Back in the days of the PRS chassis these sleds came with a square piece of corrugated plastic (w/ a corner cut off) if the trunk. Most of us never knew what they were for. I later was told that you put this over the foam in the airbox inlet to choke off the air & richen the mixture when it was very cold. Was this actually the case?

'doo has always listed that the stock jetting was good down to 0*F @ sea level. I've ridden when it was down to -36*F. Does anyone have any tips for keeping a 2 stroke running fine @ these temps?

I've heard of guys duct taping any openings in the hood (the ZX chassis has screens that can be opened or closed) to keep the snow out.

ha, ha... you have posted probably one of the better questions ever. in a real world sence all of us have probably been caught with 0` jetting on a trip and now its- 20 and your loop dog friends are riding like satan on ski`s... absoulutly restrict that box opening. i cant tell you how much, (remember theres cold air leaking in where the box meets the carbs) but i would say alot, more than you think. i would say if you made a peice of cardboard that covers up 2/3`s of the airbox inlet you might be in the ballpark. remember your offsetting both a volume of air and a density of air.. the volume hasnt changed but the density has gone bonkers. i say 2/3`s.. dont sue me if it still blows up.

if your airbox is like most ,a pita to get out to get to the carb a simple fix is to fatten the needles and stay out of full throttle to get yourself safely home .myself, I know there is a performance/mpg gain to be made by doing it but dont feel it is worth the effort .24 below is the coldest I have been in and was on the ragged edge of my jetting as my plug`s were quite white .if it`s colder than that my contacts start freezing anyway so I just stay in

if it`s colder than that my contacts start freezing anyway so I just stay in[/b]

If you're @ home that's OK :D , but when you're leaving Hornepayne & heading for Kapuskasing on a loop trip, you have to press on regardless. Plus those temps you're not that eager to wail along on the trails too fast.

Jet for the coldest temps you will see and deal with the extra fuel consumption. It might cost you an extra $100 a year but that is pretty cheap insurance. I think Yamahas are jetted for -20 or 30 and I have never had a problem even at -45. At 0c I do see a difference. Usually around 14 mpg at 0 and 16-17 at -20 and colder. Small price to pay.

A quick fix on top of not wailing on it is to pull up your Enrichment Lever (Often wrongly called the Choke.) to the first setting. This will dump in more fuel. You'll have to keep an eye on it through any bumpy trails as it can flip off quite easily. Obviously, if your sled is equipped with a primer button, you're SOL.

If your sled is equipped with DPM, it might compensate somewhat for the extreme temperature variation.

Kris, with the SDI your sled has, does that injection system not automatically compensate for the temp swings as well?

Jeff

Back in the days of the PRS chassis these sleds came with a square piece of corrugated plastic (w/ a corner cut off) if the trunk. Most of us never knew what they were for. I later was told that you put this over the foam in the airbox inlet to choke off the air & richen the mixture when it was very cold. Was this actually the case?

'doo has always listed that the stock jetting was good down to 0*F @ sea level. I've ridden when it was down to -36*F. Does anyone have any tips for keeping a 2 stroke running fine @ these temps?

I've heard of guys duct taping any openings in the hood (the ZX chassis has screens that can be opened or closed) to keep the snow out.[/b]


So at -15 - 20 its better to plug 3/4 of the air inlet off? Its still jetted stock and is in fact rich, but I guess thats a bit of insurance no?

I have found that when you run at very cold temperatures, Mother Nature takes care of things on her own to some degree. When my aviator picture was taken we were heading east out of Hearst. As we rode the snow dust from the sleds in front of you filled up the air inlet screen with snow, cutting off some of the air. We had to leave more space between riders to let the snow dust dissipate so that we could see the trail. This accomplished richening up the ratio. We stay away from wot as it is just too cold to do, but did travel at a good clip. I have found that it is most important to use gas line antifreeze and we cover our sleds up at night to keep the snow out of the controls (just one of those cheap dust covers available in Canada at Princess auto).

Early in the morning is usually the coldest part of the day for the rider until you get your clothing adjusted to stop all of the breezes. When starting the machines in the morning pull the recoil cord slowly for a few pulls to 'loosen' up the motor. Then try on the ignition, choke and start as normal. Before covering the sleds at night, we bounce the sleds and clear out any chunks of ice that we can. It's a good idea to bounce the rear of the sled in the morning and lift it to run the track for a few revolutions to warm up the drive system. Of course you need help holding up the back of the machine, so we usually do this in pairs. When the sleds have warmed up for a few minutes we put on our bags/packs and head down the trail. Fill-up with fuel the night before to keep condensation out of the tank.

There isn't a better sight than to see the ##### frost hanging in the trees and the sun shining brightly first thing in the morning as you follow a hard packed freshly groomed trail.

Snowfun, BTDT. Last year Hearst was -29*C. Yes the snow dust makes visibility a pain. We fill up & add iso when we arrive @ our destination as well.

Jeff, I'm not sure how cold the SDI compensates for. The question was more or less thrown out there for conversation. Probably a few members here wondering what that old guy is talking about (PRS chassis) :dazed: I'd never thought of using the "choke" for that. I've only had 1 sled all these years that had 1. The rest even the Elan had primers.

DPM and SDI should adjust for it. I've ridden my old DPM grand touring in -35 without issue, other than being cold.

That being said, I would say away from WOT when its that cold. Filling up and iso at the end of the day is a very good idea.

FishHog

very few dpm sleds have the enrichment feature. most have jetting for -4f and the system leans it from there. the ones that doo are early dpm grand touring ,the only one I know of is a triple 700, maybe the 800's (triples) did too.

1999 MZz 670HO too had an air pump to enrich the DPM functions.

my solution is to put in a squirt of oil right in the gas tank and a little gasline antifreeze also.

as i get older i don't run in the -20 or colder though. but for the tourers that don't have a choice, a 5 or 10 dollar spark plug is cheaper than a motor job and there is no down time.

just my 2 cents


dahmer

I run just a bit of iso at all times when it's cold. Doing it always meams it is less likely I will need lots at one time which you really want to avoid at cold temps when adding anything to the fuel usually leans it even more. Alcohol also burns hotter. Oil should not be a problem for the oil injection as most rated oils for sno-gos make it down to at least -40ºF/C. One of the things that can be useful when it's -20º F or less is to warm the rig for 15 minutes or more. It seems that heat inside the engine compartment warms even the belt, among other things, so that starting off is pretty effortless. One thing that needs to be remembered is to warm up the suspension gently when it's cold or shocks and other things can fail. Seals are very brittle and can leak if hit hard before fluid motion generates some heat. Also, grease on the system, even synthetics, can be a bit stiff until it has been "flexed" a bit. Stay off the throttle, raise the jet needles all the way, or run the carbs jetted cold or use a machine with an altitude compensating system like Polaris uses on their ACCS equipped machines. That's an air density system and cold air leaness is air density related.

Many dealers in Alaska simply jet cold when they ship machines to customers.

Iso and oil in the gas will not prevent lean burn downs in cold weather from incorrect jetting. Iso can be good in deep freeze conditons and is also as critical, if not more, at temps around freezing as it only prevents water from turning into ice and blocking curcial carb passages and jets. Adding oil to the gas will even further lean out the air/fuel mixture and does not make sense. The choking the air box concept makes perfect sense. Recently there has been aftermarket companies selling "Bulls eyes" and other adjustable vents to add to the air box to permit more air to enter the system. Some sled produce more power with these devices insatlled, which indicates an overly restrictive air box, but they say to close them at low temperatures, or increase jet size, because more power means more air and fuel. All the low restriction intake devices and air boxes require an increase in jetting, because they permit more air to enter the engine, so it makes sense that restricting the air getting to the engine will require a reduction in jetting. This will also mean the engine will make less power.

I think the best thing a person do for a carbed sled is to add a compensator, like a Tempa-Flow. There is no need to put up with an improperly jetted sled and accept loss of performance, unnecessary fuel consumption (wasted gas), unnecessary exhaust emissions, fouled plugs, etc. The Tempa-Flow is an automatic system and you get an ATAAC to add altitude compensation for a system that works like Ski Doo's DPM. Keep your carbs properly tuned for the conditions and save your engine, save your money and save the environment.

This is the coldest winter I know of for snowmobiling, that said it's only my second full year of snowmobiling, lol. I was on the Fusion 900 today with temperatures at -19*C. It's injected, so I figured no problem. Guess I was right, as I had no problems. However when the engine temperature dropped bellow a certain point, the computer prevented me from over-revving the sled. Basically, I had to drive slower to let the machine warm up a bit, and then carry on at whatever speed I was willing to travel before freezing my face even though it was under a belaclava.

Aside from that, I was impressed on how the machine handled the cold weather. Of course I freed up ice and bounced the suspension by hand before starting the sled, and let the sled warm up for a few minutes before trying to ride it (common sense).

my solution is to put in a squirt of oil right in the gas tank and a little gasline antifreeze also.

as i get older i don't run in the -20 or colder though. but for the tourers that don't have a choice, a 5 or 10 dollar spark plug is cheaper than a motor job and there is no down time.

just my 2 cents
dahmer[/b]
Oil has nothing to do with preventing a motor burning up due to a lean condition. Unless of course you put enough oil in the gas that it wouldn't run. Then it would guarantee no burn.

this is gonna go off topic but oil does have something to do with jetting..it makes it leaner. yup. its a well known fast tuning tool for moto x rs ...more oil , less burn able fuel, leaner. also adding alchohol will make it lean. the specific density of alcohol is real light compared to gas. alcohol should only be used when theres a real water and or snodust concern...or if your thirsty.

I guess technically speaking, adding oil will reduce your fuel volume and thus lean out a bit, but is the amout of oil you can put in and still keep an engine running really going to make a noticable difference?

I don't see how its going to help you, actually your hurting yourself, by making it leaner (although I'm sure its minimal), it isn't protecting from a lean burn down.

FishHog

the tempaflow system leans a rich mixture for warmer riding. meaning you would jet for very cold and the tempaflow leans the mixture. how? restriction. the system that is the oldest I know of is the dial-a-jet. which adds fuel to richen it thru its jet and hose to the bowl.

I suppose one other thing which could be done is to use higher octane fuel if you can find it. I know machines set up for regular can be more difficult to start when it gets real cold if they have high octane fuels in them - av gas for example. I suspect - don't know for certain, but suspect that they probably burn just a bit milder too, even in a warmed up engine. If you're real close to or beyond your jetting and need to get back somewhere, other than jetting correctly, I'd just use as many small things, none of which prevent a burn down alone, and use them as my ride back.

Great topic and replies guys :D

I suppose one other thing which could be done is to use higher octane fuel if you can find it. I know machines set up for regular can be more difficult to start when it gets real cold if they have high octane fuels in them - av gas for example.[/b]

I don't know about octane causing a sled to be harder to start, but having gasoline w/ the wrong volatilty or Reid Vapor Pressure can cause starting problems. According to my Grade 12 auto shop textbook (I'm sure someone on here has a more techncal answer)

For easy starting of a cold engine the gasoline must be highly volatile. Gasoline blended during the winter months is more volatile than that blended during the summer months.[/b]

This is another reason to avoid bying gas from a station that may have summer or fall gas @ the start of the season.

Nothing about av gas. I'm not sure of its volatility. Mind you it would be blended for use @ altitudes somewhat higher than sea level. Maybe it is less volatile for correct vapourization during flight @ altitude?

For easy starting of a cold engine the gasoline must be highly volatile. Gasoline blended during the winter months is more volatile than that blended during the summer months.[/b]

That's why they sell higher octane gasoline in summer, lower in winter. LL AV has an octane of around 105, I think, which is considerably more than the typical 87-92 at the service station pumps. The stuff does work fine in two-strokes when it isn't too cold. I do know though that at -20º F, the same motors can become real buggers to start with that fuel.

Higher octane does not burn quite as readily, consequently it should burn just a bit cooler I believe.

I wouldn't want to get into altitude issues and consequently confuse this question with richer mixtures that would result. Airplanes burning AV Gas in reciprocating engines have infinite control over their fuel mixtures from the cockpit and aided by a multitude of gauges - a completely different animal IOW. (This question would be moot we could just get the machine high enough, as less dense air at altitude could cause a richer mix with the same jets just as colder, denser air causes a lean mix.)

i have a good way on my sled to help with this problem. on the new proxr i got the vents in the hood can be opened and shut. i can keep heat in or get heat out. it will make life a lot easier then rejeting every weekend

i have a good way on my sled to help with this problem. on the new proxr i got the vents in the hood can be opened and shut. i can keep heat in or get heat out. it will make life a lot easier then rejeting every weekend[/b]

That may work on your sled but mine and many others draw their air from behind the windshield so it would make no difference with the screens shut.
I have a Tempaflow and jetted it for -25 and it leans the mixture up to +45.
I dont know what the limits are on a Tempaflow such as could you jet it for -50 and still have it lean clear up to +45? And as dooman said, DPM starts at -4 and goes up so not to safe there.

... non-related though somewhat related... since that ride when it was freezing cold, I got out on my Fusion once. It was cold again, but nowhere near as cold as -19 (it was -11C). Though I don't think it ever got that cold last year, save one night, I have a new problem where the Fusion gets too cold? Does that make sense? I have to slow down every now and then to let it warm up, or it's like it won't let me reach a certain rpm. Let it warm up past the typical ideal cool temperature on a warm day (125*F) and it's fine again.

It's injected, so I can't just jet the thing, lol. But I'm wondering if it's vented perhaps too well for coolder temperatures, or if the coolant is a poor mix? I don't mean to complain though, I'd rather the engine run cool and slow down once in a while, than have it run hot and have to pull over.

i have a good way on my sled to help with this problem. on the new proxr i got the vents in the hood can be opened and shut. i can keep heat in or get heat out. it will make life a lot easier then rejeting every weekend[/b]


So you're saying that your machine draws warm air directly from the engine compartment?

I would imagine that could be a part of a solution too. If one had to run in extreme cold (or sea level) when they were jetted for warmer or higher altitudes, if a portion of the baffling, the foam connectors, or whatever the machine uses to directly fresh air to the airbox were removed in such a location so that heated air from the compartment could affect the air entering the carbs, that too should help. It might be rather "guessy" and require covering some hood vents though too....just have to make sure no snow was getting sucked in through the air box and that no muffle wrap glass particles were floating free to get pulled in.

... non-related though somewhat related... since that ride when it was freezing cold, I got out on my Fusion once. It was cold again, but nowhere near as cold as -19 (it was -11C). Though I don't think it ever got that cold last year, save one night, I have a new problem where the Fusion gets too cold? Does that make sense? I have to slow down every now and then to let it warm up, or it's like it won't let me reach a certain rpm. Let it warm up past the typical ideal cool temperature on a warm day (125*F) and it's fine again.

It's injected, so I can't just jet the thing, lol. But I'm wondering if it's vented perhaps too well for coolder temperatures, or if the coolant is a poor mix? I don't mean to complain though, I'd rather the engine run cool and slow down once in a while, than have it run hot and have to pull over.[/b]

That makes me wonder if your thermostat or a sensor is not working right. Your coolant should not cool too much since the thermostat should be opening only as much as needed to maintain operating temps. The only other thing might be that your engine is getting a significant amount of cooling from moving air when your travel. If that's the case, I'd block a vent or two in the hood at those temps and speeds.

That makes me wonder if your thermostat or a sensor is not working right. Your coolant should not cool too much since the thermostat should be opening only as much as needed to maintain operating temps. The only other thing might be that your engine is getting a significant amount of cooling from moving air when your travel. If that's the case, I'd block a vent or two in the hood at those temps and speeds.[/b]

Sensor not working right? No, Polaris wouldn't install inferior sensors now would they? That can't be it... lol. Sense my sarcasm? I dunno, it's due for her checkup now, I'll see if it's different afterwards. She just past her 1,000 miles. Mah baby's growing up.

As often happens when out riding you encounter temperatures outside of your safe zone the easiest is to stuff a few rags in the external air intake ports. Use common sense on the placement so they don't get inhaled.

Real pinch, raise the needle and keep under 3/4 throttle or just keep RPM's down.

What I've done on my ZR 9 is gone to TPI valves. Simple to install and as it gets colder close em up as needed. I went with 2 on my 900. Jetting with mods taken into consideration is 1 size fat from stock. (stock is 430's, added Boyesen RAD valves +2 and gutted airbox -1, net =+1 with original 430's - looks like 440's to sled) So essentially I can go from one under to one over with the TPI's. or 420 to 440. Depending on my testing (once we get some good snow that is) I may try 440's for more margin. 9's really like there fuel though.

Watch the plugs real close and on some sleds like the XC/SP's get the hood closed up as the intake seal to the airbox is brutal and sucks snow like crazy. Buddy's was running toasty white and when we pulled the lid there was a mini drift in the airbox. Sealing the light helps out also.

My ZR 9 is pretty tight underhood so when the TPI's are closed ingestion and air leakage is minimal.

Also watch the Alcohol content from the pump or added for deicing as that also effectively leans the motor out. Not to uncommon for a sled to be jetted correct for straight gas but burn down due to alcohol content.

Marina fuel is another culprit - ask the question - when did you buy it?

Unless your all out racing, go a bit fat and then you at least have some margin for error. Some sleds like the ZR 9's really respond well to rich main jetting.

Just wanted to add more here... after getting my Fusion 900 serviced the under-heating problem has been removed. It's just like new again. Don't know what was done, but they did something to fix it, lol. Then again, it could just be the fresh gas and new plugs, lol. I dunno.