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Discussion Starter #1
I have a 454 that came with the car I just
Purchased. It has 10.5:1 compression, 325 HP
Oval port heads, msd ignition and a 750 Holley double pumper,
Solid lifter cam with 550 lift. Intake is a Weiland single plenum.

The motor runs nice except for a slight bog if you try to
Accelerate under low rpm. For, example, at rest, put can in first
Gear and then apply gas. The car will hesitate
And the accelerate.

I was wondering if this was from lack of gas? Too much gas?

Do I mess with the accelerator pump on the carb? Replace the intake?

I would like to know how to adjust this myself.
 

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Maybe ign timing or spark advance problem. Possible the centrifugal advance has slack or wear letting it come in too soon or not soon enough. Also u may be on to it with the accelerator pump issue. High lift cams seem to be a little moody at low rpm acceleration
 

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729 Posts
Discussion Starter #3
I did not consider the EHI distributor. I'm
Not that familiar with EHI. How can I test
The distributor. How can I test the carb?
 

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With engine off ,remove air filter , while looking down carb throat at front squirters slowly but steadly open throttle. Look for a steady gas flow from squirter. If not u may need another accelerator pump or adjust the pump cam. Check your timing advance with a GOOD timing light, if it seems to dance around alot that may be your dist. Hey I'm just a body man not really much of a mechanic, but hope this helps
 

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Discussion Starter #5
I will check it out at lunch today. I have a feeling it
Is the accelerator pump. I set the timing and idle mixture
A few months ago.

BTW - I was getting gas last night and 340 Z twin turbo tried to
Take me at a light. Not a chance! Gave me a big
Grin on my face. Still learning how to handle to torque of this 454
But it really runs nice. Just need to fix the bog at normal
Acceleration.
 

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The first thing to check, even before looking inside the carb is to be sure there is NO clearance between the accelerator pump lever and the linkage from the throttle arm. Fuel should flow from the squirters instantly no mater how much the throttle is moved.
 

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Have you checked your vacuum advance on distributor?
Maybe it pulls alot of advance when cruising, and when you go sudden full throttle, you may loose advance, since centrifugal advance cant keep up untill you get more rpm!

Maybe, i say maybe! You need to limit your vacuum advance, and give it more initial advance!
Total should be in 35deg. area with no vacuum. All in around 3000rpm.

Just my guess, since you say low rpm.
If it works from 3000rpm and upwards with no bogging, i think the accelerator pumps is OK!



Larsperformance
 

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The bog is likely in the carb. Your750-DP is fine for your 454 but out of the box it's set for a smaller mill. Your 454 needs more of shot from the accelerator pump/circuit.

Two things. Change the primary pump cam to a move aggressive profile. I believe you have a pink one in her now. The blue one would be a good move I think. Secondly, you likely need bigger squirter nozzles. I'd do both the primary and secondary side. That carb comes with .031's I believe. Jump up to .035's.

If problem is better with with .035's but still noticeable, go to the .037's. Trial and error,..part of the fun of what we do.

Those two changes, a 20-30 minute job, should smooth out your low RPM bog.

Good luck.
 

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Discussion Starter #9
I checked the accelerator pumps and there is no play. As soon as I depress
Either, a jet of gasoline sprays...
 

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I have a 454 that came with the car I just
Purchased. It has 10.5:1 compression, 325 HP
Oval port heads, msd ignition and a 750 Holley double pumper,
Solid lifter cam with 550 lift. Intake is a Weiland single plenum.

The motor runs nice except for a slight bog if you try to
Accelerate under low rpm. For, example, at rest, put can in first
Gear and then apply gas. The car will hesitate
And the accelerate.

I would like to know how to adjust this myself.
Can you give more information ?

What type of trans ? What's your rear gearing ?

You said you have a MSD distributor ? Does it have a vacuum advance can ?
 

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Advance initial timing, or, since running an HEI, you might plug the vac advance into full time manifold vacuum.
This route will leave plenty of reduced initial timing for hot starting, and once engine starts, plenty of induced timing for smoother running.
 

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Discussion Starter #13
I did notice something strange with the primary squirters. They appear to be pointed towards the front of the carb. Should'nt the point towards the primary inlets?

Did the previous owner put them on backwards? Can they even go on backwards?
 

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Those squirters without tubes, can be installed backwards.
BUT, the squirter is keyed to the body.
The squirts should be dumping onto the venturis when throttle is opened.
 

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Discussion Starter #15
They are on backwards then. The secondary is correct though.
I just purchased 035, 037 squirters and the Holley cam kit.

I will detach the secondaries just to see if bogg goes away. If not, I flip the primary squirters. Once squirters and cam come in, I'll plug and play.
 

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Discussion Starter #16
I flipped the front squirters and now nearly all
The bogg is gone. Very little hesitation now. Why
Would someone have put those on backwards?
 

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I flipped the front squirters and now nearly all
The bogg is gone. Very little hesitation now. Why
Would someone have put those on backwards?
Duuhhh.....oops? It happens.
 

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Discussion Starter #18
I spun the forward squirters around and the bog virtually
Disappeared. Tiny bog but not really noticeable. I put the car in drive and stomped the gas at 800 rpm and spun the tires.
 

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Cool! You might advance the initial timing a couple of degrees.
Engine should go from 800 to infinity in about 3, maybe 5, microseconds...
 
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