The Stovebolt Site Forums The Shop Area Engine Shop Carburetor YF964S

I installed an unused YF964S in my 55.1 235. It slows on the hills more than I think it should. If I pull out the choke about 3/8 inch, it does fine, or more like I would expect. Also, when I drove a choke vehicle in the past, I would be able to push the choke in after about 2 blocks. Now, I have to go for about 12 minutes and it still balks at the stop signs.

Is this an orifice size problem or some other adjustment I didn't do properly when I installed this clean new carb. Thanks-Scott

If I'm not mistaken, a 964S should be for a 216.

The 964s is for the 216 ( it should be a carter)

Sounds like it is running lean. Check the float level. You might try raiseing it a little above specs. If that is not it you will need a larger main jet or possibly adjust the metering rod.

Thanks for the tips. I will give it a try.

Scott

As previously noted by others the 964s was designed for the 216; not the 235.

This is a classic example of why more than one carburetor is produced; and why carburetor selection is so important.

The main venturi in the 964s is 1 1/4 inch. The main venturi in the 967s (for use on a 235) is 1 5/16 inch. Does this 1/16 of an inch really make that much difference? YOU BET!

Do the math:

The overall venturi area of the 964s is 1.227 inch while the overall venturi area of the 967s is 1.353 inch. So the overall venturi area is 10.2 percent greater on the 967s. Now factor in that the booster is the same on both so the percentage increase is probably more like 15 percent.

A 235 is a little more than 8 percent larger in displacement than a 216.

This carb should run well at idle and very low RPM (giving increased low end efficiency due to higher air velocity) but will run out of steam prior to the normal maximum RPM of the engine; and produce significantly less power under load (slowing down on hills).

This was a concept developed in the 1930's for use on taxis. Run a smaller venturi for a vehicle that would normally run 25~35 MPH maximum, but increase the fuel economy at the lower speeds.

You are running out of air!

Jon.

Jon,
I have a YF964S as a spare carb and wrongly assumed that is what I had on my 235 (bored 0.030 over by the way). I checked my carb on the truck and it is a YF2100S (manual choke). Sorry about my mistaken identity. I still use the old oil bath air filter. I have the 9797 fuel pump with the vac pump piggy backed to help feed the wiper motor vac on the hills. I removed the "draft tube" and put in a pcv between the draft tube port and the intake manifold. Maybe I am loosing too much vac to the pcv line.

Is the YF2100S the wrong carb for my bored 235?

Might it have the wrong orifice size?

Thanks - Scott

The 2100s is the proper carb for the 235.

As Wrenchbender said, you may have an incorrect float level, or incorrect main metering jet.

Loss of power is also a symptom of using E-10 ethanol (regardless of what our government would have you believe).

Check the specs on both the metering rod and main metering jet. Pay no attention to the numbers (people drill out jets, and emery metering rods). Use a micrometer and get the actual specs.

At the same time, check the float setting.

And, check with the manager of your local station to see if you are burning ethanol. There are calibration changes you can make.

Jon.

And one other thought: running high octane fuel in an engine designed for regular can show these symptoms. What octane fuel are you burning?

Jon.

Jon,
Thanks for the tips. I use only Shell regular unleaded 87 octane gas in the truck. The pump says it MAY contain UP TO 10% ethanol. I will have to ask to find out the actual %. I will have to explore the jet size and the other suggestions after I get the ethanol percentage. Thanks again!

Scott

I just called the gas station and they said that the current batch has 10% ethanol. - Scott