Quadrajet problems

[Richard R.]

72 base 350, orginal carter quadrajet. I rebuilt 4 years ago and has performed perfectly UnTiLL recently. Cruising at 35 mph it suddenly starts to lose power (running really rich), play with accelerater to clear out and then runs fine for a few minutes and same thing occurs, let it idle and it dies. Removed air cleaner and started up, ran fine for a couple of minutes then started to die and could see fuel running over float chamber. Removed top of carburator, float did not seem to have fuel inside, did not see any junk in bowel, removed needle and seat, no visible problem. Squirted carb cleaner in jets and reassembled with same results as before. Is their something In particular I should be looking for or just another rebuild?

[Patrick H.]

Re: Quadrajet problems

How old is the float, and what type is it?
That's my first suspect.

[Richard R.]

Re: Quadrajet problems

It's black plastic, could be the orginal.

[Joe L.]

Re: Quadrajet problems

It's black plastic, could be the orginal.

Richard------


I also suspect the float, a very common Q-Jet problem. The original nitrophyl (plastic) float was dark brown in color but may appear "black". Replace it. The GM part is discontinued. Use Standard Motor Products #FL1.

[Mark E.]

Re: Quadrajet problems

As they age, the plastic Q-Jet floats absorb gasoline which reduces their buoyancy. The result is a higher fuel level in the bowl. As Joe suggests, replace it. It's a good practice to replace the float whenever a rebuild kit is installed. You might also replace the needle and seat while you're in there.

As a final check, look down the air horn with a flash light where the secondary metering rods are located. If the float level is adjusted properly, the fuel level should be below the air horn gasket while the engine is running.

[Patrick H.]

Re: Quadrajet problems

You might also replace the needle and seat while you're in there.

In my experience the currently available needles and seats are junk. You have to look to find good ones. As a result I usually leave them alone.

[Douglas L.]

Re: Quadrajet problems

In my experience the currently available needles and seats are junk. You have to look to find good ones. As a result I usually leave them alone.

I agree, I've found that lowering the float level(just a little bit) seems to help.

[Mark E.]

Re: Quadrajet problems

I agree, I've found that lowering the float level(just a little bit) seems to help.

If your set-up is completely stock, and no modications have been made anyplace, use the stock float setting. I wouldn't suggest lowering the float level to compensate for a fuel-logged float. Just replace the float. Take the measurement from the casting to the toe of the float, no gasket in place.

I also suggest replacing an old needle/seat. It's critical these components be able to hold a seal against incoming fuel pressure. I understand the quality of carb parts varies a lot and it's hard to judge them by just looking. But there are sources for good quality Q-Jet parts; Cliff's High Performance is one. I've had good luck with their kits and floats.

[Dan P.]

Re: Quadrajet problems

Sound like a needle and seat have a little varnish on them from setting. The best way to clean them is to pinch off the the rubber inlet hose to the fuel pump. Start the motor and as it is running out of gas release the hose .The float has dropped down and the fuel rushing in will clean the needle and seat . You may have to do this several times. When the carb floods over the needle is lock to the seat until the float drops .

[Mark E.]

Re: Quadrajet problems

Sound like a needle and seat have a little varnish on them from setting. The best way to clean them is to pinch off the the rubber inlet hose to the fuel pump. Start the motor and as it is running out of gas release the hose .The float has dropped down and the fuel rushing in will clean the needle and seat . You may have to do this several times. When the carb floods over the needle is lock to the seat until the float drops .

Faulty floats, needles and seats are a leading cause of engine fires. Why mess with them? Replacing them isn't expensive or difficult.

[Richard R.]

Re: Quadrajet problems

Bought a rebuild kit and a new float and rebuilt today. Needle and seat looked ok but I think their was fuel in float. Anyway disassembled, cleaned and blew out passages and reassembled. Ran like it was suppose to, so I think the problem was the float. Thanks to everyone who steered me in the right direction.

[Mark E.]

Re: Quadrajet problems

Good deal.

For others, it might be worth mentioning to use the correct float. Don't install a brass float in Q-Jets designed for a solid plastic float, and visa-versa. More than once, I've had parts stores try to sell me a hollow brass float as a "better" quality replacement for the original plastic float.

[Richard R.]

Re: Quadrajet problems

I always take the old part with me to make sure I am getting the correct replacement part. The new float matched the old one in this case. The float and the rebuild kit were from HYGRADE and seem like good guality. The rebuild kit had gaskets and other parts that were specific to my 7042202 carburator and not a box full of universal gaskets.

[Mark E.]

Re: Quadrajet problems

I've found the quality of kits from most parts houses hit or miss.

A few years ago I began using kits from Cliff's High Performance. They contain a Viton .135" needle/seat assembly, complete accelerator pump assembly (not just the plunger), float, fuel filter w/spring, all made in the US with materials compatible with Ethanol.

Be careful with kits using black rubber pump seals. Ethanol softens and swells them. I've seen needles not holding up either; I suspect the tip was not Viton.

[Richard R.]

Re: Quadrajet problems

The pump pump seal was blue for what that's forth.