New throttle body or new carb?

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tkelley72

Well-known member
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Feb 1, 2013
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My Car
72 mustang convertible
Well my carburetor issues continue! I had a rebuilt kit put into my Holley 80457-1 thinking this would solve my issues with this carb.....nope. While try to set the air fuel mixture I noticed that I had a fuel leak coming from the rear butterfly shaft on the driver side. Obviously it revved up and down and stalled and could not be adjusted. Not to mention it's a fire hazard. So it looks like I have two options, 1, replace the throttle body or two just bite the bullet and get a new carb. Throttle body is about $165.00 but not available from Holley unto Nov. 30th at the earliest. May be able to pick it up at Jegs or someone like that if they have it stock but probably doubtful. New carb is listed as Holley 0-80457-S at about $441.00. Seeing that my carb is about 20 years old, would it be advisable to go the throttle body rout or go for the new one for another $276.00? Does anyone have any experience with the newer Holleys? Will the new Holley hook up with my original linkage/kickdown stuff and are these good quality units? I just want to get this problem resolved once and for all and get it back to being the trustworthy car it has always been. Your help and guidance is greatly appreciated.
 
I checked that earlier and it looked ok but I'll check it again. Maybe it changed after I made adjustments to the choke setting and the mixture? Haven't checked it since those settings were made. Thanks Hemikiller!
 
Fuel leaking out of the shaft is the float level being too high, dripping out of the booster onto the butterflies. Re-set the secondary float level to the bottom of the sight hole.
Would the float level being too high cause it to stumble and die at idle? Upon cold start up, it seems to initially idle somewhat OK with choke engaged, but after warm up it stumbles badly and dies. Smells like it's running really rich too but can't reset anything since it won't idle. I'm just a novice learning things the hard way. Thanks again!
 
Would the float level being too high cause it to stumble and die at idle? Upon cold start up, it seems to initially idle somewhat OK with choke engaged, but after warm up it stumbles badly and dies. Smells like it's running really rich too but can't reset anything since it won't idle. I'm just a novice learning things the hard way. Thanks again!
Yes.
 
It sure will, as it's dumping fuel into the secondaries when it's not needed. You might want to remove the needle & seat assembly from the secondary bowl and blow it out really well. Could be some trash in the seat, or you may have received a bad assembly.
 
I suspect a bad rebuild job. I adjusted the float level as you suggested but it won't idle long enough to do anything. I can still see gas leaking around the secondary shaft although less than before. At times it acts as if there might be a vacuum leak as well but if it's leaking gas from the shaft couldn't it be sucking air there as too? I'm at a complete loss right now.
 
As Hemi mentioned, check for any sort of trash in the needle. While you have that out, inspect the small o-ring on the outer body of the seat-portion of that assembly. Those can get sliced during install. Good idea to put a small amount of lube on it prior to install. Also need to check the float. On occasion, the brass ones will leak and take on fuel....the float sinks and opens the needle. The other type of float is harder to check. They are a buoyant black plastic....if the outer skin layer gets nicked or a deep enough scratch, it will absorb fuel. If it has obvious damage, replace, otherwise, it's probably fine.
 
I am going to show my age here but when you inspect the floats and float needles, if brass, take a little Brasso or Never-Dull and clean them real thoroughly. Also, as others have suggested, clean the needle seat really well, if they are dirty, it will cause the float to not seat properly and cause leaks. Good luck.

Tom
 
This carb has been apart three times in recent weeks and cleaned out each time. First time to clean it out and replace needle and seats, second time to do a rebuild and third time to address a leak at the crossover tube. If I am still getting trash in the carb maybe it's time I replaced the gas tank as well. As far as I know its original to the car. I seem to be chasing my tail with this problem! If it takes another rebuild from someone that "really" knows what they are doing or a new carb plus a new tank, I'm OK with that if my problem goes away once and for all. Extreme frustration here! Advice and opinions are greatly appreciated.
 
This carb has been apart three times in recent weeks and cleaned out each time. First time to clean it out and replace needle and seats, second time to do a rebuild and third time to address a leak at the crossover tube. If I am still getting trash in the carb maybe it's time I replaced the gas tank as well. As far as I know its original to the car. I seem to be chasing my tail with this problem! If it takes another rebuild from someone that "really" knows what they are doing or a new carb plus a new tank, I'm OK with that if my problem goes away once and for all. Extreme frustration here! Advice and opinions are greatly appreciated.
Has there been trash in the carb, each time you've taken it apart? There should be a filter between the fuel pump and carb to catch anything coming from the tank. I agree that if the tank is producing this trash, it needs to be cleaned/replaced. Tanks for our models are relatively inexpensive and readily available.
 
Can't really say if there was trash each time as I did not do the rebuild. First time there was white/gray trash in the bowels and particles from deteriorated o-rings from the needle and seats according to the guy that did the work. Subsequent times everything was cleaned out with carb cleaner just as a precaution. I have a filter between the pump and carb as well as the screen at the inlet. The inlet looked OK last time I checked it. I'm really at a loss here. I've read that the throttle shaft holes tend to wear out in the casting and could be repaired by boring out and installing a brass bushing. Personally, that sounds like a "band-aid on a bullet wound" fix to me.
 
Yes, the throttle shaft bores can wear out, but 99.99% of the time it's only the primary side. The secondaries see so little use, they rarely wear. Worn baseplate or not, the shaft will not leak fuel *unless* there is fuel spilling onto them from the secondary boosters. There should be no fuel coming out of the secondary boosters at idle, or at any time other than when the secondaries are open.

The first thing I'd do is verify your float level in the secondary bowl. Run the engine for a few seconds, then shut it off. Immediately remove the secondary sight plug and you should just see fuel at the bottom of the sight plug hole. If fuel pours out, the float level is too high. Adjust the float level down, and repeat until the fuel stays at the bottom of the sight plug hole. If it keeps rising above the sight plug, then you have a bad needle and seat or trash that's keeping it from sealing.

 
Thanks, I'll go through the adjustment process again and try to confirm that the float is set correctly and check the needle and seat again as you suggest. Hopefully I can sneak up on it and finally get this thing running correctly once and for all. Thanks for your patience with me....I'm learning.
 
If I may chime in here, I know almost nothing about carbs. I did however, look up to see what a Holley 80457 carb is, for my own edification. So, it's a 4160 @ 600 cfm. It also appears to be an older design and relatively cheap at around 450 bucks US.
At this point, if it were me, I'd just spring for a new carb, BUT from my own experience with a brand new Holley 80670 Street Avenger, it needed some "surgery" right out of the box. They are not always "plug-n-play". I replaced an 80670 that was on the car when I bought it because it would not run right, could never tune it. I had a friend, an engine builder, look at it and discovered that the primary metering block was defective from the factory. Not to go into further details, I just junked that carb and bought a new one and as said it too needed work to get it to run better. In short, my frustration point was reached, time to buy a replacement. (and yes, I could have bought a new metering block)
If you do decide to replace your tank, I strongly suggest buying the Spectra-Premium tank that is made in Canada and is Terne Coated, a process to prevent rusting. I bought mine from Rock Auto, cheaper than I could buy one locally, shipped to my door. With that, I bought the Dorman 692232 sending unit. I also bought SS fuel lines from NPD and fuel injector grade rubber hose and most importantly, correct fuel line spring clamps. I NEVER EVER use gear clamps on any fuel line and nor do I use glass or even plastic fuel filters.
Anyway, I do hope you get yours running right, It frustrating to say the least.
 
Thanks so much to everyone for their input. This has been an extremely frustrating process that I have been going through especially since I have owned this car for 20 plus years and it has always run like a top with virtually no issues until now. Guess I should consider myself lucky. In response to "basstrix", yes I did check the points as you recommended. The o-rings on the needle and seat looked OK to me. The floats are the black plastic ones and I did not see any damage on them as well. Even though I have adjusted the floats (especially the rear secondary float) a couple of times, I'm going to try again if I can get the thing to run long enough without stalling out and dying. If that doesn't work, I may just go the direction that "Stanglover" went and get a whole new carb. As I have noted earlier, I had this carb rebuilt by someone else. I am now wondering if he really knew what he was doing and screwed something up during the rebuild process, warped the metering block during assembly or just didn't do a thorough job. I'm already out about $200 parts and labor and it still won't run! At this point, if I have to take it somewhere they are going to want to do another rebuild to correct someone elses work and there is no guarantee that will fix my problem and there's more money down the crapper. Either way I go, I plan on a new tank and have already purchased the Dorman sending unit. Thought I might as well replace the fuel pump just to be safe.

If I do go down the new carb path, does anyone know anything about the new Holley 0-80457S ? This appears to be the replacement for what I have. Is it a direct bolt up to all my original linkage? My car is a 302 with the FMX trans. and original kick down linkage. Also , any recommendations on the fuel pump? Want to get the best parts the first time and not be doing this over again. Thanks to all again, everyone has been a great source of knowledge for a novice like me!
 
For information on the newer carb, perhaps just call or email Holley. I'm sure they'll know.
Just as a heads up, when I bought my 80670, it ran rich out of the box at idle and literally stank the garage up to the point the wife complained. I had a local tuning specialist do surgery on it. He drilled a 3/32" hole front and center on each primary plate. That meant the transfer slots could be set "square" and that problem went away. The AFR was damn near perfect.
I say that because Holley carbs are known to be a tad rich, so just something to be aware of..... just in case.
 
If you’ve adjusted the secondary float level two times and you’re still getting fuel in the secondaries, then there must be some other point of access for the fuel than spillover. If it was me, maybe third times the charm, I would significantly lower the secondaries float level, like 1/2” from the bottom of the glass, to eliminate the fuel access. You don’t need secondaries to get it to idle and drive around the block. Just my 2 cents.
 
Make sure the secondary metering plate, gaskets, and thin steel plate are present and the clutch bit screws are tight. Set the secondary float level low (easy to add fuel, not so easy to remove fuel). If you get it to idle, slowly (1/8 of a turn at a time) bring the secondary float level up until it is level with the bottom of the sight plug hole threads. The car needs to be on a close to level surface. Be persistent and you will get it fixed. Post what you find please so others can benefit. Chuck
 
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