66cayne
Frequent Contributor
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Reg: 08-06-08
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06-18-12 12:02 PM - Post#2238765
I have a slight 'tip-in' hesitation at all speeds when depressing the throttle. Picks up and goes fine after the initial hesitation. No hesitation from a standing start. Running a Holley 750 vac. secondary, 327 sbc, 3 speed manual. 15" vaccum at idle, 12.5 powervalve, 65/68 jets. Any ideas on a checklist?
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65 Imp SS
Contributor
Posts: 177
Loc: Central MN
Reg: 09-13-07
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06-18-12 01:26 PM - Post#2238797
In response to 66cayne
Do you have slack in your accelerator pump? Adjustment screw just should be touching accelerator pump lever. Here is vid on tuning.
Youtube link:
http://www.youtube.com/watch?v=k-Nx5HEzvlY
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65 Imp SS
Contributor
Posts: 177
Loc: Central MN
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06-18-12 01:31 PM - Post#2238802
In response to 65 Imp SS
You can also go to Holley TV they have the same vid and others just look in the Carb Tuning categories:
http://www.holleytv.com/featured_landing.php?reset...
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bobb
Super Senior Member
Posts: 4626
Loc: paradise
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06-18-12 10:35 PM - Post#2238971
In response to 66cayne
carb seems a bit large to me. if your running vac advance try unplugging it and see what happens.
| 70 L camino 350 all forged,174 baby blower, g-force 5 spd, road rage suspension. Pray first before all else fails. |
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 rumrumm
"12th Year" Silver Supporting Member
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06-19-12 05:49 AM - Post#2239040
In response to bobb
I would try a slightly smaller pump cam. If it doesn't help, then try another size smaller. I doubt you would need a bigger squirt. Unless you have a very strong 327, that carb is a little large. A 600 would be a better choice on a mild 327. But GM did run a 750 on their 302's if I remember correctly.
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68fastbak
Contributor
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06-21-12 05:17 PM - Post#2239926
In response to 66cayne
Accelerator pump cam and or arm adjustment like has been said for sure. What color pump cam is on there?u can always try a bigger squirter after u find the best pump cam and make sure the acc pump arm is adjusted. Make sure as soon as u begin to open the throttle that gas squirts out of the squirter the very instant the throttle is beginning to open but not enough tension on the accelerator pump arm to bottom out on the accelerator pump . Also what is ur setup on that 327?is it stock? I had the same carb with bigger jets on mine, and it ran perfect, i also had a 670 street avenger with those same jets that u have and it ran rediculously lean to the point I went up do many jet sizes I just switched to the 750 with 72/75 jets and it ran perfect, but mine isn't stock so much .if u have some engine upgrades the vac secondary 750 is fine,it may not be as torquey or gas friendly as a 600 Holley on a stock 327 but vac secondaries are very forgiving .don't forget 4 barrel 327s came with 780 quadrajets
"It is well that the people of the nation do not understand our banking and monetary system, for if they did, I believe there would be a revolution before tomorrow morning." -- Henry Ford
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72novaproject
Senior Member
Posts: 3186
Age: 57
Loc: D/FW Texas
Reg: 02-18-03
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06-22-12 03:42 AM - Post#2240074
In response to 66cayne
I have a slight 'tip-in' hesitation at all speeds when depressing the throttle. Picks up and goes fine after the initial hesitation. No hesitation from a standing start. Running a Holley 750 vac. secondary, 327 sbc, 3 speed manual. 15" vaccum at idle, 12.5 powervalve, 65/68 jets. Any ideas on a checklist?
12.5 Power Valve?  I am not sure they even make one. Is that a typo? It should be pig rich when you accelerate. A 6.5 or 7.5 should be appropriate.
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72novaproject
Senior Member
Posts: 3186
Age: 57
Loc: D/FW Texas
Reg: 02-18-03
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06-22-12 03:45 AM - Post#2240075
In response to 66cayne
I have a slight 'tip-in' hesitation at all speeds when depressing the throttle. Picks up and goes fine after the initial hesitation. No hesitation from a standing start. Running a Holley 750 vac. secondary, 327 sbc, 3 speed manual. 15" vaccum at idle, 12.5 powervalve, 65/68 jets. Any ideas on a checklist?
12.5 Power Valve? I am not sure they even make one. Is that a typo? It should be pig rich when you accelerate. A 6.5 or 7.5 should be appropriate.
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72novaproject
Senior Member
Posts: 3186
Age: 57
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06-22-12 03:45 AM - Post#2240077
In response to 72novaproject
Oops!
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66cayne
Frequent Contributor
Posts: 1802
Reg: 08-06-08
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06-22-12 05:48 AM - Post#2240098
In response to 72novaproject
FYI, see link below
http://www.holley.com/125-206.asp
I am running a 10:1 compression 331 (.030 over 327). Comp Cam 268H, stock 461 heads, Edelbrock dual plane manifold, headers, HEI. Holley 750 cfm vac. with stock 'white' pump cam and #25 shooter. I have a small assortment of pump cams- white, orange, red, yellow. Looking at them it is hard to tell what difference it makes running one vs. the others. I need a chart with that data. I also have an assortment of shooters-25 to 35. The accell pump seems to be adjusted and working fine. My plan is to increase initial shot size via install of a slightly larger shooter. Going to try a few sizes up-27 or 28. Hopefully that will provide the extra fuel needed to cover the hesitation. I think it is trial and error now between accell pump cams and shooter size. Thought- maybe I should check the spring on the secondaries, could be opening too soon? Large carb on small engine, perhaps would benefit from latter secondary opening??...
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68fastbak
Contributor
Posts: 610
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Loc: fort lauderdale fl
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06-22-12 12:05 PM - Post#2240204
In response to 66cayne
Try a orange cam If it gets worse than try a blue cam,and a 32 squirter ,and change the jets up to 70/75 or 72/75 , sounds like ur to lean with that setup,
"It is well that the people of the nation do not understand our banking and monetary system, for if they did, I believe there would be a revolution before tomorrow morning." -- Henry Ford
DONT TREAD ON ME! |
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MikeB
Senior Member
Posts: 9388
Loc: Plano, TX
Reg: 08-28-03
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06-22-12 01:37 PM - Post#2240224
In response to 66cayne
Comp Cam 268H, stock 461 heads, Edelbrock dual plane manifold, headers...
All that's really needed for a mild-mid performance 327 like yours is is a 600.
However, you should be able to get that 750 working fine in near-stock trim. I tested a rebuilt 0-80508 (750 VC) on a very mild 355 in a heavy pickup, and it worked great with all stock jets, squirters, and pump cam. It was smooth as silk with zero nasty habits.
Keep this in mind: The 350HP and 365HP 327s came equipped with a 585 Holley and would rev to the moon. The same-size carb was also used on the entry-level, hydraulic lifter 427.
Q-jets are a different animal because of their tiny primaries which make for great throttle response, even on small engines. The secondaries would have opened maybe halfway on a 327.
The big square-bore carb used on the 302 was probably because it was a 8,000 RPM engine, and would compliment the optional GM off-road cam and headers.
Even the much larger solid lifter 375HP/396 used "only" a 780, the first iteration of the legendary 0-3310.
Real Hot Rods have a Clutch!
1955 210 2dr: 327, Brodix IK180 heads, Jones cam, Muncie M20, Wilwood front brakes
1969 C-10 pickup: 350, TH350
My car pictures
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68fastbak
Contributor
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06-22-12 01:40 PM - Post#2240225
In response to 68fastbak
Don't worry about ur secondaries until u take care of the primaries and idle transition to acceleration circuit I.e accelerator pump cam and squirters.do the jets too. Do u have the stock spring in ur vac secondaries?do u have the quick change spring kit?keep the stock spring in till u sort out the other stuff.
"It is well that the people of the nation do not understand our banking and monetary system, for if they did, I believe there would be a revolution before tomorrow morning." -- Henry Ford
DONT TREAD ON ME! |
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68fastbak
Contributor
Posts: 610
Age: 32
Loc: fort lauderdale fl
Reg: 08-03-08
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06-22-12 01:51 PM - Post#2240226
In response to MikeB
A stock 750 vac secondary comes with a orange cam and 72 primary jets, it should work great in near stock condition. If his motor is to small the vac secondary will only suck what it wants , that's why they are very forgiving and work great in so many applications , and if he's got Tiny jets in a 750 that's a improper fix to a different problem ,his squirter and jets are to small For that carb if u want to run those squirter and jets go to a 600 or 650 , I'm not saying he needs that much cfm but it will work and pull hard midrange and top end with that carb when it's set up right
"It is well that the people of the nation do not understand our banking and monetary system, for if they did, I believe there would be a revolution before tomorrow morning." -- Henry Ford
DONT TREAD ON ME! |
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66cayne
Frequent Contributor
Posts: 1802
Reg: 08-06-08
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06-22-12 08:09 PM - Post#2240347
In response to 68fastbak
I put the orange cam in. But have not taken it out to test yet. I did jet the carb down from the stock jets when I installed it. After testing the orange cam I will post the results. Thanks for the input fellows. Later...
Edited by 66cayne on 06-22-12 08:12 PM. Reason for edit: No reason given.
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 64cv
"5th Year" Silver Supporting Member
Posts: 647
Reg: 06-05-08
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06-23-12 07:51 AM - Post#2240450
In response to 72novaproject
12.5 Power Valve? I am not sure they even make one. Is that a typo? It should be pig rich when you accelerate. A 6.5 or 7.5 should be appropriate.
Yeah, you could even be choking on too much fuel. If things aren't better with the orange cam I'd suggest a plug reading.
Brad
Life is an optimization problem; make the most of it!
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MikeB
Senior Member
Posts: 9388
Loc: Plano, TX
Reg: 08-28-03
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06-23-12 08:01 AM - Post#2240453
In response to 68fastbak
If his motor is to small the vac secondary will only suck what it wants , that's why they are very forgiving and work great in so many applications , and if he's got Tiny jets in a 750 that's a improper fix to a different problem ,his squirter and jets are to small For that carb if u want to run those squirter and jets go to a 600 or 650 , I'm not saying he needs that much cfm but it will work and pull hard midrange and top end with that carb when it's set up right
I agree. Main downside to a too-large VC carb is the larger primaries, which can sap throttle response a little. But, no, that's not his problem.
Like you said, secondaries aren't really a consideration because they are demand-based. As I mentioned earlier, the Holleys I've played with are pretty close out of the box, at least in engines with mild cams. Typically, the only adjustments required are idle mixture and idle speed, and sometime float level.
Real Hot Rods have a Clutch!
1955 210 2dr: 327, Brodix IK180 heads, Jones cam, Muncie M20, Wilwood front brakes
1969 C-10 pickup: 350, TH350
My car pictures
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66cayne
Frequent Contributor
Posts: 1802
Reg: 08-06-08
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06-26-12 06:20 AM - Post#2241450
In response to 64cv
Good news, orange cam cleaned up the hesitation. Now I am going to put the stock jets back in (72s?) and see how that works. Thanks for the help fellows.
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66cayne
Frequent Contributor
Posts: 1802
Reg: 08-06-08
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06-27-12 05:36 PM - Post#2242069
In response to 66cayne
Up the jets to 70/72s front/back. Hesitation gone and pulls strong to 5,800 rpm which is about all this cam is good for. Can't wait to put in the M20 and 4.10s. I am a happy man!
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