Any tricks to cold weather starting

1.) Pull decomp, kick 10-20 times

2.) Choke ON, go to TDC, kick again.

Try it first without gas. if won't fire after 4-5 kicks, hold the gas WFO and try it again.

All this talk about warm/cold jetting is contrary to what I've experienced. My summer jetting usually pops/backfires when the temps drop, richening it up helps (pilot screw 1/8 turn, and increase MJ one size). Perhaps the pressure is the determining factor. Dunno, and I'm not going to argue why.

Taffy, I applaud your theory, but leaning my jetting as far you've gone seems like I would be going in the wrong direction. I've tried various settings, albeit not as radical as you have. The bike RIPS, has no dead spots, doesn't foul plugs, and never stalls/hiccups. If I use leaner settings, it starts to hiccup, backfire, and looses power. It also surges to some extent. It was doing the surge routine REAL BAD with the stock jetting.

I'm not saying I don't believe you're bike RIPS too. But I do believe each bike runs a little differently, therefore needs tuned as such..

You guys are friggin nuts. Cant ask a simple question and get a simple answer. A guy asks a simple question and it turns into a debate about who knows the most.


When I first got my bike it was winter and I had a hell of A time getting used to it. Try the simple sugestions firs and I bet you will figure something out that work for you. God luck.

Thanks, Missile...the density of the GASOLINE was the thing that I was missing in the whole equation. I was sure that the gas laws were the overriding factor, but the change in gasoline density makes the biggest difference. That's the kind of technical info I was looking for.

Now I can go and look like a real egghead around my riding buddies!

you three are a bunch of tarts. join the girl guides the lot of ya!!

you boys just can't take it when your wrong can you.

one says he doesn't believe me but leaves just enough room to answer this post with "now i didn't say i didn't believe you, i just said that there is no way i could do that coz it runs ok" (read tried to change the jet once and didn't know what the heck was going on!)

one of you says let's answer the original question - as if anyone gives a flying pig at this point and the third one sits there like the school swot!!

you're all tarts. now give half your sweets to your teacher NOW!!

or i'll confiscate the lot of them! :):D:D


What's a "swot"?

Any of you guy ever do physics ?

TEMP and PRESSURE both have significant effects on gas and liquid volumes (temp only) which is what we are concerned with when we are getting out jetting spot on...right !!!

So if you follow the logic below...hang on we're going back to school :)


BOYLES LAW: If temp is held constant then the volume of the gas is INVERSELY PROPORTIONAL to the change in PRESSURE.

Basically if pressure goes from 1000 mb to 900 mb air volume will increase by 1000/900 = 1.11 and DENSITY will decrease proportionally. Air density is 1.224 kg/m3 at 1013mb at sea level at 15 degrees C. So at 900mb at sea level at 15 C air density will then be 1.087 kg/m3.

In THIS situation with a drop in pressure your carb would be getting 11% less air (O2) than normal so you would be running RICH.

I know this is not the only thing going on so bear with me.

Temperature also has an effect on gas volume which leads us to

CHARLES LAW: For a CONSTANT pressure, the increase in volume is directly proportional to the change in TEMP (in degrees kelvin = Centigrade + 273)). So you heat it up, its volume increases proportionally and vice versa. So 15 degrees C is 288 Kelvin or 59F. When temp drops from 15C to freezing (273 Kelvin or 32 F) the % drop in temp is -5% which decreases volume 5% which increase density 5%.

In this instance where temp is dropping you would be getting 5% MORE air than usual so you would be jetting LEAN.

However temp and pressure are not independant of one another so you have to do both calculations at the same time.

A rough chart follows:

Air DENSITY chart

Mb Pressure

C F 900 1000 1100 1150

-15 5 1.214 1.349 1.484 1.551

-10 14 1.191 1.323 1.455 1.522

-5 23 1.169 1.298 1.428 1.493

0 32 1.147 1.275 1.402 1.466

5 41 1.127 1.252 1.377 1.440

10 50 1.107 1.230 1.353 1.414

15 59 1.087 1.208 1.329 1.390

20 68 1.069 1.188 1.306 1.366

25 77 1.051 1.168 1.285 1.343

30 86 1.034 1.148 1.263 1.321

35 95 1.017 1.130 1.243 1.299

However we're not done because the same principles applies to LIQUIDS. You can pretty much take Pressure out of the equation as its virtually impossible to compress a liquid.

Follows is a density chart for GASOLINE at various temperatures.



Remember gasoline expands and contracts 6 times more than water. TRUE

Formula for the percentage change in volume related to a temperature change of 1 degree celsius starting at 20C is 950 x 10^6 = 0.00950 TRUE

or almost 1% per degree C - which explains the breather hole in our gas tanks !! SO WRONG


C F Density kg/litre

-15 5 1.022

-10 14 0.972

-5 23 0.924

0 32 0.880

5 41 0.838

10 50 0.798

15 59 0.760

20 68 0.724

25 77 0.691

30 86 0.661

35 95 0.634

So then the next step is to combine the two charts to see what happens to the air/fuel ratios/mixture.

Fuel to Air Ratios

Larger number = richer condition.


Mb Pressure

C F 900.00 1000.00 1100.00 1150.00

-15 5 0.84 0.76 0.69 0.66

-10 14 0.82 0.73 0.67 0.64

-5 23 0.79 0.71 0.65 0.62

0 32 0.77 0.69 0.63 0.60

5 41 0.74 0.67 0.61 0.58

10 50 0.72 0.65 0.59 0.56

15 59 0.70 0.63 0.57 0.55

20 68 0.68 0.61 0.55 0.53

25 77 0.66 0.59 0.54 0.51

30 86 0.64 0.58 0.52 0.50

35 95 0.62 0.56 0.51 0.49 it gets colder for a given pressure the air/fuel mixture RICHENS, which means you have to lean the jets. WRONG

So have I proved to you guys that basically colder weather RICHENS. Warmer weather Leans.

Higher Pressure leans and lower pressure richens the mixture. WRONG (OUCH WAS THAT A KICK!!)


Watch the barometer AND the temp guage but REALLY watch the baromter.

One last thing....fluid dynamics at different pressures/temps also have an effect as does the RPM of the engine, the size of the cylinder etc etc. Also....humidity plays its part...RIGHT!!!!

I'm done. I spent 3 hours working on this thing.


[ January 10, 2002: Message edited by: The Missile ]

A BOOKWORM. a goody two-shoes, teachers pet. anon.

and do you know what?

after all these flooded bikes, after all the above info, after all the people that say things like "i need choke in the summer but none in the winter" etc etc THERE WILL STILL BE THOSE THAT SAY "I CAN'T SEE IT, I JUST CAN'T SEE IT".


the fact that you all fall over on the first stone crossing the river even though you've been shown the route makes me feel great.

when you've tried really hard to help and had it basically thrown back at you you get a little pissed. this i hope you'll understand. i lost the entire website after just one (that's one folks!) days testing.

you've been fed on so much bull**** over there you don't recognise the real deal when you see it. when JDS did jet toward my settings he said it was like fitting a turbo to a 610!

20 years in the workshop boys and your computer, your scientists, your bull****ters, your top pro mech's where are they?

where are they?

5,000 members and none of the hot pro's bar BK have given you any worthwhile help.

don't forget i live surrounded by USAF's. i know you far better than you know me. far, far better.


Yeah I guess you're right...we Americans all suck. Geez!

You guys are killing me! ROFL This is 'rocket science' at its finest. :)


Taffy, you crack me up man. It's the parts I don't understand that make me laugh the most.

Man...go away for a couple of daze and someone forgot to pull the Crack Pipe out of his hands :) Looks like this high might last for awhile :D Somebody break out the Narcan already......

Bonzai :D

:) Ha Ha Ha! Oh dear, I am afraid that Taffy is gonna give you lot a hard time for a bit....I'm open to bribery to go and tie him to a chair for a couple of days?! :D:D Seeing as it's a bit of a trip for everyone else! He He He!

You just know don't ya...he's not gonna "Let it lie" is he!

Oops....I screwed up on the gasoline density

thing big-time, also on the range of pressure at sea level (but it was correct for elevation changes). New air/gasoline mixture table attached below... bigger numbers = richer, smaller numbers = leaner.

Air/Fuel Mixture

Assuming 20C and 1005 Mb Gives 1:14.7 Ratio


C F 990 1000 1013 1023

-15 5 0.92 0.91 0.90 0.89

-10 14 0.94 0.93 0.92 0.91

-5 23 0.95 0.94 0.93 0.92

0 32 0.96 0.95 0.94 0.94

5 41 0.98 0.97 0.96 0.95

10 50 0.99 0.98 0.97 0.96

15 59 1.00 0.99 0.98 0.97

20 68 1.02 1.01 1.00 0.99

25 77 1.03 1.02 1.01 1.00

30 86 1.04 1.03 1.02 1.01

35 95 1.03 1.02 1.01 1.00

So from my conclusion above I was wrong you actually get a SLIGHTLY leaner mixture as temp drops for a given pressure...BUT FOLLOWING MORE RESEARCH THESE ARE FAR FROM THE ONLY DETERMINING FACTORS. I admit I'm out of my depth but I did a lot of hunting on the internet as this intrigued me enormously....

My conclusion: I am still convinced by all the reading that I have done that during STARTUP very cold weather causes the system to richen considerably until it gets up to operating temp and probably even when at normal operating temp. They key here is very cold weather. I dont think the same applies when you get big temp changes but it still is relatively warm. (eg +25C to +10C)

Overall I think the 'leaning' of the mixture from temp/pressure is relatively insignificant for cold weather starting - so basically barking up the wrong tree. Why do I say this ? Climbing mountains has a huge effect on pressure & air density and our bikes pretty much handle this OK during warmer weather. This leads me to think that starting issues in cold weather are more related to TEMP than pressure changes, ESPECIALLY when it drops below freezing. DOH ? Obvious ? Maybe..


In VERY cold weather the whole system is much farther below the normal operating temp before it warms up. Regardless of the mixture you put in the overall temp of the mixture is LOWER after compression than in warm weather (which is what your jetting is based on) which means you will get LESS EFFICIENT BURNING which means you will NOT burn all the fuel which means the mixture is RICH and you will need to LEAN it.

Liquid expansion has a cooling effect. If its real cold (below freezing) you could get icing from humidity inside the carb as the gasoline atomises-expands. This could restrict air flow etc etc Too Rich.

Atomisation of Gas : colder weather reduces the ease of atomisation of gasoline (denser) so you get bigger droplets which are more difficult to burn...too RICH again.

Also... I moved from a well jetted machine with standard header and exhaust to a FMF header and Stroker exhaust. At the same time the weather drop by at least 10 degrees C and has stayed there (about -3C on average). Now....normally you have to jet slightly richer for a freer flowing exhaust, right ? I fouled my first plug and when I finally got it going my bike is TOO rich even with new header and exhaust without having made any jetting adjustments. The only factor that has got BLOODY COLD!

VERY Cold weather : Jet down is the only conclusion I can come to.

I read somewhere that you can get better performance out of your bike with a lower octane rating in winter than in summer given the changes in Octane rating of the engine due to temp reduction. I'm not sure what that means but thought I'd throw it in anyway. :)

This isnt to say that pressure has no effect. Obviously it does for perfect jetting as does humidity along with temp. Ask the racers, they know.

Oh yeah.. team sponsered riders what do you say : or do you not ride in REALLY cold weather? Just asking, not poking with a stick here !

So...I'm gonna shut up now. I threw the cat into the Chicken coop with my first message, I'm sure this is gonna throw the Tiger into the coop now.

I'm just gonna sit back and watch the fireworks and if you guys want to call me an idiot, Go ahead, I have a thick skin.

Let battle commence !!

Hey Missile, at least YOU were willing to try to provide scientific/mathematical evidence to back up what you were saying. (As opposed to SOME PEOPLE who insist that we take their word as gospel and that any questioning of his conclusions are a personal affront.) Making a math error--and then correcting yourself--is no sin and we scientists/engineers understand that if you can't question your own conclusions the scientific method only becomes dogma and not a serious tool for discovering 'truths'. I think your revised conclusions are valid in relationship to MY real-world experiences: that temperature and pressure changes (excluding altitude effects) cause more problems with warm-up, air filter/air flow efficiency, and fuel atomization than with jetting. And once the bike warms up, most of the "richness" problems seem to go away.

Na-na-na-na-na :)

[ January 10, 2002: Message edited by: Rich in Orlando ]

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