't have a tachometer. I'd say 1,000 to 700 rpm if I had to guess but I really need to find out. How can you tell without installing a tachometer? Do any timing lights tell you? Be gentle, I'm learning lol

You can get a contact type tach like this at your parts store.
http://www.lightinthebox.com/profess...FY9gfgodW4MAaQ

You need to get your idle down low enough so your mechanical timing in the dizzy doesn't start kicking in.
Then check your timing.
Put in as much initial as possible so it still starts good hot.

[1972BlueC20]

Cool, I just bought a Craftsman digital timing light with a tachometer built in. I'll recheck later today.

How much initial timing should I go to? For instance what do you run?

[geezer#99]

I run 14 initial on an almost stock 305. Just has headers on it with a stock quadrajet.
I ran a much healthier sbc a few years ago that liked 22 initial (at 3500 foot elevation) but wouldn't run more than 18 initial when I moved to sea level.

[1972BlueC20]

Originally Posted by geezer#99

I run 14 initial on an almost stock 305. Just has headers on it with a stock quadrajet.
I ran a much healthier sbc a few years ago that liked 22 initial (at 3500 foot elevation) but wouldn't run more than 18 initial when I moved to sea level.

Ok so I checked the timing again. Its at 12 btdc. Idle was at 910 rpm in park, in drive it was 650 rpm.

I drove it with the advance plugged off completely and the hesitation was much less. Still there a little but much better. However I'm sure it's getting much worse mpgs like that.

It was hard to check total timing because I was by myself and had to accuate the throttle with my hand while looking at the timing light. It seemed to be around 30-32 degrees at 3k rpm. I need to go back and read the engine manual to see what rpm they recommend to check total timing.

I dropped the idle to 850 in park, which made it 650 in drive. The idle speed in drive doesn't go down equal to the amount I drop it while in park.

What do you think?

[geezer#99]

Well that tells you that idling at 910 rpm that you're getting into the mechanical timing.
Put it in gear at 650 and set your initial at 16.
Your rpm should increase a bit.
Keep it at 650 in gear by turning the idle screw down.
In park it shouldn't increase much. Maybe up to 750 or so.
Don't worry about total timing until you find your max initial.
Other people will tell you different, but that's how I do it.
I like to find my max initial and then adjust the timing in the dizzy to give me a total of 32 to 34 all in by 3200.
I also adjust my vac advance to a limited 10 degrees.

[custom1970]

This may sound very simple but try new spark plugs. If they ever got gas soaked they're shot. I've had it happen several times after big engine mods. But for less than20 bucks is an easy check...
Good luck

[1972BlueC20]

Well I guess I'll try bumping my initial timing up to around 16 or so and see how it acts....what about hooking the vac advance to the manifold vacuum port? Wouldn't that bring up the initial timing?

What timing is everything running? I'd like to hear how everyone is running to give me some idea of whats most often used on these trucks.

Does anyone have anything else to suggest for my problems I'm having?

[dirtyjim]

brian there are a couple things I would look at.
the power valve may not be the correct one for the amount of vacuum your engine is producing or their may be a restriction in the fuel line causing a momentary fuel pressure or volume drop when you get on it from a cruise speed. holley should spec the power valve that comes standard in that carb

[1972BlueC20]

I read that with my current vacuum reading in drive that the stock power valve is ok.

Not sure about a possible restriction in the fuel line. Runs great at WOT, just hesitates right at the transition point.

I'm thinking about playing with the timing and or changing the squirter size a few sizes up. Hopefully one or both of those things will help.

[geezer#99]

Just remember the old rule!!
Timing first, carb second!!

[1972BlueC20]

Originally Posted by geezer#99

Just remember the old rule!!
Timing first, carb second!!

How do you recommend hooking up the vac advance?

I was planning on setting the timing to 14 or 16 intial to start out.

Should I run with vac advance or not? If so, ported vacuum or manifold vacuum for the advance?

[leadfoot067]

every engine is different,they all wont like the same amount of timing,or fuel for that matter.i agree with geezer more timing! i myself dont run vacuum advance..i run as much initial as possible,then adjust the mecanical to get my total,and again the total differs on whats done to the engine..

[1972BlueC20]

yeah I think i'll increase my initial timing to around 16 degrees BTDC and see how it runs. I may hook up the vacuum advance after that and see how it runs with and without the vac advance hooked up.

if none of that fixes it, then I'll try a bigger squirter

[1972BlueC20]

UPDATE!

Ok, so I tried a few things yesterday.

First, I hooked my vac advance up to the manifold vacuum port. This gave me 32 degrees initial. I had to drop the idle from like 1300 down to 850. Went and drove it, still has the same hesitation.

Then I rechecked for vacuum leaks, none.

Then I decided that I'd unhooked and plug the vac advance and increase my initial timing from 12 to 15.

Went to turn the brand new HEI and BAM! I got the crap shocked outta me!!

Is this normal? It really stung! LOL

I was scared to touch it again, so I would turn the truck off.....adjust the dizzy then restart, check timing....repeat until I got it to 15 degrees.

After all this, still has the same hesitation.

I'm really getting frustrated.

Any advice??

[bgriff]

Directly from Holley's website:
My vehicle has a stumble from a dead stop. What can I do to cure this?
The most common cause of a stumble is not having an adequate accelerator pump shot. The first thing to do is to look at the discharge nozzle and make sure you are getting a good strong pump shot. If not then you need to inspect the pump diaphragm for a hole or tear. You will also need to make sure that the pump passage is clear from any trash or debris. First you will need to check the adjustment on the pump. To do this you will open the throttle all the way (WOT). Push the pump arm lever down and then adjust the pump override spring to obtain .015" clearance between the pump arm and lever. If you are having a stumble and no black smoke out the tailpipe then you will need to increase the shooter size. If it stumbles and you are getting black smoke from the tailpipe then it will be necessary to decrease the shooter size. You can also watch our video on Holley TV that goes through a variety of other possibilities and methods to correct the problem. Click Here To View.

[1972BlueC20]

I've already done all that.

I may indeed need a bigger pump shot, but it looks to be a very strong and healthy squirt of fuel and my pump arm is adjusted to the proper clearance.