Cold Weather Jetting

[HerrDeacon]

Any of you guys rejet for colder weather? When I tuned my MB5 this past summer the average temps were around 25*C and now that it is cooling down I'm thinking I'm going to have to rejet. Last time I was out it was 10*C and I could hear a bit of pinging, and now the temps are even cooler (~5*C). Will go up a step on the main just to be safe. Bike really came alive though at around 15-18*C, really hit the sweet spot as I think I was a tad rich when the temps were higher.

Just wondering if anyone else does this as well?

 

[carnivorous chicken]

I've never rejetted based on weather conditions, but my experience has been Seattle (where it's pretty mild and doesn't get all that cold in winter) and Phoenix, where there is a great variance in temp in the seasons, but cold is 50F in the winter. Just moved to Boston, so I'd like to hear what anyone else has to say, but it doesn't make too much sense to me as it seems once the bike is warmed up it wouldn't matter (although you might have to choke it for longer to get it to warm up)... Anyone else?

 

[HerrDeacon]

Chicken, colder air is more dense and so this causes the bike to run leaner than it would under normal warmer conditions. Some bikes may not need a change but I'm finding my MB5 does, especially since its run at near WOT pretty much all the time. Don't want to burn up the piston/cylinder or cause a seize.

 

[mydlyfkryzis]

Seizing is from high temp expanding parts....the other side of cold weather is the engine is cooled better, offsetting the greater heat of combustion.

You probably should do a plug chop and see if you are really too lean...

I used to ride year round. My cb360 never had an issue ...at 20 deg. F, the engine pretty much was overcooled at speed....

 

[alzcbz]

I don't have much experience with these older bikes as of yet, but I know I need to change jetting on my 2 stroke quad depending on temp.
I believe 4 strokes are much more forgiving with temperature changes.
Seeing as you run the MB5 wot a lot, it would be much like the 2 strokes I am used to. Sounds like you are on the right track

 

[carnivorous chicken]

Chicken, colder air is more dense and so this causes the bike to run leaner than it would under normal warmer conditions. Some bikes may not need a change but I'm finding my MB5 does, especially since its run at near WOT pretty much all the time. Don't want to burn up the piston/cylinder or cause a seize.

See! I told you I had no idea what I was talking about. But sure, mydly is right -- a plug chop will give you an indication of how it's running. I'll have to remember to do that myself as the weather gets colder here in Boston. I'm hoping it doesn't get any colder than it already has, but that's ridiculous optimism on my part.

 

[runmikeyrun]

My RD400 likes the colder air but starts to pop a little on decel when it's much below 40F. So yes the colder, more dense air can throw off your mixture.

If you're pinging maybe try an octane booster first, might solve your problem. If not, you could restrict the opening on your air box slightly with a piece of cardboard or something... Easier than monkeying with jetting