281 farmall m

[Jess R]

I was looking for info ar thoughts.My problem is i have a farmall m with 4.125 step head pistons,ported head and shaved , after market cam , and a w9 carb. The tractor pulls real good and strong then falls flat on its face. I pull 3mph 10% over on rpms 5500 and 6500lb classes.Thank you in advance for info and help

 

[colekicker]

I think your issue is you have too much carb. The flow rate is not high enough for the carb to run efficiently. Remember, that carb was designed for a 350 ci motor and you are running a 281 ci motor.

 

[VicS]

Just off the top of my head, I would say your motor is to small. On a clay track with a 20 inch drawbar and 5000 lb you need 85 to 100 hp. Like 400 cu. I'm sorry. Vic

 

[ss409]

a good way to help is a smaller venturi. being that the w9 carb is bigger, your air velocity is too slow. it would wake up if you used a 23, or a 25 venturi with the w9 carb. that would be simular to running a M carb with a 35 venturi.

 

[Dblair]

colekiker has it . plus keep that timing dead on if it's stock

 

[Jess R]

Thank you guys for the info and help and what tractors used the 23 or 25 venturi Thanks again

 

[ss409]

Super H, 300, 350s used 23s, M used 25.

 

[brentp4455]

you have to watch out with cams. time and time again ive seen tractors lose all their torque because of a nonstock cam. that being said, the gentleman is right that your motor is too small for the 6500.

 

[famallfarmer]

400cu? i have no where near that. im turning 3000rpms and it is 90hp. just my .02

 

[colekicker]

Not sure he needs 400 ci, but he never said what size tire he is running.

 

[Jess R]

Im runing 15.5-38 firestone 30% tread Thanks again for everything

 

[EP]

If your head has been hogged out or not ported properly you will lose torque.I've made this mistake before on stock engines.I have a hopped up 327 chevy engine had stock heads then replaced them with some aluminum heads with bigger valves and port work.I lost alot on low end but it runs like crazy @ high rpm's.Good for a car but not a pulling tractor!That was a lesson learned.A new lp head might help.

 

[Anonymous-0]

The w9 carb is too large. Go back to the m-450 style carb and a 27 or so venturi

 

[colekicker]

Okay, go back to your stock carb. Use a letter # bit to open the jet up just a bit. Also, make sure you are full flowing fuel to that carb. You should not have a power issue with 15.5s. I run a similar set up.

 

[north puller]

What is your cam timing? Do you have a cam card? What are the cam specs?

I agree that W9 carb is too big.

 

[Dblair]

If your running a 281 use a 27

 

[The Gambler pulling team]

Super H uses a 23 venturi. The 350 uses a 25 venturi and the M uses a 27.

 

[Jess R]

I have never had my tractor on a dyno but with the M carb back on it what kind of hp do you think it would make? Thank you again for the help

 

[Jess R]

Is that run a 27 venturi in the M carb or the w9 carb thank you again guys for the help going to swap them out this weekend and wait for another pull

 

[LarryM]

Have you ever had it on a dyno? Without a dyno it is all just speculation. I have a 281 with stock cam and comformatic pistons that I have 69 hp on the dyno at 540 PTO with stock high idle RPMs. All I did when I got it was pull the head and polish it (not port) and give it a multi angle valve job. I pulled it this last summer some in first gear with 14.9s and/or 15.5s and I have yet to make it lug down in RPMs in 5500 or 6000 although they were not really sticky clay tracks. Having a dyno helps. I did figure out that there is a big difference in the horsepower different fuels make even in an 8:1 compression engine.

 

[LarryM]

My Dyno tells me that a 33 produces more horspower than a 27.

 

[colekicker]

Someone else may disagree, but I'd guess ~50-60?
I wouldn't be so worried about the horsepower number, but that you have tweaked everywhere you can. Did you polish the exhaust ports? Did you polish inside the exhaust manifold? Did you swirl the intake runners but not get them slick? Full flowing fuel to the carb? Open the jet with a letter bit? When it idles does it puff just a little carbon? When at full power it'll burn everything.