318 with Carter 2-bbl fuel leak through throttle shaft after hot engine shut-down

[67CBodyGuy]

The engine is a 318, the carb is a china clone Carter BBD (super-6). I do have the thicker gasket (3/8 or 7/16).

I've noticed after a drive and parking the car that after a while I can smell some gas under the hood. A finger rubbed across the bottom of the throttle-shaft return spring comes back wet with gas.

It can be a week or more between drives, and in those situations it takes a bit of cranking to get it to fire up. So I'm thinking the gas in the bowl is going some where, maybe boiling away, maybe helped by this seeping out the throttle shaft (odd place for it to do that?). Fuel line in connection to carb is dry, it's not leaking there.

I'm running 93 octane (with 10% ethanol, no 0% ethanol here).

Is this normal that the gas wants to evap out of a heat-soaked carb after engine shut-down, regardless of carb type or internal seal condition? Or is it that the carb bowls should never get low regardless how hot it is outside, how hot your carb gets after a drive, how long you go between drives (ie 1 day or 1 week). ?

 

[RustyRatRod]

How do you have the fuel line run? There's a fuel line mod by @slantsixdan that gets the job done. I did my own, though. I tagged him, so maybe he'll chime in.

 

[67CBodyGuy]

 

[RustyRatRod]

Oh ok. I assumed since you have a Super Six carburetor, that you had a slant 6. Any reason for using a super six carburetor on a 318? It will likely be too lean.

 

[67CBodyGuy]

I've only really had the car running with this carb since July this year after a couple years of r&r (and 20 years of storage before that). I've checked the plugs after long highway runs and they are super white. I've disconnected the vac advance to stop a tick I hear at highway cruise. I run 10 or 12 btdc and even with 93 octane I still get ping while hard acceleration from a stop. I think I measured the carb throttle bore size and it matched the old actual carter bbd this engine had back in 1985 - 1999.

This carb was billed as being for 318 and slant-6 but I don't really know if back in the day (1977 ?) there was such a carb for both the slant and the 318. Or maybe same carb just jetted differently.

But all that aside, I don't think it should be leaking through the throttle shaft (seems only the driver side) during hot-soak engine shut-down / cool off. ?

 

[RustyRatRod]

I've only really had the car running with this carb since July this year after a couple years of r&r (and 20 years of storage before that). I've checked the plugs after long highway runs and they are super white. I've disconnected the vac advance to stop a tick I hear at highway cruise. I run 10 or 12 btdc and even with 93 octane I still get ping while hard acceleration from a stop. I think I measured the carb throttle bore size and it matched the old actual carter bbd this engine had back in 1985 - 1999.

This carb was billed as being for 318 and slant-6 but I don't really know if back in the day (1977 ?) there was such a carb for both the slant and the 318. Or maybe same carb just jetted differently.

But all that aside, I don't think it should be leaking through the throttle shaft (seems only the driver side) during hot-soak engine shut-down / cool off. ?


View attachment 1716457701

The bore size is likely the same slant 6 to 318. It's the venturi size and jetting that's different. That's why your plugs are super white and possible why it's got spark knock. Too lean. You need the right carburetor.

 

[67CBodyGuy]

I see some tips here, about fuel getting past the needle valve after engine shut-off and overflowing the bowl, but if this were happening then I'd be flooding constantly during idle. They talk about "today's gas" being easier to boil away (and that was in 2003).

leaking carter bbd - Slant Six Forum

"Todays gas will expand a lot and even boil in the fuel bowl, then spill into the engine to make it hard to restart"

Maybe this is happening?

 

[RustyRatRod]

I see some tips here, about fuel getting past the needle valve after engine shut-off and overflowing the bowl, but if this were happening then I'd be flooding constantly during idle. They talk about "today's gas" being easier to boil away (and that was in 2003).

leaking carter bbd - Slant Six Forum

"Todays gas will expand a lot and even boil in the fuel bowl, then spill into the engine to make it hard to restart"

Maybe this is happening?

I went back and looked at your picture. One issue is your fusl is completely horizontal. It should be either vertical, or about 45 degrees. This gives space in the fuel filter for expansion so that it will not do exactly what you're describing. I Don't know if that's causing it or not, but it's worth correcting.

 

[slantsixdan]

This carb was billed as being for 318 and slant-6

Seller was FOS.

I don't really know if back in the day (1977 ?) there was such a carb for both the slant and the 318. Or maybe same carb just jetted differently.

Physically different carbs. You can bolt the one onto the other, but there's enough stuff that's different that it's far from optimal. Easier to adapt a 273-318 BBD to a 225 than to go the other direction.

But all that aside, I don't think it should be leaking through the throttle shaft (seems only the driver side) during hot-soak engine shut-down / cool off. ?

Means the carburetor is percolating (boiling) after shutdown, and the throttle shaft bushings are worn or, in the case of thie "100% NEW NEW NEW NEW!" Chinese knockoff of a Carter BBD, it means you are seeing the poor quality of these things.

What year is your car?

And why are you running high-test gasoline? There's no advantage to it in a stock or near-stock 318; it's purely a money-waste.

 

[67CBodyGuy]

Fuel leaking through throttle shaft

I have a problem with fuel leaking from the throttle body (2 barrel Carter WCD 3888S)after the engine...

theamcforum.com

A common complaint today is fuel dripping out of the throttle body by the throttle shaft AFTER the engine is switched off. While a number of issues may cause this problem, by far the most common issue is the volatility of modern fuel. Mechanical fuel pumps have a check valve which prevents fuel from moving back to the fuel tank. The problem is as follows:

(1) After the engine is switched off, heat from the engine heats the fuel in the fuel line.
(2) The expanding fuel (increased volatility) creates pressure in the fuel line from the pump to the carburetor.
(3) The check valve prevents the fuel backing up through the fuel pump.
(4) The pressure increases to a point the float/fuel valve combination in the carburetor cannot withstand the pressure.
(5) An amount of fuel (usually from a teaspoon to a couple of tablespoons) flows into the fuel bowl of the carburetor.
(6) This raises the fuel level in the bowl above the main discharge nozzle(s).
(7) Fuel flows through the main discharge nozzle(s) and drips onto the throttle plate(s) which is/are closed, and exits out beside the throttle shaft(s) dripping onto the intake.

Possible solutions:

(1) IF POSSIBLE, AVOID ETHANOL LACED FUEL! Sometimes you can buy real gasoline at a marina
(2) Buy the lowest octane name-brand fuel that does not ping or detonate in your engine (the higher grades often have more ethanol) - really?
(3) Install a “vapor return line” (take a look at return lines used on many factory air-conditioned cars)
(4) Learn to live with the issue. yuk

I don't have the top-hat vapor return port connected to anything - and I don't see fuel dripping from it. Does that mean anything? Or maybe it's closed when the engine is not running?

I haven't come across anything that mentions fuel line routing or fuel-filter angle.

 

[67Dart273]

It is called "modern fuel." Oxygenated/ alcoholized fuel.

Soon after I got my 67, and swapped in a different engine, I endeavored to duplicate the fuel vapor return system used on the hemi and 440 cars. You can buy fuel filters with a built in orifice / 1/4 return fitting. You will have to safely add a return to the tank and figure a way to get the return into the tank.

I also used a thick insulator base gasket.

Other issues are too much fuel pressure and poor/ leaking needle and seat, as well as mis-adjusted float level.

 

[RustyRatRod]

I haven't come across anything that mentions fuel line routing or fuel-filter angle.

Ummmm, yeah you have. I told you about it up there ^^^^^. You seem to have all the answers though, so happy trails!

 

[67CBodyGuy]

So here's the thing. I don't have a problem when the engine is running, under any condition, like idling or stop-and-go for 1/2 hour inching in line at the border under a hot july sun. My fixed 4-blade fan and stock rad seems to keep my 318 cool enough even under those conditions, keeps the fuel line and filter cool enough with the fan breeze I guess. Now maybe the fuel return line coming from the filter going to the tank keeps a steady stream of cold fuel in the filter that helps the big engines cope with vapor lock, and prevents hot pressurized fuel getting into the carb and leaking out throttle shaft or what-have-you when hot engine is shut off.

I wouldn't mind so much if a thimble worth of fuel leaks out the throttle shaft when a hot engine is turned off, but it seems to me that after a few days or a week of sitting there isin't any gas in the carb at all, and it takes a bit of cranking to get it going.

 

[slantsixdan]

Dude. You got the answer. It's not the answer you wanted, but it's the correct answer. Arguing isn't going to change the answer any — especially not when you are showing us, right out loud, that you have not enough knowledge in this area to argue successfully. If you did, you'd know that the fuel's octane rating has utterly zero to do with the leakage you're describing (even though you read it on the internet!).

Put a legitimate carburetor on the car and have fewer (and more fixable) problems.

Or stick with the carburetor-shaped trinket and continue to have more (and less fixable) problems.

Those are your two choices here, no matter how many words you might type about it.

 

[67CBodyGuy]

So none of this has anything to do with the 10% ethanol in the gas I'm forced to buy (and increasing now to 11% this year and 13% in 2 years) ???

============
Yes, it is typical for the Carter W1 carburetors to leak just a little through the throttle shaft after the car is turned off.
============

Do you know how many times I'm seeing comments like that now that I'm doing searches on this?

I suppose that they're all using chinese carbs also?

 

[RustyRatRod]

If you'll position your fuel filter correctly, like I described, that MIGHT take care of it. Might.

 

[67CBodyGuy]

If you'll position your fuel filter correctly, like I described, that MIGHT take care of it. Might.

I was looking for some pics of small blocks showing the fuel filter, and came across this:

Thread 'Honestly...how good was the 318...mpg / durability / hp'

Sep 10, 2023

Kinda funny....i always bought and drove cars with modified v8s....340s 360s etc ...crate engines bla bla bla...but my big 68 fury as a 1971 318 from a scamp and i freakin love this thing , 727 and 2.76 suregrip rear end , runs a New china *Carter* 2bbl , New belts , not even a tune up was done after her first start in 22 years , this 318 purrred like like a kitten after New carb / oil change and a New fresh battery , ive eard since this last spring sooooo many urban legends and searching all kind of stuff on this "boat anchor" engine that seems to finally win the respect that it...

• ValerianMagnum

"... runs a New china *Carter* 2bbl ... "

Huh. I'm not the only one eh @ValerianMagnum ? (makes two of us with a 318 in a C-body...)

 

[RustyRatRod]

Leave it like it is then. Good luck.

 

[slantsixdan]

So none of this has anything to do with the 10% ethanol in the gas I'm forced to buy (and increasing now to 11% this year and 13% in 2 years) ???

Oh, people blame all kinds of symptoms and conditions on ethanol. Sometimes they're right. Mostly they're not.

============
Yes, it is typical for the Carter W1 carburetors to leak just a little through the throttle shaft after the car is turned off.
============

Do you know how many times I'm seeing comments like that now that I'm doing searches on this?

Do you have a '30s-'40s Chevrolet you haven't told us is really the car you're having problems with? I mean, since you're talking about Carter W-1 carburetors, and that's the kind of car built with that kind of carburetor, and I'm sure you know what you're talking about and aren't just picking scrappets from the interweebs that look relevant to you. You would never, ever do a thing like that…right?

Look, you made a bad purchase decision because you didn't know any better, and it didn't occur to you to ask people who know better than you before smashing [BUY IT NOW]. That's unfortunate, and there are ways of fixing the situation, but this little Debbie-stole-the-cookie-from-the-cookie-jar routine of yours (whatabout ethanol! W-1 carburetors! Octane!) is not getting you anywhere, and isn't gonna.

It's kinda like when you're stuck in the winter and you floor the accelerator and the engine revs and the tire spins and the car wobbles a little and when you take your foot off the gas…you're still stuck, only more now, and you've drawn a bunch of attention to yourself and now everyone has seen and heard that you're in over your head.

But you live in a country freer than many, so if you wanna keep going LA LA LA LA LA I CAN'T HEAR YOU NOPE NOPE NOPE WRONG WRONG WRONG WRONG in response to those who've been there and done that and know the causes, and you wanna keep being snotty to those pointing you at legitimate fixes, well: bless yer heart! That translates to Canadian as "Oh, sorry!".

 

[RustyRatRod]

Oh, people blame all kinds of symptoms and conditions on ethanol. Sometimes they're right. Mostly they're not.



Do you have a '30s-'40s Chevrolet you haven't told us is really the car you're having problems with? I mean, since you're talking about Carter W-1 carburetors, and that's the kind of car built with that kind of carburetor, and I'm sure you know what you're talking about and aren't just picking scrappets from the interweebs that look relevant to you. You would never, ever do a thing like that…right?

Look, you made a bad purchase decision because you didn't know any better, and it didn't occur to you to ask people who know better than you before smashing [BUY IT NOW]. That's unfortunate, and there are ways of fixing the situation, but this little Debbie-stole-the-cookie-from-the-cookie-jar routine of yours (whatabout ethanol! W-1 carburetors! Octane!) is not getting you anywhere, and isn't gonna.

It's kinda like when you're stuck in the winter and you floor the accelerator and the engine revs and the tire spins and the car wobbles a little and when you take your foot off the gas…you're still stuck, only more now, and you've drawn a bunch of attention to yourself and now everyone has seen and heard that you're in over your head.

But you live in a country freer than many, so if you wanna keep going LA LA LA LA LA I CAN'T HEAR YOU NOPE NOPE NOPE WRONG WRONG WRONG WRONG in response to those who've been there and done that and know the causes, and you wanna keep being snotty to those pointing you at legitimate fixes, well: bless yer heart! That translates to Canadian as "Oh, sorry!".

 

[Bewy]

Make sure the n/seat is not leaking. A small leak might not be noticeable with a running engine because the engine will run richer, but use that fuel. Switching off a hot engine that has higher than normal fuel level might heat the fuel enough to expand & enter the booster....& drip onto the t/shaft. A fuel pump that holds pressure after switch-off can also do this.

 

[barbee6043]

Mom always said " When in doubt, always run to the store and buy all the "made in China" parts they have...it could fix the problem!"

When I was a young guy, I would ask the older feller 30,40, 50 years my senior for advice. He would always say, "I'll give ya my advice, opinion, and I realize you probably won't take it, but.... ya asked."

 

[67CBodyGuy]

I'll just get into my time machine and go back to 1975 and buy a carter bbd from my local Chrysler dealership, and pay in 1975 dollars while I'm there. And bring back a tank full of 1975 gasoline. Always nice to visit fantasy land, isin't it?

 

[67Dart273]

I'll just get into my time machine and go back to 1975 and buy a carter bbd from my local Chrysler dealership, and pay in 1975 dollars while I'm there. And bring back a tank full of 1975 gasoline. Always nice to visit fantasy land, isin't it?

Actually that is a thought. Around here (N end of Idaho) there's a few stations that sell "real" gas but you have to buy hi test. You might find out if it's available, run the thing down lo, and fill up with no alky fuel, and see if that makes a difference. One way or the other it will help tell you a bit about the problem.

The things I did to my 67 before I went with EFI are
Dumped the mechanical pump and went with a rear mount pump
Constructed a vapor return system
Used a thick insulated carb gasket.

Even then, on hot summer days up here--with alky gas-- it would stumble a bit on startup when hot. 318/ Carter AFB

 

[slantsixdan]

Ooh, snarky sarcasm! That's an advanced technique for making sure that the people who know how to help you, will choose not to. Good for you for carrying that off so well! Gold star on the fridge next to your name.

Run along now; the grownups are talking.