car stumbles in the air!
 

We are having issues with the car as soon as you release the trans brake and it leaves the line and starts in the air it hesitates and acts like it is out of fuel. We have change 3 different carbs and regulator, fuel pump, msd box, we have looked at rotor button, distributor cap, and when car lands to runs fine and comes clean out of water boxs. any input would be helpful. thanks

Re: car stumbles in the air!
 

What car, engine, carb?

Re: car stumbles in the air!
 

If it runs fine everywhere except "x", then "x" is the only issue.
Running out of fuel either due to pressure or just's uncovered or sloshing fuel where it's not supposed to be. Maybe a wedge plate will work? But you have to look at the whole picture.

Re: car stumbles in the air!
 

The car is a camaro, engine is a 350 and carb is a quadrajet. As far as Jeff's reply I don't understand what he's saying?? If the fuel pressure is off, then what should it be?? :confused: it has been 7lbs. When it comes out of the water box it has no hesitation, no stumble, it's just when u stage and go up on rpm's and release the trans brake button it hesitates and when it comes down and planes out, it runs great!!:) Do you think it could be a fuel pressure issue?? Thanks for any response...

Re: car stumbles in the air!
 

Jones,

judging by your first post you have checked the basics for a bad part. So, it is reasonable to look at other items. [and do not mean any disrespect, just beginning the brainstorming process] begin looking at the entire package in a different light. That is to say, go back and look carefully at every small thing. Look at every wire, every ground, every terminal connection, etc.

One idea is to have someone else drive the car while you look and listen, might give a different idea of what is happening.

Re: car stumbles in the air!
 

Fuel pressure or bad ground that only happens when you do a wheelie would be where I would start.

Re: car stumbles in the air!
 

And just to add the car is still in low gear. and I did have the trans brake button break on me and the wires touch. Do you think that the trans brake button by touching could have shorted sum thing out?:confused: Thanks for the help.. I'm stumped.. it's in low gear in the air.

Re: car stumbles in the air!
 

Hmm, sounds familiar. Re-check all your grounds. That was my problem.

Re: car stumbles in the air!
 

Thanks Ed.

Re: car stumbles in the air!
 

Just to be sure its not a fuel issue, put the .149 ( bigger) needle and seat in the carb at the same float height as the previous ones. We have had that same issue before. If it gets alot better or cures the problem, you have a supply problem

Re: car stumbles in the air!
 

when I had this problem, it was a bad regulator. I also just discovered a bad gauge. Sounds like it is running out of fuel to me. Check the flow from the out side of the regulator Gary

Re: car stumbles in the air!
 

Gary, We have put a brand new regulator on and it did not help. Thanks

Re: car stumbles in the air!
 

A Q-Jet has a very small float bowl. So does my Autolite 4300 series carb. Fuel pressure is one thing, volume is another. And it is volume you need to be concerned about. Excessive pressure can cause it's own problems by spraying fuel out of the seat assembly instead of flowing out of the seat assembly. Think garden hose at a set pressure and being wide open and then placing your finger over 75% of the outlet. You have less fluid control although at a high pressure.
I've seen some pretty innovative ways to take care of the volume issue. One is the use of a large billet type fuel filter (with the filter discarded) placed right before the carb inlet. I have that on my car. This serves to increase the bowl capacity by having a reserve of fuel with a faster response time to the needle and seat). I also have a larger seat and a float that is physically smaller and heavier than OEM. Smaller ads more fuel volume in the bowl and heavier makes the float ride the waves smoother for better needle & seat control. Think wave runner boat as opposed to U-boat.
When you race your car, the biggest draw on the fuel system is when you launch and the load is heaviest when doing a wheelie. Burnouts offer the least amount of load and the trip on the track is progressively more demanding the farther you go. Your fuel system will recover from many faults as you go down track but the launch is the shortest and hardest load.
I'm know Q-jet racing expert but I would say I think 7#'s of pressure is border line excessive. I've seen racers go faster with less pressure; back to that garden hose example. You also need to make sure the basics are there, adequate pump, adequate pump pressure, adequate fuel line sizes, adequate fuel cell or tank fluid control.
But yes, I will concede a bad electrical switch or ground will also cause problems.
So to test further, can your car wheelie without the trans-brake? It should. Try it without the t-brake and see what happens. If it still stumbles, then it's a fuel issue. If not, I would say look at the electrical items.
Can't wheelie without the t0brake? Then throw a couple of bags of something or 4 BBC cylinder heads in the trunk (secured of course) and see what happens when you launch it foot-braking it. Just go to the 330' as that's all you need.

Re: car stumbles in the air!
 

7lbs. is a lot of pressure for a quadrajet. I am surprised that you don't have other
problems. Try 5 or 6 and if it doesn't affect the et you will be better off in the long run. It might even help with your problem.
I don't know who does your carbs but some carbs will stumble coming off the trans brake. Try a carb from different builder, someone who has a track record of building quadrajets using a transbrake.
Also are you on a chip when you leave, some quadrajets don't leave well off a chip.

Re: car stumbles in the air!
 

Mr. Grant, We leave at 4,000 of the rpm's.

Re: car stumbles in the air!
 

If the carb has a 1 to 1 linkage, then it just might be the low rpm chip. I had big problems trying to run my engine on the dyno at that low of rpm, raised it to 4500 and no stumbling problems. This carried over to the race car also. Car would not run with the low chip, raised up the rpm to 4500 and was clean. Might be worth a try !

Re: car stumbles in the air!
 

data logger will help you figure out what the deal is,,fuel presure,and o2 will sort this out ,i purchased a rpm logger and you can add to it ,,,, gmonde

Re: car stumbles in the air!
 

Stalling the fuel in the line? Fuel line too big maybe?

Re: car stumbles in the air!
 

Is it possable that the fuel is sloshing out of the carb vent when you launch? Do you have it extended ? Just a thought.

Re: car stumbles in the air!
 

I went down this road a few years ago. After a new fuel pump,regulator, lines, coil, cap,wires, battery,cables, master cut off, blah blah blah it was a stinking wire that was grounding out against the frame. When the car was in the air it would touch and kill the engine. Ed

Re: car stumbles in the air!
 

thanks to All for the help!!!!!!!!! Still Looking!!!!

Re: car stumbles in the air!
 

We had the same problem sometimes on the 88 Cutlass S/S move the regulator in front of the carb that way when the car launches the fuel in line will feed to bowl .

Re: car stumbles in the air!
 

had similar problem w/quadrajet and found that i had left out the block off plate under the top of quadrajet. when i was on the dyno the carb functions perfect. put on the car and would almost quit running on the launch, the harder we launched the wose it got. who built your carb and did they even use one of theses plates they are not part of rebuild or stock equipped we used to use a peice of black electrical tape years ago but now mike mcdonald and danny ashley,at Q/jet performance rebuilds and enhances my Q/jets and he makes a custom plate that the rear meter rods fit perfect. the tape would be a quick cheap way to check,but it does not last. I am pretty sure this will fix your problem. if it does you may want to get in touch w/mike mcdonald or danny ashley. plese let us know if this works

Re: car stumbles in the air!
 

I've seen similar problems when the fuel pump is not low enough in relation to the tank.
when the wheelstand is high enough the pump momentarly starves,and then recovers as the car falls out of the wheelstand.

Re: car stumbles in the air!
 

I just went through the same situation, on my car it was a loose power supply wire in
my switch panel, it would lose power then get power and peck like a miss at the top
of the wheelstand after that it would run great.

Re: car stumbles in the air!
 

The car did not do this until we made a change to the Bindo Terminator Button. Haves anyone had to make modification to the button maybe shorting out? We made the change only.

Re: car stumbles in the air!
 

Change it out to the old button and see if problem persists. Can't imagine that button would cause the problem.

Re: car stumbles in the air!
 

Like many others who have commented, I'm not convinced that you have a carburetor issue. If I were you, I'd probably be looking for some of the electrical issues that have been mentioned.

But, let's look at two things related to the carb to see if we can begin to determine what is at fault. First, what is your fuel pressure? A good ballpark number for most Q-jets regardless of builder is 7 psi max. You will need to verify your gauge reading by comparing it to a second gauge. Typically, if a fuel pressure gauge goes bad, it will just give you an incorrect reading and make you believe it all day long. Also, do NOT use the little 1" or so gauges that screw into your regulator port for your fuel pressure reading, especially a liquid filled one. I have seen more than one racer chase similar problems that ended up being a faulty fuel pressure gauge. Your gauge could be showing 7 psi but maybe you really have 10.

Next, what size needle/seat is in the carb? I've seen too big of a seat cause more problems that it potentially solves.

These are obviously not the only two things to look at, but just some brainstorming suggestions as someone else stated. Good luck.

Dean

Re: car stumbles in the air!
 

Going racing this weekend to see if we made the Right Moves!!!!

Re: car stumbles in the air!
 

Hi,

Just a heads-up on the adjustable type transbrake buttons......

Some of the "adjustable" buttons have the return spring set as to be the softest possible and the weight of the button and plunger along with the additional "G" force of the launch are enough to slightly depress the button and cause a miss.

They have to build it this way to allow the plunger to return as slowly as possible to the top of travel to allow adjustability..

Put a different button in or if it's OK reinstall your old button and give it a shot...

Bob

Re: car stumbles in the air!
 

do you have the black tape on the secondary metering rod slots?

Re: car stumbles in the air!
 

Bob, No.

Re: car stumbles in the air!
 

jonesracing you have a PM

Re: car stumbles in the air!
 

Got this from a friend and fellow racer, a really good racer. Check the fuel pump. There was a car with this exact problem, and what was happening was that under G's from the launch, the armature of the fuel pump would move and short out. It did not show on the fuel pressure gauge. They fought this problem all year, and a new fuel pump fixed the car for the last time trial at the last race of the season.

Re: car stumbles in the air!
 

This is for real......check the main wiring terminal for loose connections...check them with a wrench---not your hand......when I let go of the tranny brake the connection would momentarily lose connection then reconnect when it hit the ground off the wheelstand.......do not underestimate this happening, do not trust checking with your hand I say again....I felt stupid when I started replacing parts and found out a nut needed WRENCH TIGHTNESS.

Re: car stumbles in the air!
 

x2!!

Re: car stumbles in the air!
 

If the rain stays away we are going to try things out tonight!!

Re: car stumbles in the air!
 

First thing you should probably do is see if a fellow racer with a similiar combo will let you borrow his carb. for one pass so that you can make sure that is what is really causing the problem before you try chasing down lose wires or any other number of things that could be causing this.Good luck ,you'll find it.

Re: car stumbles in the air!
 

Well after 3 weeks of Bad Luck we went to the track and found the issue. Thanks for all your guys help. It turn out to be the button!!!

Re: car stumbles in the air!
 

what button?