Anyone have trouble with their carb riding in sub 30 degree temps? My sons RMZ seems to be jetted right on, but after 10 minutes of running on ice track he loses lowend and bike stalls way too easy and becomes harder to start. Carb appears to be covered in frost.

I think thats a common problem. I remeber seeing a post somewhere on here about just wrapping the carb with insulation. I havent had it on my rm-z yet, so do not know if insulation will do the trick. I have had the carb ice up on my atc though.
What are you running for jetting, because I need to get my bike set up for the snow?

A KXF/RMZ running too cold now that is a switch!!!

I doubt that the insulation will solve the problem because cold air is flowing thru the carb. You may have to create some ducting to get some warm air off the exterior of the exhaust or from the radiators to solve that problem. But what do I know about ice racing being from Alabama. We generally park them in those temps. We have showed up to race MX when the clay on a MX track had ice spewed up out of it. And when it melted what a muddy mess. Been facing that earlier this week but supposed to be near 70 Friday!

(my problem would be me icing. geeshhh, ice racing, brrrrr) But I bet you could modify the airbox to suck some heat from the pipe side. Close off the top of the box and make holes next to the pipe side. Maybe some aluminum ducting riveted in? Another though is some thin aluminum ducting to grab heat from the back of the radiator and blow it on the carb. Round flexible foil tube?

Another idea which would take up less room would be to run some engine coolant around the carb. Maybe wrap a couple pieces of copper tubing around the carb and plumb it into the cooling system.

I race an RMZ250 on the ice and have not had problems with the carb icing, even at below zero temps... What are you using for fuel ? Race Gas doesn't atomize for squat the colder it gets out ... I'm running a 185 main , std clip position , 42 pilot 2 1/2 turns out with a FMF Power Core 4 and the quiet insert. Using 92 octane no oxygenated pump gas (winter blend???) .

Have to agree with Rich_Fish. Ice raced the RMZ in very cold below zero temps and no freeze up. Only thing was jetting and put some cardboard in front of the rads to keep the heat in.

Like the cardboard idea to keep the heat in the motor , how big of a chunk are you using on each radiator?

Just large enough to wedge between the air fins or you can take the air fins off and secure the cardboard via cutting the same holes that the fins bolt to and then use a large washer or small strip of thin aluminum (approx 1/2 inch wide) that goes from left to right and bolts into the same holes. It acts as a strap to hold the cardboard on. Just keep an eye on your temps as the day goes on as you may have to change jetting specs if operating temps get to high.

Personally, most of the time I just jam a piece in for the race to block the cold air and then remove it after. It isn't fancy but it works.