What are the paramaters for substituting a Carburetor

[seahuntboater]

Well after finally getting my Tillotson MD68 Back together i discover that Needle and seat are leaking and i am missing the low speed needle and spring. So I will shelve this project for a while but am wondering.

Why can’t I replace the entire carb with something similar.. What are the paramaters. i see stuf on ebay for small engines rated by horsepower. So form my 7.5 1954 Elgin Why couldn’t I use an 8hp version so long as the Intake hole and bolts match up? I could rig up throttle cable , etc depending on the design. Here is a link just to give an idea of what is out there. I did not get the measurements , etc. Just looking for some feedback here.
https://www.ebay.com/itm/Carburetor-for-Tecumseh-8HP-9HP-10HP-Snowblower-640349-640052-640054-Engines/173651021368?_trkparms=aid%3D111001%26algo%3DREC.SEED%26ao%3D1%26asc%3D20160811114145%26meid%3Dccc8558d4c91474a88865471a03c24da%26pid%3D100667%26rk%3D1%26rkt%3D8%26sd%3D173651021368%26itm%3D173651021368%26pmt%3D1%26noa%3D1%26pg%3D2045573&_trksid=p2045573.c100667.m2042

Thanks Ralph

p.S. if anybody has an actual Tillotson MS68B diagram and parts list it would be helpful.

[seahuntboater]

SORRY MD68B

[frankr]

Well of course #1 is does it bolt up and fit and can you make the throttle work. Remember the throttle is synchronized with the spark avance.

#2 is size of venturi (the big hole through the center) Too small will reduce horsepower, too big may run totally lousy.

Those are most important parameters. Otherwise, have fun.

[garry-in-michigan]

Evinrude used the Tillotson MD on three of their late 1940 & early ’50s outboards. The bolt pattern was the same but the hole through the center was different. The float bowl gasket (0551142) was the same and we sold hundreds of those because they seemed to fit everything. I am sure an early ’50s Evinrude neutral clutch Fleetwin would fit. Be sure you remove the high speed needle valve before you separate the upper & lower carburetor castings. Otherwise you WILL bend the needle and be required to get a new one. Good Luck . . .

[seahuntboater]

Thanks Garry and Frank. you guys have been very helpful

[The Boat House]

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