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04-03-2007, 05:04 PM
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#1 |
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Registered User
Join Date: Oct 2006
Location: Wisconsin
Posts: 174
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Choke problem
Alright heres my problem. I have an 86 305 with a q-jet carb.(not sure on which one it is) When i go to start the truck after it has been sitting for a while the choke kicks in and my engine revs high. After a couple mins i tap the gas and it revs down. The carb was rebuilt when i got this motor and we swapped the electric choke off of the carb that was on my 85 4.3L and put it on this carb.
What do you guys think the problem is. Also if anyone has a good condition holley or edelbrock 4bbl around 600-650 cfm i might be interested. Im sick of this q-jet. Thanks guys
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 1985 C10 SWB- *Project*
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04-03-2007, 05:28 PM
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#2 | |
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Account Suspended
Join Date: Nov 2002
Location: Winnipeg, Manitoba, Canada
Posts: 798
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Re: Choke problem
Quote:
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04-03-2007, 05:33 PM
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#3 |
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Registered User
Join Date: Oct 2006
Location: Wisconsin
Posts: 174
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Re: Choke problem
It doesnt seem like its something normal
if the truck starts without me giving it any gas then it wont do it but as soon as i hit the gas it idles way up
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1985 C10 SWB- *Project*
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04-03-2007, 05:41 PM
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#4 |
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Registered User
Join Date: Mar 2006
Location: Reynolds, ND
Posts: 78
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Re: Choke problem
It is normal for the engine to rev higher when the choke is on. If the speed of the engine is too high there should be an adjustment screw like your idle speed screw on the choke side. It sounds as if the choke is working correctly but the revs need to be turned down.
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04-03-2007, 05:46 PM
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#5 | |
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Registered User
Join Date: Oct 2006
Location: Wisconsin
Posts: 174
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Re: Choke problem
Quote:
When its like 80 degrees out, you wouldnt think the choke would kick in
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1985 C10 SWB- *Project*
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04-03-2007, 06:08 PM
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#6 |
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Registered User
Join Date: Mar 2006
Location: Reynolds, ND
Posts: 78
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Re: Choke problem
Yea you're right I wouldn't think that it should kick in at 80 either. Not really sure what temp the choke needs to get up to for it to kick out. Have patience I'm sure someone on here can get this figured out for you. For a basic sbc a Q-jet is a very good carb, I have had alot more trouble with holleys and edelbrocks than any Q-jet.
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04-03-2007, 11:08 PM
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#7 |
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Registered User
Join Date: Oct 2006
Location: iowa
Posts: 722
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Re: Choke problem
i've worked with and rebuilt ALOT of carbs. and i'd have to say that i still like the edelbrocks the best as far as getting them set.....but as far as rebuilding i like the quadra-"junks" the best....the only real down side to them is getting the automatic choke set right....when you switched the choke with the one of the 4.3 did you change housing and all?? cause there are several "step" cams....which hold your cold idle speed....and if you have the choke body off the 4.3 that might be why you are having this issue.....
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"Horsepower is how fast you hit the wall, torque is how far you carry the wall with you." '84 chevy half ton short box 2wd, 67,000 actual miles  '03 chevy 1500 HD crew cab 4x4 standard box, 6.0L 
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04-11-2007, 03:39 PM
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#8 | |
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Registered User
Join Date: Oct 2006
Location: Wisconsin
Posts: 174
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Re: Choke problem
Quote:
how do i fix this? edit: Is the choke body the piece that the wire plugs into?
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1985 C10 SWB- *Project*
Last edited by 85_SWB; 04-11-2007 at 03:46 PM. |
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04-11-2007, 03:47 PM
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#9 |
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The Crazy Machanic
Join Date: Jan 2007
Location: Nokesville Va
Posts: 1,437
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Re: Choke problem
All of my cars that are carb. do this i just figured that a carb and it never seemed to bother me.
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*1986 Sliverado longbed 400 small block mean as hell, 700r4 trans (5 speed coming one day) * 1970 chevelle 2dr sedan Latest update June 24 2007.  *1957 4 door stationwagon - pink all original needing a good restore (body great, floors bad)  newest additions 1965 shortbed fleet great granddads. Been told im nuts to bring it back from the dead (still going to happen) plans-all stock with a turbo 292 inline 3 speed column shift. and thats it big block 427 and 5 speed trans and ford 9 inch theyhave no home yet thinking what to put them in and a 79 c60 trash truck um no idea i have one
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04-12-2007, 08:34 AM
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#10 |
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Registered User
Join Date: Dec 2003
Location: CT
Posts: 454
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Re: Choke problem
maybe this helps. Before switching to TBI I messed with my 85 qjet alot. On the bench I was able to set it up and it worked great (for a while). There are steps on the fast idle cam that work in conjunction with the choke blade angle. The idea is that a cold engine requires a richer mixture. The carb does this by increasing the throttle angle to give a higher engine speed when cold. This is why you have to pump the pedal once before starting, the choke is able to close and set the idle screw on the fast idle cam. the choke blade on top acts like a restriction in the intake path. The increased engine speed pulls in more air and the choke blade that is almost closed restricts the air but causes it to flow faster. This air moving faster past the main venturis in the carb (which normallly are not used at idle speeds) now with the increased velocity of the air will start to siphon a little bit of fuel from them. This is what richens the mixture for a cold operation. THen as the choke warms and opens towards fully open the fast idle cam falls to a lower notch until it is completely riding on the normal idle cam.
When the engine is cold the fuel doesn't atomize well in the intake manifold so fuel tends to condense on the cold metal and never makes it into the combustion chamber. Richening up the mixture compensates for this until the intake manifold is warmed up and the fuel stays atomized after leaving the carb all the way to the combustion chamber.
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1985 GMC Sierra 1500, 1/2 ton, 2WD, LWB, TBI 305 5 speed, 3.42 rear 2007 GMC Sierra 1500, xtended cab, 4X4, flexfuel 5.3L 1999 BMW 528i |
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