Main jet sizes

[George Willer]

To drill out the orfice and tap it I think I'll make a split bushing so I can hold the jet by the body instead of the hex and accurately center it in a 4 jaw. This will be more accurate than necessary, but will eliminate the danger of ruining the jet if the brass grabs. Murphy's law says if it's an important part it will certainly grab!

[Phillip W. Lenke]

George

The oriface is .128 for .090 then .121 the rest of the way. Total length .310.
After drilling the .030 hole. The back side of the oriface is drilled in about .063 with a .078 drill ,Not sure if it was necessary but I wanted to copy the existing part.
I drilled the hex end, because I was'nt sure if I wanted to euckre the orifice. You could drill and tap the end of the oriface , then pull it out in you're bridge port. Then do the oriface separate. I pressed it back in place minus the loctite. Did'nt want to have any foregn material.
Let me know how it comes out!
Phil

[George Willer]

I see now. What I didn't see while sitting here at my computer... it's obvious the orfice has to be a separate piece so the body can be drilled out. Making a new orfice will be easy.

The exchange of ideas here will help us all. It won't be hard at all to patch the hole in the hex and that's necessary to push the orfice out.

Thanks for the idea.

I sure hope it helps your plug problem. We'll soon know.

[Phillip W. Lenke]

George

If you want to scrap the old oriface you can drill it from the face and tap so you can pull it out , You would'nt have to drill the hex side. I just did as I stated , I was'nt sure how it went together. Do now though.
Phil
Will let folks know if I notice a change, after tonight.

[ducati750]

George I think it is a great idea to post main jet sizes, and a discription of how your tractor runs to help others that may have problems. I have gone one step further and included photos of my spark plug. My main jet size is a #64 drill or .036", I live in columbus which I belive is about 1000 ft above sea level. The tractor runs great, and was rebuilt about three years ago (so I have been told) it does have good compression (120psi). The plugs that are in the photos have been in it for over a year. They have had one season of snow plowing, one season of mowing, and one tractor pull , and have now been used to plow snow twice this year. You can see that they are burning just fine with the new ( bad) gas that is causing problems for some folks. I hope people can use this info to compare to theirs and possibly make their tractor run better. http://www.picturetrail.com/gallery/view?p=999&gid=8873708&uid=3619582&members=1

[danovercash]

My original jet was .034, and tractor ran very rich. changed to .032 and it runs much better, no fouling. took out plug on manifold and played with air-fuel mix to determine need for smaller jet. Lurker Carl IS the man on carbs! Local dealer gave me a metering jet, but it was the same size as original. C&G doesn't have .032 jet. was able to get one from TMTractor for $10. Have extra .034 jet, rough head.

[Eugene]

Interesting topic.

Wonder if it would be possible to run a Cub through one of the state inspection stations that checks exhaust emissions - checking for unburnt hydrocarbons. Conducting a before changing the main jet test and an after test.

Still thinking - perhaps a local tech (junior college) school could conduct the test.

Eugene

[Phillip W. Lenke]

Installed revised main jet last night. .030-.032. Well may I say it ran excellent. Smooth.
Plowed last night for about 2 hrs. heavy wet snow. The change was drastic, The heavy fuel smell was gone as well as missing sound , the responce was slower than the Zenith that I had on it before. But runs Great! AHHH! Finally. I can get some seat time [/img]

[John *.?-!.* cub owner]

this was forwarded to be by another meber.

"Bus Driver" says that jet 354 192 R91 is 0.034 and jet 364 610 R91 is 0.032. That is from some old service literature I have. I have not found a reference for the other jet part numbers.

[inairam]

Michael G. Finch in Milford, Mich. Fixitmike1 AT aol.com knows everthing there is to know about the various carbs used on the cub. he has a rebuild service. I have two Cubs and from him I really looked into the numbers on the block as well as the serial number on on the plate. I have a 1949 with what I think has an original or at least age appropriate engine. I also have a 48 that I am very sure from the engine numbers is a 59-61. So the question of the right size jet may have to do with what engine is in the cub and it may not be from the same year as frame - unless of course you owned it from new and know the history.

[danovercash]

I like this:
When you only have 9 horsepower you know the names of all of the ponies!
Used to have "it's not how many horses you have, it's how well you have them trained!"