mark20

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Is there much difference between a farmall m carb,super m , and a 400? I can get my m to smoke at idle but it leans out under load, I'm thinking a little to much. I've worked on the carb bottom half but not much on the top. Can anything be done there?
 
I've drilled everything I can, put it back on the dyno with the same results. I pull it down on the dyno , pull the plugs and their a very lite brown. Under no load the tractor runs a bit rich and smokes. It works well just thought a later model carb would flow different
 
what have you done besides carb work to the engine ? light brown on the plugs is about right why change ? it will flow all the gas if it's opened up enough but why if you haven't increased the engine .
 
(quoted from post at 13:05:50 08/21/16) what have you done besides carb work to the engine ? light brown on the plugs is about right why change ? it will flow all the gas if it's opened up enough but why if you haven't increased the engine .
 
I'd like to see them a little darker. The rebuilds kits differ between the m to the 400 carbs, so sosomething has chaged.Thought it would be the same differace as the m to the 400 cam
 
(quoted from post at 18:00:15 08/18/16) Is there much difference between a farmall m carb,super m , and a 400? I can get my m to smoke at idle but it leans out under load, I'm thinking a little to much. I've worked on the carb bottom half but not much on the top. Can anything be done there?

M and SM same carb, 400-450 the idle screw is in the carb flange, the load side of the carbs are all the same. I personally do not like the later carbs, they just don't seam to tune as well as a M-SM.

You should not be smoking at idle, that is the idle circuit, set it right, when you rip the throttle back does it puff smoke? That is the load circuit. When on the dyno as you open the main jet up you should gain power and as you keep opening up you will eventually loose power.
 
I can back it down and quit smoking at idle and yes it does burp a bit of black smoke when I give the throttle a shot. I have drilled out the 2bottom holes in the tube and drilled the tube out just a hair. I'm running with the bottom load screw most of the way out, not sure if its doing anything. I drilled it out 2 number size but sounds like it should be more
 
Its a good thing you mentioned the idle circuit, went out to the shop and checked the carb and the idle air screw was just about all the way out. Don't know how she was even running. Scewed it all the way in then back out 1 3/4 turns. Much better. Gonna drill out the main jet a couple more number sizes then re dyno. Thanks for all the info
 
(quoted from post at 18:17:55 08/22/16) I can back it down and quit smoking at idle and yes it does burp a bit of black smoke when I give the throttle a shot. I have drilled out the 2bottom holes in the tube and drilled the tube out just a hair. I'm running with the bottom load screw most of the way out, not sure if its doing anything. I drilled it out 2 number size but sounds like it should be more

Can you give some more info, what size engine, how many rpms, what size do you have the main drilled, imulsion tube holes, which venturi, I assume this is in an M?

Be carefull on the imulsion tube holes especially the top hole, if you give me the above info I can give you some numbers to try.
 
Yup, it's M. It's 301 cubes ,2200rpms . The main is .086 and the bottom two holes in the discharge tube are .078 , the top hole is opened up just a touch and I'm running a # 27 venturi . Some other # would be great, I wished I had other carbs to try out, it's hard to start modifying your only carb, in the middle of the season
 
(quoted from post at 10:53:20 08/25/16) Yup, it's M. It's 301 cubes ,2200rpms . The main is .086 and the bottom two holes in the discharge tube are .078 , the top hole is opened up just a touch and I'm running a # 27 venturi . Some other # would be great, I wished I had other carbs to try out, it's hard to start modifying your only carb, in the middle of the season

Makes sense why it is leaning out under load, your top hole and especially the middle hole is way too big. As the engine comes under load and uses more fuel the fuel level around the emulsion tube drops, allowing air into the upper holes of the emulsion tube, this is by design to keep the fuel mixture correct.

Just go get another emulsion tube, the top hole should be left at the stock size of 0.041-0.046, middle hole I'd set to 0.063 and the bottom hole you can go up to 0.067-0.070. This should make it smoke with the main turned out all the way, if not take your main jet out to around 0.100", the nice thing is the main you can always adjust back down if too big, it will just be a lot more touchy if the main jet is too big.

good luck
 
That all makes sense, thanks. I'm hoping to try it tomorrow night before there pull on Sat. Thanks for the info
 

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