Rejetting for Temp. and Humidity

Hey Guys,
Just wanted to ask for some advice on having to change jets when there is a big change in outside temp and humidity?
Reason I ask is, because well I live in Minnesota, and Summer temps. are finally starting to come this week(Highs around 80) but it has also brought heavy humid air with it. Last week, it was a high of 68 with very little humidity, Bike ran great, tan plugs, pulled through the rpm range. And this week its been running a little more rough, plugs are darker or running richer, and it doesn't have near as much getty up as last week. Is this beacuse of the major temp. and humidity change? Or is there something else going on? Any advice or insite would be great. Thanks

Oh yeah, When I did the jetting the for the first time this year, it was back in April/May so the high was right around 50 to 60, so it is tuned in that temp and climate weather.

Thanks
Dylon

Sorry fo the late reply...

The temps and humidity and barometric pressure and altitude all take part in affecting the carburetion environment.

With that said, they can also wreak havoc on old, not maintained/cared for electronic connections, that should all be clean and shiney new and sprayed with a good electrical connection restorer spray that protects as well.

If you're interested in jetting for large environmental changes, there is an excellent little slide rule made by mikuni for just such purposes. You can purchase them around at Sudco, and maybe Z1Enterprises, and the like.




Regards,

Alright thanks,
All my electical is in great shape, considering I rebuilt the bike this past winter. But I am right saying that the carb. problems are due to the vast enviromental changes that have been happening. Went for a ride last night, About 70 out with lower humidity, and the bike ran great.
Thanks

For future reference....

Generally speaking I was schooled that a ambient change of temps from 10 to 15F would ideally require a one size jet change. However on a street driven motorcycle in New England, I would find myself changing jets every day... lol

This suggestion is from a pure "top racing tune" type application

I try to jet for top performance around 65F, and whatever happens there after for temps is a compramise. So my bikes run slightly rich at 80F, and slightly lean at 45F...

Thanks Guys,
That's what I figured was going on. I guess I'll have to order some more jets, and lean it up a bit.
Thanks for the info.
Dylon

Try adjusting your air/fuel screw first. I never found a need to change my jetting, on any bike, becauseof temp changes. And I ride MX 365 on the east coast.

Generally what I have found with early to mid 80's bikes is that they respond very well to bumping the pilot jet one size richer, and also shimming the stock needles to add some midrange richness. Most bikes were factory jetted to comply with EPA friendly "lean" standards. When temps fall below 60F you can really feel the "leaness" of stock jetting . The lean condition is even further aggravated by today's newer E10 fuel.

Well my jetting is not stock to begin with considering the more aggressive intake cam and the 4 into 1 exhuast and Uni filter. When I rejetted my carbs for this, I didn't want to buy a jet kit(good chunk of change), so I went to jetrus.com and ordered what i needed there; I went 1 up on primary jets(68), shimmed my stock needles up to the same as one notch on aftermarket needles with a clip(2 shims), and went 2 up on my secondary mains (135), didn't bump my pilots, only because you can get them anymore,and turned my mixture setting to 2 1/4 turns out, just off stock(2 turns). It seems that these keihin cv34 you can't get parts for anymore,need to upgrade to some semi-flat slides or all out flat slides, but more money there but maybe soon.
But I know it's weird to think that a 20 degree difference in temp could affect it that much,but it does, When I rode this past week with a high of 65, it ran like a dream. I have come to notice that my bike is very picky. None of my other bikes are like this, pretty much set and ride until you do something else to them.

I personally would check the voltage at my coils. Roy