Stumble

[beanhead]

Get rid of the POS 950 DP & install a TQ or Edel 800 AVS2.
No more stumble.

You're such a broken record. Plenty of people have issues with Carters and Edelbrocks too (see post#4). Just because you're clueless about tuning Holleys doesn't mean they're garbage...the fact that you constantly say that here and on FABO gives you about zero credibility to be advising anyone IMO...

Aron- It may end up just being a pump shot fix, but when I've had a quick-stab stumble that lasted more than about a half second it was due to the power valve being sized too low. Stab the throttle, vacuum starts to dive and the power valve wasn't there to cover the transition quickly enough. Pump shot helps but only momentarily...Of course making a change in one place affects others, so you may have to adjust primary jetting or internal restrictions afterwards to get the A/F back in line.
I always, always hook up a vacuum gauge in the cabin with a long hose when tuning in a new carb so I can watch it while driving. Carburators work on vacuum and knowing for sure how much and where/when they see it really helps get them dialed in.

If you got the carb from Dom I'd just call him first. He won't hesitate to help and won't give you attitude like some of the other pro-carb builders have been known to do after the sale. Your 950 will work and work great once it's dialed.

 

[Aron Gleason]

You're such a broken record. Plenty of people have issues with Carters and Edelbrocks too (see post#4). Just because you're clueless about tuning Holleys doesn't mean they're garbage...the fact that you constantly say that here and on FABO gives you about zero credibility to be advising anyone IMO...

Aron- It may end up just being a pump shot fix, but when I've had a quick-stab stumble that lasted more than about a half second it was due to the power valve being sized too low. Stab the throttle, vacuum starts to dive and the power valve wasn't there to cover the transition quickly enough. Pump shot helps but only momentarily...Of course making a change in one place affects others, so you may have to adjust primary jetting or internal restrictions afterwards to get the A/F back in line.
I always, always hook up a vacuum gauge in the cabin with a long hose when tuning in a new carb so I can watch it while driving. Carburators work on vacuum and knowing for sure how much and where/when they see it really helps get them dialed in.
If you got the carb from Dom I'd just call him first. He won't hesitate to help and won't give you attitude like some of the other pro-carb builders have been known to do after the sale. Your 950 will work and work great once it's dialed.

Beanhead you're spot on about different carburetors, people always say bad things about holley carburetors and think they can put a cater or Edelbrock carburetor on and go. I actually invested in a autometer vacuum gauge, while cruising I'll see 17-18 inches of vacuum. Going up a slight hill or giving it more throttle it will drop to 15 inches. I put a 10.5 pv in. Blp 75 pmj and 94 smj. Idle feed restrictors are .037 but I might have to go down to .035 ifrs to clean up the plugs or go bigger on idle air bleeds.

 

[beanhead]

Beanhead you're spot on about different carburetors, people always say bad things about holley carburetors and think they can put a cater or Edelbrock carburetor on and go. I actually invested in a autometer vacuum gauge, while cruising I'll see 17-18 inches of vacuum. Going up a slight hill or giving it more throttle it will drop to 15 inches. I put a 10.5 pv in. Blp 75 pmj and 94 smj. Idle feed restrictors are .037 but I might have to go down to .035 ifrs to clean up the plugs or go bigger on idle air bleeds.

Okay, well if you have a 10.5 in there now (the biggest one they make) then it's not that. That's a big difference in pri/Sec jetting by the way...usually like to live somewhere between 7-10 with a Pri power valve and you have a 19 size spread. Is this the Thumper carb?

 

[Aron Gleason]

Okay, well if you have a 10.5 in there now (the biggest one they make) then it's not that. That's a big difference in pri/Sec jetting by the way...usually like to live somewhere between 7-10 with a Pri power valve and you have a 19 size spread. Is this the Thumper carb?

Yes it's a thumper carb. But blp jets are numbered different from holley jets. So in reality it's not as big of a jump. The rear jets equate to a 84 holley jet. Primary is like a 74 holley jet

 

[beanhead]

Yes it's a thumper carb. But blp jets are numbered different from holley jets. So in reality it's not as big of a jump. The rear jets equate to a 84 holley jet. Primary is like a 74 holley jet

Ah BLP jets, got it.
So it sounds like it's just a small detail that needs to be tweaked to suit your combo and driving, I would give Thumper a call and see what he says. I know we like to try to figure things out on our own for the learning experience...but he can probably get you focused in a few things to look at rather than you having to try to many different things and waste too much time.
Happy hunting!

 

[Aron Gleason]

Ah BLP jets, got it.
So it sounds like it's just a small detail that needs to be tweaked to suit your combo and driving, I would give Thumper a call and see what he says. I know we like to try to figure things out on our own for the learning experience...but he can probably get you focused in a few things to look at rather than you having to try to many different things and waste too much time.
Happy hunting!

I have messaged him, and he said to try different things and that's how we learn.

 

[hunt2elk]

Yes it's a thumper carb. But blp jets are numbered different from holley jets. So in reality it's not as big of a jump. The rear jets equate to a 84 holley jet. Primary is like a 74 holley jet

Are the idle feed restrictor numbers different than Holley as well? Just asking because 4 #37's are a lot of fuel flowing at idle. I would think you should be more like #31's?

 

[Aron Gleason]

Are the idle feed restrictor numbers different than Holley as well? Just asking because 4 #37's are a lot of fuel flowing at idle. I would think you should be more like #31's?

It came stock with 35's. With 31's it was too lean. Ifrs are standard issue no matter where you get them. They're 6/32. Idle bleeds are 10/32. So you can buy them from whoever you want.

 

[hunt2elk]

It came stock with 35's. With 31's it was too lean. Ifrs are standard issue no matter where you get them. They're 6/32. Idle bleeds are 10/32. So you can buy them from whoever you want.

What size/power motor are you dealing with?

 

[Aron Gleason]

What size/power motor are you dealing with?

440. 10.5 pv

 

[R413]

What is idle vacuum and what is camshaft specs.
What do the plugs look like?

 

[Aron Gleason]

Idle vacuum is 10 inches. 284 484 purple shaft cam.

 

[hunt2elk]

440. 10.5 pv

Horsepower and ft lbs torque of the motor is what I was trying to ask.

 

[Aron Gleason]

Horsepower and ft lbs torque of the motor is what I was trying to ask.

372 horsepower 450 ft lbs of torque

 

[hunt2elk]

372 horsepower 450 ft lbs of torque

Just my opinion, but you have way to big of carb on that motor. A 750 would work a lot better. I'm not a carb guru, but maybe being oversized could be creating your issue.

 

[Aron Gleason]

Just my opinion, but you have way to big of carb on that motor. A 750 would work a lot better. I'm not a carb guru, but maybe being oversized could be creating your issue.

I've had everything from a 750 vacuum secondary, 750 double pump, 830 double pump, 850 double pump and the 950 double pump. They all had the stumble. And I was told this carburetor would be great for me by Dominic thumper.

 

[hunt2elk]

Then a guy almost has to think it is an ignition issue.

 

[68-500]

I thought the power valve was supposed to be half of idle vacuum as a rule of thumb. I believe yours maybe open at idle and your jetting is compensating for it. You may need to go down on your pri and secondary a few sizes then stick something in there around 5 and see what that does.

 

[Aron Gleason]

I thought the power valve was supposed to be half of idle vacuum as a rule of thumb. I believe yours maybe open at idle and your jetting is compensating for it. You may need to go down on your pri and secondary a few sizes then stick something in there around 5 and see what that does.

Holley is so wrong on that theory. The power valve has no affect at idle.

 

[Aron Gleason]

There's many threads that say in order to find out what power valve you need, is to actually drive the car and see how much vacuum you have while cruising.