tuning k-91

[russellmc301 600]

how to i tune my k-91, i have it idleing fine i just need it to have it when i give it gas it is tuned too. it has a model T carb i think.

[wallfish 15,912]

Section 6

Kohler K-Series SM TP-2379 LR.pdf

[953 nut 51,541]

How to adjust the fuel mixture screws on a Kohler (or virtually any early small engine) carburetor – from Brian Miller’s web site

First of all, as long as the engine runs well, don't worry about how the idle and high speed air/fuel mixture adjustments are made. The adjustments depend on the altitude (atmospheric pressure) where the engine will be used. In higher elevations, air is thin, therefore the engine requires more air than fuel to run well. And in lower elevations, air is heavy, and the engine requires less air than fuel. So there is obviously no "one set adjustment" for all carburetors. And no new or rebuilt carburetor with adjustable jet(s) for small engines, automotive or whatever, come from the manufacturer or rebuilder with the idle speed, idle air/fuel mixture or the high speed air/fuel mixture adjustments set correctly. These are initially set just to get the engine running, and due to variations in the altitude (atmospheric pressure) where the engine will be used, final idle and high speed air/fuel mixture adjustments will need to be made by the customer or an experienced small engine mechanic/technician so the engine will run smooth.

Correct Orientation and Installation of Throttle Plates -

All factory-made throttle plates, rather automotive, farm tractor engine, small engine, etc., are made oblong 3% and have a slight angle on the sides that seals against the sides of the throttle bore. The angle and oblong shape prevents the majority of air from entering the engine in the fully closed position. On the Carter, Kohler and Walbro carburetors, the C (Carter), K (Kohler) or W (Walbro) embossed on the throttle plate faces outward and toward the right when facing the carburetor with the float area down. If installed in reverse, too much air will by-pass the throttle plate and the engine won't be able to idle down at a slow speed. Some aftermarket throttle plates don't have an angle, so they can be installed in either direction. But they'll still seal just as well.

The High Speed Needle Adjuster -

On the Carter/Kohler carburetors, the hole towards the bottom of the long high speed main needle adjuster is supposed to be open, so the engine can draw fuel through it for idling from the float bowl. The idle fuel passageways for a Carter/Kohler carburetor goes as follows: Fuel is first drawn through the high speed needle adjuster via the tiny lower hole towards the bottom, then through engine vacuum, it is drawn upward through the tube, then over and down toward the idle mixture screw (which sets at an angle), and then the fuel is drawn into the throttle bore, next to the throttle plate. The information below is mainly for Carter/Kohler carburetors. The fuel mixture screws are used as follows:

• There's three adjusting screws:
  • Idle speed screw. Adjusting this screw controls the idle speed of the engine. It makes contact with the throttle lever.

  • Idle air/fuel mixture screw. This is adjusted ONLY when the engine is operating at a lower/slow idle speed.

  • High speed (main) air/fuel mixture screw. This is adjusted ONLY when the engine is operating at higher/fast RPM. (Well above idle.) Fuel is not drawn through the idle fuel passageway at higher RPM, and adjusting the idle fuel mixture screw has no effect how well the engine runs at higher RPM.

• After lightly bottoming out both fuel mixture screws, rotate each one 1-½ to 2 turns out. This is the initial setting just to get the engine running. Final adjustment can be made so the engine will run smoothly.

• On some small carburetors (gas string trimmers, chainsaws, etc.), there's two air/fuel mixture adjusting screws that's located next to each other on the same side of the carburetor. The one that's closest to the throttle shaft or plate is usually the idle air/fuel mixture screw. The screw on the side and at an angle on the Carter/Kohler carburetor is for the idle air/fuel mixture. It controls the amount of fuel that's mixed with the air at idle speed. With the engine idling at a slow speed, adjust this one until the engine runs smooth. Slow the engine down with the idle speed screw and readjust the idle mixture screw. Repeat this process until the engine runs so slow, you can count the revolutions every time the piston hits. Then set the idle speed at factory specs (usually 1,000-1,200 RPM) so the dipper on the connecting rod will strike the oil and thoroughly lubricate the moving parts inside the engine. A slightly fast idle speed will prevent damage or excessive wear on parts inside the engine.
  • For improved idling for a stock or pulling engine with a Carter/Kohler carburetor, remove the high speed main fuel adjuster and if it has only one lower hole,carefully enlarge the hole by hand with a .039" / #60 / 1mm diameter drill bit clamped in a mini micro pin vise hand drill chuck. This is the perfect size to enlarge the lower hole on high speed needle adjusters so the engine will start quicker and idle better. Being the tube is made of soft brass, there's no need to use an electric drill. Then use [150± psi] compressed air to clear out any dirt/debris from inside the tube, and then suck through the tube with your mouth to make sure it's clear and unclogged. If the tube has two lower through-holes, there's no need to enlarge them because both of them together makes the opening plenty big. Anyway, if the tube is still clogged, use a small, bendable steel wire, such as a bread wrapper twist tie (with the plastic coating stripped off), to clean out the inside of the tube. Then use the [150± psi] compressed air to thoroughly clear it out. Suck through the tube with your mouth to make sure it's clear and unclogged. If performing either of the above È doesn't clear out the tube, then acquire a new high speed main fuel needle adjuster or one in good condition. But make sure it's the correct adjuster for your particular carburetor!

  • Enlarging the lower hole will create a stronger suction of fuel at idle speed, allowing the engine to draw more fuel through the idle circuit fuel passageway so it will idle better and accelerate with no hesitation whatsoever. Doing this will also allow for quicker starts when the engine is warm. It offers no high-speed performance enhancements whatsoever.

  • For the K90/91, K141, K160/161 and K181 engines with the Carter carburetor, if the engine idles fine, but fails to accelerate, install a short 6-32 UNF screw in the emulsion hole leading to the main nozzle just under the choke plate.

• The screw on top of the carburetor body or under the float bowl, or next to the idle mixture screw is for the high speed air/fuel mixture. It controls the amount of fuel that's mixed with the air at higher RPMs (3,600 RPM or wide open throttle). With the engine running at fast speed (3,600 RPM), slowly rotate this screw one way or the other until the engine operates smoothly. By the way - the idle mixture screw has nothing to do with the high speed operation of the engine, and vice-versa.

• After making the final fuel mixture screw adjustments, set the throttle control so the (stock) engine will rev at governed speed (3,600 RPM)

[Achto 26,519]

If it does not want to run smooth above idle it can also be the condenser. I battled with the carb on one of my engines this spring and found out that it was the condenser instead. My engine would run good at low RPMs but would not run well above 1/2 throttle. Just one more thing to consider.

[AMC RULES 36,945]

How's it running now Russ?  

 

Edited December 4, 2016 by AMC RULES

[russellmc301 600]

good for an old engine