2-Stroke setup question (YZ250)

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Yrocmoto

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• Jan 16, 2016

• #1

So my YZ has been a ripping blast this year. Fresh snow every week, running circles around some turbo'd sleds (in the trees), but....

My bike runs fine going out, but a couple hours in (or less) it starts running like crap, like bad jetting. Thought it was the filter as I only have dry foam ones right now (outerwears on the way), but even pulling the filter off and riding the road still ran like crap. All carb hoses seem clear. I'm running 'heat' de-icer in the fuel, but the carb does still get all packed with ice, which I'm thinking is the culprit, except that my 2 buddies on KTM 300 Sx's are not having any issues on the same rides....sucks for me... andy ideas?

What's the best solution for keeping the carb warm? I'm thinking of wrapping the engine up with some kevlar and/or tapping into the coolant and just wrapping a tube around the carb with some coolant flowing through it.

 

egesledder

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• Jan 16, 2016

• #2

Sounds like a carb ice issue to me. The venturi's in the carb throat can get ice build up around them and start making stuff run weird. I've also had the vent lines freeze up at the ends and create jetting problems, but it sounds like yours were clear.

Carb heat can help that a lot.

 

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dirtrebel

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• Jan 16, 2016

• #3

Its carb icing, you need a heat collar on the carb, 2 strokes engines won't make enough ambient heat to warm the carb, carbed 4strokes can get by but smokers can't.

 

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Air440

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• Jan 16, 2016

• #4

Little off topic, but how does the YZ compare to the 300sx's on the snow? (Aside from the carb issue)

 

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Yrocmoto

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• Jan 16, 2016

• #5

Air440 said:

Little off topic, but how does the YZ compare to the 300sx's on the snow? (Aside from the carb issue)

Click to expand...

Don't know if it matters, but I have the newest kit ('14) and the SX's are '11 & '13. Power wise I can't really tell, they are comparable. The YZ seems to lug better, but the sx's have a wider powerband, or at least comes on sooner, so it's always on the pipe, which really could be setup and jetting. So really no real overall difference, they are both 2 stroke snowbike fun....

Thanks for all the replies, I concur that carb ice has got to be it. After I posted I remembered that both the SX's don't have snow directly on the carb, one put duct tape and the other has a rubber tube, so this makes perfect sense. Probably anything to keep the snow off the carb will do wonders for me. I'll post back after I get something on there.

 

Last edited: Jan 16, 2016

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Revy-rider

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• Jan 17, 2016

• #6

Get your pipe and engine shrouded in, keep snow off the carb. We ride deep powder, I don't run carb heat and have no issues

 

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Yrocmoto

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• Jan 17, 2016

• #7

Yeah, that's my next project. I've ordered up some Kevlar to do something like that. Some guys here have plastic engine covers that look OEM, really nice. I don't know what they are using, but I know they heat it up and mold it to the shape the need. Looks sweet.

 

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Yrocmoto

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• Jan 17, 2016

• #8

I thought I saw some sort of carb jacket pattern pic somewhere here, but I can't find it now. Anyone have anything?

 

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SEOINAGE

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• Jan 17, 2016

• #9

I added some extra T's to my carb breathers and routed a line to behind radiator. Worked fine at first. Then last ride I started having similar issues. But I also broke the casing on my throttle cable and was getting a ton of moisture in it, and my carb started freezing and running even worse. I'm assuming keeping that thing warm would help. Normal days if I clean it off a bit, even if the carb is still encased it seems to help. Also the little stuff was sticking to my prefilter, so it helped to wipe it off, but of course that didn't last long.

 

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dirtrebel

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• Jan 17, 2016

• #10

here's one of my first bike years ago a yz250

Here's one from 2012 when I was doing some heavy r&d on the 2 stroke front, lmfao trash cans (actually this one was my wife's recycle bin from her desk) and duct tape got the job done!

 

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BMF725

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• Jan 17, 2016

• #11

I am running a yz295. I ride in northern Michigan and had my carb covered in 2 inch layer of ice today and no problems what so ever with no carb heat or iso in the fuel.

Your problem is your vent lines are getting plugged. I was having similar symptoms bike would run great for first 15mins then start running super fat at wot and super lean on the needle.

You need to put T-fittings on all the vent lines and run them up to the air box into a piece of foam. or buy the PC racing Carb vent kit for like $20.

 

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Revy-rider

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• Jan 18, 2016

• #12

I run my carb vent hoses into a pill bottle with foam at the bottom and holes drilled for drainage. Bottle is zip tied to the frame. Works great, costs nothing.

 

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Yrocmoto

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• Feb 1, 2016

• #13

Okay, routed my carb vent tubes to just above the header, which is like the only place to not freeze up with snow. They are always clear. Went on a ride last week and it had been warm for a couple days, so the snow was heavy and it ran great all day. (no snow getting in the airbox, not even much on on the engine, I had to uncover one of my rads to keep it cool) 2 more storms came through, and Saturday my bike was completely submerged in snow all day. Got a good hour out of it and then it slowly ran worse and worse. Every time I stopped I 'tried' to get the snow out of the airbox (sucks cause it's like a bucket and with the filter in there I can't really grab a handful). I cut out the flap at the bottom, but it still clogs up easily. Turns out, I'm getting enough snow past the filters (dry foam filter and Outerwears) that it's running like crap after the carb is filling with water. (always runs good again after draining the bowl).

I've already enclosed the entire box with Frogskinz, which didn't work as snow would sit on top of it under the seat and 'grate' it's way through, and then I couldn't get it out since it was all enclosed, so I tore that out as it was not helping.

Seems that removing the airbox and using some type of pod filter is the only solution, but I don't really want to do that. Any other ideas I'm missing here?

 

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jskattum606

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• Feb 2, 2016

• #14

i dont know how eveyone is getting by with no carb heat. My first ride out my carb was icing up inside the throat and then the throttle started sticking in different throttle positions. NOT fun.

Put on an Avid carb collar and all is well. Have had Zero issues the rest of the season and my carb tubes are hanging under the kit with no T's

 

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Yrocmoto

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• Feb 2, 2016

• #15

jskattum606 said:

i dont know how eveyone is getting by with no carb heat. My first ride out my carb was icing up inside the throat and then the throttle started sticking in different throttle positions. NOT fun.

Put on an Avid carb collar and all is well. Have had Zero issues the rest of the season and my carb tubes are hanging under the kit with no T's

Click to expand...

Yeah, me neither. This is the #1 most important thing or it will not run long at all. We haven't had to put actual heat there though, just covering it to keep the snow off works fine. I tried to keep mine enclosed to transfer some heat from the cylinder, but it makes getting to the carb a little harder, not much. Hardest thing is I didn't cut any holes so turning on the choke is a little tricky through the rubber, but not bad.

 

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SEOINAGE

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• Feb 3, 2016

• #16

I have had no carb ice problems. The only time it stuck was when the cable broke and let snow in. Replaced cable and fine.
If it starts to run worse later in the day, first thing I do is clean off the prefilter. I actually want to get a larger prefilter, I think it would help. If that doesn't solve the problem I clean some snow off the vent tubes, even though they are routed to two places. It seems to help still, usually it is just wiping off the prefilter and making sure temps are up and I am fine. My carb gets completely iced over and still no problems. I take off the intake and check for ice internally, nothing, and even on the intake side there is enough of like a light oily film from my premix that I don't think ice could even stick. I haven't had float bowl issues either.

Personally I would get yourself a nice pod type intake. A good silicone reducer to go up to 3" then something like a boondocker turbo intake.

Are your temps over 100 deg? Mine runs poorly if it is much under 90.