Tuning a Holley 750
#911858
01/23/11 08:46 PM
01/23/11 08:46 PM
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Joined: Sep 2004
Posts: 1,226 Cookeville
Chilort
OP
Will Work For Mopars
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OP
Will Work For Mopars
Joined: Sep 2004
Posts: 1,226
Cookeville
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I have an 80508S on my 440. I've got a Lunati 60303 cam, around 9.2:1 compression, Performer RPM intake, Eddy heads, full length headers, and full 2.5" exhaust. The rear gear is not great (2.73). I'm running an auto with a 10" converter from TurboAction. The off-the-line hit is great. Cruising down the highway is great. I'm thinking about going to an 850 from Quickfuel or an 870 from Holley. But, before I go that route I'd like to sort out an issue I'm having before I decide if I'm going to swap it out. Primary jets are 74 (original jets were 70) and it has a metering plate for the secondaries that works out to a 75 jet. The problem I have is that when I'm cruising at any speed and then decide to punch the throttle the engine bogs, sometimes sneezes out the carb, and then takes off like a raped ape. After looking at Holley's website I may need to go with a lighter secondary vacuum canister spring. Since it is great off the line it sounds to me like the secondaries are coming in too late. I don't know the weight, but this is in a '68 Sweptline pickup, which I've been told is between the weight of an A-body and a B-body.
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Re: Tuning a Holley 750
[Re: Chilort]
#911859
01/23/11 08:56 PM
01/23/11 08:56 PM
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Joined: Dec 2008
Posts: 1,200 UK
602heavy
pro stock
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pro stock
Joined: Dec 2008
Posts: 1,200
UK
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Won't be a secondary problem , if the secs are coming in too late it would't buck , just the opposite.............have you looked @ pump arm adjustment? , maybe turn the mixture screws out a tad & go try it.........................with the car idleing tap the pump shooter & if the motor picks up it's too lean , if the motor slows down it's usually to rich...........could also be a transition issue.
Last edited by 602heavy; 01/23/11 08:58 PM.
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Re: Tuning a Holley 750
[Re: B5 Bee]
#911862
01/23/11 10:00 PM
01/23/11 10:00 PM
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Joined: Sep 2004
Posts: 1,226 Cookeville
Chilort
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Will Work For Mopars
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OP
Will Work For Mopars
Joined: Sep 2004
Posts: 1,226
Cookeville
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Quote:
There are several things it could be. To keep from hiding the symptom and not fixing the problem, check things in a certain order. 1. make sure ignition is advancing properly 2. make sure carb is clean, no blocked passages 3. jetting, your's sounds fat enough 4. power valve needs to open at the needed vacuum 5. accelerator pump needs to supply enough fuel till the boosters come on line
1. I'm chasing down a part throttle ping so I've been working with the advance quite a bit: it works. 2. It is a relatively new carb. I can't say for sure I don't think it is funked up. 3. I agree. Could possibly go back to 72s on the primary even. 4. My idle vacuum is 12inhg. So I'm running close with the 6.5 PV that comes in the carb from what I understand. 5. I'll check the pump shot out on Tuesday this coming week when I've got a bit of time free during daylight.
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Re: Tuning a Holley 750
[Re: Chilort]
#911864
01/23/11 11:20 PM
01/23/11 11:20 PM
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Anonymous
Unregistered
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Anonymous
Unregistered
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In my experience on a motor very similar in build to yours, 72 jets are perfect.
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Re: Tuning a Holley 750
[Re: Mr.Yuck]
#911865
01/23/11 11:44 PM
01/23/11 11:44 PM
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Joined: Sep 2004
Posts: 1,226 Cookeville
Chilort
OP
Will Work For Mopars
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OP
Will Work For Mopars
Joined: Sep 2004
Posts: 1,226
Cookeville
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Quote:
it won't get any better until you get some gear. Putting a 2.73 in a 440 car is like having a pretty girl friend that has bad breath. yeah you can get past it but it will take a second or 3.
While I like how highway friendly that gear set is, this isn't the first time I've been told to ditch it. If I had a spare 3.23 set sitting around it would already be installed.
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Re: Tuning a Holley 750
[Re: Chilort]
#911868
01/24/11 09:26 PM
01/24/11 09:26 PM
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Joined: Feb 2005
Posts: 4,314 Prospect, PA
BSB67
master
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master
Joined: Feb 2005
Posts: 4,314
Prospect, PA
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Quote:
Quote:
There are several things it could be. To keep from hiding the symptom and not fixing the problem, check things in a certain order. 1. make sure ignition is advancing properly 2. make sure carb is clean, no blocked passages 3. jetting, your's sounds fat enough 4. power valve needs to open at the needed vacuum 5. accelerator pump needs to supply enough fuel till the boosters come on line
1. I'm chasing down a part throttle ping so I've been working with the advance quite a bit: it works. 2. It is a relatively new carb. I can't say for sure I don't think it is funked up. 3. I agree. Could possibly go back to 72s on the primary even. 4. My idle vacuum is 12inhg. So I'm running close with the 6.5 PV that comes in the carb from what I understand. 5. I'll check the pump shot out on Tuesday this coming week when I've got a bit of time free during daylight.
"-make sure carb is clean, no blocked passages"
this would be my first guess. Take it apart and clean it. Could cause the ping as well.
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Re: Tuning a Holley 750
[Re: Chilort]
#911869
01/24/11 09:52 PM
01/24/11 09:52 PM
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Joined: Nov 2003
Posts: 36,040 Lincoln Nebraska
RapidRobert
Circle Track
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Circle Track
Joined: Nov 2003
Posts: 36,040
Lincoln Nebraska
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What 602heavy said, pump shot related. I'm assuming floats/jets are good & no vac leak.
live every 24 hour block of time like it's your last day on earth
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Re: Tuning a Holley 750
[Re: Chilort]
#911874
01/25/11 12:43 PM
01/25/11 12:43 PM
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Joined: Jul 2006
Posts: 4,319 Puyallup, WA
StealthWedge67
master
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master
Joined: Jul 2006
Posts: 4,319
Puyallup, WA
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Quote:
Holley's FAQ says this:
"QUESTION I have a vacuum secondary carburetor that bogs when the secondaries come in. What will cause this? ANSWER Bogging and hesitation are caused by the secondaries coming in too quickly. You can install a heavier secondary spring and this will prevent the secondary from coming in too soon. If the engine is sluggish in response at full throttle then the secondaries may not be opening soon enough. You will then need to go to a lighter spring. The spring kit is part number 20-13 which will have 7 different springs to fine tune with."
Is this possibly what I'm chasing?
Start with the obvious and easy fix, then work from there. Pump shots and cam changes will tailor the enitial and mid throttle tip in, but if its coughing when you nail it all at once to the floor, the most likely problem is that you're secondary's are opening too fast.
Put the strongest spring possible in the vacuum canister and see if the problem goes away. If it does, then we know we're on to the right issue. From there, start weakening the spring, I'd go (2) springs at a time, until the problem starts to show itself again. Back off to the last spring that didn't bog..... done. From here, you can start to mess with pump shots and cams, and nozzle sizes. Being off on those shouldn't cause a complete cough, though. Those are things that will add throttle response if tuned properly, but it sounds to mee like the secondary spring is your issue. Especially if those other items are at stock spec. for an 80508.
It seems to me that a good running 440 really should be able to take all of 750cfm right away, I had the same carb on my old 383 with the lightest spring available in the vacuum can, and it would take a tromp to the floor without hesitation. But, your gearing being so far out of line with the rest of your combo is likely to blame. Going to a set of 3.55's would make a world of difference, and still allow 60 MPH fairly comfortably. I'd look to change the gearing ASAP.
Last edited by GEnsrud; 01/25/11 12:49 PM.
LemonWedge - Street heavy / Strip ready - 11.07 @ 120
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Re: Tuning a Holley 750
[Re: Chilort]
#911876
01/25/11 09:57 PM
01/25/11 09:57 PM
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Joined: Dec 2008
Posts: 1,200 UK
602heavy
pro stock
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pro stock
Joined: Dec 2008
Posts: 1,200
UK
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Fix a paper clip or similar (tie strap) to the arm on vaccume pod & go take it for a blast , if the paper clip has moved down rod the secs are opening , you will also be able to tell how far if any they opened. Have you checked for slack in the pump arm?.............maybe try a higher rated power valve or try going up 6 sizes on primary main jets.
Last edited by 602heavy; 01/25/11 10:03 PM.
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Re: Tuning a Holley 750
[Re: Chilort]
#911877
01/25/11 09:58 PM
01/25/11 09:58 PM
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Joined: Jan 2003
Posts: 5,443 Indiana
YO7_A66
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master
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Indiana
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Have you pulled the existing spring to confirm that it is the black one?
""Primary jets are 74 (original jets were 70) and it has a metering plate for the secondaries that works out to a 75 jet."" A 75 secondary jet seems lean on a built 440 to me.
What color pump cam and what size squirter do you have in it?
Are you are getting 12"hg in N or D? I think that one of your circuits is lean. Either the pump cam is too small, the PV is too low, or the secondary plate is too lean.
1970 YO7 A66 [Canadian Export] F8 Challenger 340 (Currently in shop for stroker assy.)
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