well i still have a hesitation in my holley carb number is 0-80508S 750 dual feed vaccum seconday. i posted about this before and was told to change the pump cam well i did that and the other day after i drove the car it was flooding out real bad. So i found out that it was dripping gas after i shut it off. Well i changed the pump cam from the brown one which is the biggest to the red one and now my hesitation is back when i punch it. I contacted holley and this is what they emailed me.

The first thing that you need to do is adjust your float level, no fuel should run out the sight plug with the engine running. and check to make sure that your fuel pressure is not over 7 PSI. I suggest 6-6.5 PSI Make sure the acc. pump is properly adjusted. It should be at zero lash at idle. and have at least .015" gap at Wide open throttle with the pump lever pushed all the way down. Then try turning in the idle air screws all the way in with the engine running. If the engine continues to run with both screws all the way in, then the carb is letting fuel into the engine from someplace other than the idle circuit. We have to find out where from and correct it (with the screws all the way in the engine should die) Next you want to check the manifold vacuum with the engine idling in gear. This will tell you which size power valve to use. If your vacuum is 9" and under divide by two, and that is the size you need. If it is 10" and over use a 6.5 PV. You may have to replace it with the correct size. If you get all of this corrected and the engine still runs rich then you will probably have to remove the carb and adjust the secondary throttle plates open to the bottom of the transfer slots. This will allow you to close the primary plates down some. If either plates are open too far then fuel will be pulled in to the engine from the transfer slots in the base plate. By adjusting those plates like I said, the carb will get the same amount of air at idle, but it will get it evenly from the front and rear instead of just the front. Once you get it so the engine dies with the idle air screws, then you can continue with the rest if the adjustments. Next you need to adjust the idle air screws. Turn them in until they seat lightly then back them out 1.5 turns. Start the engine and let it warm up. Hook up the vacuum gauge to manifold vacuum. Check it at idle in gear. Adjust the idle air screws evenly until you get max vacuum (the vacuum will drop off if you go to rich or lean) With that done you can start working with your jetting Unfortunately I can't tell you how to jet it. Each engine is different and has different requirements. It is a trial and error process. Start with the stock jetting and go from there, Run the engine under a load and read the spark plug color to find out which way you need to go. Black is rich and white is lean. It is best to tune the primaries first at part throttle and the secondary's at WOT run the vehicle at least a quarter mile and shut it down under throttle in order to get an accurate plug reading. This should be accomplished on a track or a long stretch of road with a wide shoulder that it can be done safely.Adjust it until you get a nice light brown color on the porcelain of the plug. when you get this adjusted . If you have a off line hesitation that is less than a second Increase the shooter by one size. If it is over a second increase the shooter by Two. If it makes the hesitation better you can increase accordingly if it gets worse drop the size.
Thanks Tom

Also according to holley the stock primary jets are 70 and the seconday is a 21 plate.
Motor is a yearone roller motor 350 vortec heads 9.5:1 compression, rpm air gap manifold.

Any more help on this is appriciated Sorry for such a long post and the questions.

 

You need to contact Lars!! He is the man.

I had a bad hesitation with mine when I got it.

I checked and I don't recall the sizes off the top of my head, but; the jets in mine were too small.

Mine is a 650dp. I looked it up on Holley's web site and then ordered the factory jets for it. When I installed them, the problem went away.

I don't know if your problem is that simple, but; it is worth a look.

good Luck!!

 

So did you just do this, or follow any of Holley's recommendations as well?
I would from start to finish, paying close attention to the opening of the throttle plates and possible adjustment of the secondary plates.

 

1). what size engine is this on?
2). Also where do you live so I can relation to sea level.
3). What kind of intake?
4). What was your intake vacuum in gear at idle?
5). What is your intial timing set at with what camshft?

I have to run at least a 73 on the primary. I played with my quick fuel carb for months until I went up to a 74 jets on my primary and 80 jets on my secondary. Also I went down to a 3.5 power valve.

 

Read the last part of my post about the motor. I live in huntsville ala. and my vaccum is 14-15inches at idle. Timing is set at 36 degress all in about 2800 cam specs are as follow 218/228 .520 int//ext roller cam.

 

I have not done what holley emailed me yet i just got the email today.

 

Sounds like you've got a good grip on it. I like to go with a low power valve, so it only comes in at wot and makes it a little easier to set up the midrange and cruise.
Follow their recommends and you'll be fine.

 

Take the 750 off and put a 650 on, probably clear up immediately.

 

Sorry didn't see the last sentence. I had a 750 Quick fuel on my 350 with rpm air gap, cc XE268 224/230 .477/.480 lift Hyd ft cam, it ran like crap(huge hesitation when hit the throttle aggressively), I put their 650cfm with a 3.5 pv 72 primary jet 80 secondary jet and had no problems at all. Ran like a champ, no hesitation at all. Holley and quick fuel are basically the same carb, they both use the proform main body. Quick fuel in my opinion put a lot better options/parts in for less $$$. A 750 is too much carb for a 350. A 350 ci at 6000 rpm at 100% VE only requires 607 cfm. Your engine might hit 100% VE at one point in the rpm range and I bet that is at about 4500 to 5000 rpm. I think if you switch out to a 650 all your problems will be solved. What ever you do, do not under any circumstances buy at DEMON. Pure crap out of the box. I went through about 6 of them before going to quick fuel. Just my $.02

 

 

why do derebery preformance recommend and dyno the motor with a 750 if its not going to work even yearone and hi tech which is the other builder recommend a 750.

 

I have no fault at all that you say that or recomend it. However, when they dyno it they show top HP and top TQ(the bottom numbers that are on the street suck). You will get a higher HP at your top end RPM with the 750, but when your at your 1500 rpm street cruising speed the 750 falls on its face. It took me about 6 carbs to figure this out. You can get rid of your hesitation at WOT, but you will have to manually downshift to get your rpm's up to hit it. My 750 cfm carb worked great on my 350 if you want to shift your th400auto like a manual tranny but if you want just to put it into drive and go then do a 650cfm.

 

I have no hesitation any where else in the power band but just at off idle. My tranny is the other problem i need to get it rebuild

 

If you only have a hesitation off idle then I would open up you idle screws 1/4 turn at a time until it is gone. I had an off idle hesitation with my screws at one turn out, then when I went to 1 1/4 out it got rid of it. However, at this setting just sitting and running in park with no load it is too rich, but once I hit the gas it went straight to lean causing the hesitation. when I brought the idle screws out it got rid of the lean off idle condition. Also I bumped up my initial timing to 16 degrees at idle.

 

Bend the cam follower for the accelerator pump to make sure that it is snug on the cam - not tight but snug. Then as soon as you start to open the throttle plates you get an instant shot of fuel rather than a second later.

I have a Holley 570 cfm on my base 350 and had the same problem until I figured out that the cam follower wasn't close enough to the cam. Bent it - problem solved.

***

A friend called to question why I would bend the cam follower (accelerator pump lever) rather than just adjust it. Well the answer is that I had no adjustment left. The Nyloc nut was at the end of the threads and the tension spring was loose and still the cam follower was nowhere near the cam. If, when you push the pedal down to 1/4 throttle and you're just starting to get accelerator pump, it hesitates big time.

Lars has stated in numerous threads that carburetors when new, need serious work before you use them. After having this problem and also a leaking primary inlet valve that caused fuel to run uncontrolled into the engine, I know he's right.

BTW, the car now runs GREAT!

 

Check the power valve, Holley's without the POWER VALVE protection tend to blow out the valve eventually and leak fuel into the motor. . The Valve should be 1/2 of the idle vacuum. Foe example if you have 14" of Vacuum at idle that would be a 7 but go with a 6.5. There is a kit to put a check valve in the power valve circuit to prevent the blow out, about $10.00.


There are two settings for the cam. setting 2 will allow a faster and bigger squirt. This may help also.

 

Just curious- how did you come across a thread that's over 7.5 years old?

 

 

WAS SENT TO ME ?

Have been working on my 71, thank goodness for my original 72, it's my go to for info.
I just rebuilt the power window relay, he had the feed wired directly to the battery?, from the switches.
He had the car from 88, guessing he never replaced a part, just "fixed" things.
Last night

I rebuilt the high speed relay for the blower motor. 2 broken tabs. don't ask.....it will be a 383 and 5 speed when done. yes it's matching numbers. but the 72 has 22,268 miles.

 

We just got done putting in a m20 4 speed in my 72 and took out the th400. Not an experience I care to repeat. Cant wait to get it back on the road after the rebuild. Mine is a 383 as well.