Here's a couple thoughts I had while going through this thread:

- A "hotter" plug probably doesn't make a lot of difference to a cold engine (as far as I know). Hotter plugs typically have a longer insulator, and therefore a longer heat path to the head & cooling system. It may make a difference after the bike is started and will probably warm up quicker, but it doesn't seem that it would make much difference in getting started. (I have no experience to back all this up, though.)

- A cold engine probably has lower compression than a hot engine. (Note: I'm not talking compression ratio - that is a mechanical property that doesn't change with temperature.) The lower compression is due to the colder cylinder and head, which can absorb the heat when the fuel/air mixture is compressed. Is it a significant difference? I don't know, but other people's experience with heat lamps and propane torches to warm the head would indicate that it is.

- Unless you have a carb heater, atomization of the fuel is probably not changing with temperature, since the carb itself doesn't really change temperature when the engine is cold or hot. Condensation of fuel downstream of the carb (i.e. in the cylinder) when the engine is cold is more significant.

- I get the impression from my bike that a free-flowing exhaust system makes starting harder than the stock exhaust, which has more back-pressure. This doesn't change with temperature, but might be a significant factor during cranking (i.e. there's no real momentum to the exhaust gases, so the more restrictive exhaust keeps more air/fuel mixture in the cylinder during cranking).

Again, these are just my thoughts and observations, and I could be way out in left field, so, no real answers here, just more food (fuel?) for thought.

On the last point, I remember after drilling my stock exhaust, I was wondering how much exhaust back-pressure there was, and how it would affect the engine. The exhaust wasn't hot, so I wanted to see what plugging the end would do. I stuck my thumb over the outlet and to my surprise, the engine kept running without showing any effects. I let go after about 5-6 seconds, thinking "Isn't that interesting!"

So now I'm wondering: Would holding your hand over the exhaust while cranking help to start a cold engine?

I might just try that and post my results!

EDIT: Well, I tried it, but I can't say definitively if there was any significant difference. It took 3 tries with the starter, but its been like that before. Its also taken 4 and 5 tries at times, too. This was only 1 cold start, so I'll try again next time.

Mike

 

Buckley is about 15 miles east of Tacoma in the foothills of Mt Rainier. I live next to a very large lake called Lake Tapps.

 

Cool my brother-n-law lives in Fircrest and I go to Puyallup a couple times a year.

 

I have tried to start my bike twice with no luck. Its cold here, single digits. I hate to sound like a dummy but where do I spray the starting fluid? Do I just spray a bit into the airbox or do I need to remove the air filter and spray it through the spark screen? I dont want to put it away for the winter. I think that I would like to start it and run around every few days. Is this going to be hard on it? It sits under a cover under my carport shivering as we speak. If my wife would let me bring her in I would.

 

You don't need to remove the filter, just spray a little into the airbox opening. The stuff is pretty volatile though, so heed the warnings w/regard to open flames, sparks, etc. It doesn't take much to get the engine firing.

 

Seems from what I've been able to find to date, that most of these "cold climate engines" have some sort of primer mechanism to get the gas to flow more freely when starting cold...

I would guess that short of jury-rigging a primer button onto our carbs, the starting ether seems to be the best bet....

You might find this article interesting as it discusses how cold gas doesn't evaporate very well... as pointed out in earlier postings above..

http://auto.howstuffworks.com/question74.htm

 

Ok, who ever suggested putting your hand over the exhaust while starting might be good advise. I don't know if it was dumb luck or what but the bike cranked and cranked and was not starting...then I put my hand over the exhaust and it fired right up hmmmm, makes you wonder.

 

To have to take off the seat every time to start it is an inconvenience to say the least. I tried the small space heater about a foot away from the bike with temps around 20 and after just 5 minutes the bike started up as if it had been running already. I tried it on the other bikes and same thing, 5 minutes and they started right up. And I know that's less time than taking off the seat and spraying starting fluid in there, but to me its an easier solution.

 

Well this might be one of those urban legends but I heard if you put your hand over the exhaust you can blow a head gasket........any thoughts guys? I suppose it would depend on how long you held it there?

 

Just buy a Mikuni TM33 pumper carb. No problem starting with that in place. Twist the throttle and you automatically spray a shot of gas into the intake tract. Works great, don't it Nobrakes?


On the urban myth about holding your hand over the exhaust will pop the head gasket . . . . .

Exhaust is a gas and is very compressible. The old trick was to stick a potato into someone's exhaust and watch them ride away for a short distance and then the bike would stall. They would start it and ride another short distance and then stall once again.

Heck, I've sent the exhaust block off almost across the street when I start the bike up if I forget about taking it out!

Not a problem.