Adjust carb for cold weather?

[Mortgaged]

Just to clarify, colder more dense air requires a RICHER mixture not leaner. This is supported by the Ideal Gas Law which is simply:
(Pressure1 x Volume1)/Temperature 1 = (Pressure2 x Volume2)/Temperature2.

Think of the colder more dense air as having more oxygen to support combustion. In order to keep the same roughly 15:1 air/gas ratio you will need more fuel to support combustion at the same burn ratio. We experience this all the time with our older carburetored engines that require a little extra choking to run. On my KTM motorcycle, the needle is adjustable and is richened for cold weather and leaned out for warmer weather. The engine is much more finicky than most and really complains with the lean setting. Thankfully, our tractors are a lot more tolerant!

Interestingly, the gas law explains why airplanes fly so high. Of course the air resistance is lower so there's less friction, but also the air is much thinner with less oxygen requiring the mixture to be leaned out which ends up resulting in fuel savings.

[havoc1482]

Holy necro thread batman. Bud this post is from 2008

[Scrivet]

BudTuba ...... 5+ year member and two posts. I thought I typed slow

[BudTuba]

I have a Zenith carburetor for this 53 Cub and after looking at the cross-sectional illustrations have concluded that the same low speed adjustment is exactly the same. The screw on the back side of the venturi casting (upper half of carb) is turned clockwise in to enrich the mixture. That is counter-intuitive. The main jet on the IHC carburetor is at the bottom of the float bowl, facing outwards from the engine. The main jet on the Zenith carburetor is at the bottom of the float bowl, facing backwards toward the tractor seat. The idle jet is fed from the supply channel as the main jet in both cases. Cleaning the jets therefore, does not require carburetor disassembly, but you must remove it from the tractor so that you can turn the jet seat hole upwards to receive carb cleaner. I use Gumout. Spray a small amount into the main jet seat hole. Follow be blowing a jet of air into the main jet hole. This will clean both the main jet and the idle jet. I would recommend AGAINST removing the two halves of the carbuerator unless you believe the float is either sticking or has developed a leak not allowing it to raise up high enough. If this happens, the tractor will be flooded and gas will drip out of the bottom of the carbuerator at the weep hole under the venturi. If you must remove the top half and do not have a new gasket, apply a thin coating of Form-A-Gasket to the gasket with a fine paint brush. Use only the removable From-A-Gasket. Make sure your governor linkage is lubricated at each link point..especially the main rod to which the throttle adjustment attaches. The throttle adjustment does not directly interface to the carberator but compresses a spring visible through the left side of the tractor engine. When this spring is compressed, the governor seeks a higher engine speed. You can test the governor by removing the link to the carburetor and starting the tractor with the link pulled forward toward the radiator. Once the tractor is warmed up, accelerating it by moving the throttle link toward the back of the tractor. It should accerate without stalling the tractor. If the tractor stalls, it is because too little fuel is being supplied by the idle jet during the speed change. Turn the idle screw inwards 1/8 turn at a time until the tractor will accelerate without stalling. You can avoid a stall by immediately pulling the throttle link forward toward the radiator. While the engine acceleration is occuring, watch the through linkage motion. It should immediately move backwards toward the operator's seat. It it does not, you will probably have to rebuild the governor by the procedure described elsewhere on this forum.