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Discussion Starter · #1 ·
Have a stock 1967 Mustang with a automatic transmission and recently rebuilt 289 four barrel. Had a Motorcraft 4300, but was not satisfied with idle and top end power. The carburetor had great bottom end power with no stumble at all. Bought a new Holley 4160 and it runs great, but stumbles every time you give it throttle. It'll die about 30% of the time. If it makes it through the stumble the engine has power like I've not seen before. I've been working on it for a while and can't figure it out and no shops around my area to help. Here the stats and what I have tried:
1967 Mustang stock 289 2BBL automatic.
Timing 10 BTDC. Vacuum 18 inHg at 750 RPM. Vacuum 15 at idle in drive.
*Note. There was no stumble with the Motorcraft.
*Note does not stumble in neutral. Only under load. Also NO backfire.
What's been tried:
Adjusted timing from 4° to 14° TDC.
Vacuum advance is working properly. It's a Pertronix distributor which worked great with the Motorcraft carb.
Accelerator pump is adjusted properly.
Tried orange and white cam.
Tried nozzels 35, 31, 28, 25. When I tried the 25, I got a little hesitation in park as while as in drive.
Power valve is 6.5 and new.
Running 66 jets.
Wired secondary shut for test and stumble still there.
Checked everywhere for vacuum leaks. No leaks.
Mechanical fuel pump pressure 4.75 at idle and increase to 5.9 with RPM. Fuel level at bottom of sight hole.
Put the Motorcraft back on and there is no stumble at all.
Conclusion: Must be in the setup of the carb. HELP
 

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A few things I would do/check. Increase the fuel level so it is in the middle of the sight hole, not at the bottom. This should be the correct setup for a Holley with sight hole. Give the engine slightly more fuel at idle (just a 1/16 turn on the primary side) to see if it helps. Last thing would be to connect a vacuum gauge and check if the vacuum drops to much in the transition from idle to open throttle. If vacuum drops too much the power valve might opens too early and will make the mixture too fat.
 

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Have a stock 1967 Mustang with a automatic transmission and recently rebuilt 289 four barrel. Had a Motorcraft 4300, but was not satisfied with idle and top end power. The carburetor had great bottom end power with no stumble at all. Bought a new Holley 4160 and it runs great, but stumbles every time you give it throttle. It'll die about 30% of the time. If it makes it through the stumble the engine has power like I've not seen before. I've been working on it for a while and can't figure it out and no shops around my area to help. Here the stats and what I have tried:
1967 Mustang stock 289 2BBL automatic.
Timing 10 BTDC. Vacuum 18 inHg at 750 RPM. Vacuum 15 at idle in drive.
*Note. There was no stumble with the Motorcraft.
*Note does not stumble in neutral. Only under load. Also NO backfire.
What's been tried:
Adjusted timing from 4° to 14° TDC.
Vacuum advance is working properly. It's a Pertronix distributor which worked great with the Motorcraft carb.
Accelerator pump is adjusted properly.
Tried orange and white cam.
Tried nozzels 35, 31, 28, 25. When I tried the 25, I got a little hesitation in park as while as in drive.
Power valve is 6.5 and new.
Running 66 jets.
Wired secondary shut for test and stumble still there.
Checked everywhere for vacuum leaks. No leaks.
Mechanical fuel pump pressure 4.75 at idle and increase to 5.9 with RPM. Fuel level at bottom of sight hole.
Put the Motorcraft back on and there is no stumble at all.
Conclusion: Must be in the setup of the carb. HELP
I don't have anything to offer other than thanks for the extensive documentation as to your settings. So refreshing compared to "Car stumbles".
 

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A few things I would do/check. Increase the fuel level so it is in the middle of the sight hole, not at the bottom. This should be the correct setup for a Holley with sight hole. Give the engine slightly more fuel at idle (just a 1/16 turn on the primary side) to see if it helps. Last thing would be to connect a vacuum gauge and check if the vacuum drops to much in the transition from idle to open throttle. If vacuum drops too much the power valve might opens too early and will make the mixture too fat.
Or the vacuum may not be dropping enough and the PV opens to late. Might try a 7.5 PV
 

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Have you adjusted the mixture screws? I’ve got a Holley 4 bbl and it would stumble a little. Mixture screws stock location was 1 1/2 out, adjusted it to 1 out and it helped vacuum as well as no stumble.


67 coupe, 289, performer intake, 302 heads, Holley 570, Pertronix II dizzy, C4, 9” rear, 3.50, 17” wheels
 

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Discussion Starter · #6 ·
Thanks for suggestions. I will check the vac in transistion. I like the suggestion of a 7.5 pv. I ordered it today. I am really thinking that this is a too rich condition rather than too lean. It will be a few days to get the pv i will update everyone then.
 

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A few things I would do/check. Increase the fuel level so it is in the middle of the sight hole, not at the bottom. This should be the correct setup for a Holley with sight hole. Give the engine slightly more fuel at idle (just a 1/16 turn on the primary side) to see if it helps. Last thing would be to connect a vacuum gauge and check if the vacuum drops to much in the transition from idle to open throttle. If vacuum drops too much the power valve might opens too early and will make the mixture too fat.
Agree with above ^^^^^^... what also caught my "eye" was the throttle linkage cam, which ultimately activates the squirt system....IIRR they come in the #1 position (there are 3 positions)... try it in the #2 (middle) position, this will brig the squirt of fuel in much sooner!
 

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I agree the 6.5 pv sounds right. There are a couple different diaphragms for the accelerator pump. I assume you are using the smaller not the larger.

I dont have much to suggest. Youve looked at everything I would have thought of
 

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maybe too much carb @600 CFM for a stock 289

which 4300 did you have

came in 441 CFM and 600 CFM
 

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Discussion Starter · #10 ·
I realize the carb is a much bigger carb than the 4300(C7DF AF) but the 600 should not be too much. I am running 600s on several other small v8 with great proformance. AMC 304 and Gm 5.0. I hope the pv takes care of it. Talked with Holley tech late yesterday(finally after trying to get them for a week). He was very intensive and he agreed that the power valve maybe the problem. Agreed that i should reset everything back to factory and try a 7.5. I will update when i get it.
 

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I've got a 600cfm 4160 Holley on my 289 as well. I'm at altitude, so I had issues with it being adjusted for sea level. It sounds to me like you need to adjust the accelerator pump lever. It should be set so that it just contacts the lever at idle, and squirts when you tap the throttle. My DPO had this adjusted so it only gave additional fuel when you were at full throttle, so I had a lot of trial and error to get it to where I can actually accelerate properly. BTW, I'm still using the original white accelerator cam.
Due to my elevation (9000') I had to install two steps leaner mains and a 5.0 (IIRC) power valve, I wrote the main size and PV size on my vacuum dashpot so I never have to scratch my head over what jets I'm running.
HTH,
 

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I realize the carb is a much bigger carb than the 4300(C7DF AF) but the 600 should not be too much. I am running 600s on several other small v8 with great proformance. AMC 304 and Gm 5.0. I hope the pv takes care of it. Talked with Holley tech late yesterday(finally after trying to get them for a week). He was very intensive and he agreed that the power valve maybe the problem. Agreed that i should reset everything back to factory and try a 7.5. I will update when i get it.
Consider that not all carburetors are rated in the same manner. Ford's 600 CFM rating may not be the same as Holley's 600 CFM. FWIW, a 600 is just fine on a 289.

I'll agree with the Holley tech's assessment, but I'd actually go a little further and put in an 8.5 or 9.5 PV.
 

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Discussion Starter · #14 ·
Thanks. If the 7.5 doesn't work I plan to try 8.5. I really like this Holley. Once the engine gets thru the stumble it really takes off.
 

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To determine if it's a lean hesitation or a rich hesitation have a trusted assistant sitting in the car while it's running in drive and holding the brake firmly. With air cleaner off, you lean over the drivers side fender and operate the throttle with one hand while holding carb cleaner in the other. You should be able to duplicate the hesitation now as you give it some gas as the engine is under load now. Now give it a squirt of carb cleaner as you operate the throttle and see if the hesitation goes away or gets worse.
I would also think if it was a rich condition there would be some black smoke after hesitation passes and engine takes off.
 

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Discussion Starter · #16 ·
I haven't seen any black smoke. I appreciate your suggestion and if the 7.5power doesn't i will consider it if i can find someone REALLY trust.
 

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A couple comments... First, 18"hg is a bit low for a stock engine. I would want to see 20-21"hg. Next, if the stumble is immediate upon acceleration, but there IS an initial increase in rpm, and continues to some degree until rpm's "catch up" or you lift from the pedal, then I'd suspect a problem with the transition circuit/power valve calibration. If it craps out IMMEDIATELY on mashing the pedal then accelerator pump calibration. Also, double-check your vacuum advance connection and initial timing. With the line disconnected and plugged your stock 289 should tolerate 12-16* initial advance with additional from the vacuum advance immediately upon cracking the throttle. Last question... Are you running a carb spacer and what kind with what gaskets?
 

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Have a stock 1967 Mustang with a automatic transmission and recently rebuilt 289 four barrel. Had a Motorcraft 4300, but was not satisfied with idle and top end power. The carburetor had great bottom end power with no stumble at all. Bought a new Holley 4160 and it runs great, but stumbles every time you give it throttle. It'll die about 30% of the time. If it makes it through the stumble the engine has power like I've not seen before. I've been working on it for a while and can't figure it out and no shops around my area to help. Here the stats and what I have tried:
1967 Mustang stock 289 2BBL automatic.
Timing 10 BTDC. Vacuum 18 inHg at 750 RPM. Vacuum 15 at idle in drive.
*Note. There was no stumble with the Motorcraft.
*Note does not stumble in neutral. Only under load. Also NO backfire.
What's been tried:
Adjusted timing from 4° to 14° TDC.
Vacuum advance is working properly. It's a Pertronix distributor which worked great with the Motorcraft carb.
Accelerator pump is adjusted properly.
Tried orange and white cam.
Tried nozzels 35, 31, 28, 25. When I tried the 25, I got a little hesitation in park as while as in drive.
Power valve is 6.5 and new.
Running 66 jets.
Wired secondary shut for test and stumble still there.
Checked everywhere for vacuum leaks. No leaks.
Mechanical fuel pump pressure 4.75 at idle and increase to 5.9 with RPM. Fuel level at bottom of sight hole.
Put the Motorcraft back on and there is no stumble at all.
Conclusion: Must be in the setup of the carb. HELP
I’ve seen this stumbling issue before. It was not quite as severe as you’re dealing with though.
I looked at the accelerator pump cam profiles and wasn’t super impressed with tip-in on any of them. I ended up running one of them “backwards.” It moved the pump lever at the slightest rotation of the primary shaft….. which wasn’t happening with any of the cam profiles or tuning positions.
It did solve the off-idle stumbling issue I was having.
 

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Holley uses straight or down leg boosters. They're good for high speed WOT but at low speeds, they're not so good at metering the air for the boosters. Especially when you use a carb that's on the big side for the displacement of the engine. This is why Ford used annular boosters in their carbs for the most part or size the carb right.

If you don't have enough air velocity of or any one given condition, the straight and down leg boosters don't react to low air flow and the carb goes lean.
 

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Discussion Starter · #20 ·
No i am not running a carb spacer. Concerning base gasket i ha e tried open and 4 hole. Actually i didnt see any difference. I have tried advancing the timing to 14 but no improvement. Still joping the 7.5 power valve will help. Should be in here by sat. I be sure to update one way or the other. Btw the Holley tech told me to reset the card back to factory specs before trying the new pv. Just curious what stock 289 owner think about. Here they are:
66 jets
Mixture screws out 1 1/4 turns
Square transition slot
Fuel at bottom of sight hole
Orange accel pump cam
Accel adjustment bolt(red spring) just touching(zero gap) accel pump arm
 
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