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Re: Holley 750DP adjustment. Secondary stumbling
[Re: BSB67]
#1020566
06/26/11 03:12 PM
06/26/11 03:12 PM
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Joined: Nov 2007
Posts: 21,844
Kirkland, Washington
Pacnorthcuda
Too Many Posts
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Too Many Posts
Joined: Nov 2007
Posts: 21,844
Kirkland, Washington
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Quote:
The 50cc pump does not add any additional fuel. The only way to change the amount of fuel is to change pump cams. Some pump cams require the larger pump diaphram capacity.
Sure it does. 50cc vs 30cc for a full shot. Yes, the cam needs to be changed to affect the RATE of the shot, and is likely needed in this case.
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Re: Holley 750DP adjustment. Secondary stumbling
[Re: BSB67]
#1020568
06/26/11 03:57 PM
06/26/11 03:57 PM
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Joined: Nov 2007
Posts: 21,844
Kirkland, Washington
Pacnorthcuda
Too Many Posts
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Too Many Posts
Joined: Nov 2007
Posts: 21,844
Kirkland, Washington
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Quote:
Quote:
Quote:
The 50cc pump does not add any additional fuel. The only way to change the amount of fuel is to change pump cams. Some pump cams require the larger pump diaphram capacity.
Sure it does. 50cc vs 30cc for a full shot. Yes, the cam needs to be changed to affect the RATE of the shot, and is likely needed in this case.
The pump diaphram size serves only to store the need volume.
And a 50cc pump stores 50cc, a 30cc stores 30cc. 50-30=20. Yep, 20cc's more. Not rocket science.
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Re: Holley 750DP adjustment. Secondary stumbling
[Re: BSB67]
#1020569
06/26/11 04:00 PM
06/26/11 04:00 PM
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Joined: Mar 2005
Posts: 862
Iowa State fan
kilroy
super stock
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super stock
Joined: Mar 2005
Posts: 862
Iowa State fan
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I also agree I think its the secondary pump.
First though check to make sure the linkage to the pump arm is above of the pump arm and not hanging down below it. If the back bowl has been off (or the front for that matter, as this would apply to front accelerator pump also and make the front do the same thing) it easy to forget to put the pump arm under the linkage, and this equals NO pump and bad stumble.
I would also push the back bowl pump arm down; you want to see if it pushes fuel through the accelerator pump nozzles.
If it does, then check to make sure there is no slack between the linkage and the pump arm. If there is this will also cause a delay in the pump and cause the said stumble.
make sure rear fuel bowl also has fuel in it, or the pump wont work either and cause this to happen.
DO ALL THIS WHILE VEHICLE IS OFF SO THE MOTOR DOESNT ACCIDENTALLY GO WIDE OPEN.
1973 Charger, former SE, former auto
I'm not trying to be difficult, it comes naturally....
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Re: Holley 750DP adjustment. Secondary stumbling
[Re: Pacnorthcuda]
#1020572
06/26/11 05:24 PM
06/26/11 05:24 PM
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Joined: Jan 2003
Posts: 5,447
So Cal
Sinitro
master
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master
Joined: Jan 2003
Posts: 5,447
So Cal
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Quote:
Yes, make sure that the pump arm is actuated by the linkage AS SOON as its moved---NO slack.
You can try different cams to actuate the arm faster in order to bring the shot in quicker.
Make sure you adjust the accelerator pump properly..
Here is the way direct from Holley..
QUESTION:
My vehicle has a stumble from a dead stop. What can I do to cure this?
ANSWER:
The most common cause of a stumble is not having an adequate accelerator pump shot. The first thing to do is to look at the discharge nozzle and make sure you are getting a good strong pump shot. If not then you need to inspect the pump diaphram for a hole or tear. You will also need to make sure that the pump passage is clear from any trash or debris. First you will need to check the adjustment on the pump. To do this you will open the throttle all the way (WOT). Push the pump arm lever down and then adjust the pump override spring to obtain .015" clearance between the pump arm and lever. If you are having a stumble and no black smoke out the tailpipe then you will need to increase the shooter size. If it stumbles and you are getting black smoke from the tailpipe then it will be nessasary to decrease the shooter size.
Just my $0.02... 
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Re: Holley 750DP adjustment. Secondary stumbling
[Re: Pacnorthcuda]
#1020573
06/26/11 05:34 PM
06/26/11 05:34 PM
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Joined: Feb 2005
Posts: 4,318
Prospect, PA
BSB67
master
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master
Joined: Feb 2005
Posts: 4,318
Prospect, PA
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Quote:
Quote:
Quote:
Quote:
The 50cc pump does not add any additional fuel. The only way to change the amount of fuel is to change pump cams. Some pump cams require the larger pump diaphram capacity.
Sure it does. 50cc vs 30cc for a full shot. Yes, the cam needs to be changed to affect the RATE of the shot, and is likely needed in this case.
The pump diaphram size serves only to store the need volume.
And a 50cc pump stores 50cc, a 30cc stores 30cc. 50-30=20. Yep, 20cc's more. Not rocket science.
Correct, it is not rocket science, but you still don't seem to understand.
Because the cross sectional area of the two diaphragms is the same (i.e. the 50 cc diaphragm is only deeper) perpendicular to the direction of diaphragm movement, only changing the arm travel will change the quantity of fuel discharged.
The example would be two syringes of the same diameter, one is longer than the other. One is 30 cc, the other 50 cc. If you push the plunger the same amount on both of them, the same volume of fluid comes out.
The 50 cc diaphram is deeper is because the largest pump cams will cause the 30 cc pump to bottom out due to the greater distance the arm travel.
By the way, you don't really think that the pump shoots 50 cc do you?
You should be careful how sternly you react, as it only makes you look sillier when you are wrong.
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Re: Holley 750DP adjustment. Secondary stumbling
[Re: 70AARcuda]
#1020575
06/26/11 06:14 PM
06/26/11 06:14 PM
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Joined: Mar 2008
Posts: 571
Western NC
68Bullit
OP
mopar
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OP
mopar
Joined: Mar 2008
Posts: 571
Western NC
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Quote:
Quote:
Try a larger shooter in the secondary, 2 sizes larger than what's in there.
I always write the jet info & such on the top of each bowl with a marker, so the info's right there.
also make sure the acelerator pump linkage is properly adjusted...that there is no delay in the squirter shooting gas went the secondaries start to open
OK right now I'm thinking this would be the 1st place for me to check, as I HAVE had the rear bowl off before. I am just the person who would accidentally put the linkage back in the WRONG spot. So I'll check this and report back. Be a couple days before I can get it to it though 
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Re: Holley 750DP adjustment. Secondary stumbling
[Re: 68Bullit]
#1020577
06/27/11 05:44 PM
06/27/11 05:44 PM
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Joined: Jan 2003
Posts: 24,562
Brookeville, Md
Mr.Yuck
Not enough dumb comments...yet
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Not enough dumb comments...yet
Joined: Jan 2003
Posts: 24,562
Brookeville, Md
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Quote:
I checked the timing just under 2 years ago and as best as I can remember I'm all in at either 33 or 35 total. I'll check it again no doubt, but I'm at/over 10:1 compression right now, so thinking that's the limit??? Also I did rejet this carb, can't remember what exact jets are in there until I go back and look but I'm pretty sure AED sent it with 72/84 without elevation being a factor. Seemed a little rich at first then I re-jetted 70/80 IIRC, and we live about 2100 feet.....
I'd try more timing 35-36* in full early. 70/80 seems like agood palce to start. I had a very mild 340 w/ a 750 dp I ran 74-80's and a 6.5pv and 28 squirters ran good that way. How do the plugs look? How long has it been running like this?
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Re: Holley 750DP adjustment. Secondary stumbling
[Re: 70AARcuda]
#1020578
06/27/11 05:47 PM
06/27/11 05:47 PM
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Joined: Feb 2005
Posts: 5,221
Branson, Mo.
joedust451
super gas
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super gas
Joined: Feb 2005
Posts: 5,221
Branson, Mo.
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Quote:
Quote:
also make sure the acelerator pump linkage is properly adjusted...that there is no delay in the squirter shooting gas went the secondaries start to open
This is "by far" the most logical responce you have gotten, "some" of the others just made me 
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