Re: Tuning a Holley 750
[Re: Chilort]
#911879
01/25/11 10:20 PM
01/25/11 10:20 PM
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Joined: Jan 2003
Posts: 5,446 Indiana
YO7_A66
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Posts: 5,446
Indiana
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I believe that you have plenty of carb tuning left before you consider another carb. You could buy a metering plate for the secondary and this way you can rejet the secondary until you get it correct. Many carb companies sell the metering plates. Please let us know the answers to my previous response.
1970 YO7 A66 [Canadian Export] F8 Challenger 340 (Currently in shop for stroker assy.)
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Re: Tuning a Holley 750
[Re: Mr.Yuck]
#911880
01/25/11 10:43 PM
01/25/11 10:43 PM
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Joined: Nov 2007
Posts: 21,909 Kirkland, Washington
Pacnorthcuda
Too Many Posts
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Too Many Posts
Joined: Nov 2007
Posts: 21,909
Kirkland, Washington
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Quote:
With that cam the lowest gear I'd run would be 3.55's. 3.91's would be ideal. I doesn't start working until about 2k...so keep that in mind.
I agree, I run that same cam in a 440, and the powerband starts at 1900-2000 rpm. Normally not an issue in an automatic (converter would normally slip past 2K under heavy foot) EXCEPT that you have those really tall gears and you don't state the diameter of your rear tires.
You might want to see if the bog occurs under 2000 or not. The issue can be fixed with carb tuning if not, but if you are lugging the motor that much at 'cruise' it may require 3.23's
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Re: Tuning a Holley 750
[Re: Magnum]
#911882
01/26/11 11:31 PM
01/26/11 11:31 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:
I had a similar problem. In neutral the engine would take a quick snap of the throttle. In low gear, again no problem. In a higher gear a quick snap and it would cough.
Do not accept it will not work with a tall gear. My truck is a manual trans and even in 5th, I overcame the bog.
My resolution about 15 replies down this thread.
Your description of what is happening is much closer to what my vehicle is actually doing than what I described. I will have to look into this.
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Re: Tuning a Holley 750
[Re: Chilort]
#911885
01/29/11 04:54 PM
01/29/11 04:54 PM
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Joined: Jan 2003
Posts: 5,446 Indiana
YO7_A66
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Joined: Jan 2003
Posts: 5,446
Indiana
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If you have 10"hg in D than the 6.5 should be fine. You can figure out the pump cam by looking at the drivers side of the carb, just behind the throttle linkage bracket on the primary butterfly. There should be a small plastic cam that is held into position with one screw that is on that same throttle linkage bracket. You might be able to see the color better by standing in front of the engine and looking just to the left of the throttle bracket. It could be pink which seems to be a standard pump cam color. If you are going to buy parts, it might be cheaper to start with the pump cam kit from Holley. It comes with 6-8 different colors of pump cams and they are very simple to swap in and test the 3rd gear bog issue. I think once you have that tuned better than maybe purchase the secondary metering plate (no need for the pv on the sec side) and you can figure about 6-10 jet sizes larger on the sec side than what you have in the primary side if you need to order a couple of jets to test with. Start with one change at a time and the pump cams should be under $20. Once you know what color you currently have, then we can help you with a guess on the next one to test. You can use the attached chart to help select a pump cam. The pink cam (for reference) is the "slowest" cam for delivering fuel. You can see this by referencing the chart and looking at the left hand side at the Throttle Degrees versus the number under the pink cam. The numbers under the cam colors are easier to read if you just use them as a "number" (so many cc's of fuel). If you look at the 10 degree number of the pink cam and the orange cam (.050 sersus .022), you will see a big difference of how much fuel each cam will activate at 10 degrees of throttle movement. This chart will help you make a guess at your cam change as long as you know your current cam color and you know that your current cam is setup correctly with the linkage. You want the cam to activate fuel as soon as the throttle moves. You have to readjust the cam pump arm after each cam swap. All you have to do is shorten the pump arm bolt (clockwise on the bolt), then swap cams, then readjust the pump arm bolt so that you get a squirt as soon as the throttle is moved. You may have to make your final adjustmet when the engine is running. If your car is bogging just off idle, then pick a cam with more fuel delivery at 10 or 20 degrees or so. If you need more fuel at 40 or 50 degrees of throttle, then reference the chart to pick the next cam.
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Re: Tuning a Holley 750
[Re: Chilort]
#911889
01/30/11 05:20 PM
01/30/11 05:20 PM
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Joined: Jan 2003
Posts: 5,446 Indiana
YO7_A66
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Indiana
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""The bigger jets did not alter my knocking issue.""
If you have pinging, then you either have too much timing too quick or you are lean.
The orange cam is the second most aggresive cam for the 30cc pump and I would have guessed that cam would have taken care of the issue. If the orange did not cure it, I would guess that your primary side jets are still too lean. You have to remember that the pump is just a "bandaid" to tranfer the carb from circuit to circuit. I would suggest that you now bump up your primary side jets and retest. That blue cam will run out of fuel by 50% throttle movement which may affect your kickdown performance at highway speeds, or when you are above 50% throttle. Also, the 82 jets are only activated after the black spring allows the secondaries to kick in. So you are using your primary jets most of the time with that black spring installed. This is why I suggest that you look at the primary jetting. You could also swap out the 6.5pv for a higher rated unit since you have 10-11in of vacuum in gear. I would not go past an 8.5 because they are not super accurate.
1970 YO7 A66 [Canadian Export] F8 Challenger 340 (Currently in shop for stroker assy.)
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Re: Tuning a Holley 750
[Re: Chilort]
#911893
01/30/11 09:14 PM
01/30/11 09:14 PM
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Joined: Jan 2003
Posts: 5,446 Indiana
YO7_A66
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Posts: 5,446
Indiana
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What octane are you running?
You might need to run a cooler spark plug. What heat range are you running? If you are running too hot of a plug, the pinging will only get worse during the Spring and Summer temps. A cooler plug will allow you to run a quick timing curve and also allow less jetting to some degree.
The brown cam is for the 50cc pump.
Your timing curve looks good!!
1970 YO7 A66 [Canadian Export] F8 Challenger 340 (Currently in shop for stroker assy.)
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Re: Tuning a Holley 750
[Re: Chilort]
#911895
01/30/11 10:32 PM
01/30/11 10:32 PM
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Joined: Jan 2003
Posts: 5,446 Indiana
YO7_A66
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Since your are running the highest octane from the pump, I would suggest that you either keep jetting up the primary until it stops pinging, or try a cooler plug. A plug is only too cold if the plug keeps fouling. You have to feed a hot plug with more fuel.
1970 YO7 A66 [Canadian Export] F8 Challenger 340 (Currently in shop for stroker assy.)
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Re: Tuning a Holley 750
[Re: Chilort]
#911897
01/31/11 11:31 AM
01/31/11 11:31 AM
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Joined: Jan 2003
Posts: 5,791 Hamilton, Ontario Canada
Magnum
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Hamilton, Ontario Canada
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You set your jets for most power. Fattening them up to cover a bog will just use more fuel. Same with bigger shooters.
Before the washer trick. I was able to cure my bog with a 35 shooter but come on. I have a stock 5.9L with a vacuum carb. It shouldn't need so much shooter to cure a bog that was like yours, only under that one condition of fighting the tall gear. That's when I decided to preload the spring a bit. Ultimately I was able to go back to a smaller shooter too.
When you snap the throttle open. Can you see the spring compressing?
69 Super Bee, 93 Mustang LX, 04 Allure Super
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