I have a problem that I can't seem to fix, hopefully someone here can help. I have a 65 Gran Sport 401 with an AFB. This carb has been rebuilt twice, and it still refuses to work right. It will idle all day, and when you can get it through the stumble/bog/hesitation/flat spot, etc., Wide open throttle is fine too. It doesn't matter what speed you try to drive and maintain a steady mph, you have to constantly mess with the throttle to keep it going down the road.Doesn't make me think it has anything to do with the accelerator pump, the pump gives it a shot to get you moving, but once your up to speed, your not moving your foot making the pump work, the carb then has to "pull" fuel. It doesn't seem to be making the switch from the squirt from the pump to where it should pull fuel. When you come off idle and slowly open the primary throttle plate's, the carb has a really, really bad hesitation, and starts to sound like it's sucking air,and if you don't mess with the accelerator it will die. I can't be convinced that this has ANYTHING to do with the accelerator pump, because it alway's squirt's fuel when the linkage is moved. It seems to be a problem with the transition from the idle circuit, to where it should pull fuel from the primaries at cruise condition's o No: I can remove the primary metering rod cover's and have someone hold the metering rod's up, and it will rev freely, just like it should This is what I thought was telling me I have a lean condition/stumble coming off the idle circuit, so I put in smaller tip primary rod's, and it made it die instantly when I would even attempt to touch the throttle??? So then I put the original rod's(I think original,.063 tip?)back in, and at the advise of a friend, I changed the primary metering rod spring's to the heavy spring's in hope's of popping the rod's up quicker, but it didn't make a bit of a difference. Please help, I give, I'm crying Uncle :ball: What should this thing have for jet's/rod's from the factory?
yes With the top of the carb upside down, the tip's of the floats are roughly 3/16 down from the gasket surface, if anything on the high side right o No:
Float needle seat #38 Low speed jet #65 Metering Jet Primary 120-256 Metering Jet Secondary 120-158 Metering Rod 16-219 Ted
Thanks Ted Do you have sizes for these part number's, or a chart that tells what the part #'s and sizes are? Anyone else have THIS problem with an AFB? o No: Could I be mis-diagnosing this as a lean condition? Is it possibly too rich when it starts to pull fuel? I guess I'm open to any and all suggestion's at this point ou:
If the metering is correct for the application, I would be looking at the metering rod spring, which should push the power piston up with no vacuum applied. It is very possible that the power piston springs, one or both were omitted during the rebuild, causing the rods to remain in the jets when the engine is revved. If you cannot push the power piston down with the engine is off, it is very likely that they are already down indicating that the springs are missing, or defective. Ray
carter Ray is right on. I am suspicious that you have some stopped up fuel passages either in the boosters/tubes or the main body. From what you describe the carb is running super lean at certain stages. The Carter is not that bad of a carb. It can be pretty good actually. I am a holley man but I think the carter can be a good set up.
Thanks guy's Ray, I already have changed the spring's under the primary power piston's several time's to no avail Doc, I would agree with what your saying about a plugged fuel or vacuum passage, but someone would have to tell me where the hidden one is that may be my culprit. Where do the passages go from the bottom of the accelerator pump bore,and would something in this area cause my problem? As far as different accelerator pumps, I have tried two different style's, one has a nipple in the center on the underside of the umbrella that has a one way check ball valve that feed's back up to the top side of the umbrella seal, my carb will not run with this style pump. The one that will work is solid brass under the umbrella and has no nipple in the center. FWIW?
I just want to make sure- does it have the metal gasket between the carb and the fiber gasket? I don't have a reference as to sizes associated with the needles. I have had all my carbs rebuilt by Carmen Faso :grin: Just got one back that belongs on the red 65 coupe. Ted
Tom - a couple of questions: (1) What is the tag number of the carburetor you are using? (2) Is your engine stock? The AFB is probably the easiest of all 4-barrel carburetors to tune, provided the proper carburetor is being used (Carter produced 505 different ones). You should be able to make this one work well with a little guidance. If you are using the original carburetor, and the engine is stock (overbore OK), then simply install the original calibration if you are using gasoline. If you are using ethanol, some calibration changes will be necessary. We suggest a 5 percent increased main calibration for E-10; a 10 percent increased main calibration and a 5 percent increased idle calibration for E-15. One item often overlooked on Carter AFB carburetors that could cause the symptoms you describe: there will be wear at the bearing surfaces where the vacuum pistons move up and down. Carter knew this, and deliberately designed and produced the vacuum pistons from a softer aluminum, so the vacuum pistons are sacrificial; they should always be replaced when rebuilding a Carter AFB. The good repair kits contain the pistons. This is an instance where the carburetor company actually was thinking of their customers. Much cheaper to replace the pistons than replace the carburetor. One other suggestion (and you may have already done this): a compression test. With todays fuel, it is quite easy to burn a valve. An engine with a burned valve will run fairly well at WOT, but will surge at cruise. At least the compression test would eliminate this possibility. Jon.
I bolted on a different AFB I had laying on the shelf, and I couldn't ask for a better running engine. The carb I'm having problems with is the original. The car has sat in storage for 5-7 years with dead nasty gas in it. Good solid 40,000 mile survivor, engine is fine, I know it's a hidden gremlin in the carb. Now what Jon? I'm all ears :TU:
wear? Would a carb with only 40k miles have sufficient wear on the primary piston's to cause this much of a problem? I swapped in a set of primary piston's and .057 tip metering rod's from another carb, and it didn't make a difference. Jon, can you tell me how the fuel passages run in the carb body? I need to know of a place where a clog/obstruction could be for the fuel feeding the Primary cluster's? This sound like I'm looking in the right direction?
Tom - since the engine will rev freely if somewhat holds the pistons up, this pretty well eliminates a blockage in the circuits. The pistons SHOULD be down at cruise. The area of the rod with which you should be concerned is the high vacuum step (about 1/2 inch above the tip). The tip is used only under WOT. Is it possible someone swapped in the incorrect rods? Need to know the tag number of the carb, plus the numbers on the rods, and the diameter of the primary jets. Incidentally the tolerances on the rods are plus/minus 0.00002 (two one-hundred thousands of an inch!). One thousanth thick on the high vacuum step will cause surge; one and one-half thousanths thick on the high vacuum step will cause the engine to not want to run without feathering the accelerator pump. Since the fuel metering is only 1/2 the story (the air jets are pressed into the clusters); you cannot arbitrarily swap rods without knowing the airjets and expect the carb to work. I am guessing you may have some mismatched parts here. If you want numbers, sizes, etc., please call me at work. I do not have all of the books available at the home computer (where I work on the forums). Jon.
Good info! Thanks Jon. What are your thoughts on swapping the primary clusters,jets,piston's,and rod's from the carb I have that works into the original carb? The tag is missing,but the # stamped into the front carb base is the right # for a 65 GS with A.C., from what I have read. o No: I would have to go out and look again to be sure, but I think it's a 3921s .
If both carbs have the identical stamping number, then there should be no problem. There are also machined areas in the main body, so switching these items if the stamped numbers are different is a crap-shoot. Jon.
Right or Wrong, it worked I don't know what the other carb is o No: pt# L2 9510s o No: I took the primary cluster's,jets,metering rod's out of it and put them into my carb, and problem fixed, I mean at least it's driveable :TU: You can stomp it from a dead start, and there is no stumble,bog,hesitation whatsoever, just lot's & lot's of squealing and tire smoke :3gears: I need a Posi in a bad way, this thing will burn the tire for as long as you want to keep your foot to the floor :laugh: :bglasses: I can't say the carb is now perfect,and doing this didn't give me the answer to pinpoint the problem, so that kinda suck's. If anything the car smells a bit rich at idle but at least it's running.
rich If it is rich at idle, pay attention to two things ; fuel pressure and float level. Lower the float level just a little first. Ck the fuel pressure at the carb. About 4 lb. is sufficent. I have seen as little as 2 lb work fine if the lines are big enough. Carters tend to run rich at idle.
