carb help?

hello im new to this website, ive made a few posts on here asking questions and have always gotten great responces and advice from you guys! thanks everyone! im in the proccess of building a motor for my tractor! ive got a farmall M motor bored out with 4 and 1/8 pistons and sleeves, there the high compresion step head pistons for a 450 like what you would buy from tisco.. ive got a brand new 450 lp head and lp manifold,petronix electronic ignition, and new 450 cam im going to use in this motor. ill more then likly be putting the motor together this weekend if i get the gaskets this week.. im wondering what carb work i will have to do and what octane fuel to use ? i dont want to spend a week scratchin my head,cussing,and taking the bowl off 40 times and wrecking carburetor bowls drilling them out trying to find the best thing to work. i have a ihc carb off of a cobine motor that has the bigger main jet and metering stem in it that would bolt on the upper half of an m carb. i have a few different size venturies to pick from. would this bowl work or am i better off with something different or not changing anything to the stock carb? any help or advice would be greatly helpful! thanks guys!

God knows i am not a carb guy,that being said,i sent my e-gleaner carb to mo-tech engineering in tipton,in.they re-build it to your engine specs.treadwell carb in new york is another source.good luck!

For now, use a 27 venturi. Too big will run fine at high rpm, but will die off quickly when trying to lug.

Take the bowl off and drill out the main jet to .095" - .100". Clean out good and put back together.

Drill out the bottom set of holes in the metering stem a bit bigger than stock. I forget the size - maybe .080" or so.

With the larger main, the load needle will need to be in most of the way.

thanks! what octane gas would you suggest using? would 93 be to much or not enough? as it will proably have quite a bit of compression

Well a 450 LP with flat top pistons has 8:1 compression. With the domes, I would say you're gonna be between 9 and 10. I would say that 93 would be the minimum you want to try. If you can get a hold of something that is 100 or better it would be good to have on hand when you start running.

If you are pulling against me then I would agree that you should use a 27 venturi. The guys who say use a 27 on a 281 cubic inch engine have never taken the time to actually test their hypothesis. I have plain jane C-281 with comformatic pistons that I am getting 69 hp at 540. I have a hybrid carb. The top is off a C-281 power unit and the bottom, the metering nozzle, and venturi are off a 301 combine engine. I gained 2 hp going from a 27 to a 33. I gained one more gong from a 33 to a 35. I do suspect that if I lug it down it will die off sooner with the bigger venturi but I want the horsepower at higher RPMs. If I am pulling and my engine lugs down because she ain’t got enough it is time to rethink some things. In the words of Sergeant Friday “just The Facts Ma’am; Just the Facts” All ideas are opinons until tested on a Dyno and opinons are like armpits; everyone has two and… well you can figure the rest out. Engineers Rule! Never under estimate the power of Geek! P.S. I have had few beers so if I come across as an A-Hole… Well I guess that means I am on the A-Team!

110 is what your should run , sounds like mine and if you don't it will run after you shut it off and slowly but surely melt those domes away . ask me how I know.