Carbs on small engines seem to be a mystery to some people, sometimes even mechanics that work in other fields. There really is no mystery to them but when you look at a young tech in the auto industry, it turns out many of them have never worked on carbs. I mean everything these days is fuel injected so why would they? Sure a lot of guys will work on anything but even then the small two-cycle carb seems to be a mystery.
If you have taken apart a carb from a chainsaw, weed wacker or in this case an ice drill then you know that there are gaskets in there. Where they go isn't an issue but in what order seems to pose a problem and I'm gonna try to clear that up.
In the above pic you see an example of a typical two cycle carb. In the center of the carb facing up is a small arm called the metering lever. This controls the opening and closing of the needle valve that allows fuel to enter the metering chamber. The height of that lever is important but we're not talking about that today. Laying on top of the carb is a gasket and in my hand is another called a metering diaphragm. The metering diaphragm moves up and down and pushes on the metering lever but we're not talking about that today. The point here is that the order shown is how 99% of small engine carbs are assembled. Gasket, metering diaphragm then a plate like the one in the top right corner of the pic.
In the above pic you see the gasket sitting on top of the carb. Think of that round area as a carb bowl and the gasket depth increases the volume of that bowl. This may help remind you of the assembly order. I dunno, works for me.
On the other side of the carb is an odd shaped gasket and a thin flexible gasket. The thin flexible one always goes against the carb. You don't need a pic if you've ever done one but a lot of guys do get it wrong. The thin flexible gasket acts as a valve over some holes in the carb. Remember that it could never seal those holes as a valve if it had a spacer (the gasket) between them.
So what is the exception? I'm not sure of all of them but I know one for sure is on certain Tecumseh engines. This is a carb from an older Jiffy ice auger. It seems a lot of ice fishermen are ambitious folks and try to repair these carbs themselves. We sell a lot of rebuild kits. The problem is that even if a guy has experience rebuilding carbs, this one is different.
On these Tecumseh carbs, some of them are assemble bass-ackwards. If you take a close look in the area I circled...
...and you see the letter F then you know this is one such beast. The correct assembly order of the gasket and diaphragm is as follows:
You can try and do it the other way but then you just get frustrated and bring it in to me for repair. When I see one of these come in and the work order says the customer just rebuilt the carb but it still doesn't run right I always know the first place to look...and now you do too! So go now and walk in confidence with your head held high armed with the secret of the type F Tecumseh carb.
Later.
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