2 barrel carb vs 4....

azfordman · #1 (**permalink**) 10-02-2010, 01:15 PM

Trying to dial in my carb is just one of the things I have been working on to get the car running at it's best. I have been swapping jets and getting the float bowls adjusted. About a week ago I did the paper clip test on the secondaries and came to realize they were not kicking in until I got up to the 5000+ RPM range....not very practical for street driving! For all intents and purposes the car has been running on only the primaries....basically a 2 barrel carb. Picked up a Holley spring kit and quick change adapter. Worked my way down to the lowest (white) spring and still no change. In fact, I could not get the secondaries to kick in at all! Before I got too frustrated I decided to go back to square one and pull the secondary vacuum advance off and see if I had installed something wrong.....found the rubber diaphragm had a tiny tear where one of the bolts had caught and twisted it!!! I replaced the diaphragm much more carefully this time. I currently have the long yellow spring in, and may step down to the short yellow, but I gotta tell you....what a difference!!!!! With the secondaries kicking in at a lower RPM the car is actually staring to get scary fast!!!! Once I get the timing nailed down I will be in great shape!

Excaliber · #2 (**permalink**) 10-02-2010, 03:08 PM

I hear ya about the increased power level. I've disconnected my secondaries from time to time and it's night and day in the power difference.

azfordman · #3 (**permalink**) 10-02-2010, 03:47 PM

The funny thing is I had no clue I even had a problem....with all the tune up research I have been doing, I came across the paper clip test, and just tried it out of curiosity.... I knew I had been getting a "surge" of power at 5,000+ RPM's, but attributed it to the motor itself. It is an unbelievable difference.

Finallygotit · #4 (**permalink**) 10-02-2010, 10:16 PM

So at what RPM do the secondaries open up? And where is the burn-out video?

charles roybal · #5 (**permalink**) 10-03-2010, 06:49 AM

Quote:

Originally Posted by azfordman

I came across the paper clip test,

Can you share this tech. with us?

patrickt · #6 (**permalink**) 10-03-2010, 08:50 AM

Quote:

Originally Posted by charles roybal

Can you share this tech. with us?

You can't tell if your secondaries are opening by just revving in the driveway. You put a paperclip on your plunger flush up against the vacuum spring housing. Then take your car for a brisk run getting on it enough that you think your secondaries should have opened. Then pull over to the side of the road and look at the paperclip. If your secondaries opened, the clip will now be positioned farther down the plunger, like you see in this pic. If the paperclip is still flush up against the housing, then your secondaries are not opening.

Excaliber · #7 (**permalink**) 10-03-2010, 09:06 AM

I recall the old Quadrajet (mostly on GM stuff). With the small primaries and very large secondaries you could FEEL and HEAR those secondaries coming into play.

But, generally speaking and specifically speaking of Holleys you should not be able to feel or hear it very much or at all. It should be a smooth transition, if you can feel it, your secondary spring is likely to light weight. Thus the need for a paper clip test.

azfordman · #8 (**permalink**) 10-03-2010, 01:59 PM

That's it exactly. I have also used a zip tie in place of the paper clip, just tight enough to stay in place, but loose enough to slide up and down. If running correctly there should be no feeling the secondaries kicking in with the Holley, like the power boost I used to get at higher RPM's. I have yet to make any controlled runs to see exactly where they are kicking in, but I do now have a lot more power at lower RPM's than before. This is just one of those little things I had never thought of checking.....nothing worse than giving up free power!!!

azfordman · #9 (**permalink**) 10-03-2010, 02:07 PM

Quote:

Originally Posted by Excaliber

I recall the old Quadrajet (mostly on GM stuff). With the small primaries and very large secondaries you could FEEL and HEAR those secondaries coming into play.

But, generally speaking and specifically speaking of Holleys you should not be able to feel or hear it very much or at all. It should be a smooth transition, if you can feel it, your secondary spring is likely to light weight. Thus the need for a paper clip test.

Not to correct you....but from what I understand, if you can feel the secondaries kick in, as in a boost of power, the spring is too strong and the secondaries are kicking too late. If the spring is too light and the secondaries kick in too soon, there will be a bog in the acceleration. After I replaced the vacuum diaphragm I put in the long yellow spring, the 3rd lightest. I will try the short yellow spring today. I think the lightest spring in the kit, the white one, may be too light, but I will see.