Off-road capable YF carburetor - JeepForum.com
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post #1 of 49 Old 07-08-2019, 05:37 PM Thread Starter
eprobe1
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Off-road capable YF carburetor

Quit laughing, you haters! My YF runs as smooth as butter except when I get it on an incline, when it floods and dies. Now, I know what you're are going to say: "buy an MC 2100," "you need EFI," etc. Well, I can remove the YF and break it down into its component parts in 5 minutes. I could take it apart blindfolded. It's super-simple. And it does everything it's supposed to do except idle on a hill.



I've read up on carb mods to make them hill-friendly and there's no reason they shouldn't work on a YF, except they don't. I plugged the bowl vent and plugged in a new outlet to a charcoal canister via the auxiliary port on top. Drilled it to provide access (see pics). But it's still flooding through the idle circuit.


I need help from the YF doctors out there, by which I mean the 70-year olds with long beards who spend their off-hours rebuilding old carburetors and muttering to themselves. How to make a YF climb a hill?

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post #2 of 49 Old 07-08-2019, 06:23 PM
skizriz
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Best thing i did for my YF was smash it with a hammer, and go 2100. Sorry....
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post #3 of 49 Old 07-08-2019, 08:17 PM
John Strenk
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With mine, the hinges for the float were worn allowing the float to drag on the walls of the fuel bowl. Check to make sure the float doesn't touch anything when you rotate it.
Make sure you use a fuel filter with a return line so the fuel pressure isn't too high.
Also make sure the top of the carb is centered and use the correct pattern when tightening down the cover. There is a lot of slop in the cover and it also messes up the float.
Make sure the float drop as well as the float height is correct. there are two settings.
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post #4 of 49 Old 07-08-2019, 08:17 PM
Fourtrail
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Up hill or down hill? Factory float level or lowered float? what is your fuel pressure? the 50 year old yf on the fhead in my '56 did inclines no problems with no mods.
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post #5 of 49 Old 07-08-2019, 09:05 PM
Cutlass327
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Mine ran up and down hills with no issue either, before I swapped to EFI for other reasons.

Rick

1978 CJ5 5.0HO/T177/D300, '86 D30/D44 WT axles, 'glass body, 31x10.5 BFG A/T, TDK galv'd frame - DD and weekend toy


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post #6 of 49 Old 07-09-2019, 07:09 AM Thread Starter
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Seriously? You guys could climb hills w/ a YF? As soon as I start up a steep slope it begins sputtering and then I have to give it gas, which is hard to do while jamming the brake and clutch. It puts out black smoke, so I know it's running rich. I don't think the float is rubbing against the side but I'll check. Float is set to factory specs. I have a fuel regulator set to 3.5 lbs.
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post #7 of 49 Old 07-09-2019, 07:27 AM Thread Starter
eprobe1
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Cutlass, you don't still happen to have that old YF sitting around gathering dust, do you?
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post #8 of 49 Old 07-09-2019, 07:29 AM
John Strenk
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I probably would not of plugged that bowl vent. But it appears that you provided a vent to the charcoal canister.
Are you sure the new vent works? Is there any suction on the line going to the charcoal canister? There should not be.

I plugged the bowl vent on mine and caused all sorts of flooding problems. I then unplugged the vent and just let it vent to atmosphere then and it worked fine.

If there is a vacuum on the vent line, that lowers the pressure in the fuel bowl. so you're sucking fuel into the bowl as well as pushing fuel in
Normally if there is suction on the vent line to the charcoal canister, the vent tube you plugged would compensate, not allowing a drop in pressure in the fuel bowl.
That regulator id set at 3.5 PSI when the atmosphere is at 14 PSI. Drop the pressure in the fuel bowl by 3 psi is like having the regulator at 6.5 psi.

It will be difficult to measure the pressure in the fuel bowl unless you have a gauge that reads absolute pressure and not gauge pressure but it would help in figuring out the problems.

I would have to drag one of my old YF's out and see. I switched over to a BBD and have not had any problems with that carb either.
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post #9 of 49 Old 07-09-2019, 10:17 AM
pedal2themetai
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HI, I'd unplug the vent and lower the float so there isn't as much fuel IN the bowl... and you should be good to go.. make sure all your gaskets are good inside so fuel should not flood into other parts.
good luck
Tim
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post #10 of 49 Old 07-09-2019, 03:20 PM Thread Starter
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OK I should have made a few things a little more clear. The vent that I drilled out goes to a charcoal canister on the fender, not to a vacuum source. With the original vent (plugged) the gas just spilled over into the airhorn and killed it. Now, it flows down to the charcoal canister. I'm including some pics to make that clear.



BTW the JB Weld holding the vent tube in place is already cracked. That stuff's not good for much except plugging.



I've tried lowering the float and it just runs rough. It wants to be at factory specs, not above or below. Gaskets are all good.


The pressure regulator is set at 3.5 psi. Most mechanical fuel pumps put out between 5 and 10 psi. I think most people who use a regulator on their carbs set them between 3 and 4.5.
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post #11 of 49 Old 07-10-2019, 05:44 AM
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Quote:
Originally Posted by eprobe1 View Post
OK I should have made a few things a little more clear. The vent that I drilled out goes to a charcoal canister on the fender, not to a vacuum source. With the original vent (plugged) the gas just spilled over into the airhorn and killed it. Now, it flows down to the charcoal canister. I'm including some pics to make that clear.


....
charcoal-canister.jpg

Is this charcoal canister vented? Otherwise it's just a fancy plug filled with fuel. It sounds as if you are using it as an fuel overflow reservoir.

The OEM charcoal canister IS connected to a vacuum source to draw the gas fumes out of the canister when cruising. It's usually sealed off, trapping the gas fumes until the engine reaches a certain temperature (CTO valve) and the throttle is open (Ported Vacuum connection). When both conditions are met, a purge valve opens and the fumes are sucked out (manifold vacuum) of the canister and burned.
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post #12 of 49 Old 07-10-2019, 06:29 AM
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The phenolic floats used in some of the YF carbs are known to get fuel soaked making them heavier causing an increase in the fuel level. Get a new one.

If you can find a brass float, that would be better but check to make sure the brass float does not have any leaks in it. You can check that by putting it in hot, not quite boiling water and look for air leaking out. That can be fixed with a dab of solder or epoxy.



There were also several different types of needle valves. My best one was spring loaded with a viton tip.


Also some of the aftermarket seats have a bigger orifice in them that leads to flooding problems. a orifice that is bigger lets in more fuel at 3.5PSI than an smaller orifice @ 3.5PSI. I think that any opening larger than 0.090" causes flooding problems. It's hard to find the exact size replacement anymore as it's easier to stock one size for all so it wouldn't surprise me to find the same needle and seat used in an Carter AFB 4BBL sold in the same kit for a YF 1 BBL.
needle-seats.jpg


Also make sure your accelerator diaphragm isn't cracked, twisted or has a hole in it. Just letting it sit and dry out can cause it to crack. I also lightly tighten the screws then push down on the diaphragm and then tighten the screws to make sure it has enough travel.

If there is a crack in it, then it can be sucking fuel through the diaphragm down through the manifold vacuum ports in the carb. But usually this will cause problems with idle and acceleration and mixture control. The diaphragm is important to control the mixture depending upon engine load.

When there is light load on the engine, the manifold vacuum is high and it pulls the diaphragm down along with the mixture needle allowing less gas to flow through the main jet to create a lean mixture. When the demand on the engine goes up, the manifold vacuum drops allowing the the diaphragm to move up also raising the mixture needle, allowing more gas to flow through the main jet richening up the mixture.

Also make sure the ball and weight in the accelerator pump nozzle sits tight.
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post #13 of 49 Old 07-10-2019, 06:45 AM
pedal2themetai
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HI, HHHHMMMM, I've never seen a charcoal canister like that before?? is that something you made or bought??
The charcoal canister is ONLY suppose to have Fumes only NOT liquid fuel..
You are having problems with your float or its adjustment Period.. You may have just screwed up your carb by drilling those holes in it and plugging the vent.. If you are having fuel run out of ETHER of those orifices you HAVE TO MUCH FUEL IN THE BOWL. your float is sticking or may have a pin hole and filling up with fuel making it heavy and sinking in the bowl.
Your carb needs that vent.. to operate properly.. it can't let fuel out if it can't vent. Take a plastic bottle and poke a hole in it.. fill it with water turn it upside down dumping the water out NOW put your finger over the hole notice how it STOPS running out same with your carb and plugging the vent..
good luck
tim
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post #14 of 49 Old 07-10-2019, 08:13 AM
Fourtrail
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Quote:
Originally Posted by eprobe1 View Post
Seriously? You guys could climb hills w/ a YF? As soon as I start up a steep slope it begins sputtering and then I have to give it gas, which is hard to do while jamming the brake and clutch. It puts out black smoke, so I know it's running rich. I don't think the float is rubbing against the side but I'll check. Float is set to factory specs. I have a fuel regulator set to 3.5 lbs.

I think your issue may be more due to elevation and gearing than a carb that is overflowing fuel out the bowl. Your crawl ratio is not great for low rpm steep hill climbing and likely your jets might be a size or two too big being you are at around 4,000'. The rest of us commenting that ours ran well are at around 1,000', so not really a good comparison.


If you have another carb top, I would try to extend the factory vent up taller. should be able to get the extended vent up high enough that you don't overflow fuel when on an incline.

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post #15 of 49 Old 07-10-2019, 08:59 AM
John Strenk
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And Farnsworth Peak just 4 miles away is 9,000 feet.


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