car stumbles in the air! - Page 2

Gary Parker · 06-05-2011, 06:01 PM

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

TinSoldier 3215 · 06-05-2011, 06:19 PM

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

Jeff Lee · 06-05-2011, 06:43 PM

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.

Richard Grant · 06-05-2011, 06:47 PM

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.

TinSoldier 3215 · 06-05-2011, 07:25 PM

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

ss3011 · 06-05-2011, 08:09 PM

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 !

gmonde · 06-05-2011, 08:11 PM

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

Tod Lane · 06-05-2011, 09:14 PM

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

X-TECH MAN · 06-05-2011, 09:20 PM

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

Ed Carpenter · 06-05-2011, 10:32 PM

Quote:

Originally Posted by jonesracing

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

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

06-05-2011, 06:01 PM	#11
Gary Parker Senior Member Join Date: Apr 2004 Location: Westfield Mass Posts: 519 Likes: 343 Liked 373 Times in 50 Posts	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 __________________ Gary Parker 1617 STK

06-05-2011, 06:19 PM	#12
TinSoldier 3215 Member Join Date: Jul 2009 Location: Bulington, Ky Posts: 359 Likes: 0 Liked 6 Times in 5 Posts	Re: car stumbles in the air! Gary, We have put a brand new regulator on and it did not help. Thanks

06-05-2011, 06:43 PM	#13
Jeff Lee VIP Member Join Date: Jul 2007 Location: Anthem, Arizona Posts: 2,766 Likes: 0 Liked 2 Times in 2 Posts	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. __________________ Jeff Lee 7494 D/S '70 AMX

06-05-2011, 06:47 PM	#14
Richard Grant Member Join Date: Jan 2002 Location: West Monroe, La. Posts: 301 Likes: 9 Liked 13 Times in 7 Posts	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. __________________ Richard Grant 4988 STK

06-05-2011, 07:25 PM	#15
TinSoldier 3215 Member Join Date: Jul 2009 Location: Bulington, Ky Posts: 359 Likes: 0 Liked 6 Times in 5 Posts	Re: car stumbles in the air! Mr. Grant, We leave at 4,000 of the rpm's.

06-05-2011, 08:09 PM	#16
ss3011 Senior Member Join Date: Feb 2002 Location: Southeast Michigan Posts: 885 Likes: 63 Liked 221 Times in 102 Posts	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 !

06-05-2011, 08:11 PM	#17
gmonde Senior Member Join Date: Nov 2007 Posts: 615 Likes: 56 Liked 166 Times in 59 Posts	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

06-05-2011, 09:14 PM	#18
Tod Lane Member Join Date: Jul 2008 Posts: 152 Likes: 0 Liked 2 Times in 2 Posts	Re: car stumbles in the air! Stalling the fuel in the line? Fuel line too big maybe? __________________ Tod Lane Swartz & Lane 66 Nova Swartz & Lane 79 H/CM Trans Am

06-05-2011, 09:20 PM	#19
X-TECH MAN Banned Join Date: Dec 2007 Location: Lake Placid, Florida Posts: 3,207 Likes: 1,049 Liked 235 Times in 110 Posts	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.