Farmall M Carb

[Dan in TN]

I have a farmall super m with 4.125" dome pistons, a 450 lp head and manifold, and a pulling cam. makes 200 psi. running stock 1600 rpm high idle.

tractor only dynos 65 hp.

carb main jet and metering stem have been drilled out and it is getting enough fuel.

it has the stock #27 venturi still in it. would a #29 venturi help with hp? if so, where can i get one?

thanks

dan
 

[Earl-IL]

708-305-4945 has venturi M-450
 

[LarryM]

I have a C-281 that was mildly stuck when I bought it and it just has the old Tractor Supply pistons that makes 67 hp at 540. I believe those pistons make it an 8:1 comprerssion ratio engine. It made 66 with a size 33 venturi but when I tried a size 36 it gave me another horse. The other things that I did was polished the intakes ports, multi angle valve job, port matched the gaskets, electronic ignition, a 450 gas manifold, and the carb is off a C-281 power unit so it looks like an M carb with the choke on the outside versus inside like a Super M. I am running 93 octane with 10% ethanol. Going to a better fuel gave me 3-4 hp even with the lower ompression engine. A size 29 is what the 706 carb had in it. One last note... I have a really good governor and cannot pull it down to 70 hp when I go below 540 PTO rpm.
 

[mm585]

I dont think your going to gain much more with out more bore and stroke. I have a super m with a shaved down head, 4.125 M&W pistons and governor, Heisler manifold and bigger venturi and the best I can get on the dyno is 57. I hear bunches of big power stories of tractors with a stock bore and stroke but on the track its never there. There is no substitute for cubic inch. When you bring the tractor down to rated speed on the dyno that is waht you have, not what it reads when you give it anouther turn!