Q-Jet over loading
Thread Starter
Instructor
Joined: Jun 2010
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Q-Jet over loading
ok so here's my issue my Q-Jet is over loading when the secondaries open and dumping massive amounts of fuel in the secondaries. causing a sever bog. and the car will pick itself back up after a moderate time and run like a bat out of hell. but what would cause the secondaries to over load happens on hill climbs or when ya wanna smoke that lil rice burner giving you the pipes. basiclly is happening on the secondary opening like i said it will pick itself back up. had it outside let it warm up to temp the ccracked the throttle and watched the secondaries they are dumping massive amounts of fuel on the start of opening.
Thread Starter
Instructor
Joined: Jun 2010
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yes pretty sure its dumping fuel when at choked it revs fine and the secondaries will open a lil bit and a steady stream will spray in the secondaries. when warmed up the secondaries when throttle cracked open seems to be much more of a heavier stream that sprays in and causes a sever bog. then it plays catch up as the top flappers open more. i am totally open to suggestions at this point any trouble shooting will help alot more.
Le Mans Master
Joined: Dec 2007
Posts: 6,422
Likes: 591
From: McHenry Illinois
The air valve is the large flap at the top of the rear barrells. The air velocity when the lower rear throttle plates are open causes it to open on demand as the engine needs more air than the primaries can deliver. It will usually not open while the car is sitting still.
There are plenty of experts here for the q-jets, some will likely chime in with better info.
There are plenty of experts here for the q-jets, some will likely chime in with better info.
Thread Starter
Instructor
Joined: Jun 2010
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ok so their the top flappers on the secondaries. they do open when rev'd sitting still. is there a setting or a way to check if they are to loose. the car never did this this is something that just started and has progessivly gotten worse. they dont open far about a 1/4 of a inch when rev'd sitting still but they do open and at that first crack you can seem the fuel spray in the secondaries then just striaght bog.
Tech Contributor
Joined: Aug 1999
Posts: 14,377
Likes: 6,376
From: At my Bar drinking and wrenching in Lafayette Colorado
Your secondary airvalve spring windup is too loose. Set the windup to 3/4 turn as outlined in my papers.
Lars
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Lars
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Melting Slicks
Joined: Mar 2005
Posts: 2,838
Likes: 10
From: Austin TX
Quadrajet got a bad name because many thought like you, that 'fuel was being dumped' causing the infamous q-jet bog.
The bog is really 'too much air' from the air valves opening too quickly.
Easy fix,..
The bog is really 'too much air' from the air valves opening too quickly.
Easy fix,..
Thread Starter
Instructor
Joined: Jun 2010
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lol hmmmm not why i heard they had a bad rep. always heard cuz they were so hard to tune and get running right. but once you brain stormed every lil thing to adjust they were great. i am not a carb guy never was its like forgien language to me lemme rebuild your block and ya goto town. but how she breathes i get lost lol. oh and by the way adjusted the air valve spring as per lars instructions and still doning the same thing and bogging bad. and after reading lars great info WOW i must say i learned alot 
. possibly thinking of attempting a rebuild. Heard it's not worth rebuilding a Q-Jet and better off buying a new one but i kinda like having the numbers matching carb lol
. possibly thinking of attempting a rebuild. Heard it's not worth rebuilding a Q-Jet and better off buying a new one but i kinda like having the numbers matching carb lol
Melting Slicks
Joined: Mar 2005
Posts: 2,838
Likes: 10
From: Austin TX
There's no one adjustment for every engine.
Thread Starter
Instructor
Joined: Jun 2010
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yes i am loosing the allen head lock bolt then turning the air valve spring winder i am currently at one full turn after the spring touched the the lil post for the air valves. as per lars said 3/4, my manual says 7/8 for my carb 17057204. i went in 1/8 inch turn and went for a cruise and on any hard accel or hill she dies. also the air dash pot valve is new and functioning well. starting to come at a loss here.
Tech Contributor
Joined: Aug 1999
Posts: 14,377
Likes: 6,376
From: At my Bar drinking and wrenching in Lafayette Colorado
If you're bogging going into the secondaries with the airvalve at 3/4 turn or tighter, you have other issues related to either timing or fuel flow.
Lars
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Instructor
Joined: Jun 2010
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ok lars fuel pump was replaced the lil s- hose was a bit dry rotted and leaked it was replaced all new filters. timing not sure about prev ower said he placed a mild cam in the motor but not totally sure and not up to pulling the motor. so not sure if the timing should still be 6-8 degrees btc but i think he was just blowing smoke for the sale but yet he didn't know i was buying it anyways lol. the car gots 85k on it this lil bog has shown up and progeressively getting worse. is it possible for the carb to be just plain out worn and pushing to much fuel i was playing earlier seems if i crack the throttle to W.O.T. and take my finger and poke the air valve open a lil more it catches up faster. or possibly other things like maybe jets since i am going with the guy saying theres a cam in it and headers and true duels. but the car ran fine for like a 2 years then this gremlin has popped up ugh (would be pulling my hair out if i had any). i want to sell this car but i will not sell it unless it mechainlly sound and runs like a champ. i really want me a 67-69
Thread Starter
Instructor
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oh was looking at this dont see where this is not new as summit sells remans
http://www.summitracing.com/search/P...t&autoview=SKU
http://www.summitracing.com/search/P...t&autoview=SKU
Thread Starter
Instructor
Joined: Jun 2010
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ya 75 i am leaning towards planning a rebuild but never have done a carb none the less a Q-Jet kinda worried and don't wanna screw anything up i tried a place and see what they would charge to do it and they wanted well over 200 bucks and that a price of a reman. thats why i was looking at that one from summit. is it a real diffucult job or more on the needing alot of patients end?
Melting Slicks
Joined: Mar 2005
Posts: 2,838
Likes: 10
From: Austin TX
Better describe the bog.
At what RPM?
Is it only at WOT or can it happen by simply pulling away from a stop sign (normal driving)?
Does she run great otherwise? (This being the only problem?)
At what RPM?
Is it only at WOT or can it happen by simply pulling away from a stop sign (normal driving)?
Does she run great otherwise? (This being the only problem?)
Thread Starter
Instructor
Joined: Jun 2010
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ok better description. idles fine cruises fine bogs starts on WOT and really slowly catches up, climbing a hill she dies, passing gear as soon as it shift just get blaaaaaaaaahhhhhhhhhhhhhhhhh. dragging from a light if floor to WOT just blaaaaaahhhhhhhhhhhhhhhh. now if i drop the tranny into first racing someone get the RPMs up around 2500, 3000 with my foot on the break great off launch slam second manually then third manually car never skips a beat and runs like a bat outta hell. ONLY WISH I HAD 1 MORE GEAR stubborn 3 speed auto. its basically when the secondaries are just coming in then is goes blaaaaaaaaahhhhhhhhhhhhhhhh pretty much what it sounds like.
never really caught the rpm range when this happens cuz as soon as it does the rpm needle drops quicker then a stone. but basiclly best described above. passing gear and hills kills the car. and really seems to be when the secondaries start to come out to play. highway cruising it will cruise all day. around town good. sitting will redline damn fast great throttle responce sitting.
never really caught the rpm range when this happens cuz as soon as it does the rpm needle drops quicker then a stone. but basiclly best described above. passing gear and hills kills the car. and really seems to be when the secondaries start to come out to play. highway cruising it will cruise all day. around town good. sitting will redline damn fast great throttle responce sitting.
Last edited by elke_10; Jul 7, 2010 at 02:53 PM.
Melting Slicks
Joined: Mar 2005
Posts: 2,838
Likes: 10
From: Austin TX
Sure sounds like the air valves are opening too soon.
You can lock out the secondaries as if the choke is engaged. I'd try that and see if you can duplicate the bog on the primaries alone. My guess is, it won't bog at WOT like before.
And if my guess is right, I'm 95% certain the air valves are out of adjustment.
You can lock out the secondaries as if the choke is engaged. I'd try that and see if you can duplicate the bog on the primaries alone. My guess is, it won't bog at WOT like before.
And if my guess is right, I'm 95% certain the air valves are out of adjustment.