Carter YF differences, manifold vacuum port size and drilling out.

I've got a Carter YF 1bbl on my Jeep's 232. I also have a spare YF. Earlier this fall I had to swap the spare onto the Jeep. What I discovered is that the two carburetors are different. My spare has a language assembly on the side of the bowl that opens and closes the bowl vent? Whereas the other YF doesn't. The other significant difference is that the manifold vacuum source I connect the PCV hose to are different sizes. My original carb has a 1/8" nipple and the spare has a 3/8".

This larger size has a big impact on how well the PCV system works and I'm considering whether or not I could drill out the hole on my original carburetor and insert a piece of 3/8" steel tube. I have not yet looked closely at the base of the carb to see how feasible it would be to drill, haven't measured tube or drill sizes, and don't really want to take the working carb off the Jeep to compare if I don't have too.

Our other vehicles are in need of repair and the old CJ is currently primary transportation. However, it being what it is, it won't run indefinitely without some maintenance. In the last month I've gone from 16mpg down to 11. Hence my efforts to get the original carb rebuilt. I'm simultaneously pursuing the performance loss with other efforts, but having a fresh carb rebuild is one of those.

Is anyone else aware of these differences between YF models? Got any advice for me about the port size?

Thanks,
Dave

I've got a YF without any PCV port.
Some with 2 ported vacuum sources some with one
Some with vented fuel bowls and some with the vent in the throat of the carb.

The YF has a long and varied history.
The largest YF found on the Ford 300 cu-in I6. It's about the max size you can go with for a 1 bbl carb.

The YFA even has a pulse modulated mixture control.

There are also high altitude variations.

Casting Number Carburetor Number Application
630 768s, 938s, 951s Willys
630 787s, 964s, 2008s Chevrolet
630 832s Willys
648 738s, 937s Willys
648 814s, 820s, 833s Henry J
650 735s, 736s, 740s, 741s, 939s International
728 756s, 965s Chevrolet
776 757s, 824s, 876s, 877s, 892s, 2014s, 2098s, 2137s, 2163s Nash
788 788s, 966s Chevrolet
791 789s, 967s Chevrolet
866 879s International
875 924s, 2071s Willys
875 2094s Kaiser Darrin
1052 2046s Chevrolet
1105 2079s Reo
1121 2101s Chevrolet
1127 2100s Chevrolet

The YF enrichment is based upon manifold vacuum so if there is a vacuum leak someplace the YF will run rich reducing your MPG's.
Check for vacuum leaks. The plastic spacer is usually a good place to check as well as worn out throttle shaft guides.

Also the mixture needle (not idle needle ) adjustment could be off causing it to run rich. Check an instruction sheet to see how it can be adjusted.

Are your sure your 'language' assembly on the side is not a mixture control and is really a YFA?

This is a YFA:


This is a YF:



http://jeep.smallcraft.net/carburetor/

as for drilling out the PCV port, that carb was built with a certain balance of vacuum and atmospheric pressures to operate properly. Drilling out a passage could upset the balance and might not ever run right again.

John Strenk said:

I've got a YF without any PCV port.
Some with 2 ported vacuum sources some with one
Some with vented fuel bowls and some with the vent in the throat of the carb.

The YF has a long and varied history.
The largest YF found on the Ford 300 cu-in I6. It's about the max size you can go with for a 1 bbl carb.

The YFA even has a pulse modulated mixture control.

There are also high altitude variations.

Casting Number Carburetor Number Application
630 768s, 938s, 951s Willys
630 787s, 964s, 2008s Chevrolet
630 832s Willys
648 738s, 937s Willys
648 814s, 820s, 833s Henry J
650 735s, 736s, 740s, 741s, 939s International
728 756s, 965s Chevrolet
776 757s, 824s, 876s, 877s, 892s, 2014s, 2098s, 2137s, 2163s Nash
788 788s, 966s Chevrolet
791 789s, 967s Chevrolet
866 879s International
875 924s, 2071s Willys
875 2094s Kaiser Darrin
1052 2046s Chevrolet
1105 2079s Reo
1121 2101s Chevrolet
1127 2100s Chevrolet

The YF enrichment is based upon manifold vacuum so if there is a vacuum leak someplace the YF will run rich reducing your MPG's.
Check for vacuum leaks. The plastic spacer is usually a good place to check as well as worn out throttle shaft guides.

Also the mixture needle (not idle needle ) adjustment could be off causing it to run rich. Check an instruction sheet to see how it can be adjusted.

Are your sure your 'language' assembly on the side is not a mixture control and is really a YFA?

This is a YFA:

This is a YF:

http://jeep.smallcraft.net/carburetor/

as for drilling out the PCV port, that carb was built with a certain balance of vacuum and atmospheric pressures to operate properly. Drilling out a passage could upset the balance and might not ever run right again.

Click to expand...

John,

The carb I'm rebuilding looks much like the one in the link you posted, the "YF". Mine is a #7073S. The other carb I have has the extra stuff on the side and the instructions that came with the NAPA kit refer to it in Fig. 14 as the "bowl vent lever". What I have looks the same as their diagram. That carb (the one I'm currently running) is a #7274S.

As for drilling the PCV port larger, I was pretty much thinking exactly what you said, that it wouldn't be a good idea, but still had some small hope (born out of ignorance) that it might be possible.

Here are a couple photos of my carbs.
This is the one I'm rebuilding today


And this is the one on my Jeep now


I also pulled my plugs this morning - all six are carbon fouled, replaced w/ new. Pulled the wires - #1 to cap was full of corrosion. Removed the distributor cap - oily and dirty inside, swapped for a clean spare. Losing 5mpg is pretty noticeable, I'm going to keep plugging.

Thanks for your reply John.

Yeah, when the throttle opens (or closes) it moves a lever on the bowl cover assembly. Supposedly that is a bowl vent lever. I'm hoping to put the newly rebuild carburetor on the Jeep tomorrow, as long as I did a good job on it I'll be able to take this one apart.

The bowl vent on the YF I rebuilt today has a flapper in it like a PCV valve, but larger in diameter. I guess as long as there is vacuum it will suck vapors out, if not then is remains closed, but only by it's own weight.

I think I have a carb with that vent on it. I had another YF without the lever and had problems with it running right when I plugged the vent up.


Have fun with the carb rebuild, check the float hinges to make sure they are not worn out.