Hot Rods Quadrajet With New High Rise Intake Off-Idle Stumble

Hello. I have a 1969 350 v8 stuffed into a 48 Studebaker. It has a QJet, and used to have a low rise intake manifold. It burned serious rubber off idle, but seemed like it could pull more RPMs at WOT. So, I talked to an older dirt track racer, and he told me to get a bowtie intake. I did. I installed it.

The 750 CFM QJet was always running rich. The oil always smelled like gas, and there was always the rich gas stink. I knocked out the APT hole on the air horn, and I did some tuning, and that helped. The idle screws still didn't do a whole lot. That being said, here is what happened after the bowtie intake install. I stomped the gas from idle, and it hesitated..."buhhh" and then off it went. It seemed to run cleaner thereafter through the whole RPM range. Additionally, while cruising at 30 or 40, when I stomped it there is zero hesitation all the way to RPM redline. It still had the same gas stink in both the oil and at idle. The Studebaker needs new hood, trunk, and door seals. I did have the tailpipes fixed so that they point out after the rear wheels.

My questions are:

Do I need to modify the accelerator pump rod so that it depresses the accelerator pump 100%?
Do I need to change my metering rods?
Do I need to change my jets?
Do I need a larger shot from the accelerator pump all together?

I appreciate any help. I'm close. Engine temp is good. Power is good. Just the stink and the stomp off idle are my problems. I have read about QJets a bit. Complicated!!!

 

Tell more about the motor,Dist and timing both base and total?

 

I believe distributor is a HEI with a 65k coil. I don't know what base and total are. I don't have a timing light. I tuned it by ear and road tests. I will buy a timing light this weekend.

 

And the motor is a 69 Chevy Nova 350 V8 with an RV cam. That's all the seller could tell me. Stock exhaust logs with 2 1/2 exhaust.

 

And a stock torque converter, too, I suppose?

When you start mismatching parts, it won't work right until you get all the parts matched again. The carb isn't the problem...the intake, not matching the rest of the car, is the problem. The carb changes are just a symptom

 

Yes, stock converter. Engine is rebuilt with RV cam. Spark is excellent. Compression is excellent. Valve train is excellent. No vacuum leaks. I think the problem is the carb.

 

What exactly is the intake manifold you installed? Link? Part number?

 

Are you saying that the Qjet didn't hesitate before with the old manifold but it does now after a manifold change?
This could be from a number of things related to the carb. The spring tension on the opening of the air control valve over the secondaries could be too loose, for one. I don't know what you may have purposely or may have accidentally changed. But that raw gas contaminating your crankcase oil worries me. It seems like there's too much gas winding up in the wrong places. I"m a believer in new gaskets, so again, I don't know what you did about that.
Just tweaking the metering rods and/or accelerator pump is probably not the answer. Years ago, I had some good luck "blueprinting" a Qjet but it was a newish unit and was a good solid base to start with. Yours is a bigger unknown and may have been hacked a lot in the past.
Personally, I would get a rebuild kit and have at it but I don't have the experience to be able to spot any less obvious issues.

 

MERCRUISER 5.7L GM Bowtie Highrise MARINE INTAKE MANIFOLD 14096242

 

The QJet didn't hesitate with the low rise. After the high rise, it hesitated off idle. The QJ was blueprinted before I put on the high rise. The gas in the oil concerns me, too. Do you think I should change out the base gaskets between carb and manifold, and start there? I've heard some use a metal gasket.

 

Oh...ok, it's still a dual plane GM intake, just a bit larger inside. The term "bowtie intake" applies to lots of different intakes, I assumed it might be a single plane, which is designed for higher rpm operation.

Anyways..tell me about "the Qjet was blueprinted"

 

And, yes, I did adjust spring tension on air doors. But, it stinks of gas at idle. Idle screws aren't doing much.

 

Ok. Well, a man who worked on QJets for 25 years in California rebuilt the carb. Soon as I got it, I installed it. Fired right up and ran pretty well. I adjusted air door tension and APT and got it running much better. The accelerator action is excellent. Vacuum advance and plunger and choke all work well. It just seems like the carb is dumping too much gas into my motor at low speeds.

 

And, BTW, the QJet was a solid base for rebuild. Very clean carb.

 

You said the carb was running rich before the rebuild? What do you have for a fuel pump?

 

Right. I have a mechanical fuel pump. And I have a fuel pump regulator set to 6 pds. You know, when the carb had the fuel filter in it, after WOT it would run out of gas for a second. I took the fuel filter out for a test, and that problem stopped.

 

He has no timing light nor has he timed it.

 

What should the psi be for gas for the QJet?

 

I thought it was 6-7

 

6 psi should be ok.

Do you know if the float was replaced?

 

Yes floats were new

 

Do you think that the carb is simply too large? I know it's theoretically only using the amount of CFM the engine demands, but I always wonder. Someone told me to put a Holley 625 on it and be done.

 

No, it's not too large. The Qjet is a great carb, it works on everything from 250 ci 6 cyl engines to 500 inch V8s. But some times you have to fiddle to make them work right, and that usually means getting them back to stock condition.

My guess is you might want to start with ignition timing, get a timing light, see what it is, let us know.

 

Alright. What should total timing be?

 

36?

 

Probably 34, but might be ok at 36. Also, the initial timing, and when it starts to advance, and when it has full advance, all are important for drivability.

 

I would be looking at the IDLE AIR BLEEDS if you don't have much control with the mixture screws,check the hangers for the secondaries at part throttle,,great carb just takes a little tuning

 

Check your Vacuum advance, mechanical advance and rpms of full advance, tip of the rotor should not touch the sparkplug terminals in the cap. Check and make sure your balancer is in alignment with TDC. Make sure your coil is not leaking.
All OK, A quadrajet that is running rich can be a few things.
1. main well leakage
2. removal of the primary metering rod, mis-adjusted primary metering rods
3. too high float level.
4. too big of a ject compared to the metering rod, must match.
Hesitation from a stop:
1. removal of the primary metering rods or too small a rod.
2. too weak pump spring
3. too small drill size for nozzle holes.
4. secondary air valve popping up when accelerating (not opening)

 

If it ran fine before you swapped the intake, it's very possible that the issue is the ignition timing since you set it with your ear.
As to the smelly oil and exhaust, to high of a float setting will cause it if it's flooding over the gasket where the air cleaner stud goes in. Also, nozzle drip will make the exhaust stink.
Does the Qjet have a choke?