Qjet Question

[Hacksaw]

Robert: Did you figure it out?

[Robert Simpson]

Originally Posted by Vic Santos

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.

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.

[Rich Biebel]

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....

[Robert Simpson]

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

[Mike Pearson]

Originally Posted by Robert Simpson

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

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

[Robert Simpson]

Originally Posted by Mike Pearson

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

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.

[Hacksaw]

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?

[Mike Pearson]

Originally Posted by Robert Simpson

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.

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?

[monte385]

Originally Posted by Robert Simpson

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.

Are you allowed to use screw in air bleeds?

[Robert Simpson]

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.