I will pull the carb & inspect the diaphragm.
(Probably) Simple Carb Question
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Laughing Gas
Joined: Aug 2010
Posts: 1,049
Likes: 230
From: Amarillo, TX
(Probably) Simple Carb Question
I have a 670cfn Holley street avenger on my 400. Recently(about the last year), it's bogging & dying whenever I hammer the throttle - If I don't roll into it gradually. My first thought is accelerator pump; is it most likely not giving a big enough shot & stalling, or giving too big a shot & flooding? Starts right back up after it dies, & no other driveability issues.
Hotshot
Joined: Feb 2004
Posts: 10,847
Likes: 2,615
From: The Shenandoah Valley
You didn't put a screw in the secondary slot did you?
If not, then my guess is likely the single accelerator pump under the primary float bowl has a busted diaphragm, and is delivering near NO shot.
Hotshot
Joined: Jul 2020
Posts: 10,549
Likes: 2,669
From: Near Salt Lake City
No need to pull the carb to inspect the diaphragm, you can visually inspect the squirt and then pull the carb if it needs replacement.
What tbear853 means (I think) is that if you install a screw in the secondaries, it will lock out the accelerator pump.
I believe that is just for the double pumpers but your 670 may be a double pumper
Those plastic accelerator pump cams are replaceable and adjustable by color and the slot the screw goes in
That adjustment times when the accelerator pump shot is delivered.
You can also get a 50cc pump housing and diaphragm.
The nozzles are also numbered and are adjustable by diameter
It is common for the steelie or weight to stick down under the nozzle rendering the pump inop
What tbear853 means (I think) is that if you install a screw in the secondaries, it will lock out the accelerator pump.
I believe that is just for the double pumpers but your 670 may be a double pumper
Those plastic accelerator pump cams are replaceable and adjustable by color and the slot the screw goes in
That adjustment times when the accelerator pump shot is delivered.
You can also get a 50cc pump housing and diaphragm.
The nozzles are also numbered and are adjustable by diameter
It is common for the steelie or weight to stick down under the nozzle rendering the pump inop
Logistics Pro
Joined: May 2015
Posts: 4,474
Likes: 974
From: Tri Cities, TN
Agree that there is no need to pull the carb to check the squirt. Did this problem exist when you first installed the carb?
I have a 670 Avenger on my truck right now and they are decent entry level carburetors but not very tunable without doing surgery on the metering block.
Along with just moving the accelerator and looking at the squirter make sure the accelerator pump linkage is properly adjusted. It should start squirting fuel the instant the throttle is moved. Also, if your idle mixture screws are less than 1 turn out it can starve the transition circuit for fuel and cause a stumble.
Almost all the Holley Street carbs come with a number 31 squirter the first thing I do before I put one on is put a 35 squirter in there.
I have a 670 Avenger on my truck right now and they are decent entry level carburetors but not very tunable without doing surgery on the metering block.
Along with just moving the accelerator and looking at the squirter make sure the accelerator pump linkage is properly adjusted. It should start squirting fuel the instant the throttle is moved. Also, if your idle mixture screws are less than 1 turn out it can starve the transition circuit for fuel and cause a stumble.
Almost all the Holley Street carbs come with a number 31 squirter the first thing I do before I put one on is put a 35 squirter in there.
Hotshot
Joined: Feb 2004
Posts: 10,847
Likes: 2,615
From: The Shenandoah Valley
There are people who have put a self threading screw into that slot next to the link to force the secondaries open. To do so before rpms are up, with no secondary accelerator pump, creates a really huge bog "BWAAAAA" as it falls flat on it's face ... as suddenly the engine gets extra air, but no extra fuel. Air alone doesn't burn.
No joke, that was all.
Thread Starter
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Laughing Gas
Joined: Aug 2010
Posts: 1,049
Likes: 230
From: Amarillo, TX
Well, I've verified I am getting a squirt from the accelerator pump. Pretty sure the secondary linkage has not been manipulated. I assume the next step is to adjust the accelerator pump linkage - should I try a smaller shot first?
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Logistics Pro
Joined: May 2015
Posts: 4,474
Likes: 974
From: Tri Cities, TN
If it was working when you first installed it and it's not now, something changed. You need to start it let it idle for a minute or two then pull the brass plug form the front bowl and make sure the float level is correct. But I will say the golden rule is ignition before carburation. If you want to change squirters go bigger if it is too big all it will do is cause it to blow a little black smoke when you floor it. But keep in mind a bigger squirter will give you more fuel at the beginning but it won't last as long. In other words, a 35 nozzle will give you 30cc really quick, but a 31 will spread it over a longer period, but no matter what size nozzle you will still get 30cc. A 50cc pump is not needed on a 400 unless you have a tunnel ram intake.
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