quadarajet still running rich

tommyhawk13

tommyhawk13

New Member
Joined
Dec 5, 2005
Messages
144
Reaction score
0
Points
0
Location
Jacksonville, Florida
I'm about to give up on this. I've been trying to figure out why my Cad is stumbling for way too long now. I've got black sooty plugs, and the choke butterfly looks the same.

The car (74 com ch)) idles a little bumpy, and the motor vibrates like a dryer with a pair of shoes in it.  :banghead:
Off idle, the motor hesitates and you can hear that it is not firing for at least a full second. It does this all the way up to highway speed, at steady throttle or speeding up. If I mash the go pedal, it gets worse. At a steady speed of 65mph or more, it seems to settle down.

I've gone through everything in the ignition, so I last night I went back to the carb again. The fuel pump is stock.
The air cleaner is fresh.
I tied off the secondaries with some wire, so they would not open. That did not help.
I checked all of the vacuum lines. Ok there.
I turned in the idle mixture screws all the way in, and the car still ran! :censored:
I let it idle for a good bit, hoping it would just burn up the gas in the bowl, but it just kept on running. It did sound a little smoother.  :screwy:

I figured the float must be set too high, or the needle wasn't seating properly, so I took the air horn off (carefully). I rebuilt this carb, so I was beginning to doubt my handiwork. I checked the float level, it was at 9/32", and the commercial chassis level s/b at 19/64". I'm ok with that, right?
I checked the hook on the needle, to make sure it was in the right place. :thumbup:
I pulled the needle out & everything looked ok.
I put it all back together & the problems are still there. I gave up at 1:00 am. :tired:

The carb should run out of fuel with the idle mixture screws all the way in, right?
Right? :listen:
 
Sounds like the age old problem of the plugs leaking on the underside of the carb. They are famous for doing this. When people rebuild these, they epoxy or jb weld the plugs in so they do not drip fuel constantly. Can you look into the throat of the carb and see if it is dripping. Be careful a backfire doesnt get you eyebrows etc....Dont ask how I know..lol

Maddog
 
When I rebuilt the carb, I epoxied the plugs. When I look down the throat, do I need to hold the throttle open & look past the carb into the plenum of the intake?
 
Just take a flashlight and look in to the throat of the carb at idle and see if you see too much fuel dripping into the plenum. But the way the factory intake is designed I dont know that you would see it. I would pull the carb off and pressurize it with an electric pump and see what you have. But I am sure there are much more experienced people than me who can help with this. i last ran a Q-jet in 1990..They dont flow enough fuel for a serious airboat...

Maddog
 
When the car is running try to tap the carb around the needle and seat with a hammer.  Don't break it in two just nice firm taps.  Sometimes this will seat the needle and all will be fine.  Worked for me several times in the pass.

TED
 
-HEI's had a problem where the wire going into the pickup coil would crack so when the vacuum advance moved it would loose the connection (and therefore spark) as soon as you let off it goes back to its happy place and connects again.
-'New' fuel pumps seem to be much higher pressure than older ones so they can easily overcome needle pressure, I just put one on my 6 cyl mustang that is running at 9 PSI!, I am only running 11 on my EFI 500.  Its worth the trouble to get a gauge and see what it is running, may even need a regulator.
-Hook up a separate fuel source (outboard boat tanks work well) to make dang sure its not an issue with the current batch of fuel or something in your tank or lines.  I have wasted a lot of time and money dealing with bad gas.



Here is what happened to me on my 78, may or may not be any help to you, pretty much same symptoms.

I hesitate to use the word rebuilt, I think a more accurate term would be cleaned and threw in a kit.  Had the carb apart several times.  Finally looked down the throat while running and could see fuel.  Bought new brass float to replace original black one.  Discovered that that plastic plug thing that goes in over the top of the float would hit the float rails before the needle seated.  Did this with both floats so I suspect perhaps the needle that belongs with this combo must be longer than the current ones.  A little work with a file fixed the problem and by holding things in place and turning carb upside down I was able to verify that it was seating.  At least at this point the car would idle but not that well whereas before you had to keep revving it up to keep it running and even at that it would rattle your teeth out.  A couple of weeks ago after getting down to 1 drivable car out of 5 in my fleet (we need at least 2) I decided to have another go at the 78.  Tore the carb apart again (this time didnt forget any screws or have any extra parts when I was done) and blew the crap out of every possible hole.  Ran slightly better but still shook like heck at idle.  Decided to check the timing, got the light and yanked off the vacuum line...  all of the sudden nice and smooth?  Put it back on and checked timing, around 45*.    Turns out the mechanical was 100% stuck.  Worked at it for about an hour and was able to just get it to wiggle when I remembered I had another dizzy.  Dropped it in and all is well. 
 
Thanks for the replies.
I have a points distributor, and I adjusted the dwell and timing a long time ago.
I even threw another dizzy on that I had, as well as the coil.
I'll try tapping the carb when I get home.
I suspect gas is getting past the needle and seat, even though they were both replaced when I cleaned the carb.
I suppose I could use some fittings to put a pressure gauge on the carb, and if that's the culprit, I'll go with a regulator.
 
How much cam?

Even if the carb is whacked, it should smooth out at 1500 or so imo. The carb might be a problem, but it sounds like you might have other issues. What sort of ign timing curve are you running? Vac advance? Ported or manifold?


Even so, some rambling on carbs:

Are you sure that the power piston is not sticking? You can stick something into the vent, and push the power piston ass'y down. A piece of drinking straw will sit on it to tell you if it is staying down at idle. A blip on the throttle should cause it to rise.


How old is the float? I always replace it, as they break down and suck up fuel, making them heavy.

Always test the needle/seat with a "mighty vac" hand pump. 3/8" hose on the seat, adapted down to the tester. It should hold vac. If not, and the needle looks ok, reform the seat, using an old pump check ball. Set the seat on a steel bench or vice etc, and drop a steel ball in, and whack it with a blunt punch. Re-test.

With a lumpy cam, there usually isn't enough idle air with the throttle plates set where they should be, and there also isn't enough idle fuel [signal is low], so the throttle plates must be opened more. This exposes all of the transfer slots, and more fuel flows there, so closing the idle mix screws off doesn't make the engine lean. This sometimes also causes the main circuit to start. There should be NO fuel dripping from the boosters at idle or off idle. The main circuit should not start at light throttle until well over 2000 rpm. Probably closer to 2500 imo.

At curb idle, there should be only 40-50 thou of the transfer slots exposed under the throttle plates. If more of them is exposed, you need more idle air. Most carbs have idle bypass air, and the holes in the throttle body can be enlarged. I'd try 60-70 thou to start [they are usually smaller]. If the carb doesn't have bypass air, the throttle plates can be drilled to give it more idle air. Start at 90 thou or so, enlarge until it'll idle with 40-50 thou of the tranfer slots exposed.

Also, sometimes the idle mix screw springs don't allow the idle mix screws to close off all the way. If that's the case, you can snip a few coils from the screws.

Dave
get the ruggles QJ book, and the Rowe QJ book
 
> The carb should run out of fuel with the idle mixture screws all the way in, right?
Right? :listen:


Btw, the idle screws only set the amount of fuel coming from the discharge holes. The rest of the idle fuel comes from the transfer slots. The amount of the slots exposed under the throttle plates effects the amount of fuel coming from the slots. Off idle, the engine gets all of it's fuel from the holes and slots.

Actually, once the carb is working properly, it'll probably want more idle and off idle fuel. Larger holes in the bottom of the idle tubes and idle down channel restriction orifices required for that. Did I mention those books? :soapbox:

Dave 
 
I have the Doug Roe book, as well as the 74 Factory Shop Manual.
The float was replaced with a new one when I rebuilt (clean & kit job), as well as the needle, seat, rods & jets to factory specs.
This is on my '74, which is bone stock. Stock cam, exhaust, intakle, etc. The dizzy is turned as far as it would go before the vacuum advance stopped against the ac compressor. It is advanced a bit, but it's fairly mild. I have never had a
The vacuum lines are all connected according to the factory manual.

I wonder about the transfer slots. If I adjusted the fast idle screw wrong, could that be the problem? Maybe I should back it off a bit & see what happens. 
 
Hmm.

I would disconnect and cap ALL vaccum lines on the engine and carb and see what happens. If it improves, you could track the problem down. If now, it's hard to say where to start.

Dave
p.s. - yes, Roe, not rowe....



Weird
tommyhawk13 said:
I have the Doug Roe book, as well as the 74 Factory Shop Manual.
The float was replaced with a new one when I rebuilt (clean & kit job), as well as the needle, seat, rods & jets to factory specs.
This is on my '74, which is bone stock. Stock cam, exhaust, intakle, etc. The dizzy is turned as far as it would go before the vacuum advance stopped against the ac compressor. It is advanced a bit, but it's fairly mild. I have never had a
The vacuum lines are all connected according to the factory manual.

I wonder about the transfer slots. If I adjusted the fast idle screw wrong, could that be the problem? Maybe I should back it off a bit & see what happens. 
Click to expand...
 
You must log in or register to reply here.
Back
Top