Yamaha kt100 tuning – diy go kart forum electricity and magnetism physics

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I have a KT100 with a two hole intake on a Walbro WB3A carb with a four hole can exhaust. I am able to get it to run fine at high speeds and actually idle decently while cold. However, at half throttle it begins to four stroke unless I turn my low speed down quite a bit but if I do this it bogs when I give it gas which isn’t a huge deal I just turn my low speed back up. The issue that I am trying to solve is the amount of un-burnt gas/oil it spits out and leaves on the axle, I believe this is referred to as spooge. Now the easy answer to this is I am running too rich, which, as I was trying to point out before, is that I believe I have found that sweet spot between too lean and what would be just rich enough to go full out without bogging. Note: my high speed is around 1/16th to 1/8th of a turn during all of this and I just put a fresh spark plug in.

I have a feeling I may be running a too oil rich mixture of 1:16 as instructed by the previous owner. A friend suggests I need to clean/rebuild my carb which I do not know when the last time that happened was as I have not owned the kart too long. Finally, my father suggests that "this is just what two strokes do".

Here is my take on synthetic two cycle oils. After many years of desert racing two stroke powered dirt bikes and using full synthetic two stroke engine oil in all the snowmobiles and chainsaws I have and having more than 40 years of engine repairs and modifications I can tell you that indeed there is a difference in synthetic oils.

I have had a lot of engines apart in my time working on them and rebuilding them etc. One thing about oil mix ratios one has to remember and this is very important that when the oil mix ratio is say 16:1 the fuel is more viscous than it is than if the mix ratio is 20:1 for example. That being said say that you had been running a engine with a 20:1 oil mix ratio and you have set up the air fuel mixture correctly depending on the carburetor that is in use either fixed jets or adjustment screws and then you switch to a 16:1 oil ratio now that the fuel has become more viscous in order to achieve the correct air fuel ratio for the engine the carburetor settings will need to be set richer than the previous settings that were set up for the 20:1 oil ratio as the now thicker fuel resists going through the adjustment needles settings which is just the taper of the adjustment needles changing the size of the fuel circuit delivery or the orifice size in a fixed jet carburetor. This is where some people get confused because air fuel ratio and oil to fuel ratio are different. Some people think that when you mix a heavier oil ratio mix that you are richening up the air fuel ratio when indeed it is being leaned out due to the increased viscosity of the fuel. That’s right just what I said increased fuel viscosity. I have seen two cycle engines burnt up and seized because of what I have just stated. So just the opposite will happen if say the engines air fuel mixture was correctly adjusted for a 16:1 oil ratio and then the oil mix ratio was changed to 20:1 then the air fuel ratio would be richer and then for maximum engine output the air fuel ratio would need to be leaned out a bit. That being said take note of this fact and adjust the air fuel ratio accordingly as needed. Spooge is a normal thing for two stroke engines. Run them hard and flat out and the spooge will reduce if not go away.

I have a KT100 with a two hole intake on a Walbro WB3A carb with a four hole can exhaust. I am able to get it to run fine at high speeds and actually idle decently while cold. However, at half throttle it begins to four stroke unless I turn my low speed down quite a bit but if I do this it bogs when I give it gas which isn’t a huge deal I just turn my low speed back up. The issue that I am trying to solve is the amount of un-burnt gas/oil it spits out and leaves on the axle, I believe this is referred to as spooge. Now the easy answer to this is I am running too rich, which, as I was trying to point out before, is that I believe I have found that sweet spot between too lean and what would be just rich enough to go full out without bogging. Note: my high speed is around 1/16th to 1/8th of a turn during all of this and I just put a fresh spark plug in.

I have a feeling I may be running a too oil rich mixture of 1:16 as instructed by the previous owner. A friend suggests I need to clean/rebuild my carb which I do not know when the last time that happened was as I have not owned the kart too long. Finally, my father suggests that "this is just what two strokes do".

Here is my take on synthetic two cycle oils. After many years of desert racing two stroke powered dirt bikes and using full synthetic two stroke engine oil in all the snowmobiles and chainsaws I have and having more than 40 years of engine repairs and modifications I can tell you that indeed there is a difference in synthetic oils.

I have had a lot of engines apart in my time working on them and rebuilding them etc. One thing about oil mix ratios one has to remember and this is very important that when the oil mix ratio is say 16:1 the fuel is more viscous than it is than if the mix ratio is 20:1 for example. That being said say that you had been running a engine with a 20:1 oil mix ratio and you have set up the air fuel mixture correctly depending on the carburetor that is in use either fixed jets or adjustment screws and then you switch to a 16:1 oil ratio now that the fuel has become more viscous in order to achieve the correct air fuel ratio for the engine the carburetor settings will need to be set richer than the previous settings that were set up for the 20:1 oil ratio as the now thicker fuel resists going through the adjustment needles settings which is just the taper of the adjustment needles changing the size of the fuel circuit delivery or the orifice size in a fixed jet carburetor. This is where some people get confused because air fuel ratio and oil to fuel ratio are different. Some people think that when you mix a heavier oil ratio mix that you are richening up the air fuel ratio when indeed it is being leaned out due to the increased viscosity of the fuel. That’s right just what I said increased fuel viscosity. I have seen two cycle engines burnt up and seized because of what I have just stated. So just the opposite will happen if say the engines air fuel mixture was correctly adjusted for a 16:1 oil ratio and then the oil mix ratio was changed to 20:1 then the air fuel ratio would be richer and then for maximum engine output the air fuel ratio would need to be leaned out a bit. That being said take note of this fact and adjust the air fuel ratio accordingly as needed. Spooge is a normal thing for two stroke engines. Run them hard and flat out and the spooge will reduce if not go away.