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Old 04-29-2010, 04:44 PM
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Holley 4150 bog/hesitation

I have a 86 z28 with a 350 flat top pistons . summit vortec heads ( ported )
Lunati bracket master 2 cam .490 lift .490 lift in 235* dur at .50 ex 240*
1.6 roller rockers. Edelbrock eps intake. Headers, 2 1/2 inch cat back.

My problem is my carb which is a 670cfm Street avenger is giving me a bog/hesitation problem. When leaving a stop sign or giving it just a little gas off idle while cruising it just hesitates for a couple seconds. And when you dead rev it or launch it it will just bog for about a second. i tried .35 discharge nozzles
all the accel pump cams. and they just made it smoke a little more out the exhaust when you rev it. i've try a bunch of different timing and changed the initial and then tried running a manifold vacuum to ported vacuum ( changing the curve in the distributor as well ) and it doesnt help.
I was told these carbs are jetted lean from holley and My plugs a little white but have a very light tan tint to them.

O yeah and when the choke is on at all it doesn't bog at all and sounds great until the chokes off then it bogs.

I bought this new and ive been fighting with it since

And thoughts??
thanks for any suggestions. im all ears.

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Old 04-29-2010, 05:40 PM
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Check the float height first, could be too low.

Many people report these being too lean, seems to be more so with cams sized like yours. You are actually outside the recommended use for this carb. You may need to jet it bigger along with opening up the idle feed restriction in the metering block to provide a richer A/F mix to the mixture screws, this influences off idle transition a lot. You may also need to change power valves and increase the PVCR(power valve channel restrictions) to get everything to work together, I am not familiar off the top of my head with the valve rating and channel restriction size on these newer carbs
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Old 04-29-2010, 05:45 PM
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bog is to fat, lean is a back fire, go to a smaller nozzle like a 32 and maybe jet down
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Old 04-29-2010, 06:17 PM
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Well it has a .31 nozle in it now and your both telling me the opposite things.
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Old 04-29-2010, 06:20 PM
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Quote:
Originally Posted by ericnova72
Check the float height first, could be too low.

Many people report these being too lean, seems to be more so with cams sized like yours. You are actually outside the recommended use for this carb. You may need to jet it bigger along with opening up the idle feed restriction in the metering block to provide a richer A/F mix to the mixture screws, this influences off idle transition a lot. You may also need to change power valves and increase the PVCR(power valve channel restrictions) to get everything to work together, I am not familiar off the top of my head with the valve rating and channel restriction size on these newer carbs

what about jets? It has 65 primary and 67 secondary jets factory. Does 67 primary and 70 secondary sound bettter. Or maybe more? im not sure ive always used edelbrocks before and never had this type of problem.

I do think its a little lean and i have no idea about power valves.
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Old 04-29-2010, 06:33 PM
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Let's clarify some things-

When floored from a dead stop, does it cough or stumble, maybe even backfire??

The fact that it will take throttle slowly tells me it is too lean, too rich rarely results in a problem with a vacuum secondary carb when floored, it will be a little sluggish if rich but it won't stumble badly.

Too rich would have it pouring black smoke when floored and slow acceleration but not have a real stumble that you can "catch back" by feathering the throttle, feathering will just make a rich condition worse. If you can throttle back and the engine"catches up" with the carb it is not a rich problem.

If you are unsure, have someone watch the car from a dead stop when floored, there can be a quick puff of black smoke but if the black smoke continues the entire time the engine struggles then it is too rich.
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Old 04-29-2010, 06:39 PM
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Quote:
Originally Posted by vortec86z29
what about jets? It has 65 primary and 67 secondary jets factory. Does 67 primary and 70 secondary sound bettter. Or maybe more? im not sure ive always used edelbrocks before and never had this type of problem.

I do think its a little lean and i have no idea about power valves.
Front doesn't sound bad, I would expect to see 65-67, but 72-74 sounds a lot better to me in the rear, but determine from the above post first whether you have a rich or a lean condition.

Just off the top of my head 67 secondary just sounds way too lean for any 650-700 cfm Holley carb.

Others have reported the same thing you are having trouble with.
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Old 04-29-2010, 07:07 PM
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I don't know anything about the 670cfm Street avenger, from the symptoms
you describe it sounds like the transition circuit and or shooter size is too
lean. What you tried with the choke proves that to be correct. When an
engine bogs there is no fuel flowing through the boosters so jet size has little
or no impact.

Earlier you said you tried more ignition advance, I would make sure its
somewhere around 15 - 20 degrees advance at idle.
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Old 04-29-2010, 07:47 PM
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ok check this out.

My 670 comes with 65 primary jets and 67 secondary jets.
A regular holley 650 comes with 67 primary jets amd 73 secondary jets.
Does this make sense to anyone. Why would a higher cfm carb have smaller jets.

Well anyway I think im going to try 67 and 73 jets.
Could this possibly cure my hesitation problem?

And again thanks for all your guy help with this im was getting pretty Mad at this stupid thing.

O yeah and the 650 comes with a .028 nozzle as mine comes with a .031.
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Old 04-29-2010, 07:57 PM
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Quote:
Originally Posted by automotive breath
I don't know anything about the 670cfm Street avenger, from the symptoms
you describe it sounds like the transition circuit and or shooter size is too
lean. What you tried with the choke proves that to be correct. When an
engine bogs there is no fuel flowing through the boosters so jet size has little
or no impact.

Earlier you said you tried more ignition advance, I would make sure its
somewhere around 15 - 20 degrees advance at idle.

Well i used a .035 nozzle and tried different cams and all it did is make the car puff a little black smoke when its revved. So i took it back down to .031
My initial timing is at 13 degrees right now.
And when the choke is on the only real difference is it makes the air/fuel richer right. So wouldnt jetting it bigger do the same thing?
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Old 04-29-2010, 08:02 PM
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Read what AutomotiveBreath has said about the ignition timing, this is very important.

Jetting may help some when you have the timing right but the problem could just as well be in the transition circuit(much more likely) like we both have posted.

The Street Avenger carbs are not intended for engines with as much cam duration as you are using, they are intended for mild engines, this is the reason some parts of it are so incorrect for your application.

Holley does a poor job of putting all the info you need to pick a correct carb in their literature or web site, been a peeve of mine for years - they just want to make the sale and get your money, don't seem to care if it is right or not.
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Old 04-29-2010, 08:04 PM
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Double of above post

Last edited by ericnova72; 04-29-2010 at 08:05 PM. Reason: double post
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Old 04-29-2010, 08:12 PM
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Quote:
Originally Posted by vortec86z29
Well i used a .035 nozzle and tried different cams and all it did is make the car puff a little black smoke when its revved. So i took it back down to .031
My initial timing is at 13 degrees right now.
And when the choke is on the only real difference is it makes the air/fuel richer right. So wouldnt jetting it bigger do the same thing?
Not if it is the transition circuit that is too lean. Jetting doesn't effect the fuel curve until the airspeed through the carb is high enough to pull fuel from the boosters, until that happens it is running off the transition circuit and the idle screws, it could be too lean from those circuits.

With a camshaft that size you need to get the initial timing closer to 20.

If you are using a single plane intake it may also take a 50cc accelerator pump and big pump cam to get a longer lasting shot(same size holes but shot lasts for a longer period of time) from the same size shooter you already have - to help cover that lean hole you have now
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Old 04-29-2010, 08:41 PM
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Eric and I are saying the same thing, the carburetor is not keeping the air fuel
mixture consistent when the throttle is opened, there is a lean spike. This is a
very common problem and easy to resolve.

The lean mixture burns too slow, thats why it's important to make sure it gets
enough ignition advance during transition from idle to open throttle.
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Old 04-29-2010, 09:21 PM
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Ok well i'll advance the timing a little more rejet it up a few sizes and try a different accel pump cam tomorrow or maybe saturday.

Holley recommended me this carb saying ( its just a bolt on and go carb with minimal to no tuning required ). What a joke. Well with a little tuning im sure it will be worth it still.
Im let you know how it turns out and if i still have a problem. Thanks for your help.
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