I'm not sure I can describe this problem so anyone can understand it, but here it goes--

I bought this car about a month ago. It's got a remanufactured (by Holley) Qjet on it that's almost brand new. The last owner replaced an aftermarket Holley carb that was on it with this last year. He'd dorked up the choke when he installed it & I've put that right and put new gaskets under it.

When I drive the car it seems to "let down" very suddenly when I let off the gas, so that the ride is very jerky. When I give it the gas from a stop, it runs up smoothly, but when I take my foot off the gas to shift or slow down, it wants to nose-dive. If I don't put the clutch in I end up with this kind of jerking motion, not a surging exactly (I know, I could probably describe this better), but it about gives me whiplash. I guess the best I can describe it is it feels like the rpms drop too fast or something.

Does this sound familiar to anyone?

JB

 

What makes you think that the problem is the carb?
Check for dragging brakes or worn rear wheel bearings.

 

I guess I'm thinking carb because it doesn't do it all the time and if I disconnect the drive train (push in the clutch), it stops. It doesn't "feel" like a transmission thing, either. I'm having trouble describing it, but it feels like a fuel thing. That's not terrifically helpful, is it?

JB

 

I don't mean to insult you but, is this the first "standard shift" car you've owned? Most drivers are use to automatics the "drift" to a stop. Manual transmissions are tightly coupled to the engine, so when you let off the gas the engine immediately starts to slow down, and slow down the car. I can "pop" the heads off my passengers if I want to without ever touching the brakes.

Now if your engine dies when you let go of the gas and release the clutch then you will feel a "sharp" de-acceleration when you come to a stop. The engine is literally braking the car to a stop, rather than "idling" it to a stop. What is the engine's idle RPM? Too low will effect the stopping "feel". Too high isn't good either. And, as the previous post asked, does you car roll freely with the clutch depressed? No dragging drive train problems? A single person should be able to easily push/roll the car in level ground.

Andy

 

Aw, man, that hurts. I've been driving a stick since I was 15. :) I'm just doing a really crappy job of describing what's happening.

I drove it extensively for the first time yesterday, and I think maybe what I'm dealing with is a miss. I started to realize it happens too, though not as noticibly, when I accelerate but not very hard (when I go ahead and accelerate normally hard, it's not noticible). It's just a jerking sort of thing, and it does kind of feel like when you're in a car with somebody that can't handle a clutch very well and they get it jerking and have to put the clutch back in and try again. It seems most evident when I let off the gas & before I push the clutch in. There doesn't SEEM to be a miss at idle, but there you go. I replaced all of the plug wires & plugs, & put on a new distributor cap & rotor & it's no different. I'm going to do a compression check next, I guess. It's not a big deal, just irritating.

JB

 

Captain Obvious to the Rescue

:)

If you suspect the carb, try to find a known working carb to swap in for a test, or sign up for the lars loaner carb program just to try a different carb. If it still does the same thing you can look elsewhere! MJ

 

I have the same problem, and it sucks. Try taking off the vacuum advance to make sure it isn't over advanced timing. If not that, try leaning the idle a little, it worked for my last engine.

 

If the QJet had a dashpot, that's what I would guess. But does sound like a fuel delivery problem.

I solved my carb problems with an Edelbrock QJet. Lovely. So you're welcome to borrow my old carb (being 10 years newer it may not be compatible). Or you can borrow my Rochester Carburetors book, which only served to convince me I needed a new carb! :smash:

 

JB -
Drivability issues as you describe are due to one of two things: ignition or carb. I always recommend that people give their ignition system a good checkout first, as this is most often the cause for strange drivability issues. On your ignition, get yourself a good dwell meter and an adjustable timing light. Make sure your dwell is set up at 30-31 degrees, and then verify that your centrifugal advance system is working correctly and smoothly as you rev the engine up. With the vacuum advance disconnected, verify that your maximum timing when all pegged out (at about 3000-3500 rpm for a stock motor) is right about at 36 degrees. Then, hook up your vacuum advance to the ported source on your carb (if you have a '69 carb on your car it will be the fitting on the forward driver's side of the carb).

If the problems persist after doing this ignition checkout, you probably have a carb with a little "creative" jetting done to it. If you send me the carb number and the application you're using it on, I can give you my opinion and recommendation on the jetting if you check your jet size and rod sizes.

I can also send you out one of the loaner carbs - we have a couple of very nice running '68 carbs that will run well on your '69 if you'd like to try one out. Drop me a note if you need info on this program.

A 4-spd car should be smooth and responsive throughout all its operating ranges when properly set up - your situation is not normal, and should be corrected.


[Modified by lars, 2:28 PM 6/16/2002]

 

Thanks, guys. Got out there to start messing with it and smelled gas. Seems I've got a leaking fuel pump. Could that possibly be my problem?

JB

 

First thing I had to replace when I bought mine. Make sure the rubber hoses aren't kinked when you replace 'em! :smash:

 

FOLLOW UP: replaced leaking fuel pump, checked dwell and found it 5degrees off. Now it runs like a top. Woo, woo!

JB