cold weather problem

[mopar]

my bike was running fine when it was warm the other day but yester day it was -8 and i think the wike was deonating, it had the wiseco 10.25 comp piston, what the best way to cure this, jetting ,colder plug..........?

 

[dave76]

-8 is a little cold, I would say if you intend to ride ride in such extreme cold, to mebe put a hotter spark plug in. You have to understand that at that temp if there is any moisture present in the air, as it is being pulled into the engine it's feezing. Also at that temp it's possible the fuel is dropping out of suspention back to a liquid state, and you know liquid fuel doesn't burn well, thats why I'm against jetting it fatter. Some time in these places people put pre heaters on the intake side. Someone else mabe able to answer it better.

 

[palerider]

What octane fuel you using?

In cold weather you can use a lower octane fuel. It will help with the cold running issues. A lower octane fuel will start better and run better due to its easier ignition.

In the 80's when the petroleum industry did there big push for higher octane fuels being so much better. (Cost of premium gas is only 3.5 to 5 cents a gallon more to produce than regular unleaded but retail price is usually around 14 to 25 cents more) A lot of cars were brought into dealers with cold weather issues so it prompted a lot of service bulletins advising to run lower octane fuels in the winter.

 

[dave76]

I didn't even think of that. Lower octane (87) burns faster and hotter, and higher octane (93) burns slower and cooler.

 

[palerider]

Right, but do not get caught up in the generalization that lower octane burns hotter than higher octane. They burn at the same temperature but have different "resisteance" to ignition. Where the heat problems come from is when they are burning and in some cases exploding.

Low octane fuel in a high compression engine will actually explode due to the pressure and not burn resulting in the pinging and high heat. But also if you are running too high of octane the burn can end up taking to long/starting too late and continue till the exhaust valves open resulting in more problems, such as loss of power, and extremely high exhaust temperatures.

That is why I find it funny when people talk about running "race gas" in their lower compression engines.

Remember for the most power and the lowest temperature results use the lowest octane you can with little or no predetination.

 

[griff]

Correct, octane is strictly measurement of the ability of the fuel to resist (pre) detonation. Its not energy potential.

In any case, when you originally tuned the bike (the jetting), what time of year was it, average outside temp?

 

[griff]

Never came back huh?

Well....

My guess is that he probably tuned it during the summer, anywhere from 70* to 90* outside. GENERALLY speaking, carbureted tuning is really only good for a 30* to 40* swing in ambient outside temperature.

So, very basically (its more complex, but for this discussion it'll do) if you tuned the bike when it was 80* outside, and it ran perfect, then say anything 40* or below would be outside the threshold of the A/F ratio (for running properly)

At -8* outside, it wont run probably at all, all that cold very dense air doesnt have enough fuel to combust properly.

You'd have to tune it specifically for cold climate operation, and theres a variety of techniques for doing that.