What are the symptoms of carb icing?

TeamOrange · Feb 20, 2011

I rode maybe 10 times last year and today was my third day this year.
I ran into a problem when I would run with the throttle pinned for a few seconds and let off the gas, the bike would want to pop, sputter and want to die.
Temperature was on like 25F at the coldest but did have some semi deep powder.
Short bursts of WFO or less than full throttle didnt seem to promote a problem.

I have an 06 KTM 525 with a 2moto kit.

Oz

Jon Mutiger · Feb 20, 2011

It could be one of 2 things, first off carb icing occurs inside the throat of your carb, and usually happens at a warmer temperature, typically just above freezing. The reason is all the moisture in the air being squeezed through the carb at speed caused moisture to be deposited as ice on the inside of the card. To be honest, I haven't seen this to be a big issue on my 2moto or my buddies Timbersleds at all.

What I have seen is the air filters get clogged with snow and ice, and reduce the amount of air they flow, messing with your jetting.

The only thing you can do for this on the trail is knock the frozen bits loose and hope your air filter passes more air.

My 2moto is not nearly as finicky as the Timbersleds in this regard, but I also think I got really lucky with my rear fender setup as it seems to block of the snow from ever getting to the filter, and since I have no air box I'm only sucking in the flying snow, not the stuff filling an airbox.

Good luck!

Jon

TeamOrange · Feb 20, 2011

The filter wasnt really covered in snow and ice, just that the pre filter was kinda wet looking.
I knew I should have pulled the air filter to see if there was ice in the venturi.
I need to test ride again before I spring for the carb heat kit.

Oz

tomk · Feb 21, 2011

it isnt the filter, your bike is too lean, back fires happen when the combustion is starved of o2... remember the movie back draft, same idea. if it only happens when you hold it WFO for a while then u know it is your main circuit. try a bigger main jet and see if that helps

TeamOrange · Feb 21, 2011

Since it never happened until this ride, I think I'll take the carb apart to check for contaminates, maybe there is some crap in there too.

Jon Mutiger · Feb 21, 2011

Also, your jetting at altitude and without an airbox is different.. So if you haven't played with your jetting it's quite possibly that.

I've had my bike, a fuelly occassionaly after a long hard pull sputter at lower rpm.. Maybe I'm getting some icing issues.. I dunno.

Go richer on the jets and you should see less farting and popping.

Jon

tomk · Feb 21, 2011

good call with the sh*ty fuel these days carbs can gum up quick!

Sled Neck · Feb 21, 2011

I'd agree with everyone else. Sounds like you need more fuel to that baby. The main jet may not affect the fuel ratio when you let off the throttle though so it may be your secondary jet that needs the adjustment. If it happens again I would double check your air filter and carb for icing or blockage just to be sure.

TeamOrange · Mar 1, 2011

Still icing!?!

Well I went through the carb and found it to be super clean, nothing in the float bowl, nothing. I even lowered the clip on the needle one notch to fatten up a little and that just ended up losing me performance.
After icing up a couple times I simulated the same scenario with tools to pull the filter-sponge and pre-filter sock off to check for ice and sure enough there was a big ol ring of ice before the venturi.
I had a wool hat, so I wrapped it around the carb best I could to keep snow of it and no change. I ended up pulling the pre-filter off the course element and slapped the element on the back of my hand to see if there was any water and it sure enough there was a bunch.
Is the prefilter supposed to block all water? Maybe the outerwear is just worn out. I does rub against the shock a little. I didnt see any holes in it but Ill fill the sock up with water to see how bad it leaks.

Oz

TeamOrange · Mar 1, 2011

As far as the carb heat kit, the one Ktm has is listed for my specific bike (06 525 exc). Do you tap the float bowl or what? Of course I have a charging sys. so it should adapt to my bike right?

Oz

Ausm7499 · Mar 1, 2011

whats the part number for that kit. I have an 06 525 and have the same problem.

TeamOrange · Mar 1, 2011

The only KTM kit I found was part#55131003044. But It does not list my bike in the application.
Its for XC and XCW's 200,250 and 300cc.
Let me know if you find anything.

Oz

Ausm7499 · Mar 2, 2011

Thats all I have found too. Carb icing must be more prevalent on the 2 strokes. My buddy is running a MH kit on his 300 and just ordered this carb heater hoping that it will eliminate his issues.

Ausm7499 · Oct 14, 2011

Just wanted to throw this out there for anybody running a RFS KTM. This modified airbox cover was off of my 06 KTM 525 that I sold this summer and I no longer have a use for it so first $15 takes it.

After I sealed my airbox and drilled these holes in the cover and put frog skinz over them I didn't have any problems.

PM me if your interested

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What are the symptoms of carb icing?

TeamOrange

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