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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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Re: Holley 750DP adjustment. Secondary stumbling
[Re: Pacnorthcuda]
#1020581
06/27/11 06:02 PM
06/27/11 06:02 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:
All I said was he could try a 50cc pump. Yes it comes with its own cams. (and arm) see link.
....well, except for this: "The 50cc pump does not add any additional fuel."
http://www.holley.com/data/products/pictures/large20-11.jpg
I understood what "you" were trying to say from the get go, & if anyone would think a 50cc pump "with its own cams" doesn't deliver more fuel the a 30cc pump needs to go back too science or math class 
Just remember this though, even though these buckets carry this amount of volume, The cams they come with never deliver the "full" amount of that volume, the cams just change the timing & dur. of the volume, the squirters just dump that volume quicker or slower through the shot depending on there size, but your still getting that same amount from the cam you choose.
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Re: Holley 750DP adjustment. Secondary stumbling
[Re: 68Bullit]
#1020582
06/27/11 06:12 PM
06/27/11 06:12 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:
"Dead Spot" would be another way to describe it. In fact, it's probably a better term to use over "bog" but at any rate it just does not come on like a mech secondary carb should come on and it's clearly noticeable - just falls on it's face for second.
Sounds like a lean stumble/dead spot then recovers when the main curcuit kicks in, make sure there is no slack or up & down motion on the secondary pump arm, this will cause the issue your decribing, if you do get it adj. propperly, & its still there, try the next squirter size up, a .033", you never want to jump way up on sizes, 1 at a time, Now also, make sure the float level is currect, at idle, it should just barely trickle out of the side plug.
If anything, i always advise to get a holley perf. tuneing book, there at any Books-a-million or any major book store like them.
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Re: Holley 750DP adjustment. Secondary stumbling
[Re: joedust451]
#1020583
06/27/11 06:58 PM
06/27/11 06:58 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:
All I said was he could try a 50cc pump. Yes it comes with its own cams. (and arm) see link.
....well, except for this: "The 50cc pump does not add any additional fuel."
http://www.holley.com/data/products/pictures/large20-11.jpg
I understood what "you" were trying to say from the get go, & if anyone would think a 50cc pump "with its own cams" doesn't deliver more fuel the a 30cc pump needs to go back too science or math class
Just remember this though, even though these buckets carry this amount of volume, The cams they come with never deliver the "full" amount of that volume, the cams just change the timing & dur. of the volume, the squirters just dump that volume quicker or slower through the shot depending on there size, but your still getting that same amount from the cam you choose.
Agreed! A 50cc pump with a 30cc cam (any of them) is going to behave as a 30cc pump. Trying a 50cc pump means the obvious to most all of us. As stated the bigger cams even come with the kit. Who wouldn't try them??? Its part of the pump package. As far as not actually 30 or 50ccs being delivered 'per shot' I have no doubt thats true. But its become Holley's nomenclature to refer to it as a "30 cc shot" or "50 cc shot". Hopefully the OP gets it worked out.
Squirters may certainly be a better fix for the issue.
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Re: Holley 750DP adjustment. Secondary stumbling
[Re: Pacnorthcuda]
#1020584
06/27/11 10:35 PM
06/27/11 10:35 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:
As stated the bigger cams even come with the kit.
Right. But thats not always the case. You can, or use to be able to buy only the pump, no cams.
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Re: Holley 750DP adjustment. Secondary stumbling
[Re: joedust451]
#1020585
06/27/11 10:50 PM
06/27/11 10:50 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:
All I said was he could try a 50cc pump. Yes it comes with its own cams. (and arm) see link.
....well, except for this: "The 50cc pump does not add any additional fuel."
http://www.holley.com/data/products/pictures/large20-11.jpg
I understood what "you" were trying to say from the get go, & if anyone would think a 50cc pump "with its own cams" doesn't deliver more fuel the a 30cc pump needs to go back too science or math class
Just remember this though, even though these buckets carry this amount of volume, The cams they come with never deliver the "full" amount of that volume, the cams just change the timing & dur. of the volume, the squirters just dump that volume quicker or slower through the shot depending on there size, but your still getting that same amount from the cam you choose.
"with its own cams" came well after the discussion regarding just the pump. No where prior to that was it mentioned that he was referring to the pump and its own cams, not even implied. In fact he clearly states the cam is soley for rate.
And of course you understand that the total pump volume (not cam delivery volume) is not 30 or 50 cc either....right?
Was math and science backgrounds comment directed to me?
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Re: Holley 750DP adjustment. Secondary stumbling
[Re: BSB67]
#1020586
06/27/11 11:11 PM
06/27/11 11:11 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:
Quote:
All I said was he could try a 50cc pump. Yes it comes with its own cams. (and arm) see link.
....well, except for this: "The 50cc pump does not add any additional fuel."
http://www.holley.com/data/products/pictures/large20-11.jpg
I understood what "you" were trying to say from the get go, & if anyone would think a 50cc pump "with its own cams" doesn't deliver more fuel the a 30cc pump needs to go back too science or math class
Just remember this though, even though these buckets carry this amount of volume, The cams they come with never deliver the "full" amount of that volume, the cams just change the timing & dur. of the volume, the squirters just dump that volume quicker or slower through the shot depending on there size, but your still getting that same amount from the cam you choose.
"with its own cams" came well after the discussion regarding just the pump. No where prior to that was it mentioned that he was referring to the pump and its own cams, not even implied. In fact he clearly states the cam is soley for rate.
And of course you understand that the total pump volume (not cam delivery volume) is not 30 or 50 cc either....right?
Was math and science backgrounds comment directed to me?
I understood exactly what he meant by his 1st. reply  , when you buy the 50cc pump assembly, it comes with the cams, & why would anyone be stupid enough to buy just a 50cc pump & arm & use the 30cc cams  , What good would that do , I'm sure he meant the KIT with the cams, thats how most if not all of them come, as a "complete" kit. I think you just jumped the gun on your responce as he clearly stated in his other responce that he knew they came with there own cams.
Now why would you try an emphasize about them not holding that amount of liquid , Do you know this for a fact! Its CC "Cubic Centimeters" of liquid, It'll push that amount fully compressed from its extended position though the cams won't allow it, but the assembly as a whole buttoned up holds more then 50cc.
http://shop.ebay.com/i.html?_from=R40&am...-All-Categories
Last edited by joedust451; 06/27/11 11:59 PM.
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Re: Holley 750DP adjustment. Secondary stumbling
[Re: joedust451]
#1020587
06/27/11 11:51 PM
06/27/11 11:51 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:
All I said was he could try a 50cc pump. Yes it comes with its own cams. (and arm) see link.
....well, except for this: "The 50cc pump does not add any additional fuel."
http://www.holley.com/data/products/pictures/large20-11.jpg
I understood what "you" were trying to say from the get go, & if anyone would think a 50cc pump "with its own cams" doesn't deliver more fuel the a 30cc pump needs to go back too science or math class
Just remember this though, even though these buckets carry this amount of volume, The cams they come with never deliver the "full" amount of that volume, the cams just change the timing & dur. of the volume, the squirters just dump that volume quicker or slower through the shot depending on there size, but your still getting that same amount from the cam you choose.
"with its own cams" came well after the discussion regarding just the pump. No where prior to that was it mentioned that he was referring to the pump and its own cams, not even implied. In fact he clearly states the cam is soley for rate.
And of course you understand that the total pump volume (not cam delivery volume) is not 30 or 50 cc either....right?
Was math and science backgrounds comment directed to me?
I understood exactly what he meant by his 1st. reply , when you buy the 50cc pump assembly, it comes with the cams, & why would anyone be stupid enough to buy just a 50cc pump & arm & use the 30cc cams , What good would that do , I'm sure he meant the KIT with the cams, thats how most if not all of them come, as a "complete" kit. I think you just jumped the gun on your responce as he clearly stated in his other responce that he knew they came with there own cams.
Now why would you try an emphasize about them not holding that amount of liquid , Do you know this for a fact! Its CC "Cubic Centimeters" of liquid, so i'm sure it holds damn near that amount of liquid like in a Syringe 
http://shop.ebay.com/i.html?_from=R40&am...-All-Categories
Quote:
What good would that do ,
apparently we agree...nothing.
Quote:
I'm sure he meant the KIT with the cams, thats how most if not all of them come, as a "complete" kit.
Maybe that is what he meant, but not what he said. If that is what he meant, then we all agree.
For as many 336 cams that I have around here, they have probably been coming with the 50 cc kit for a while.
I only mentioned it as the 20 cc difference seemed to be used as an actual volume. I have not measured them, but I do know what 1 cc looks like, and certainly most here would know what 90 cc might look like.... I think you would agree.
The total rated displacement of the cams is rated on 10 pump strokes, and the cams with greater than 30 cc total discarge after 10 strokes will require the larger pump capacity. As mentioned, it is Holleys way to describe them, it not the actual volume.
Last edited by BSB67; 06/28/11 12:02 AM.
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Re: Holley 750DP adjustment. Secondary stumbling
[Re: GwaiiEagle]
#1020589
07/27/11 10:39 PM
07/27/11 10:39 PM
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Joined: Nov 2004
Posts: 2,825
Sk. Canada
RemCharger
master
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master
Joined: Nov 2004
Posts: 2,825
Sk. Canada
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BSB67 has been correct on every post. One needs to be clear on the internet, to avoid assumptions, intentions, telepathic expectations etc. I could see someone putting on just a 50cc pump with no diff cam (maybe had one laying around). After all that I believe everyone is on the same page. To the question on hand,,, I just put on a QF 750 dp in a customers 68 R/T 440, and it had the biggest hole in the secondarys I've evr seen. After a lot of gas and tuning.. I put a 1" open hole spacer and a 50 shooter. The thing would do beautiful rolling stomp on smoke shows. The shooter is probably too big, but I had one and it works. The other problem I saw was the bottom shooter gaskets were wrong and closing up the spacE between the threads.. not good. 
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