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quadrajet carby

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kunbarrie

Contributing Member
problem started a while ago,running rough when cold starting,evened out when warm,thought it might be the choke,check
ed works ok,now when started runs to rich,fuel dribbling from main jet discharge nozzles [both sides]have checked float and fuel level,seems ok.carby replaced 2years ago same model no as original carby with electric choke fitted,came from an american company,[national carbureters i think]what else can force fuel from discharge nozzles other than flooding float bowl, thanks for any advice
 
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Hey, that's my exact motor. Good little rig.

She's flooding on you for certain and needs a rebuild. (Nothing lasts forever.) Also, a tank of bad gas can raise all kinds of hell. A case in point:

When I first ran my boat, it stalled right out when it planed off--brownish crap in the filter inside the carb. Cleaned it out several times and replaced the main filter, but the brownish crap (that went right through the main filter) kept reappearing. (Surprisingly, the carb did not flood on me, the particles apparently being small enough to pass through.)

Eventually I had to pump the entire tank out and replace all the fuel before the problem went away. You might have to do the same.

Jeff

PS: Happy New Year all!
 
may be dirt....

I'd start by lowering the idle speed (try for 650, in gear).

"nozzle drip" is more frequently seen on big blocks, especially when the idle speed is elevated. due to the efficient design of the nozzle assembly.
 
kunbarrie said:
problem started a while ago,running rough when cold starting,evened out when warm,thought it might be the choke,check
ed works ok,now when started runs to rich,fuel dribbling from main jet discharge nozzles [both sides]have checked float and fuel level,seems ok.carby replaced 2years ago same model no as original carby with electric choke fitted,came from an american company,[national carbureters i think]what else can force fuel from discharge nozzles other than flooding float bowl, thanks for any advice
Click to expand...

Got here really late. Did you get the problem fixed? Be interested to know what you found.....

I've had a lot of experience whth Q-Jets on cars, trucks and boats. In my experience, when I encounter this problem, I have found that the primary needle assembly gets hung up. You can check this by accessing the top or the needle assembly through an opening in the top of the carb. the assembly is a spring-loaded piston with a "tee" on the top that carries both of the needles. Use a small screwdriver and poke at the tee. if the assembly is hung up, you'll notice - feel - it immediately. you can usually free it up by poking, wiggling, and cycling the assembly up and down against the spring on the bottom of the piston. If you can free it up, the motor will idle and run just fine. For a while.

If this turns out to be the problem, you gotta figure out what causes it to hang. It could be crud, or there could be a problem with the carb that requires replacement (I've had to replace a couple carbs, even went to a Holley on a truck I had).

Would appreciate knowing how you (finally?) addressed your problem.
 
BenThere said:
Got here really late. Did you get the problem fixed? Be interested to know what you found.....

I've had a lot of experience whth Q-Jets on cars, trucks and boats. In my experience, when I encounter this problem, I have found that the primary needle assembly gets hung up. You can check this by accessing the top or the needle assembly through an opening in the top of the carb. the assembly is a spring-loaded piston with a "tee" on the top that carries both of the needles. Use a small screwdriver and poke at the tee. if the assembly is hung up, you'll notice - feel - it immediately. you can usually free it up by poking, wiggling, and cycling the assembly up and down against the spring on the bottom of the piston. If you can free it up, the motor will idle and run just fine. For a while.

If this turns out to be the problem, you gotta figure out what causes it to hang. It could be crud, or there could be a problem with the carb that requires replacement (I've had to replace a couple carbs, even went to a Holley on a truck I had).

Would appreciate knowing how you (finally?) addressed your problem.
Click to expand...

ended up by buying a reco carby from the usa put it on ,started same problen,contacted the supplier he said fuel pmp,put a new pump on and fixed it,now after being a qualified motor mechanic here in aus for 50 years i have never seen a mechanical fuel pump over pressure,only seen leaking or no pressure[broken spring in a valve],always learning,have a new problem now ,when at idle 800rpm intermitent back fire from carby,and can hear strange noise from around no 7 cylinder ,possible inlet valve hydraulic cam follower problem or sticky valve.
 
kunbarrie said:
ended up by buying a reco carby from the usa put it on ,started same problen,contacted the supplier he said fuel pmp,put a new pump on and fixed it,now after being a qualified motor mechanic here in aus for 50 years i have never seen a mechanical fuel pump over pressure,only seen leaking or no pressure[broken spring in a valve],always learning,have a new problem now ,when at idle 800rpm intermitent back fire from carby,and can hear strange noise from around no 7 cylinder ,possible inlet valve hydraulic cam follower problem or sticky valve.
Click to expand...
Well, I've been around a while too, and I've never seen a mechanical pump over pressure either.

Had an '82 Chevy truck with a 305 and a Q-Jet that did a similar thing, started popping back through the carb especially under load. Seemed to idle OK, but when you started giving it revs, it'd pop back. Figured it had a sticky valve (unlikely), or a bad lifter or valve, or maybe a flat cam lobe. Compression was OK on all, so I decided to remove the valve cover on the side I heard something and run the motor. Sure enough, one of the rockers wasn't "rocking" as much as the others; on #7. Pulled the intake a verified the cam was flat on that one lobe. Took advantage of the situation to put a hotter, "RV" cam that increased power across the range but was specially tuned for low and mid-range power which turned out perfect for my 4X4 truck off road and especially pulling the boat. I really noticed the improvement pulling the 4,000 pound boat up long hills.

Good luck with your latest challenge. You know what they say about a boat being a hole in the water you pour money through......:(
 
I seem to remember that some of the Composition floats used on some Quadrajets would actually break down, absorb gasoline(Ethanol?) and no longer have enough buoyancy to properly shut the float needle when the bowl was full. There was no way of visually checking these floats but when removed, there was a definite weight difference. One test involved actually putting them into an open tray of gasoline to observe their buoyancy. I am not sure if this comment is still relative in 2020....it might be 20 year old advice.
 
The preferred test is to weigh the float. The rochester provided floats (composite) wasn't bad....the big issue is the aftermarket suppliers aren't always as selective. Since rochester isn't around, you have to find a trusted source and stick with them....
 
..."The rochester provided floats (composite) wasn't bad...."

THEY were the problem; the aftermarket ones (good ones) were far better.

Jeff
 
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