The Stovebolt Site Forums The Shop Area Engine Shop Replaced a Rochester B with a Carter YF today...

Finally got around to playing with the Carter YF Hotrod Lincoln gave me for my 261. It had come from a GMC 270. It looked very clean and serviceable so I thought, "What the heck?" And I installed it this afternoon. It replaced a leaking Rochester B that was from a 235 car engine.

So far, only one minor issue but no leaks or anything like that. The carb seems to be fine.

But what a difference!

The minor issue is that after pressing and releasing the accelerator, the carb won't return to a normal idle. It stays at a higher RPM unless I tap the accelerator and then it returns to a normal idle speed. Is that the return spring or something else?

John, I have the same issue with mine.

It turns out that the throttle is getting hung up on the manual throttle cable barrel nut. I've tried to rotate it and change its orientation but no luck. It's only a little fast, not racing.

I installed the small washer, hoping it would provide a surface for the nut to rub against and allow the throttle to return fully home. It doesn't.

A light tap of the pedal releases it and idle returns to normal.

Mine kinda does that too. Inspect the hole in the throttle rod that your throttle cable goes through. They get grooved. I reworked mine and added a little ball joint thing. Made it better but it doesn’t always fully return to lowest idle setting.

My next move is to add a little stronger return spring.

Sometimes that problem is caused by the throttle plate not being exactly centered in its bore. The fix is to loosen (NOT REMOVE) the two screws that retain the plate to the throttle shaft, back the curb idle screw off until it's not touching anything, and gently tap on the plate to center it, then retighten the screws. Those screws are peened on the end opposite the head, so they won't get sucked into the engine if one gets loose. Never remove those screws without grinding the peened-over part off or you'll ruin the threads in the shaft.
Jerry

Pics are crummy. Best I could do in a dark shed.

I cut off the 90 on my throttle rod, and used a die to attach one of these:
https://www.autozone.com/fuel-deliv...1-4in-28-throttle-ball-joints/102978_0_0

During that same project, I drilled and pressed in bronze bushings to all the pivot points in the bellcrank and such. They were all wollered out, egg shaped. The whole works is way smoother now and hangs less. But it will still hang maybe 100 rpm high unless I goose it a little to settle it down.

I also tried the fix HRL is describing there with the throttle plate procedure. That might be your issue, but it didn’t seem to be mine.

John, that YF may have come to you from a GMC 270, but it didn't come from the GMC factory originally (says the guy who has a Carter YF on his GMC).

I was trying to figure out what John has there. YF 1879? 1379? I can’t quite read the stamp right above the throttle body.

The stamp says YF 137 S

Embossed number on bowl is 1896

I think the stamped number says YF 437 S. Although the 4 is pretty lightly stamped and may be a 1. John could verify.

According to Carbking's website, there are the following Carter numbers:
CARTER — Carter carburetors by number all have the letter ‘S’ appended to the end. The ‘S’ is omitted from this list. Tag numbers 4, 33, 43, 46, 60, 75, 85, 86, 89, 101, 102, 109, 117, 125, 126, 130, 136, 142, 150, 156, 167, 181, 186, 188, 197, 200, 209, 222, 225, 235, 241, 245, 251, 253, 255, 258, 259, 266, 275, 276, 281, 283, 284, 287, 291, 295, 298, 309, 311, 314, 315, 316, 319, 323, 324, 328, 329, 330, 331, 334, 336, 337, 339, 340, 341, 342, 344, 346, 350, 351, 352, 366, 368, 373, 378, 384, 385, 389, 391, 397, 400, 401, 402, 407, 410, 411, 413, 414, 420, 421, 423, 424, 425, 426, 430, 432, 433, 435, 436, 437, 438, 439, 440, 444, 447, 448, 450, 453,

Note that there's no 137, but there is a 437. But his listing is the ones he has (had) for sale.

The carb we're discussing was on a GMC 270 I bought a couple of years ago in Texas, from a pretty much unmolested 57 or 58 GMC pickup that was getting the resto-mod treatment- - - - -IFS, LS engine, 4-link rear end, etc. I got virtually all the running gear from a running, driving original truck that was getting butchered up. I'm not sure if the carb was numbers-correct, but it was from a pretty much OEM vehicle. Glad it works for John- - - -when I'm finished modifying the engine, it's going to need a carb capable of handling 300 cubic inches or so. I've got four (count 'em!) intake manifolds for GMC 302 military engines with the 4 bolt 2 barrel footprint. Those manifolds will also bolt onto a 270, or even a 248. A Stromberg 2 barrel for a 318 MOPAR V8 would be a good fit for that engine, I believe.
Jerry

Thanks for the input. I'll try to get to it over the weekend.


John

Jerry, are you taking steroids ?

Yes, now knowing that there is no 137, I can make out the rest of the number '4'.

Curious what is the YF application for a 437s. I’m rather certain Carter never made a replacement carb for a 261 Chevrolet, based on some lists Carbking has posted here in the past.

Perhaps they did make a YF for the GMC 270.

Talk about "shade tree mechanic!"

"I know the voices in my head aren't real- - - -but man, do they come up with some good ideas!" The same set of Toyota Diesel forklift pistons and flanged slip-in sleeves that I'm planning to use on a Chevy 261 can also be fitted to a GMC 270, and the GMC crankshaft looks like it can get around the same 3/8" stroke increase as the Chevy crank. That can turn a 270 into a 300-something engine, probably with considerably more torque that the 302 that uses the same stroke as the 270. 270 core blocks are a lot more plentiful than 302s, also. GMC cylinder heads breathe a lot better than Chevy, and they're much more modification-friendly!
Jerry

A tip for eliminating the interference of the throttle cable stop, preventing the throttle lever from returning to the idle position is to move it an inch below the throttle lever. There is no reason for it to be close to throttle lever. Nobody ever needs to pull the throttle knob all the way out.

Just be careful not to have too much tag end. Then it might hang on the manifold surface and stick WOT driving down the road. I “know a guy” who’s experienced that.

JW - Carter 437s was original equipment on a 1939 Hudson, and it is a W-1.

In the FWIW category, 137s was an experimental carb for a 1935 Hupmobile, that did not make production.

Jon

Someone 86'd the throttle cable before I got the truck. When I bought the new one and hooked it up, I was told to leave it an eighth inch below the rod.

I suppose that an inch below won't matter since I rarely use it anyway and, as you say, it will still work but will have to be pulled a little farther out before it engages.

Ah…..

What do you reckon John’s YF is then?

Typo - should have been 1925 Hupmobile not 1935.

John's carb looks to me like a 4371s,

Jon

From Jon’s Tech Tip in this very same sub-forum. Looks like a 4371s was for a 250 6 cyl, standard trans application (California). Curious what the Cali designation means….assume it’s some sort of jetting difference for emissions?

Ought to be a pretty good match for that 261, I’d bet.

A quick link for you. HERE IS where you'll find all those carburetor Tech Tips that JW51 mentioned that are in the Engine TT Forum.

I'm seeing the one now. Pretty faint like the 4. Thanks for the clarification.
Makes more sense than a carb for a Hupmobile, for sure.

Now if you need a carburetor for your Hupmobile, just let me know (Sorry Peggy, the devil made me post it )

Jon

JW - as a general rule (ALWAYS check the specification sheets) the California carbs were calibrated leaner than the 49 state carburetors.

Interesting (at least to me) how they often accomplished this.

The government figured out that most enthusiasts could change main metering (fuel) jets, so these were often left as is; and the air bleeds made larger.

Not too many enthusiasts can pull an air bleed, machine a smaller one on their jewelers lathe, and install it in the carb.

In this case, this was early calibration changes, and John should have no problems (maybe go up a couple of thousandths on the main metering jet).

Jon

As I seem to recall, John's "261" is bored a little bit oversize, so it's probably a bit closer to 270 than the original engine would have been. A 261 bored 60 over is 269 and a fraction cubic inches.

Jerry

Fixed the problem with the throttle return. Otto nailed it. Added a washer and a better cotter pin.

New problem is that I am experiencing now a very rough idle. At idle, I have to set the idle way too high to keep the engine from stalling out.

Is my vacuum/idle jet not adjusted properly? Or do I just need to pull the carb and give it a good cleaning or even a rebuild?

Thanks,
John

That Carter has a diaphragm accelerator pump. They deteriorate and leak or get stiff and don't pump gas when you goose the throttle. A clear sign that the diaphragm has a hole in it is a rich condition especially at idle. Heavy soot on the plugs will be very apparent.
I'd buy a kit from CarbKing Jon and clean and rebuild it. Have him include the red accelerator pump diaphragm. They are supposed to hold up better to ethanol.

I'm pretty sure that Jon told us that his rubber supplier said the red ones and black ones are made from the same material. It seems to be an urban legend that the red ones hold up better - sort of like a placebo.

I have had one of his black ones in my carburetor since Feb 2021 and this truck burns ethanol exclusively. No problems whatsoever.

Since his main supplier uses black rubber now, he has to buy the red stuff elsewhere at a higher price and sell it at a premium to the customers who think it's better.

Thanks Gents.... Kinda what I was thinking ... but I was hoping ... I know what to do.



Also have a Carter RAJXO that needs help, but the answer will most likely be the $$$ame ...

The NEW red diaphragms, so far, have not failed in ethanol-diluted fuel. And, yes, they ARE pricey.

The black ones also seem to work well as long as the engine is started sufficiently often to keep fuel in the carburetor so the diaphragm stays wet.

Jon

Remind me, Jon. You only sell the diaphragms in a full kit, correct?

And please define "Sufficiently often" ...

The opposite of not often enough..................

Jon

Neoprene that has been in ethanol AND ALLOWED TO DRY tends to harden.

Hardened neoprene cannot flex, as a diaphragm must, and cracks.

As long as the neoprene is not allowed to dry, it doesn't seem to harden.

Jon

I cannot define that. I can give you a data point.

The fuel in my YF’s bowl has almost always evaporated between driving sessions. Rarely driven on consecutive days. Sometimes it sits a week, and sometimes it sits a month. I have tried really hard to only run non-ethanol fuel, but I haven’t been 100% in that arena.

My black diaphragm lasted a little over two years under those conditions. The black ones aren’t expensive, nor a big deal to change. But I would gladly invest in a more resistant one just to avoid the hassle.

If not driving it, maybe just crank it to fill the fuel bowl every other day or so.

Maybe I'm just lucky, but ...

My GMC 228 with a Carter YF 964S starts COLD with the choke pulled half way out in any temperature from 20F to 90F ...
... in less than a second if sitting overnight to 3-4 days
... in less than 3 seconds if sitting for a week

It doesn't seem like the bowl goes empty in either of these conditions.

BUT (big but) it does have a 12 volt battery spinning a 6 volt starter.