65 273 Carter AFB won't start

-
RichB

RichB

CherryCuda65
Joined
Feb 10, 2016
Messages
295
Reaction score
139
Location
South Carolina
I'm down to a few punch list problems on the full restoration of my 65 Barracuda. A big one is that I have not been able to get the 273 to start up normally with the Carter AFB 4 bbl #3854S carburetor. I have tried two different kits and had an old mechanic try his hand but its not right.
When I do get it running with a lot of cranking and pumping it will run but doesn't want to idle down and stay running until its real warm. There is 4 - 6 psi from the fuel pump. The carb has never been completely rebuilt but has a new accel. pump, new needle and valve seats, and factory clearance specs on the floats and the choke. The ignition has a new coil and new condenser.
Before I give up on the Carter carb and buy a new Edelbrock I'm hoping that some fellow members can help solve the problem. Any idea?
 
Murray said:
Why do you think the problem is carb?
Click to expand...
Murray could be right. Here is an easy way to diagnose whether you have a carb problem. Do you know someone with a known good 4 bbl carb who would allow you to do a quick swap to test whether the problem truly is the carb? If you put a known good carb on and it runs beautifully, you will know the problem is your carb. Then you have a choice to make. Spend money on a professional rebuild or buy a new one. I realize that kits are available, and a LOT of people on this site will tell you how easy it is to rebuild a carb. I consider myself to be an excellent mechanic. I have rebuilt engines, rebuilt transmissions, converted my car from an auto to a 4 speed, etc, but I have never had much luck with carburetors. I CAREFULLY follow the instructions, but I just don't have much luck. By all means, try to rebuild it yourself if you want, but unless you are going for an original look, I'd get a new carb AFTER you determine that it really is your problem. If it still runs the same with the known good test carb, start looking elsewhere.
A long time ago, I was an assistant manager at a big car parts place called Western Auto. People used to come in all the time to buy a new or rebuilt carb. I would always ask them if they were sure the problem was a bad carb, because a new carb might not fix the problem. About 50% of all carbs we sold came back as "defective", and I had to issue a refund. The company's return policy was SO REDICULOUSLY liberal that I had no choice. Those were the kind of customers who would continue to purchase and return parts until the accidently fixed their problem. Western Auto's defect rate was at least double or triple what any other reasonable place would stand for. Gee, I wonder why they went out of business.
 
I'm sure you would have noticed if the float(s) have failed. How long since it worked correctly? Perhaps it will take some tweaking to compenate for modern fuels. If you choose to go with a new edelbrock carb, I'd be happy to purchase your old carb.
 
Vacuum leaks?

Are you sure the accel. pump is working properly? With the engine off, look down the primary throat and blip the throttle. Is there a steady, strong stream of gas out the nozzles?
 
I don't know why we are going down this carb road, but have you just poured a little gas down the carb and noticed if it starts right up and runs briefly?
 
Give Scott Smith (HARMS) a call. He restores carbs
 
I installed an OOTB Edelbrock on a 390 Galaxy. The guy couldnt understand why it would barely start with tons of pumping and high idle. The friggin vacuum brake port on back was wide open. Sounds like you have a vacuum leak. My 273/4 would idle down to 600 with its original 4bbl and if the fan wasnt hooked up, you wouldnt even know it was running. Put a vacuum gauge on it! Also confirm the choke is working: choke closes, step up cam engages and throttle is cocked open a tad and of course timing is correct. That 273 is a tight motor.

Oh yeah, clean the crap out of the lower body. A good soak and compressed air blow out of the passages.
 
Last edited:
rustycowll69 said:
I'm sure you would have noticed if the float(s) have failed. How long since it worked correctly? Perhaps it will take some tweaking to compenate for modern fuels. If you choose to go with a new edelbrock carb, I'd be happy to purchase your old carb.
Click to expand...
The floats are good. The Carter is a superior carb - when it works, and it's original. For example, when Edelbrock bought the Carter design, they eliminated the idle circuit and cut corners. Thanks, but I will keep it.
dart4forte said:
Give Scott Smith (HARMS) a call. He restores carbs
Click to expand...
I will try that. They usually say to send it in to them and they will let you know. Its worth a call.'
 
the fact that it runs much better when warm, points toward choke and/or vacuum leak. When it warms up, it might tighten up potential leaks. The Ram forum is full of members complaining about exhaust leaks at the head/manifold surface at cold start up, which subside after the components heat up.
Another thing to consider is the gas. Is the fuel old? Bad gas will make an engine run pretty crappy, too.
 
pishta said:
I installed an OOTB Edelbrock on a 390 Galaxy. The guy couldnt understand why it would barely start with tons of pumping and high idle. The friggin vacuum brake port on back was wide open. Sounds like you have a vacuum leak. My 273/4 would idle down to 600 with its original 4bbl and if the fan wasnt hooked up, you wouldnt even know it was running. Put a vacuum gauge on it! Also confirm the choke is working: choke closes, step up cam engages and throttle is cocked open a tad and of course timing is correct. That 273 is a tight motor.

Oh yeah, clean the crap out of the lower body. A good soak and compressed air blow out of the passages.
Click to expand...
I cleaned it with spray can choke cleaner and compressed air. Maybe I should soak the crap out of the lower body for a couple of days.
 
I
rustycowll69 said:
the fact that it runs much better when warm, points toward choke and/or vacuum leak. When it warms up, it might tighten up potential leaks. The Ram forum is full of members complaining about exhaust leaks at the head/manifold surface at cold start up, which subside after the components heat up.
Another thing to consider is the gas. Is the fuel old? Bad gas will make an engine run pretty crappy, too.
Click to expand...
The gas is new. I fixed one vacuum leak. Vacuum is now good. My son helped and we tried different choke openings. It didn't help it to start.
 
RichB said:
I

The gas is new. I fixed one vacuum leak. Vacuum is now good. My son helped and we tried different choke openings. It didn't help it to start.
Click to expand...
If you can't get it to start and run properly, how do you know "Vacuum is now good"?
 
It does sound like a vacuum leak. There is an often missed vacuum outlet on the very rear middle of the carburetor base plate. Look and make sure that it is either plugged off, or that something is plugged in there.
 
Back to basics
do a compression test.The first shot should be at least 50 or 60 psi.But keep cranking it until you get two consecutive same or near same readings, even if it takes 10 compression cycles, and don't stop in the middle.
Then squirt a small amount of oil into each cylinder. Wind her over for a good 8 seconds, and do another compression test.
Report your results.
If an engine doesn't make good compression, it also won't make proper vacuum, and so the poor old carb can't do it's thing.
If you can't get decent numbers; lash the valves, and try again
Gap your plugs while they're out.

Taking another tack
A brake booster is a prime culprit. It could have an internal leak and you might not be aware of it; while idling clamp the line off, or otherwise plug it. The idle rpm and quality could briefly flutter and then it should return to whatever it was doing prior.
PCVs are another source of trouble. At idle, they're supposed to be a fixed orifice device. Old dirty ones might not be. If the idle vacuum is too low, they will mess you up.
And the sneakiest things are the emulsion tubes in the idle wells. You have to take the clusters out to see them and clean them. While they're out, this is a good time to blow out the idle circuits. Cover the carb with a rag, remove the mixture screws , and have at it. The air should come out of the now-empty cluster pockets, and the rag is there to keep the first slug of fuel from hitting the underside of the hood
And finally....... make sure the secondary air valves are closed up tight but not sticking.
Gaskets and such,you know about. Testing for vacuum leaks,you probably know about.
Good luck
 
Last edited:
Another critical area on a 273 is valve lash. Out of adjustment rockers can lead to the symptoms you describe also. Are you sure yours are set correctly.?
 
If its not getting fuel try and see it it is pumping to the carb. Is it pumping out of the supply line into the carb? Try to start w/o fuel filter. Check the fuel inlet to the carb body. Pinched metal or rubber fuel line? And the classic, is the linkage opening all the butterflies when you press on the gas pedal? Pressure does not mean volume.
 
Reading it with a vacuum gauge. It shows high vacuum, normal engine after I do get it running and warmed up.
It sure does act like it has a vacuum leak but I think it's not getting enough gas rather than getting too much air. What are possible causes of starving for fuel?
 
RichB said:
Reading it with a vacuum gauge. It shows high vacuum, normal engine after I do get it running and warmed up.
It sure does act like it has a vacuum leak but I think it's not getting enough gas rather than getting too much air. What are possible causes of starving for fuel?
Click to expand...
Worn fuel pump, floats set too low, fuel filter plugged, rubber hose swelled closed inside, line from tank plugged, in-tank filter plugged, etc, etc....basically anything in the fuel system not working right.
 
You must log in or register to reply here.
-

Back
Top