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Discussion Starter #1
I cant seem to get the stumble out of my 4779 750 DP.
I actually think its running rich and not lean.
At part throttle- response is great.
WOT- carb falls on face for a moment then gets it.
Disconnect secondaries and bog is gone.
Seems like its too rich in the secondaries.
Ive got pink cam at the primaries and orange at secondaries.
no play in accelerator pump actuator arm.
30cc accelerator pumps.
71/86 jets with 6.5 PV.
stock setting I read may have been 70/80 on jetting.
I switched 31cc squirter up front and 28cc squirter in secondaries

Ive set total timing to 36 degrees-mechanical advance
and have 13-15mm Hg vacuum at idle.

thoughts greatly appreciated.

thanks

steve
 

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Big Al is at the boat races in High Point today...... so he's off-line for a while.

That's why it's been so quiet around here. :sleep::rolleyes::D

Cheers, Tim
 

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try

switching the 31 to the rear and 28 to the front ,, whats this carb on ?? i had a 750 dp on my 355 ,,i had to go to the 50cc pump on the secondary to get rid of the " lean " bog,,, if you roll into the throttle slow to WOT ,, does it bog ? ,, that jetting looks a little crazy ,, whats ur compression ratio and what gas do u use
 

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Don't know what your engine combo is. problem is not enough fuel on the transition. As all the other threads that people have posted on here they all experience the same problem. Jetting is not a factor here. You need to get the squirters dialed in first. Try swapping the squirters like levis says, if it improves you can leave it or put a bigger squirter in the back, or fine tune it so the squirters are even front to back. You may need to play around with the accel pump cams too. Try putting the bigger cam in the secondary side on the #2 hole. Be sure the pump arms are adjusted properly. Once you get it responsive then you can fine tune the jetting and PV. You can also fine tune the PV too for best combo of fuel mileage and power.
 

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Discussion Starter #5 (Edited)
thanks guys.
ive played with the pumps- it initially came with pink cams front and back.
im thinking about jetting down to stock settings- 70/80, but increasing the squirters to 35/35.
it was initially 28/31- i swapped em initially thinking the problem was the primarys being too lean but i think secondaries are too rich.
if you lean into it- acceleration is smooth, but blipping throttle WOT bogs.

engine is 383, air gap intake, about 9.9:1CR, 350 trans with 2800K converter and 373 gears. lunati flat tappet 268/274 with .489/.504

91 octane.

thoughts greatly appreciated.

steve
 

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I had the exact same problem and shimmed my accelerator pump spring tighter with washers. Problem solved.

Someone said it sounded hoakey:rolleyes:, but I learned that trick from a well known Bay Area carb expert.
 

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every carb is differant just like every motor is diferant. i would agree with 6nova4 and put the 31 back in the rear. it shouldnt need more than that. also some acc. pumps like alittle play in them. try giving it around .010 or so and see what happpens. its all part of the tuning process!!! good luck.
 

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40's

You may need to go as high as #40 squirters. Both ALLT4 on his ZZ383 and myself on the ZZ4 needed 40's front and rear to clear the stumble.
FWIW am running 78/86 on the jets but mine did show it wanted more fuel then most during the dyno pulls.
 

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I cant seem to get the stumble out of my 4779 750 DP.
I actually think its running rich and not lean.
At part throttle- response is great.
WOT- carb falls on face for a moment then gets it.
Disconnect secondaries and bog is gone.
Seems like its too rich in the secondaries.
Ive got pink cam at the primaries and orange at secondaries.
no play in accelerator pump actuator arm.
30cc accelerator pumps.
71/86 jets with 6.5 PV.
stock setting I read may have been 70/80 on jetting.
I switched 31cc squirter up front and 28cc squirter in secondaries

Ive set total timing to 36 degrees-mechanical advance
and have 13-15mm Hg vacuum at idle.

thoughts greatly appreciated.

thanks

steve
Go to 73s on the front.
 

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Discussion Starter #12
thanks for the replies guys!
squirters are ALL squirting fuel.
I guess the consensus is to increase rear squirter back to the 31's.
gosh- 40's seem big for this basically mild motor.
i will go back to about 73/80's on the jets and play with the accelerator pump cams and actuating arms a little.
i am curious to try the 35/35 squirters as well.

thanks again to all.

steve
 

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Did you ever look at the plugs after a cruise run on the primaries and the a second reading after a WOT run to see where your jetting is before you start swapping jets around? That is what I would do 1st before swapping jets.

The bog 9 out of 10 times is as the others have said a lean condition upon opening the 2ndaries.

I would up the 2ndary squirter to a 35. You mentioned a "blipping WOT throttle bog" what do you mean? Does it run good then fall down a little, and is hat repetative if you keep you foot into it? If so you may want to throw a fuel pressure gauge on it to make sure you have adequate fuel pressure throught the RPM range. How are your floats?
 

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rich /lean

have you read the plugs.... white...to black being too rich white too lean I run a plug in the power valve hole, cars with big cams don't always have much vaccume and they are a pita, check float levels , whats your fuel press? fuel filter dirty? check all the basics, first! the easiest problems often stump the best of us! jmo I ran 86 front 92 rear jets 30 cc pumps don't remember which squirters on a 650 mechanical double pumper 9 psi fuel pressure no bogs, stall or flat spots
 

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what he said

Did you ever look at the plugs after a cruise run on the primaries and the a second reading after a WOT run to see where your jetting is before you start swapping jets around? That is what I would do 1st before swapping jets.

The bog 9 out of 10 times is as the others have said a lean condition upon opening the 2ndaries.

I would up the 2ndary squirter to a 35. You mentioned a "blipping WOT throttle bog" what do you mean? Does it run good then fall down a little, and is hat repetative if you keep you foot into it? If so you may want to throw a fuel pressure gauge on it to make sure you have adequate fuel pressure throught the RPM range. How are your floats?
great minds think alike huh Denny:rolleyes:
 

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Discussion Starter #16
thanks guys.
the only piece of info i dont have is the fuel pressure.
its a new holley 110? pump.
i only pulled the #1 plug and its light brown. looked good.
gas seeps outa both bowls when running.

i think i will put the 35/35 squirters in there and just go back to 80 jets in the secondaries (stock setting). then mess with the accelerator pump cams- aiming for increased fuel in the secondaries.
okay, hearing that its likely lean will make me change my tuning direction.
i will let you guys know how it goes.

thanks again.

steve
 

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gas seeps outa both bowls when running.

steve
What do you mean it "seeps out"? Is is coming out the vents? Then you need to adjust your float, got a clogged needle or excessive pressure. If that is the case it could be when you get on it fuel sloshes into the mains and drowns your car for what feels like a lean bog.
 

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Discussion Starter #18
What do you mean it "seeps out"? Is is coming out the vents? Then you need to adjust your float, got a clogged needle or excessive pressure. If that is the case it could be when you get on it fuel sloshes into the mains and drowns your car for what feels like a lean bog.
actually, i meant to say that at idle, when removing the site plug the gas trickles out- doesnt gush and does not flow out of overflow tube.
i did however have this problem and replaced the bad float with a brass one.


edit: i also just ordered the 35's squirters, holley jet kit: 64-81, and 50cc accelerator pump (i might try for the secondaries).
steve
 

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Need a little more info.

You could be chasing what can't be caught!

Cam???
Converter?
Engine size type?
rear gear?

Al
 
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