[Mastif]

Ive got to do some carb tuning to find the lost power. I installed a new Holley 750 vac Carb and a new Edelbrock RPM intake, and the results are,,,,
The car runs great, very smooth, perfect for a driver, but when you push it in low gear and go thru the gears, the car never seems to pull good. Maybe I should say it (DOES NOT) pull like it did with the original cast 67 intake and Q-jet carb.
You never feel it open up, but it is a vac carb.
When in drive at 70 mph and pushing it, it seems to open the back barrels.
Thoughts?
Mark

 

[aukai]

Put lighter springs in the vac pod to open the secondaries sooner

 

[R67chevelle]

Now this is just my opinion, but I will never again go back to a vac. secondary Holley again. Changing the springs works, but in my opinion a properly adjusted Double pumper will always out perform everywhere in the RPM range. On my little 331 (327) I use a 750 DP behind a stick and has out performed a carter, holley 650 VC and never a boog. I had an 350auto behind the motor also and always worked well with the DP.

Also, give some specs on your engine. Jetting, timing and Depending on the cam the engine may not like the RPM intake...

Blessings,
AMS

 

[Jason Snyder]

double check your timing ! see if the engine wants more total timing ?

a vacuum secondary carb can run good ,so dont blame the secondaries as long as they are opening ! make sure your throttle is opening all the way FIRST !

 

[GoatDr]

Make sure your throttle blades are fully open at WOT.

 

[mr 4 speed]

Now this is just my opinion, but I will never again go back to a vac. secondary Holley again. Changing the springs works, but in my opinion a properly adjusted Double pumper will always out perform everywhere in the RPM range. On my little 331 (327) I use a 750 DP behind a stick and has out performed a carter, holley 650 VC and never a boog. I had an 350auto behind the motor also and always worked well with the DP.

Also, give some specs on your engine. Jetting, timing and Depending on the cam the engine may not like the RPM intake...

Blessings,
AMS

when you mention "outperform" do you have timeslips to back that up or just the "butto-meter" ?

 

[Mastif]

Butt meter, the car is not pulling like it did.
I just put a bread tie around the vacuume rod and slid it to the top so that it would have to be at the bottom if it did fully open. Then I took it out and pushed the car from 30 mph to the top of 2nd gear, drove it back home and pulled the air cleaner. The rod moved maybe 1/8" inch, it would have had to move 1" inch to be fully open. The back is not opening.
Will a lighter spring fix this?
Timing is fine, 36* total at 2800 and 18*@ idle with no Vacuume. The the vacuume is hooked up, (I think it is near perfect).
Mark

 

[GRN69CHV]

Talking automatic trans cars here. JMHO (and experience), a vac sec carb will always outperform a mech secondary (DP) in any application with less than a 2400 stall converter. Get to a 3000 stall and it's becomes difficult to get the vac sec to respond correctly.

 

[mr 4 speed]

Mark,use one of the yellow springs or the white spring to get full opening of the secondaries.

 

[Mastif]

OK, I will buy a spring Kit tomorrow.
I just removed the spring and it is Gold with Black at the very top.
Even with the Black spring in it, should it not at least open up at some point?
I took the car from 3000 rpm to 5200 rpm in low gear, and then to 2nd gear to redline again.

 

[Bob Tiley]

Vacuum secondary carbs never feel as fast in the butt-o-meter.

 

[Mastif]

I understand ,,, but I have used the paper clip trick and the secondaries are not opening. Now I need to find out why. I know the black spring in the strongest, but it still would have to open at some point. Mine is not. This is a new carb.

 

[Tuner.]

This doesn’t surprise me at all. If you actually have the original QJet that came on the car when it was new, not a rebuilt replacement, you are incredibly fortunate, hang on to it.

This is your most likely problem, for starters.
http://www.chevelles.com/forums/showpost.php?p=2027861&postcount=8

The next issue is the QJet is a less restrictive carb than the Holley is, it’s bigger, it flows more at the same pressure drop.

If it is the actual original carb, it has a mixture distribution device in one secondary throat, either a small flap, spot-welded to the underneath side of the secondary air door, or a box like duct at the exit of the nozzle tube, spot welded to the vertical baffle. Those distribution devices were coordinated with the original manifold to cause a more even A/F distribution to all cylinders at WOT. The original carb and manifold have the advantage of the distribution having been engineered as a coordinated package. Never mind the decades of advertising to the contrary, keep in mind the factory was motivated to engineer the lowest cost solution to having to keep warranty expenditure as low as possible in the face of 5-years & 50,000 miles warrantees.

How is it if you put the QJet on the new manifold? The Performer is the manifold used on the ZZ crate engines and they run great with a QJet.

 

[Mastif]

I called Holley this morning, and they ask that I return the carb to them for flow testing, and repair if need be. I will be shipping it today for them to have it tomorrow. I ask if they could get right on it as I needed it back by Friday is possible, he said he "Should" be able to make it happen.
Mark

 

[mr 4 speed]

Mark,the black spring will never ever let the secondaries fully open.
According to the Holley chart,they are not even fully open at 8000 rpm with that spring
here is a link to the chart,you need to scroll at least half way down:
http://ca.geocities.com/[email protected]/holley.htm

you don't need to send the carb to Holley...just buy the spring kit. Any one of the yellow springs will work on your 396

 

[GRN69CHV]

Hey Mark, not to get off topic - but that is a really great looking '67! I like it both ways - with the rally's and redlines and with the 17's (those are 17's - right???).

 

[Mastif]

Thanks for the compliment, and yes, they are 17" Torque Thrust.
I know your going to think I am crazy, but I am now going to look for, and buy me some stock steel wheels, and paint them Gold, and add the Dog Dish caps. Then I will have what ever look I want, when ever a different mood sets in,,,,,,,,lol.

Mr 4 speed.
The secondaries will not even attemp to open per the paper clip trick. If it would open a little, or half way, I would then think the black spring might be the problem. What do you think?

 

[GRN69CHV]

Thanks for the compliment, and yes, they are 17" Torque Thrust.
I know your going to think I am crazy, but I am now going to look for, and buy me some stock steel wheels, and paint them Gold, and add the Dog Dish caps. Then I will have what ever look I want, when ever a different mood sets in,,,,,,,,lol.

Mr 4 speed.
The secondaries will not even attemp to open per the paper clip trick. If it would open a little, or half way, I would then think the black spring might be the problem. What do you think?

Absolutely on the wheels. Redlines on steel painted wheels w/ Dog Dish caps would be great. Allow you to go old school or modern at the flip of a coin. I'd consider just doing steel rims in a gloss black with the redlines and caps. You have a black roof, think it would make the redlines pop a little more.

As for the carb, make sure the little cork o-ring gasket is in place between the vac pod and the carb main body. Black spring will come in real late - or very little. Not even sure why they produce that spring in the first place. You probably need the silver (no color coding), purple/pink or long yellow in there. Only other thing that will create an issue is a vacuum leak.

 

[Mastif]

Thanks guys,,,
I am going to buy the spring kit today and try the yellow tonight. If it works, great. If it works and Bogs, Ill go a little stiffer.
If it does nothing at all, I will send it back.
Mark

 

[mr 4 speed]

Mr 4 speed.
The secondaries will not even attemp to open per the paper clip trick. If it would open a little, or half way, I would then think the black spring might be the problem. What do you think?

Mark,that black spring will do it everytime.
Use the shortest yellow first...this is the lightest spring in the kit.
If it doesn't bog (which it shouldn't) you'll be good to go.