Cold weather mixture conundrum...

[XenonDream]

I hope the exact answer to this hasn't been posted anywhere. If so, I could not find it... Here goes:
I'm currently running a SkyHawk 66cc with stock NT carb, 20:1. I generally run a black plug, sometimes even wet. Yesterday's ride to work made me keenly aware that cold weather will lean out the air fuel mix. It was one of those unseasonably "OMG" cold days. The bike seemed to lose power a couple times. I did a plug check on my lunch break, and it was a light tan color. Knowing that it would be just as cold at 10 pm (mid 30s), I raised the needle a notch and then choked the engine half to death on the way home, resulting in a slightly darker tan, but still pretty light.
Now, I know you're supposed to richen up the mix for cold weather, but is there a threshold where the effects of low air temps could become prohibitive to running the motor?

 

[ibdennyak]

Hmmm, that's a good question. I will say that "mid 30's" isn't that cold. I have run my tecumseh 50cc at 0 F with no problem (other than having to warm it up to start it). I also have run the little 2 stroke snow blowers at below zero. Are you sure you don't have some other temp related problem? I don't see the temp having that great an effect on your mixture.....just my opinion of course. I see the riders ability to handle the cold as a bigger problem.

 

[XenonDream]

Thanks for the reply. Well, for me, mid 30s is plenty cold. The average summer temp where I live is about 108. The bike was calibrated to run a little rich in warm weather. So there was something like a 50-60 degree difference in ambient air temperature between the calibration temp and Wednesday's temp. My current guess is that the jet is too small to supply enough fuel to run right at that temperature. But we'll see. I'll run it this weekend when it's a little warmer. If the plug comes out black, I'll have my answer.

 

[happycheapskate]

Have you tried installing a hotter plug or changing the gap? Why do you change needle settings so whimsically based on what a used plug looks like instead of how the bike runs?

How about wrapping the carb with some kind of insulation or heat tape to keep it warm?

 

[ibdennyak]

Thanks for the reply. Well, for me, mid 30s is plenty cold. The average summer temp where I live is about 108. The bike was calibrated to run a little rich in warm weather. So there was something like a 50-60 degree difference in ambient air temperature between the calibration temp and Wednesday's temp. My current guess is that the jet is too small to supply enough fuel to run right at that temperature. But we'll see. I'll run it this weekend when it's a little warmer. If the plug comes out black, I'll have my answer.

Woah, 108 average. That's warm. If you don't mind saying....where do you live????? And please don't tell me you've died and gone to ****.

Still trying to put this in perspective.....I've run weed eaters at over 100, and run other two strokes at below zero. All worked successfully. The other side of the coin is that these engines had easily adjustable carbs. You might have something there....keep us posted. Cold air would tend to lean an engine out.

 

[Motorbike Wanabe]

I've also got a Grubee GT5 and the other weekend (very cold) I went riding with some friends. I have been running the bike with the clip on the top ring for some time. Well, on this cold day, I needed to run with the choke on part way to get any power out of the engine. It has been cold for some time and it continued to act this way (bogs down with any throttle movement at all but revs nicely with a little bit of choke) so I moved the pin down one ring. Now, it runs much better but, with a little bit of warmer temps, it 4-strokes if I am just cruising along, without much strain on the engine. If I hit a little hill, it starts 2-stroking again and runs fine. With the clip on the second ring, it runs okay until I go to WOT, then it 4 strokes all the time. Tells me that the main jet is too big for this setting but, when it's warmer, it does fine.

Thanks Xenon, I was starting to think it was just me!

 

[XenonDream]

I was beginning to think I was the only one myself. That's exactly what mine does. My needle has 5 notches, and I run mine in the middle notch--deliberately a bit rich. I've come to two conclusions on cold weather's effects on these engines based on my automotive experience: Colder air will cool the cylinder's internal temperature to a lower-than-optimum operating range, and since cold air is more dense, there is a greater volume of air being compressed in the cylinder, leaning out the air/fuel mixture. I choke (more like gag) my engine on cold days, adjusting the choke to the point where the engine begins to emit a throatier sound. Boggy performance aside, running rich lends itself to longevity. Since I'm only commuting (not racing), that's what I want.

 

[happycheapskate]

For what its worth, I have a grubee 48cc. I ran it on a few of the 30-35F days last month. It required full choke and some pedalling to start, till I started heating it up with a hair dryer first before leaving the house.

When its very cold outside, it needs to run about 1-2 miles on 1/2 choke to warm up properly so it stops running erratically. After that, it runs just fine on the same carb adjustment that I used for the warm weather (60-80F).

See my pics for a choke lever extension made from fuel hose, so you can move it while riding.