Holley carb question

[sgt1022]

I recently installed a Holley 3310 750cfm carb on the 300hp 350 ci motor in my 71c10. its jetted 72 in the primaries and 74 in the secondaries. I am experiencing stalling at low rpms, ex. slowing down for a turn or coming to a stop. I recently resealed the manifold due to oil leak. I have a rough idle so I will checking for a vacuum leak at the manifold. Any suggestions on a starting point.

[Jcfcamaro]

Check your timing also.

[sgt1022]

Dizzy is set at 12 BTDC on initial timing. I was pulling 12 in of vacuum @ 850 - 900 rpm. anything less than that and it would stall.

[geezer#99]

At what rpm did you set that 12 degrees initial timing?

[sgt1022]

1000 rpm

[geezer#99]

So that means your 12 degrees could be actually closer to 4 to 6 degrees.
At that rpm you're well into the mechanical timing in the distributor. It usually starts kicking in at about 850.
You need to get your idle down to at least 750 rpm to get an accurate reading.
Bump your timing up 8 degrees and then slow the idle down on the carb. Fine tune from there adding more timing and slowing down the idle until you have it idling around 750 rpm.

Curious what intake you have?

[sgt1022]

ok. need to check for vacuum leaks first to solve problem of surging

[sgt1022]

Will motor increase rpm if I spray brake cleaner around edges of manifold while running looking for vacuum leak.

[geezer#99]

Originally Posted by sgt1022

Will motor increase rpm if I spray brake cleaner around edges of manifold while running looking for vacuum leak.

It should.
Your surging might not be from anything other than no initial timing and your primary throttle cranked open in order to idle and idling on the power circuit.

[sgt1022]

would improper throttle linkage adjustment be a contributing factor to the stalling?

[geezer#99]

Maybe!
What would you call improper?

[sgt1022]

allowing the venturis to complete close blocking airflow

[GASoline71]

Pretty big carb for a lower performance 350. The 3310 comes with a really heavy vac secondary spring (black one) right out of the box. You will need to switch to a purple or yellow spring. You will also want to step down your primary jets as well. Can't remember off the top of my head what they come with as far as pump squirters go. But you'll need to probably change that as well. How do your spark plugs look? Black and wet?

A 3310 isn't even working until over 3,000 RPM's in most applications.

Gary

[sgt1022]

Primary jets are 72's. I cant remember what spring is in the vac. secondary. haven't checked the plugs yet

[GASoline71]

Try 68's up front. The metering plate in the rear is fixed to flow, I believe, like 72 jets.

Gary

[sgt1022]

ok

[geezer#99]

Originally Posted by sgt1022

allowing the venturis to complete close blocking airflow

That's normal and why you have two circuits in the carb. Idle and power circuit.

Can you adjust either mix screw in all the way without the motor quitting?

[sgt1022]

just checked metering screws. I can screw them all the way in without motor stalling. I did discover vacuum leaks at base of carb and manifold. Back to square one.

[geezer#99]

Originally Posted by sgt1022

just checked metering screws. I can screw them all the way in without motor stalling. I did discover vacuum leaks at base of carb and manifold. Back to square one.

THat tells you that you're idling on the power circuit.

What's your motor set up like?
What intake? What cam? What headers?

[sgt1022]

Edelbrock RPM, 1 5/8 long tube headers, GM .450 int. / .460 cam, 222 dur. on both intake and exhaust @ .050. Iron heads

[geezer#99]

Your basic 290 hp crate.
No compression, poor heads, too much cam.
But tuneable.
Fix your vac leaks and then put some timing in it and adjust your carb.
Here's a link on timing.
http://www.badasscars.com/index.cfm/...d=76/prd76.htm

Did the intake come with the motor or did you put it on?

[davepl]

Sounds to me like a vacuum leak that has forced you to open the idle speed screw far enough that the primary blades have uncovered the transfer slots, which means your carb is actually in between states, operating on the transition circuit, which you can tell because the mixture screws don't function.

[demian5]

Originally Posted by davepl

Sounds to me like a vacuum leak that has forced you to open the idle speed screw far enough that the primary blades have uncovered the transfer slots, which means your carb is actually in between states, operating on the transition circuit, which you can tell because the mixture screws don't function.

Agree with that. How about float levels? Stalling in turns and stopping could be a high float on one or both.

[davepl]

Originally Posted by geezer#99

http://www.badasscars.com/index.cfm/...d=76/prd76.htm

Nice guys on that page:

"It's not rocket science! We can't explain it any easier, better, or different, so do NOT call us and ask us to explain to you...

We get calls every freakin' week from people who seem to think we've got nothing better to do than to just hand-out free advice all day, or hold people's hands any time they call-in. Not gonna happen, so please don't call."

Turns out they're out of business anyway, coincidence or not!

[sgt1022]

Found the problem. It wasn't the intake or the carb base vacuum leak. The Holley carb has a crack in the base. I installed my old Edelbrock and truck runs like normal.