440 hesitates on light throttle

[71GTXdragpack]

Post number 56

I hate to say it, but after running great for almost a year, the hesitation is back. I'm going to order the AVS rebuild kit this time.

 

[Geoff 2]

These type of carbs rarely cause problems or lose their adjustment. Before spending $$$, why not tell us the EXACT symptoms, plus anything else that has been done to the car/engine.

 

[Orig69]

The hot weather that we have lately can easily cause minor vapor lock which will make it stumble.

 

[RJRENTON]

I hate to say it, but after running great for almost a year, the hesitation is back. I'm going to order the AVS rebuild kit this time.

The Carter AVS is a great carb. Since you're going to rebuild it anyway, when you disassemble it for cleaning prior to rbuilding ir, pay particular attention to the PRIMARY BOOSTER ASSEMBLIES, as these control the idle, off idle fuel metering function. There are small drilled passage ways in the assembly. It's possible that one of these internal restrictions have accumulated crud, upsetting the idle mixture and off idle fuel causing your hesitation experienced. Soak the primary BOOSTER ASSEMBLIES in solvent and blow out all passages with compressed air....and make sure that the gaskets are oriented correctly upon re assembly. The idle and off idle fuel mixture transitions to the idle mixture screws and off idle transfer slots thru internal passages.
BOB RENTON

 

[71GTXdragpack]

These type of carbs rarely cause problems or lose their adjustment. Before spending $$$, why not tell us the EXACT symptoms, plus anything else that has been done to the car/engine.

symptoms are as follows, the engine misses or hesitates during very light throttle during cruising. Anything more than light throttle the miss or hesitation seems to go away but returns as soon as I'm off throttle.

 

[71GTXdragpack]

The Carter AVS is a great carb. Since you're going to rebuild it anyway, when you disassemble it for cleaning prior to rbuilding ir, pay particular attention to the PRIMARY BOOSTER ASSEMBLIES, as these control the idle, off idle fuel metering function. There are small drilled passage ways in the assembly. It's possible that one of these internal restrictions have accumulated crud, upsetting the idle mixture and off idle fuel causing your hesitation experienced. Soak the primary BOOSTER ASSEMBLIES in solvent and blow out all passages with compressed air....and make sure that the gaskets are oriented correctly upon re assembly. The idle and off idle fuel mixture transitions to the idle mixture screws and off idle transfer slots thru internal passages.
BOB RENTON

I agree Bob. I'm unfortunately not knowledgeable enough to determine if this hesitation is a electrical or fuel issue. The car ran great for almost a year once I updated to Petronix but now the irritating miss/hesitation has returned.

 

[71GTXdragpack]

The hot weather that we have lately can easily cause minor vapor lock which will make it stumble.

shouldn't the vapor lock be gone once the fuel cools down? After the car sat for a few days, I took it for a test ride and the hesitation was there right away.

 

[Geoff 2]

Sometimes a more powerful ign system can cause a lean surge. Try this simple test: warm up engine, engine idling [ in gear if auto trans ]. Slowly close the choke blade on the carb until the engine note changes. Wire choke in this position & test drive.
If the miss is better/gone, then the carb is lean. Report back for a fix.

 

[Orig69]

shouldn't the vapor lock be gone once the fuel cools down? After the car sat for a few days, I took it for a test ride and the hesitation was there right away.

Is this the first time you have driven it this summer?

Does the tank have old gas in it from last year?

Have you checked for vacuum leaks?

What temperature does the engine run at?

 

[71GTXdragpack]

Is this the first time you have driven it this summer?

Does the tank have old gas in it from last year?

Have you checked for vacuum leaks?

What temperature does the engine run at?

I replaced with Petronix about the same time last year. Car has been running great until recently. Car has fresh fuel. I sprayed some carb cleaner near the base of the carb at the gasket and did notice a slight increase in rpm. Car never overheats etc even in very hot conditions.

 

[71GTXdragpack]

Sometimes a more powerful ign system can cause a lean surge. Try this simple test: warm up engine, engine idling [ in gear if auto trans ]. Slowly close the choke blade on the carb until the engine note changes. Wire choke in this position & test drive.
If the miss is better/gone, then the carb is lean. Report back for a fix.

it's a four speed. I will try this today and report back.

 

[Orig69]

I replaced with Petronix about the same time last year. Car has been running great until recently. Car has fresh fuel. I sprayed some carb cleaner near the base of the carb at the gasket and did notice a slight increase in rpm. Car never overheats etc even in very hot conditions.

Check to see if the carb hold down bolts are loose.

You can use a vacuum gauge and unplug the vacuum advance at the carb plug the vacuum port and see if the gauge reading changes. You can do the same thing with the choke pull-off.

Same thing with the original air cleaner I believe there is a vacuum port on the back of the carb for that.

 

[71GTXdragpack]

Check to see if the carb hold down bolts are loose.

You can use a vacuum gauge and unplug the vacuum advance at the carb plug the vacuum port and see if the gauge reading changes. You can do the same thing with the choke pull-off.

Same thing with the original air cleaner I believe there is a vacuum port on the back of the carb for that.

bolts are all secure and all the screws on the body of the carb. I sprayed the carb base area with carb cleaner and could hear the idle change. Assuming that indicates a small vacuum leak at the gasket?

 

[Orig69]

bolts are all secure and all the screws on the body of the carb. I sprayed the carb base area with carb cleaner and could hear the idle change. Assuming that indicates a small vacuum leak at the gasket?

Yes if the carb hold down bolts are snug then that would be a minor vacuum leak.

A high quality carb rebuilt kit will come with that thick carburetor heat insulator gasket or you can just buy the gasket.