Farmall 400 Carb Adjustments - HELP

[l***@invalid.com]

Hello

After an extensive search of the web for information regarding Farmall
carburetor adjustments, I found nothing.

I have a friend with a Farmall 400. I know the 400 is sort of rare
and is similar to the M. He often helps me with my farm work and in
trade I do my best to keep his tractor running. I was recently
noticing a gas drip below the carb when he trys to start it in cold
weather. I had also seem too much black smoke from the exhaust and
his gas usage was excessive.

I went to adjust the carb and found three screws. The bottom one
appears to be the power screw, and adjusting that one did make it run
much better. Going upward, the middle screw is obviously the idle
screw and with that one, I was able to change the idle speed. But
there is that 3rd screw just slightly above the idle screw. It does
nothing when I turn it. What the heck is that one for?

Also, is there a pattern to adjust them, meaning which one should be
adjusted first, next, and last?

If you know of some online diagram and discussion about this, a web
URL would be appreciated.

From what I have seen, this 400 has the identical carb as the Farmall
M. From what I have read online, the 400 is basically the same
tractor as the M with slightly more engine power, and a few other
bells and whistles.

Thanks

George

[Don Young]

Post by l***@invalid.com
Hello
After an extensive search of the web for information regarding Farmall
carburetor adjustments, I found nothing.
I have a friend with a Farmall 400. I know the 400 is sort of rare
and is similar to the M. He often helps me with my farm work and in
trade I do my best to keep his tractor running. I was recently
noticing a gas drip below the carb when he trys to start it in cold
weather. I had also seem too much black smoke from the exhaust and
his gas usage was excessive.
I went to adjust the carb and found three screws. The bottom one
appears to be the power screw, and adjusting that one did make it run
much better. Going upward, the middle screw is obviously the idle
screw and with that one, I was able to change the idle speed. But
there is that 3rd screw just slightly above the idle screw. It does
nothing when I turn it. What the heck is that one for?
Also, is there a pattern to adjust them, meaning which one should be
adjusted first, next, and last?
If you know of some online diagram and discussion about this, a web
URL would be appreciated.
From what I have seen, this 400 has the identical carb as the Farmall
M. From what I have read online, the 400 is basically the same
tractor as the M with slightly more engine power, and a few other
bells and whistles.
Thanks
George

I believe you are referring to an idle mixture screw. If so, it is adjusted
for the fastest and most regular idle. The adjustment sequence is generally
high speed or power first, idle mixture next, and idle speed last. They tend
to interact somewhat so a good adjustment of all thre may take several
tries. The engine and carburetor must be in good shape for good results, of
course. Proper valve clearances, good compression, good and properly gapped
spark plugs, good spark, and correct ignition timing should be verified
before carburetor adjustments. The engine should be at normal operating
temperature and the gasoline must not be stale. A leaking float needle,
improperly adjusted float level, or clogged passages in the carburetor will
also prevent good results.

Carburetors, once cleaned and properly adjusted, rarely require readjustment
unless tampered with. The black smoke does generally indicate excessive fuel
and can be caused by a clogged air cleaner as well as carburetor problems.

Don Young