Q-Jet Carbs

[Broncoholics]

Anyone have some insite on adjusting a Q-jet?

The Bronco started to run real rough 2 hrs into my wheeling trip. @-)

I went straight to the carb and tried to adjust thinking "its a q-jet".

Later I found the vacume advance was bad. Replaced it and the engine does run better but not like it did before (rough idle and no power). I think I got the carb way out of wack messin around. :-"

I ran both bottom adjustment screws in all the way to start over. The motor only slightly changed?? Why is this? Most carbs have drastic changes when turning these adjustment screws. I never had to mess with this carb until now. Q-jets can be touchy from what I hear but work well when adjusted correctly.

I tried turning out both screws 1 turn at a time until it ran better. No luck.

I even played with the timing to see if I skipped a tooth. I replaced the fuel filter in the carb and on the frame rail with no luck.

Anyone know how to adjust this bad boy? or maybe have instructions with photos on rebuilding the carb if all else fails?

Could be a clogged jet or stuck float. Its always nice to read up on it before I tear into it.

Thanks!

 

[Bully Bob]

Mr. Holics,

I'm hardly & expert on 4 brls. .....

Your suspicions, float, jet, (& also needle & seat) are good choices.

Bouncing around loosens things & down-stream they go.. :glare:

There's an old trick you can try....

Run the RPMS up a bit & choke the carb completely 'til it kills eng. Do this a few times.... It's been known to be a "mystery" cure .... [-o<

Bob

 

[Broncoholics]

Wouldn't that just flood out the carb each time?

I'm thinking of pulling the adjustment scews out and see if there is anything blocking.

When replacing the vacume advance I noticed its very dirty in there. It moves but not soomthly. I'll clean this up and add a new condenser (helps run better on load only) and see what happens.

Otherwise I need to look at spark plugs, compression tests (blown piston or ring), air leak down tests (leaking valves).

Only reason is I see slight amounts of blue smoke comming out the exhaust (only in sun light can be seen). The engine has never burnt oil but I have blown pistons before... Sucks cuase its probably the carb.

 

[Seabronc]

.When replacing the vacume advance I noticed its very dirty in there. It moves but not soomthly. I'll clean this up and add a new condenser (helps run better on load only) and see what happens.

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While you are in the distributor check the condition of the centrifugal advance mechanism. The part with the two springs on it. That part gets rusty and sticks sometimes.

Sounds like you need a complete set of adjustment proceedures for the carb. Try doing a "Dogpile" or "Yahoo" search on Q-Jet adjustment. Also you can probably find a Edlebrock or Rochester, (depending on which one you have), carb book at most book stores.

Good luck,

>-

 

[Bully Bob]

"Wouldn't that just flood out the carb each time?"

No, ......It causes a suction back thru the air-horn & sometimes, if your lucky, it will **** & obstruction loose. (assuming there is one)

It can't hirt anything....it'll only spin for a few seconds.

Yah, if the idle adj. screws have no affect....something's a-miss in the carb. (Better there than internal eng.)

 

[Broncoholics]

I'll give it a try.

My guess is, since I park the truck for months at a time, the fuel is shelacking inside the carb. After 2 hours on the trail, some broke loose and clogged a jet.

I'll let you know what happens tomorrow, got home late, the bronco would have the cops here in no time if I fire her up right now. Seems too simple, hope it works, I'll also clean the advance mechanism and replace the condenser for kicks.

 

[Broncoholics]

Just came across this and thought I would include it for anyone thats interested.

http://www.florida4x4.com/tech/quadrajet/

 

[Bully Bob]

I'll give it a try.My guess is, since I park the truck for months at a time, the fuel is shelacking inside the carb.  After 2 hours on the trail, some broke loose and clogged a jet.

I'll let you know what happens tomorrow, got home late, the bronco would have the cops here in no time if I fire her up right now.  Seems too simple, hope it works, I'll also clean the advance mechanism and replace the condenser for kicks.

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It's not guarenteed... just worth a try. Just a trick handed to me by a professor at UC Irvine. :-B

 

[Broncoholics]

Well I gave that a try (reved motor to 2500 rpms and covered the carb until stall 4 times) with no luck.

I'm going to do a compression test before I take apart the carb. Just in case I have to replace a piston or ring.

I think I'll ditch work early, its in the 80's here in Seattle. Goodday to get a sun burn on my back and figure this out before Memorial Day weekend!

Everyone is headed to Funny Rocks (Naches, WA).

I hate to say it but I might tak it to the carb shop on my flat bed on Friday if all else fails. Got to play on that Lava Rock! I'd hate to have to watch and drink everyones beer. :wacko: