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Message started by Guido on 08/24/06 at 14:09:55

Title: humidity
Post by Guido on 08/24/06 at 14:09:55

How much of an effect does humidity have on carburation? My S40 has been running great, until today. I've got it set a little rich and it has been doing fine, and I haven't changed anything. No exhaust leaks. This afternoon on the way home the POPS decided to show their ugly head again!! Just when I was bragging to my buddy on a Road King about how they were gone! Anyway the humidity here has been pretty wet in the mornings but in the afternoon today it is only 35%. Just wondering if this could be screwing up my settings.

Title: Re: humidity
Post by 911radioman on 08/24/06 at 14:46:06

I personally think it has all the effect in the world on carburetors. About all one can hope for is to dial it in to a happy medium for most weather/atmospheric conditions and just let it go at that.

I will say this though. After adjusting my valves the other day, whatever leftover pops are now gone. So, I have a theory that even correct valve settings have a bearing on not just performance, but backfires.

Title: Re: humidity
Post by Guido on 08/24/06 at 18:25:22

Well the stealership was supposed to have done the valves for me about 700 miles ago. Guess I should check into the settings myself.
Any clue which way to go on the mix for humid vs dry conditions?? I'm at 2 1/4 turns now.

Title: Re: humidity
Post by 911radioman on 08/24/06 at 18:40:59

Right now, I'm at a 52.5 pilot jet and 1 1/2 turns out. I've been there before and had no success. All I can say is that I kept plugging along the exhaust gaskets, the intake/exhaust boots on the carb, vacuum line, and all of that stuff until I finally got it.

I rode home this morning and it was very foggy and humid. No backfiring. The last few days it has been pretty dry humidity-wise, no backfires either.

Only thing I can figure is I finally got lucky. My best midrange is coming from my spacer shaved to about 1/3 thickness. No sooting at the muffler, no black smoke when I roll off the throttle. No surging or hunting in the midrange either.

A week or so ago it was suggested I go thicker on the spacer, but that only made it worse, so I thinned it down more and it took that surging/hunting all the way out.

I set my valves at a loose .004 all the way around and the bike seems to just be breathing better. I hadn't taken the time to get into them since I had just bought the bike in February, but they were really snug. I didn't gauge them to see just where they were, but I would venture they were at low end tight spec or maybe a bit tighter, so it's a good thing I caught them now.

My fuel mileage is running between 50-52. Thinking back on everything, where I used to get 54-57, I truly think that reduction is coming from the NC Dakota shield I put on. It does drag more than my Street Shield did. That, and I'm sure I'm a tad more aggressive on the throttle since I've accustomed myself to the Savage. ;D

Title: Re: humidity
Post by serowbot on 08/24/06 at 21:57:13

Anything that effects air density, effects carb jetting.
Humidity is up here, too. I'm popping all over the place.
Notice this is a rich condition.
If you backfire more in high humidity, higher elevation, hotter temps, you're rich.

Barometric pressure chart.

thinner air = go leaner = bp decrease

hotter air = go leaner
more humidity = go leaner
higher altidude = go leaner

thicker air = go richer = bp increase

cooler air = go richer
less humid = go richer
lower altitude = go richer