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#1
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Qjet rich after wot
I took the firebird out today to tune the carb. I recently installed a 17056262 qjet. AFR at cruise is about 15.5:1. WOT is about 13.5:1. After WOT the cruise AFR goes to 11:1 for a few minutes before it leans back out to over 15:1. What could cause this?
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#2
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Got any specs on your carb, for the knowledgeable folks here to help you?
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1977 Black Trans Am 180 HP Auto, essentially base model T/A. I'm the original owner, purchased May 7, 1977. Shut it off Shut it off Buddy, I just shut your Prius down... |
#3
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Float sticking? Full throttle puts a good drain on the Quadrajet bowl and the float would drop low as the fuel level drops, and possibly the arms of the float are hanging up? That would overfill the bowl and cause the rich condition. Could also be the needle valve taking time to seat properly after dropping down farther than normal cruising loads. Best I got.
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Mick Batson 1967 original owner Tyro Blue/black top 4-speed HO GTO with all the original parts stored safely away -- 1965 2+2 survivor AC auto -- 1965 Catalina Safari Wagon in progress. |
#4
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Yup!
The float and or the needle is hanging up once the level of fuel in the bowl drops to a certain level for a while. That cruse mixture ratio is going to lead to part throttle ping and maybe even hot running issues my friend !
__________________
Wernher Von Braun warned before his retirement from NASA back in 1972, that the next world war would be against the ETs! And he was not talking about 1/8 or 1/4 mile ETs! 1) 1940s 100% silver 4 cup tea server set. Two dry rotted 14 x 10 Micky Thompson slicks. 1) un-mailed in gift coupon from a 1972 box of corn flakes. Two pairs of brown leather flip flops, never seen more then 2 mph. Education is what your left with once you forget things! |
#5
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Inlet needle may/will bind in seat if clip is located in one of them holes in float arm.
Clip needs to be hanged in from behind of float arm. With proper fuel delivery to carb, fuel level in bowl wont change much or at all at WOT. |
#6
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I find the afr gauge to be helpful. You might set the engine for best idle and it turns out to be 13:1 afr. But it can then be leaned out to 14:1 and there be virtually no difference. Also with light throttle cruise, the afr could easily be 13:1 and it feels fine, but leaning it out to 16:1 has no negative effects
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#7
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Quote:
https://www.afrplus.com/AFRplus-unit-functionality.asp
__________________
77 Trans Am, 469 w/ported E-Heads via Kauffman, matched HSD intake, Butler Performance forged rotating assembly, Comp custom hyd roller, Q-jet, Art Carr 200 4R, 3.42s, 3 inch exhaust w/Doug's cutouts, D.U.I. Ignition. 7.40 in the 8th, 11.61@116.07 in the quarter...still tuning. |
#8
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Stock engine?
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Carburetor building & modification services Servicing the Pontiac community over 20 years |
#9
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Thanks, I'll check the needle and seat out. The engine is a 455, 9.5:comp, 6x heads, 232 at .050 cam.
Steve, what AFR do you like to see. I've never had any issues at 15.5:1 cruise. Runs to cold if anything. |
#10
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15.5 at cruise with no load is fine, doesn't hurt anything as long as it's not to the point it's causing a surge or running hot, which you said it's not.
Some engines get away with it and work well, some don't. It's a trail and error thing. The WOT AFR might be a bit on the lean side though. It's not dangerous but it's something to watch. Since you're not pushing the compression ratio and have a decent cam it probably won't complain. With that said I found my Formula runs it's best times at the track when it's right about 12.9-13.0 AFR. It takes either a dyno or lots of track time to find a happy spot. Every engine is a little bit different in this department too. Some like richer, some don't. There is no real magic number, I just give the engine what it likes. |
#11
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Make sure the power piston isn't sticking in the bore, and the little plastic retainer hasn't popped out of the bore.
WFO--power piston rises all the way up. If it sticks up, cruise mix will be rich until it drops back down again. |
#12
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I canīt see the power piston nylon retainer going anywhere as long as the airhorn is in place?
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#13
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Doesn't the boss, cast into the carb top press against the retainer???
__________________
1977 Black Trans Am 180 HP Auto, essentially base model T/A. I'm the original owner, purchased May 7, 1977. Shut it off Shut it off Buddy, I just shut your Prius down... |
#14
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Quote:
While installed however, the "retainer" is held in place by the air horn gasket and due to the air horn design. I see the nylon "retainer" mostly as a rich stop for the power piston. |
#15
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The mixture ratio changes with the octane level in the fuel that you run also and the 455 tend to scavenge pretty hard so if this is a new motor your tuning I would start off with 15.0 ratio at cruse for now just stay totally on the safe side.
As you prove out all phases of throttle usage / rpm temp and load then creep back up to being near lean at cruse.
__________________
Wernher Von Braun warned before his retirement from NASA back in 1972, that the next world war would be against the ETs! And he was not talking about 1/8 or 1/4 mile ETs! 1) 1940s 100% silver 4 cup tea server set. Two dry rotted 14 x 10 Micky Thompson slicks. 1) un-mailed in gift coupon from a 1972 box of corn flakes. Two pairs of brown leather flip flops, never seen more then 2 mph. Education is what your left with once you forget things! |
#16
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Quote:
Everything you have written in this thread is wrong.
__________________
77 Trans Am, 469 w/ported E-Heads via Kauffman, matched HSD intake, Butler Performance forged rotating assembly, Comp custom hyd roller, Q-jet, Art Carr 200 4R, 3.42s, 3 inch exhaust w/Doug's cutouts, D.U.I. Ignition. 7.40 in the 8th, 11.61@116.07 in the quarter...still tuning. |
#17
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There is some truth to what Steve is saying but it's more in depth than octane.
The ethanol content will certainly affect the AFR, because stoich is much different (richer) with more ethanol content, and the carb should be adjusted and modified accordingly. Not all pump gas is the same. As far as race fuel and pump gas, yes there will be different jetting requirements for it as quite a few race fuels are oxygenated. There's a lot to it that Steve, and even I didn't elaborate on but I think that's what he meant. |
#18
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Quote:
There are bean counters and chemists working at the refinery to make sure the right blend of gasoline and ethanol makes it to the premium and regular tanks. It isn't something that you can tune your carb around. That's why I run a mix of 90 octane ethanol free and 100LL. Ethanol has less energy per unit of volume, so you can make more power by getting rid of it from your fuel system.
__________________
77 Trans Am, 469 w/ported E-Heads via Kauffman, matched HSD intake, Butler Performance forged rotating assembly, Comp custom hyd roller, Q-jet, Art Carr 200 4R, 3.42s, 3 inch exhaust w/Doug's cutouts, D.U.I. Ignition. 7.40 in the 8th, 11.61@116.07 in the quarter...still tuning. |
#19
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Quote:
Back when I was testing that stuff, I found as much as 17% ethanol at pumps that were advertised at 10%. There was no real consistency that I found. You can tune and crutch it to some degree. In order for a car to run properly on it the circuits have to be modified. Mainly the idle circuits have to be richened, and it's a good idea to run the engine a little on the rich side of stoich to cover any inconsistencies. But the real point of my post was to elaborate a little on what I felt Steve meant. |
#20
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would a higher volume pump help this in keeping the bowl full?
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