69 Quadrajet fuel filters, and float setting

[Paul K.]

1. is it necessary to install the carburetor inlet paper fuel filter if the stock fuel line filter is installed?

2.WOT 427/390 pulls hard to 4500 rpms, then bogs big time, no sputter, just bog. ( Like there is no more fuel)
I reset the float from 3/8 to 1/4, I have the stock jetting, and primary rods, stock secondary rods, secondary rod hanger in spec
Do you think resetting the float will help??

Paul Klemetson (372780

[Russ S.]

Re: 69 Quadrajet fuel filters, and float setting

Have you checked the condition of the fuel screen in the tank?

[Mark E.]

Re: 69 Quadrajet fuel filters, and float setting

1. Great question. Every Q-Jet I've seen has a filter at the inlet, yet I believe '69 Corvettes have an inline filter between the pump and carb. If you don't get a definitive answer here, try posting the question to the forum at http://cliffshighperformance.com . Cliff is a true authority on Q-Jets, plus his forum has an active community of knowledgeable folks.

2. A couple things to check. First, is there sufficient fuel volume? Low fuel volume can cause starvation problems during heavy loads at higher RPM. If low, then check the pump, fuel filter, pick up screen, and fuel lines. Second, is there sufficient air volume? Likely suspects are a restricted air cleaner, stuck choke, improperly adjusted throttle linkage (butterfly valves not fully open with the accelerator floored), and secondary air doors improperly adjusted.

Check throttle adjustment by looking down the carb. with a flashlight while an assistant holds the pedal to the floor (with the engine off, of course). Adjusting secondary air door spring tension varies how quickly/slowly they open. Opening too quickly causes an immediate lean condition which feels like a "bog" as soon as the accelerator is pressed. Opening too slowly restricts air flow, which feels like the engine is running out of breath (which it is).

The FSM describes how to check fuel pump volume and adjust the secondary air door tension.

[Joe L.]

Re: 69 Quadrajet fuel filters, and float setting

1. is it necessary to install the carburetor inlet paper fuel filter if the stock fuel line filter is installed?

2.WOT 427/390 pulls hard to 4500 rpms, then bogs big time, no sputter, just bog. ( Like there is no more fuel)
I reset the float from 3/8 to 1/4, I have the stock jetting, and primary rods, stock secondary rods, secondary rod hanger in spec
Do you think resetting the float will help??

Paul Klemetson (372780

Paul------


You need to install the carb inlet filter regardless that 1968-69 also use a in-line filter (GF-432). The inlet filter will cause no problems, whatsoever. If you have carb problems, the inlet filter has nothing to do with it.

[Mark E.]

Re: 69 Quadrajet fuel filters, and float setting

Paul------


You need to install the carb inlet filter regardless that 1968-69 also use a in-line filter (GF-432). The inlet filter will cause no problems, whatsoever. If you have carb problems, the inlet filter has nothing to do with it.

Joe,

Why do you think these cars were designed with two fuel filters?

[Joe L.]

Re: 69 Quadrajet fuel filters, and float setting

Joe,

Why do you think these cars were designed with two fuel filters?

Mark------

The GF-432 external filter provides two functions: first, it obviously provides fuel filtering. Second, though, it provides the fuel return nipple which provides for fuel return to the tank. With Q-Jets GM liked to have fuel return. So, I believe the primary purpose of the GF-432 was to enable the fuel return function.

For 1970 new fuel pumps were introduced which included a fuel return from the fuel pump. Curiously, and not-so-coincidentally, the in-line filter disappeared at the same time.

So, with the in-line filter used for 1968-69, why did the fuel inlet filter remain? Well, I strongly suspect it was because the Q-Jet was designed to function with an inlet filter, whether or not that filter was necessary for all applications. Removing the filter can "disrupt" the proper overall functioning of the carb.

[Paul K.]

Re: 69 Quadrajet fuel filters, and float setting

Thank you all for your information, I did reinstall the carb filter, did some other adjusting, hopefully when spring come's, I can open the big door and take it for a drive, and see if I have solved the problems.

Paul Klemetson

[Patrick H.]

Re: 69 Quadrajet fuel filters, and float setting

hopefully when spring come's, I can open the big door and take it for a drive, and see if I have solved the problems.

Paul Klemetson

I would suspect not.

I would check the secondary air valve adjustment.

[Mark E.]

Re: 69 Quadrajet fuel filters, and float setting

Mark------

So, with the in-line filter used for 1968-69, why did the fuel inlet filter remain? Well, I strongly suspect it was because the Q-Jet was designed to function with an inlet filter, whether or not that filter was necessary for all applications. Removing the filter can "disrupt" the proper overall functioning of the carb.

Thanks Joe. I know some Q-Jets have a fuel inlet filter with a valve that prevents the fuel bowl from draining with the engine off.

Also, maybe this filter helps regulate/diffuse the flow of fuel to the needle/seat?

[Gene M.]

Re: 69 Quadrajet fuel filters, and float setting

1. is it necessary to install the carburetor inlet paper fuel filter if the stock fuel line filter is installed?

2.WOT 427/390 pulls hard to 4500 rpms, then bogs big time, no sputter, just bog. ( Like there is no more fuel)
I reset the float from 3/8 to 1/4, I have the stock jetting, and primary rods, stock secondary rods, secondary rod hanger in spec
Do you think resetting the float will help??

Paul Klemetson (372780

It sounds like the engine just stops pulling hard. I suggest look at the advance curve since you have no sputter. Your indicators do not sound like fuel starve, but could need air......... Air cleaner off and try again.