The Stovebolt Site Forums The Shop Area Engine Shop Carb mixture adustmen- not IDLE mixtuer adjustment

My '53 216 has a Carter (YF) carb that is running too rich, I think. My plugs are sooty, as is the tailpipe, and my mileage is only 10 mpg. I also don't seem to need much choke at all to start it up.
I rebuilt the carb (not great, but it runs ALOT better than when I got the truck). I do drive it gently every day now and it runs well and reliably.
I've searched and searched, but all I've ever found in regards to 'mixture' is for IDLE mixture. The truck idles great, so I think that it's OK as far as that goes.
I think I just really need to know how to lean up the running mixture... but as far as I can tell the metering rod is not adjustable. Am I supposed to BEND the arm that connects it to the plunger? That seems a bit crude, as well as very tedious since multiple adjustments may be needed until it is correct.
Can this be done? Should I just get a replacement carb? Thanks for any advice.

Use the instruction sheet to adjust the metering rod. Many carbs use bending the lever or link to make adjustments. Check your float level. A high float level can cause a rich mixture. You might try setting it a little lower then specs.

In 59 Chiltons manual gives this procedure for MR adjustment:
"Pump adjustment to be made before the MR adjustment-remove the top & with the throttle valve seated press down on the upper end of the diaphragm shaft until it bottoms and hold it there.The MR arm should now contact the pump lifter link at the outer end nearest the springs.Adjust by bending the pump connecting link at it's lowest angle.The pump connector link connects the pump rod to the throttle shaft".That adjusts the pump.MR adjustment:"Top removed, throttle valve seated,press down on upper end of diaphragn shaft and hold it,on the models where a MR gauge is not given in the spec chart the MR shpuld contact the bottom of MR well and it's arm should contact the lifter links between the springs and the supporting lug.adjust by bending the lip of the metering rod arm to which the MR is attached".
Did you renew the MR diaphragm and would it allow fuel to pass into the vacuum passage if it were porous?If it is exposed to the fuel it would and would serously richen the mixture at all times.

Assuming that SLC stands for Salt Lake City, the altitude is higher than recommended for the standard metering rod.

Carter used the standard metering rod from sea level to a maximum of 4000 feet.

4001 ~ 6000 feet used one size lean rod

6000 ~ 7000 feet used two sizes lean rod

Leaner rods are thicker than standard, thus raising the A/F ratio (higher is leaner).

Since the effective metering area is the area of the jet less the dynamic area of the rod, simply changing jets will not give the proper A/F ratio at all values of vacuum.

Jon.

Yes, the diaphragm and shaft are new. The metering rod did not have a replacement in the rebuild kit so it is original. It doesn't look really smooth. Would polishing it help or possibly ruin it?

Yes I am in Salt Lake- about 5000 ft elev. Thanks for that clarification on MR sizes Jon.
Is it possible to buy a new MR, one step leaner than standard? Anybody know where I can get one?
I guess polishing or fine sanding would just make the MR thinner and thus richen the mixture even further.
The first thing I might try though is to adjust the float level slightly lower as Wrenchbender suggested, since it is easy and quick to do.

Thanks,
John G.

Metering rods are available.

The first step is to determine the ID number of your specific carburetor. On the YF, this will normally be stamped (not raised) on the center section (bowl) of the carburetor. The ID number will be in the format of either 3 or 4 digits, followed by the letter S as in (S)am. Example 967s or 2101s.

Jon.

Okay, then... I guess I have some work/research to do this weekend.
I hope I can find the data without removing the carb, but I'm not betting it will be that easy.

I found the ID number for my carb. It was easier than I expected- no need to remove anything-I just shined a flashlight and there it was.
It reads 964S... so how do I use that info?

Thanks,

John.

If it was me, I'd call (573) 392-7378 (9-4 Mon-Wed central time)
http://www.thecarburetorshop.com/

http://chevy.oldcarmanualproject.com/carb/carter this might help.

Thanks. I called the carb shop. They have a minimum order of I think $90, and then a new MR would be another $70.
So, after reading a few threads and seeing that adjusting the MR height is common, I will try that.

I did take off the carb and set the float height... it was way low (about 1"). If it ran rich that way then I guess the MR must really need lowering. Going to do that by just taking the top off.

I have a question for anyone who knows (Carb King??): My Carter YF choke doesn't seem to really go fully open- on the rear of the carb there is a coil spring that keeps the choke turned about 15 degrees toward closure. Is this normal position during warm engine driving? I can push it filly open with my finger but it springs back that 15 degrees or so.
I guess the spring is there for a reason. There is a linkage that goes from the choke and coil spring to the throttle linkage, but it doesn't seem to affect the choke.

Can anyone tell me what that coil spring on the choke is for and wether the accelerator is supposed to be able to counter its effect?

Thanks.

Mileage increased from 10 MPG to 14 MPG!

I got up the guts to go ahead and bend the arm that holds the metering rod. I set it about 1mm lower than it was previously.
I was worried that I would see no improvement - or make things worse.

Anyway, I noted the mileage, filled the truck, fiddled with the MR, then drove around as usual for a few days, and then re-filled to see how much gas I had used. From that and the odometer change I calculated the mileage.

I think I got lucky and nailed it. After driving the truck around for a few days I calculated my mileage as having jumped from 10 mpg to about 14 mpg! It may be even a slight bit better than that, since I didn't actually make the carb adjustment until 2 days after I had filled the tank (chickened out)... So for the first couple of days of the 'test' the truck was still driving around rich.

I am tracking my mileage again for calculation on my next fill-up to confirm these results. I think 14 mpg is great- especially since almost all of my driving is short around-town trips- the truck isn't really fast enough for highway driving.

Woo hoo, thanks for the tips and advice.