Hello all.

This year i bit the bullet on my 5 litre VB SL/E, brought a re-manufactured Rochester quadrajet 4 barrel carby for it. While i was at it, decided to add an electronic choke as well. This is where it gets a tad annoying.

1. When starting the car, it revs straight to 4000rpm and doesn't drop.
2. I thought electric choke might be an issue and re adjust it, makes no difference.
3.Idle screw doesn't do a thing it seems, actually it doesn't even touch where it looks like it should do.

Now i understand there is a fast idle cam screw below the choke housing, would this be causing an issue?

I know on the front of the carb there is two idle mixture screws, I'm sure these are preset on who re-manufactured the carby and should need adjusting?

What is causing this high idle?

Right side of the carby behind the throttle linkage bracket (Technical terms, off-side) there's a small cam and a counterweight which controls the choke and idle. I've found these some can get sticky; a good drench in WD40 worked. Also the choke idle screw could be wound in too much.

It's been a while since I stuffed around with Quaddys, yet I've seen how easy it is to tune Holley carbs.... but that's another story which polarises opinions.

Edited by user Tuesday, 21 October 2014 7:21:26 AM(UTC)  | Reason: Not specified

Make sure both the primaries and secondaries are completely closed when at rest (engine not running). You'll need to hold the vaccum flap down with your fingers to see the secondaries, and probably flip the choke flap up to see the primaries.

If something is holding the secondaries open, no amount of playing with the choke will fix it, and they don't need to be open far to get it to rev to 4000rpm with no load.

Failing that - check all your vacuum ports - especially the one on the back that would go to a trimatic - which is not used on your 4-speed, but might not be plugged up.

One has a brass screw-in port - simply unscrew it, and fit a gas plug into the port in it's place (see Enzed or a hydraulics shop - couple of bucks).

The other I think is just pressed in - you can cap this off with a length of vac hose & a screw/bolt plugging it - as a test to see if it's a leak.

A closed/cold choke locks out the secondries/airvalve.
You need to fully open the choke to unlock the little lever.
Check that your base gasket matches your base plate and the manifold.
Ive seen a few different base gaskets that don't match the base plate and have a big vac leak around the rhr side.

Primaries shouldn't really be open.
Did you check everything for vacuum leaks?

Is it only a cold idle that's high (on the choke) - ie, can you "drop" it off the choke and get the idle to a more normal speed?

Reason I ask, is if you can isolate the issue to being just on the choke, or if it's still there when it's off the choke, it makes a big difference in where you need to be looking.


You don't need to touch the mixture screws to fix this - they are a fine tuning tool for the mixtures when it's running normally - they won't cause this issue.

You mention that the "idle screw" is not touching - I think you mean the throttle stop (to prevent the butterflies binding in the bore) - this is your biggest clue. They should be allowed to come back & sit against that stop (and be fully closed). Something in the choke mechanism may be holding the linkages open - hence why I asked is it doing it all the time or only on the choke.

quote:

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Originally posted by SLENUT
Seems the secondires are shut firmly. The primaries are open a little bit, spose its norma; due to idle.

While i love to pay a person to look at it, my city has no one that knows the ins and outs of a qjet.

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Good opportunity to learn!

If you read up on how these Quadies work, you'll understand a lot more about them.