She is sitting on my 250 IL. 2 barrel. The picture shows a port that while running and I put my finger over the opening I feel a patter, like a fast acting suction then pushing. It’s under the automatic choke. It has threads on it. Wondering what its function is? Also behind it (it’s not clear in the picture) is a screw that looks like a mixture screw. I can’t tell it does anything while the motor is running. Anyone know what it is for? Thanks.
Last edited by Gdads51; 02/23/20242:18 PM. Reason: remove pic link from text to allow attachments to all display
1953 Chevy 153A 3/4-ton Working on my project since 2015 Follow along in my DITY
The threaded flare port on the choke housing is used for warming the choke from an exhaust heat stove, a metal line would run from that port to an exhaust heated coil of tubing. You need to cap that port with a flare cap since you have an electric choke, (like a 75 Johnson, electric choke). Also, if there are any other open nipples or ports on the carburetor, those need to be capped. The adjustment screw under the choke is a fast idle adjustment, it works in conjunction with the choke, when the choke is automatically fully closed, that screw will be on the highest step of the fast idle cam, as the choke warms up, the cam drops down to progressively slower steps, If the engine is way too fast or blowing black smoke on a cold start-up, you need to adjust the fast idle screw. Are you running with 2 PCV valves? one of those PCV hoses should have a PCV valve, the other hose should be connected to filtered air with no valve in the rocker cover.
Last edited by 78buckshot; 02/23/202411:46 AM.
1957 Chevrolet 5700 LCF 283 SM420 2 speed rear, 1955 IH 300U T/A, 1978 Corvette 350 auto, 1978 Yamaha DT175, 1999 Harley Davidson Softail Fat Boy
Is there some reason you're choosing to use an offshore copy of a Ford V8 carburetor on a Chevy six engine? There's no telling if the calibration is even in the right ballpark for the size of the engine- - - -probably not. It looks like you're deliberately stacking the deck against yourself. Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt! There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway Love your enemies and drive 'em nuts!
The threaded flare port on the choke housing is used for warming the choke from an exhaust heat stove, a metal line would run from that port to an exhaust heated coil of tubing. You need to cap that port with a flare cap since you have an electric choke, (like a 75 Johnson, electric choke). Also, if there are any other open nipples or ports on the carburetor, those need to be capped. The adjustment screw under the choke is a fast idle adjustment, it works in conjunction with the choke, when the choke is automatically fully closed, that screw will be on the highest step of the fast idle cam, as the choke warms up, the cam drops down to progressively slower steps, If the engine is way too fast or blowing black smoke on a cold start-up, you need to adjust the fast idle screw. Are you running with 2 PCV valves? one of those PCV hoses should have a PCV valve, the other hose should be connected to filtered air with no valve in the rocker cover.
Yes 2 PCV valves. One goes into a vacuum port (I think) the other is connected to the inside of the breather air filter. It cranks up almost instantly but it will cut off if I don’t keep it running with the gas pedal. After a few minutes it continues to idle very well.
Last edited by glennj3; 02/23/20246:05 PM.
1953 Chevy 153A 3/4-ton Working on my project since 2015 Follow along in my DITY
Is there some reason you're choosing to use an offshore copy of a Ford V8 carburetor on a Chevy six engine? There's no telling if the calibration is even in the right ballpark for the size of the engine- - - -probably not. It looks like you're deliberately stacking the deck against yourself. Jerry
This carb was on it when I bought it 17 years ago. If it has a problem I don’t know what it is. It may be running a little rich as I see it on my finger after rubbing it inside the exhaust pipe.
1953 Chevy 153A 3/4-ton Working on my project since 2015 Follow along in my DITY
Is that the vacuum port? I can’t tell from the pictures.
There is a Nipple below the electric choke that I connected the timing advance hose to. But I can’t tell it has vacuum on it. The timing does advance well as the motor accelerates. I could put my vacuum gauge on it & see. I’ll post some more pictures. I don’t see how that screw regulates anything? I found 2 screws on the side i believe are idle adjuster screws?
Last edited by glennj3; 02/23/20245:09 PM.
1953 Chevy 153A 3/4-ton Working on my project since 2015 Follow along in my DITY
The 2 brass screws with springs that are threaded into the aluminum body of the carburetor are idle mixture screws, the screw behind the choke should be a fast idle adjustment, and the screw near the throttle cable is curb idle adjustment. The PCV hose that is connected to the air cleaner housing should not have a PCV valve on the other end, that hose admits fresh air into the engine crankcase, the PCV valve and hose suck the combustion blowby gases out of the crankcase and re-burn them. If it's running well enough for your use then "if it ain't broke, don't fix it"
1957 Chevrolet 5700 LCF 283 SM420 2 speed rear, 1955 IH 300U T/A, 1978 Corvette 350 auto, 1978 Yamaha DT175, 1999 Harley Davidson Softail Fat Boy
Good luck, guys- - - -I've seen so many glaring mistakes on this one I'm running out of fingers to count them on, and I don't really want to take my shoes off!
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt! There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway Love your enemies and drive 'em nuts!
The 2 brass screws with springs that are threaded into the aluminum body of the carburetor are idle mixture screws, the screw behind the choke should be a fast idle adjustment, and the screw near the throttle cable is curb idle adjustment. The PCV hose that is connected to the air cleaner housing should not have a PCV valve on the other end, that hose admits fresh air into the engine crankcase , the PCV valve and hose suck the combustion blowby gases out of the crankcase and re-burn them. If it's running well enough for your use then "if it ain't broke, don't fix it"
It runs great but I’d like to have it functioning best as possible.
So what is used to connect the hose from breather to the valve cover if not a pvc? Do I have the rear PCV valve hose connected to the carburetor base correctly? I checked the niple that the timing advance hose connects to with a vacuum tester. It reads 15 lbs at fast idle, slow idle not anything. Thanks for the help!
Last edited by glennj3; 02/24/202412:34 AM.
1953 Chevy 153A 3/4-ton Working on my project since 2015 Follow along in my DITY
The threaded flare port on the choke housing is used for warming the choke from an exhaust heat stove, a metal line would run from that port to an exhaust heated coil of tubing. You need to cap that port with a flare cap since you have an electric choke, (like a 75 Johnson, electric choke). Also, if there are any other open nipples or ports on the carburetor, those need to be capped. The adjustment screw under the choke is a fast idle adjustment, it works in conjunction with the choke, when the choke is automatically fully closed, that screw will be on the highest step of the fast idle cam, as the choke warms up, the cam drops down to progressively slower steps, If the engine is way too fast or blowing black smoke on a cold start-up, you need to adjust the fast idle screw. Are you running with 2 PCV valves? one of those PCV hoses should have a PCV valve, the other hose should be connected to filtered air with no valve in the rocker cover.
The fast idle cam does not work. Maybe it’s not adjusted right? My VW works like that one. It keeps the motor running faster until it warms up and I press the throat to release it.
1953 Chevy 153A 3/4-ton Working on my project since 2015 Follow along in my DITY
The PCV hose from the air cleaner base to the rocker cover could use just a simple hose barb elbow, something like a 3/8" x 3/8" hose angle might work, or you could try to take the spring and disc out of the PCV valve so it's an open connector. For the fast idle you could screw it in a couple of turns to see if it increases the cold idle. For the vacuum advance, I don't know what is spec'd for that application, right now you have it connected to a ported vacuum source so at curb idle it is not advancing the timing. Off idle and above it will advance the timing as vacuum dictates. Someone here probably has more info for that application.
Last edited by 78buckshot; 02/24/20242:23 AM.
1957 Chevrolet 5700 LCF 283 SM420 2 speed rear, 1955 IH 300U T/A, 1978 Corvette 350 auto, 1978 Yamaha DT175, 1999 Harley Davidson Softail Fat Boy
