Qjet Question
 

I am having a problem with my Q-jet on my footbrake street car and I could use some advice on how to fix it. I have a nova street car with a sbc/t350 combo that I drive and bracket race. It has a stock valve body with a shift kit and I use a Q-jet. I leave at 16-1700 and it flashes to around 25-2800 and it shifts on its own if left in drive or second. It runs low 12's to high 11's. The problem that I have just started to experience is if I have caught someone early in the run and try to pedal the car it starts to slow down like you took your foot off the gas! But it is on the floor. On this particular run I pedaled once at about 1000' and lost .30sec,12mph and lost the rd! The engine makes a different noise like it is straining but still running but just not pulling. Any idea what this might be in the carb? Could the secondary flap close and get stuck in the closed position? Any idea what this is and how to fix it? I have not modified the linkages at all, and only have done the usual things to rebuild and set it up to run on the car and leave clean without a bog etc. Any advice would be appreciated. Thank you

Re: Qjet Question
 

Choke mechanism allowing choke plate to pop shut and, in turn not allowing secondaries to open when back on the throttle?

Re: Qjet Question
 

Check the rear flap. Maybe hanging shut somehow.

Re: Qjet Question
 

Thank you all for the suggestions. The choke is wired open and it does not serve any function. I will look and see if somehow the secondary flap is getting caught on something. Please keep any suggestions coming. Thank You.

Re: Qjet Question
 

The secondary air flap is controlled by the forward located choke pull (air valve dash pot / secondary dampener ) . This will not allow the flap to open after a high vacuum for a second , so it sounds like normal operation . The size of the air bleed restriction inside the pip controls the time it takes to open .
Got this from Doug Roe' s book Rochester carburation H.P. Books
...Trevor

Re: Qjet Question
 

Is your linkage reworked to the secondaries or still factory stock. If still stock, could the rear throttle blades somehow stick closed when you pedal?

Re: Qjet Question
 

Not sure of the exact problem here, but I would say to look at each possibility.
Start with the sec. flapper, and make sure it doesn't come anywhere near the top opening.
You can loosen the screws and shift the plates around a bit, and then re-tighten.
Or, just file the casting a little bit, where ever it's close.
Of course, you wouldn't want to do this on a S/SS carb. I'm sure you know this.

Re: Qjet Question
 

Just remembered this. I once had the split pin that secures the cam for the hanger walk out slightly and that interfered with the flap.

Re: Qjet Question
 

What's the float level measurement? And fuel pressure?

Re: Qjet Question
 

Had this problem approx. 30 years ago. What happens is that when you shut the secondary throttle at high vacuum the pressure across the throttle blades holds them in place when you try to open them again especially if the bores are a little oxidized and the actuating lever is NOT PINNED TO THE SHAFT. The fix is to pin the throttle shaft to the actuating lever; do not rely on the torsion spring to open the throttle. A $.10 rollpin is most common fix.

Re: Qjet Question
 

Robert: Did you figure it out?

Re: Qjet Question
 

Vic, I believe you are correct. When I pulled the carb off and started to play with it I discovered the spring holding the shaft. Even in the wide open position you could manually close the secondary on the baseplate. So I put a roll pin in it. I will see if this helps it this weekend. Everyone has given me some good advice and I appreciate it. I dial honest so I have not had this problem occur. It has just been recent when a couple of times I caught them real early and I just wanted to scrub a little. We will see thank you all.

Re: Qjet Question
 

The secondary spring arrangement is not really very safe.

I once had that spring pop off and my throttle went wide open.

Engine sucked it wide open......

The car was on the trailer inside my garage. I was messing with something, probably the carb.

I revved it up a couple times and it went wide open.....

I shut the air valve with my hands and a friend managed to kill the ignition switch.....He hit the switch so hard it broke off.....but did shut it down....

I never saw it happen before that on any Q-Jet.....street car or race car...

The spring must not have been properly in place but it showed me what could happen.....

Drill and pin the lever to the shaft.....

Q-Jets are great when they work well.....but can really give you fits....

Re: Qjet Question
 

Update. Removing the spring on the secondary shaft and pinning it was the key. I made a pass last weekend and drove past the finish line and pedaled it a couple times and it worked. I dial honest but now I know if I need to pedal it should respond ok. Thanks to all the suggestions it is appreciated. Now if I can just figure out how to lean up the mid range it would be good, any suggestions out there on that?

Robert

Re: Qjet Question
 

Are you still using the metering rods in the primary jets. If so most are not using them any more. Drop down about 5 jet sizes on the primary jets and remove the primary metering rods and plug the hole where the power valve used to be. That should give you better control of the fuel metering

Re: Qjet Question
 

No I'm not using the primary rods. I did drop down as lean as I can (65), that is as lean as I got. My carb is rich down low and mid range and slightly lean up top. Any idea's on how I should approach this? Thank's again.

Re: Qjet Question
 

Try a smaller main jet to lean it early in the run, although a 65 should be lean enough. Make sure the primary plunger cavity is plugged. Put a thinner metering rod in to richen it up at the top. What rods are you using now?

Re: Qjet Question
 

Check the plugs on the bottom of the carb body with the base plate off to make sure the plugs are not seeping. That will richen up the idle and low end if they are leaking. put some JB weld on them just to make sure. Also check the float level and fuel pressure. 6.5 lbs should be more than sufficient. I also put a 90 degree spark plug boot on the vent tube facing forward. Do you have electrical tape around the secondary metering rods to control slosh that can splash up around the secondary rods? My cab has a small plate that fills the area around the secondary metering rods but you have to mill the bottom of the carb top for the plate to move freely. What rod size are you running in your carb?

Re: Qjet Question
 

Are you allowed to use screw in air bleeds?

Re: Qjet Question
 

Thanks guys for the suggestions. This is a 77-78 model carb that I use on my street car/footbrake car. I do not have primary rods in it. I have been playing around with it to make it better for what I am doing. I can put air bleeds in it if I wish. My main question is what part of the carb helps deterring the mid range fuel mixture? I am asking if the air bleeds in the main body would have the largest effect on tuning the fuel curve in mid range? In my case 28-4000. I did discover that I have to much total timing so that prob is contributing to the slight lean occurring up top. I am working on the dist to fix that. Thanks again.

Re: Qjet Question
 

Is it a dual main air bleed or single?
Have you checked in here?
http://racingfuelsystems.myfunforum....989c4839377ee5
See if you can get Tuner's attention, wealth of Qjet knowledge.

Re: Qjet Question
 

What does the 90 degree spark plug boot do? Pinning the shaft is always a good idea for all the reasons listed.