Carter YF parts interchangability...

I was just wondering how critical it is that all the parts on a YF match as far as the series (SA, SC, SD) are concerned. All the parts in my carb are correct for an SD except the metering rod, which is a standard metering rod for the SA (pn 75-996). Will this work or will i need to find the pn 75-1500? Thanks
Ben

 

It can be an issue depending on the parts being combined, Performance and economy can both be affected.

Main jet sizes were not all the same between the S,SA, SC and SD models, The late production 938SD models had an "idle well to bowl bleed" not present in earlier models.

The correct main jet orfice size for the 938SD is .0935, Some ( possibly all ) SA models came with .096 main jets to the best of my knowledge.

If your carb has the .0935 main jet and the 75-996 metering rod ( this rod should measure .0745 *.06725 *.0625 * .047 ) you could be running your engine a little to lean and not getting the performance its capable of. The standard one step lean metering rod for the .0935 main jet is a 75-1570 and it measures .070 * .063 * .056.

If you are attempting some shade tree tunig you should look up the " Density Altitude " thread that jayhawkclint started, Really good information on the effect of air density on air fuel ratios.

The difference in area restriction from a .070 rod to a .0745 rod in a .0935 jet is huge considering that the standard two step lean rod for the 938SD is the 75-1571 and it measures .073 * .067 * .059.

If you can accurately measure your main jet orfice diameter it would be allot easier to determine if you should be using a different "series" of rods.

The tiny orfice in the bottom of the idle jet tube should be .028, That was the standard for the 938SD.

Measure the main jet and post back, I may have a 75-1500 and an extra 75-1570 in my stash you would be welcome to have.

 

Brian. I just discovered that sometime over the years I replaced my .0935 main with a .089 and still using the 75-996 rod. This may be causing my flat spot under load so I dug up the .0935 from long ago and put that in. Now I'm looking for a matching 75-1500 rod. Does this make sense?

 

Some 75-1500 metering rod possabilities are.
Jon of The Carburetor Shop LLC.
Or try ebays nos4jeeps
He has a genuine Carter kit that ncludes the 75-1500 metering rod

Also see: http://z4.invisionfree.com/CJ3B_Bulletin_Board/ar/t2718.htm

 

I've got an e-mail in to Jon and I hope he replies. I'll look into that other site too.

 

Got my 75-1500 in the mail today from a local oldtimer Willys guy at Willys Mpls and this should complete my SD conversion. I'm pretty confident the too long "S" type connector between my throttle shaft and pump lifter link along with the .089" jet were the cause of my flatspot. I'm looking forward to getting it together. Both were parts provided in carb kits. Thanks all.

 

What is "Willys Mpls"?

 

Old timer ran a Willys restoration/repair business called Willys of Mpls in Farmington MN years ago. That's where I learned alot about my CJ when I first bought it. He sold the business to a customer who moved it to Dassel MN and named it Northstar Willys. When old timer sold business he kept alot of stuff and now runs it out of his garage. He has machining tools and even an old L-head plumbed up to run different parts on right inside his garage. Northstar Willys closed up shop and they now run a mailorder parts only business online under the same name.

 

Can we get the contact information for Old Timer? I'm obviously very interested.

 

Just spoke to him and asked if he wanted his info sent out and he said "sure". His name is Louie Larson, Willys Mpls, 612-802-1860. Local articles have been written about him back when he ran the store. PS: don't call him old timer.

 

The 75-966 works with the jet size .935". This is the same jet for all they just use different rods from what I can tell. I forget the part number for the .935 jet but it's printed on the jet. I've put ones in from kits in the past that had no markings and I assumed they were the same but one I had in was only .089". I went back to the original .935".

 

dumb question: The steps on the metering rods go up pretty high. How much of the rod actually drops into the jet?