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Old 10-25-2006, 06:58 PM
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boging problems

i have a 350/330 horse crate motor with the vortec heads with a eld air gap and holly 750 vam sec ever time i try to floor the car from a dead stop it bogs down almost to where it stalls out or it does stall but other then that it runs great. the timeing good, had the carb ajusted, on vac leaks any suggustions thanks.

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Old 10-25-2006, 09:33 PM
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Did you adjust the accelerator pump....or check it for a blocked passageway? Sounds like you are not getting that shot of gas when you need it.
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Old 10-26-2006, 08:19 AM
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We had the same problem several years ago with a RPM Air Gap intake.

Same problem on two diffrent engines now that I think of it.

We tried pumps,pump cams,squirters, Different carbs.. ect.. it somewhat helped the problem but it was still there. We ended up putting a regular RPM intake on it and never had another problem...

Don't know why those Air Gap's cause that lean condition but we've had it happen to us twice on two totaly different engines.

Try a larger squirter and pump cam adjustments.. and good luck! We spent many hrs playing with it.
~Scott
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Old 10-26-2006, 11:25 AM
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I have the same problem (355 w/600 vac sec. and a RPM air gap) I just assumed the accelerator pump was undersized.

Hearing that the air gap causes a lean condition makes me nervous.

I wonder if other people with the air gap are having the same problem.
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Old 10-26-2006, 11:35 AM
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I wonder if other people with the air gap are having the same problem.

I'll bet there's alot of people with this problem. We had new RPM heads.. 355engine RPM Air gap intake and a 600 carb too. Tried a 750 that worked great on another car.. 406cid... it did the same thing...

Might be a design deal..?
Unless you realy floored it there would be no problem.. but from idle to snap the throttle it'd always act weird.. stumble when you snap the throttle and a hesitation when you were driving it... once it got past that point it'd be fine.
Glad I'm all EFI now Hated little problems like this.
~Scott
If you fix it let me know what cured it.. I've been wondering what it would take to smooth that area out.!!!!!
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Old 10-26-2006, 03:36 PM
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Change the accelerator pump cam to a more agressive one and change the squirter nozzle up one size. I had this exact issue and this resolved it for me. Note after you change the cam you will need to re-adjust the accelerator pump arm. There are instructions for this on Holleys site and several other places.

One other thing to chack is that your vacuum advance is working properly. I would try disconnecting it to see if the issue goes away or at least gets better. I have the same engine as you and I run ported vacuum to my advance unit and it works fine. there is a huge debate on this but my theory is run what works for the particular application.
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Old 10-26-2006, 04:20 PM
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Hey Bill,

I never heard of a holly "750 vam sec", but do know of Holleys with Vacuum secondaries. You should tell them ecxactly what carb you have by Holley model. I thought the problem seems more like a to rich at initial full throttle, but if i exactly knew what the problem was it would be fixed. His set up on the car is right out of the box with a vacuum advanced HEI with vacuum ports caped and timing set at 34 Deg at 3000. Listening to the idea that its going lean makes me think about the power valve and vacuum secondaries opening to soon, which at this point is all possible. Now I was under the impression that the (?power valve is suppose to be around half the manifold vacuum reading?) and then you work your way from there. Does anyone have a trick to see if the secondaries are opening to fast, say I place some so that they only open half way so I could see if there is to much Initial air and not enough fuel. Now his get up and go after the bog is impressive I thought, but of-curse the driver and owner never seem to be satisfied , there always looking for more. The motor shows great torque, and you know it is torque that will get you down the strip faster with 3600 lbs of car. Oh yeah the owner being chubby don't help .
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Old 10-26-2006, 09:00 PM
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If vacuum secondarys, try a different spring in the secondary. Holley has a kit that has 7 different springs, from light to heavy which control when the secondarys open. A noticable bog is usually having too light a spring
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Old 10-27-2006, 08:34 AM
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The Air Gap style intake manifolds act more like an open plenum intake manifold; meaning at low speed the air velocity is going to be slow. Combine that with a carburetor this is probably marginally big for the combination and you can run into these types of problems. If it only does this under a “Hard” acceleration you should be able to cover up some of it by installing a larger squirter nozzle, and going to a heavier secondary spring. This will get the fuel into the engine a little quicker from the squirter, and delay the opening of the secondary butterflies, which should allow you to build enough air speed to draw fuel through the carburetor.
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Old 10-27-2006, 10:56 AM
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88Monte...your bog is probably a lean bog, created in part because the RPM Air Gap flows so well...I had the same lean bog on my 383 with a Vic Jr Air Gap, and an RPM Air Gap...

Take a manifold vacuum reading at idle and just off idle...

Change out the power valve to 2 numbers lower than your manifold vacuum.

Replace the squirters which should be 29's to 35 or 37's and use the hollow mounting screw which Holley sells.

Be sure, with your set up, that full advance is in by 2000rpm.

A lean bog will occasionally backfire and stumble, then rpm's will pick up and the engine will scream.

A rich bog will stumble and cough, then pick up rpm's and run strong. A rich bog will normally throw off a tell tale black exhaust smoke.

If it's rich, do the PV change will help and your timing advance must be double checked.

Good luck

Paul
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Old 10-27-2006, 11:18 AM
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Now that sounds like some good advice!

I know when a power valve is bad but usto get confused on which way to go when installing the right one when you've realy got a issue like this one.

Now I just change that area on the fuel map and skip the unleaded hand wash ..


~Scott
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Old 10-27-2006, 03:20 PM
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Quote:
Originally Posted by vabeach56wagon
88Monte...your bog is probably a lean bog, created in part because the RPM Air Gap flows so well...I had the same lean bog on my 383 with a Vic Jr Air Gap, and an RPM Air Gap...

Take a manifold vacuum reading at idle and just off idle...

Change out the power valve to 2 numbers lower than your manifold vacuum.

Replace the squirters which should be 29's to 35 or 37's and use the hollow mounting screw which Holley sells.

Be sure, with your set up, that full advance is in by 2000rpm.

A lean bog will occasionally backfire and stumble, then rpm's will pick up and the engine will scream.

A rich bog will stumble and cough, then pick up rpm's and run strong. A rich bog will normally throw off a tell tale black exhaust smoke.

If it's rich, do the PV change will help and your timing advance must be double checked.

Good luck

Paul
Good advice, most Holley's have a 6.5 powervalve, I bet with that mild cam you could use a 10. Also what is the timing set at? and where is the vacume advance connected?, also how much total timing do you have with the vacume disconnected? The powervalve swap will definately help your response from part throttle to wot but I think your bog from a dead stop is more related to a bad timing curve and poor idle fuel curve.
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Old 10-27-2006, 06:12 PM
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Quote:
Originally Posted by baddbob
Good advice, most Holley's have a 6.5 powervalve, I bet with that mild cam you could use a 10. Also what is the timing set at? and where is the vacume advance connected?, also how much total timing do you have with the vacume disconnected? The powervalve swap will definately help your response from part throttle to wot but I think your bog from a dead stop is more related to a bad timing curve and poor idle fuel curve.
Quote
"Hey Bill,

I never heard of a holly "750 vam sec", but do know of Holleys with Vacuum secondaries. You should tell them ecxactly what carb you have by Holley model. I thought the problem seems more like a to rich at initial full throttle, but if i exactly knew what the problem was it would be fixed. His set up on the car is right out of the box with a vacuum advanced HEI with vacuum ports caped and timing set at 34 Deg at 3000. Listening to the idea that its going lean makes me think about the power valve and vacuum secondaries opening to soon, which at this point is all possible. Now I was under the impression that the (?power valve is suppose to be around half the manifold vacuum reading?) and then you work your way from there. Does anyone have a trick to see if the secondaries are opening to fast, say I place some so that they only open half way so I could see if there is to much Initial air and not enough fuel. Now his get up and go after the bog is impressive I thought, but of-curse the driver and owner never seem to be satisfied , there always looking for more. The motor shows great torque, and you know it is torque that will get you down the strip faster with 3600 lbs of car. Oh yeah the owner being chubby don't help ."
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Old 10-28-2006, 08:48 AM
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Disconnect the secondaries at the plunger arm and test if the bog is gone. I doubt it's the secondary opening causing the bog because there really isn't enough airflow going through the carb at this time to provide the vacume necessary for secondary opening.
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Old 10-28-2006, 12:59 PM
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re: boging

I have a 350 small block with a rpm air gap and a Holley 670 street avenger carb in my rod. I struggled with this situation for 6 months before I came up with the best combination. I first installed a 50cc accelerator pump, actuating arm and cam with the stock (31 squirter). I then bent the actuating arm back so that it squirts max at the beginning of the stroke and nothing after about half throttle. The bend should start right after the peak of the cam and the tang is kick up about 10 degrees at idle. I had to add some washers above the spring on the actuating arm screw to allow it to come in contact with the diaphragm arm since I bent the tang. The cam should be set up with the small radius up against the actuating arm with the flat before the small radius almost horizontal. The large radius of the cam should be downward. The screw in the cam should be in the number 1 hole. By the way this doesn't make full use of the 50cc shot but the key here is to take advantage of the large cam to get a lot of fuel at the beginning and nothing at the half way point when the other circuits start to come into play. I then installed a manual choke which I only allow to close about half way. This allows a slightly rich mixture when its cold and increases the rpm about a couple 100 rpm depending on how you set up your throttle stop. I usually wait until the engine hits about 150 degrees and then I shut it off the choke. I only have a mild 350 with headers and a mild cam. Believe me this setup runs a lot better than the single quad on the tunnel ram setup I had when I bought the car. By the way I'm new to the group so bear with me.
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