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Posted by David Sherman [24.32.202.83] on Friday, January 08, 2010 at 14:44:49 :
In Reply to: Carb. heat posted by T-roy [66.172.253.91] on Friday, January 08, 2010 at 14:27:54 :
I had that problem with my first Sno-Cat. Ran fine going up the mountain, but coming down it lost power steadily until it would barely go. The carb had iced up because the heat riser was inexplicably (for a sno-cat) set to the "summer" position. Some 230s have a thermostatically controlled heat riser, and some of them have a manual control where you loosen a nut and move the pointer to how much heat you want. The trouble with the manual ones is that they never get moved and so they rust in place. Twisting the shaft with vise-grips will just break the flapper loose inside. The only way to fix it is to pull the manifolds and separate them, which means getting a manifold gasket set and probably getting the the manifolds resurfaced. It's a piece of work. On that Sno-Cat, the entire heat riser space under the carb and above the flapper was filled with soot. Going up hill, the engine was hot enough to keep the ice from forming, but when I turned around it cooled off and iced up fast.
You might get lucky and be able to break the heat riser loose by grabbing the shaft with vise-grips and wiggling it. Penetrating oil on the shaft won't help much because it's probably the flapper itself that's jammed. But just in case it isn't it's worth a try. Just don't force it and break the flapper loose from the shaft or then you'll even have more work to do. Generally the worst icing conditions are high humidity and temperature just above freezing. 15 below is not typically icing weather. At that point the air is dry enough not to ice up.
It might be worth mentioning that there's a bit of a trick to putting the manifolds back on properly, since the intake and exhaust are bolted to each other and to the block. Once you have everything cleaned up, put the heat riser gasket in between the two manifolds and bolt them together with the bolts left loose. I add hi-temp silicone because the mating surfaces are always rough and you can't grind them without getting other things out of alignment. Then bolt the assembly to the block. You can put manifold gaskets in or not. Don't put any gasket dope on them because this is just a test fit. Snug the bolts to the block down (actually nuts on studs). Then torque the 4 bolts that hold the two manifolds together. These bolts will now stay tightened. Remove the assembly from the block and take it to the machine shop to have it surfaced. The point here is to get the block sides of both the intake and exhaust manifold in the same plane. Otherwise, if you had them done separately, the mating surfaces in the heat riser section wouldn't line up exactly and when you tighten everything down you'd end up with leaks and/or a high-stress twist that's likely to result in a cracked exhaust manifold at some point. 230 exhaust manifolds are scarce enough and fragile enough as is.
If you do have the manual-adjust heat riser, once you have it cleaned up and working, remember to loosen the nut and work it back forth now and then to keep it from getting jammed again.
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