Warm weather.

Its so freaking amazing how 70 something degrees versus 30-40 degree weather makes such a difference in the wifes xj650. In warm weather it takes lil to no choke to fire off and runs like a champ not missineg a lick. Its freakin frustrating all the work and tinkering in the cold trying to get it to run decent. Sorry guys just needed to rant a bit.

 

These things run their best right at the ragged edge of "too lean." As such, they're ungodly cold blooded, unless you have the carbs PERFECT.

 

I noticed I ran real lean when it got cold so I retuned. Will return again in a week or so as it warms up here. The 650 is certainly cold natured.

 

Mine was running pig rich in the cold. But she was doing good yesterday

 

Interesting - as it got colder I noticed her running leaner and leaner....

 

Ive noticed the same with my 750. Colder it is the leaner and def runs better when its warmer then 60.

 

Mine doesn't even want to start let alone run right in less than 60 degree weather. Even living in a heated garage. It brings a new definition to "Fair weather Vehicle"

 

Belle, clean your enrichment circuits in the carb bowls. My bike started for crap until I cleaned the bowls. Boil them and then shoot the circuit clean with carb spray that has that thin red tube.

The only difference the cold makes for my bike is that I have to choke it mostly all the way to get it started quickly. In the "really cold" weather the bike is almost scary powerful.

 

Did that last week. It now starts but still hates cold days. Boil them? psht I ran 'em through the dishwasher

 

See, a woman can do that. A guy does it? Watch what his wife says. Next, Belle will be telling us that she painted her exhaust headers and cured the paint in the oven. :roll:

 

That's because it's running close to "scary lean." These things run stronger the leaner they are right up until they hole a piston.

 

could this happen due to humidity in the air? my 750 definately runs sweeter when its cold although a pig to start, on a hot day with high humidity it starts fine runs ok on a hot day with low humidity it runs better and starts better than ever its quite a mystery really

 

I believe that high humidity can be a factor. Not only do you have moisture in your combustion chamber, but heat dissapation in humid conditions is much slower...terrible in fact. Think about it- When you're sweating your arse off in humid conditions, the sweat isn't evaporating, so you're not cooling down as much. In a dry heat, it evaporates right off of you, cooling you better.

I'm from south Florida so I'm familiar with the process.

 

Bell, did you do the spray with the red tube and get the spray to go several feet away from you? You must prove to yourself that the enrichment circuit is working.

Fitz, I am not convinced that its running lean when cold. The efficiency of an engine is proportional to the difference between the hot and cold reservoirs of the engine. Thats why drag racers pack their engines with ice bags between runs. I would have to see plug chops at 15 degrees and compare to summer plug chops. The last thing I want to do when it 15 degrees is work on the bike outside. Somehow its ok to ride it, though.

 

Quite right. Evaporation is what chemists refer to as an "exo-thermic" process, meaning that the energy for the reaction to occur must come from OUTSIDE ("exo") the components involved in the reaction. So the energy needed to change liquid (sweat, water, etc.) into a gas is a physical process that requires energy (in the form of heat) to come from somewhere....and that energy comes out of/from your skin, thus dropping your skin temp.

Same same thing happens inside your carbs, too....the process of "atmoizing" the fuel into tiny little droplets gives each droplet a huge surface area (compared to the one big drop of fuel they used to be), and that increased surface area allows evaporation of the fuel to occur rather rapidly, and the evaporation process extracts energy from it's surrounding environment, meaning from the carb bodies itself........and thus you can get "carb icing" conditions even when the outside temp is much higher than 32-degrees.

High relative humidity (meaning that at a given temperature, the air is saturated with water vapor already) means that the evaporation process occurs much more slowly, as it's hard to force a square peg into a round hole, and it's hard to force more water into already moisture-saturated air......so much less evaporation occurs.

By the way, "humidity" is always properly expressed as "RELATIVE" humidity, since there is no "absolute" measure of water vapor saturation in air....the percentage of water-vapor saturation is always RELATIVE to the air temperature. The actual absolute amount of evaporated water (a/k/a "water vapor") in the air may be greater at, let's say, 40% "humidity" when the air temp. is 70-F as compared to the amount of actual water vapor in the air at 50% humidity when the air temp. is 90-F.

 

holy hell chacal u r the man! did u do something silly like speacialise in astro physics in a previous life?

 

Yesss..my cat was on the wall by my drive way, he ran for cover. I think I killed one of my rose bushes from carb cleaner....

It does start, I have to choke it, about the third try it will start right up and idle. After it warms up for about 4 minutes I can push the choke back and it idles perfect. When it's warm out the bike will fire right up with very little or no choke.

Where as before it wouldn't start at all, just try to start and wouldn't idle with out rolling back on the throttle a bit.

Chacal it's great getting science lessons!

 

At that point it just sounds cold blooded, plus some fuel is evaporating out of your bowls. If it sits for a week or more, prime it for about 30 seconds, then start it. Let it warm for your usual 4 minutes and ride it.

 

These carbs man.. Craziest things I've EVER seen. So picky picky

 

Yeah it sits usually until weekends when my kids are with their dad. (Can't fit four kids on the back of a bike ) Sometimes longer if the weather sucks, or I have other things to do.

 

I didn't see it mentioned here and in case any of you are interested...

The reason a bike set up to run near lean at warm temps runs even leaner at colder temps is NOT due to humidity.
It's because the colder air is more dense.
Here's how it works.
1. Colder air is more dense than warmer air.
2. Denser air, by definition, has more oxygen in it per cubic volume.
3. With carb jetting left the same, you're getting more oxygen for the same amount of fuel draw in the mix, which equals a leaner condition.

If you don't add more fuel to a mixture, even if you have the same CFM of airflow, if the oxygen content of that flow goes up, you will run leaner. Rich vs lean is simply an indication of the ratio of fuel to oxygen in the mix. The spark then supplies the ignition factor in the fire triangle.

This, incidentally, is why engines have the POTENTIAL to make more power in colder temps, provided they are jetted accordingly or have adaptive fuel injection maps.

Ever been watching top fuel drag racing and see someone light the tires up and blame it on too much power, because of lowered air temps between rounds? This is why.

I didn't stay at a Holiday Inn Express last night, but i AM an engineer.
8)

You're welcome,
Christopher.

 

ABsolutely right, and although it may come as a bit of a surprise, most bikes are set up (jetted) at the factory to run a bit RICH, in order to compensate both for the air-temp factor explained about, and also for altitude factors........by doing things in this manner, the factory didn't have to worry about whether a bike was going to end up being used in Southern California, or Alaska, or mile-hig Denver, or below-seal-level New Orleans.

Its jetting is "rich enough" to handle all typical situations (on a stock engine). Of course, that means if you're in an extremely warm climate, or living in Denver (or the Alps), then your engine is running really rich...

 

Chacal's even absolutely righter!

The reason you start to run richer and bog down and lose power as you go up in altitude (assuming same air temp and carb settings) is because the air is less dense up there.
There's just less oxygen in a cubic foot of air in Denver than there is in Baton Rouge. If your carb jetting is set perfectly for Louisiana and you don't touch it when you move to Denver, you're gonna run rich.
In fact, the Pike's Peak racers have to make this trade off, since perfect jetting at the start (bottom) will be too rich at the top. But if you jet for perfection at the top, you'll be lean at the start. It's a huge trade off game they must play, looking for that last 0.001 second of time.
:|
This is also why you'll see 2 dragstrip times in a magazine report. The actual time and the "Corrected" time.

The "correction" is to convert the actual atmospheric conditions to a set of conditions called the "Standard Atmospheric Condition".
SAC is air temp = 68 Degrees F, pressure = 14.696 psi (equating to sea level).
Drag racers toss in another factor of humidity, but NOT due to lean vs rich concerns. It has to do with the natural cooling effect moisture in the air has on the fuel/air charge.

I love it when Fitz, Chacal and i agree so thoroughly.

 

That's because ALL engineers love to be right.

My (ex) father-in-law used to say "arguing with an engineer is like wrestling in the mud with a pig. It doesn't take long to realize the pig enjoys it."

 

I'm pretty sure that most people who ride a bike (or drive a car/truck/insert favorite vehicle here) would never notice the effect of humidity on performance. Do you notice engine performance changes when it is foggy or raining out (100% humidity?).

Temp swings somewhat, but remember the effect is related to the absolute temperature so temperature swings are not as big an effect as they might seem (40 degrees to 80 degrees is not a doubling of the temp as far as the air is concerned). The difference in density for air is 6% greater at 40 as compared to 80 degrees. (S.P.) That might be noticeable.

Should we tweek our carbs for winter/summer driving?

I'll let one of the others handle the whole differnce in temperatures in work output of an engine thing...

 

Modern vehicle computers automatically compensate for mixture conditions caused be extremes in ambient temperature. I drive a '74 VW Thing. Do I notice a difference in performance when it's 5F degrees vs. 75F? Yes.

 

Do you adjust the carb on the thing in the summer/winter to compensate?

 

ha, i powdercoated the intake on my buddy's tri-power GTO like that!

 

I retuned my bike when it got cold because I ride every time it's nice enough and did not want it running too lean. Will be retuning again in a few weeks for the warmer temps...

 

I'm not sure whether you're saying that I'm like an engineer or a pig, but either way you're right.............. :lol:

 

Also sprach Chacal
(Thus spoke Chacal) Amen!

 

Actually, I was referring to all three of us, and I believe the double entendre is part of the punch line...

 

I just did my carbs yesterday. I read the post here on the forum about how to do it step by step and followed it to the letter. I went thru every port and journal, used my air compressor to blow out all the small holes and got everything sparkly clean. When installing the air screws, I turned them out 2-3/4 turns (don't ask me why 2-3//4")
I only bench synched them so far (will do the full synch today) Then installed the carbs (gotta love those air box boots!!)
It started like a brand spankin' new bike with hardly no choke needed. The enrichment ports were plugged on two of the 4 carbs (kinda suspected that) because some of the cylinders were flooded, when the others weren't getting any gas at all, so it needed to be done.
A fuel filter is a MUST. I always make sure I use clean gas and change the filter as soon as it looks a little but dirty, and I still had sediment on the bottom corners of the fuel bowls (just enough to see it) So I assume there is still fine dirt particals getting by the filter. My old filter was the fine (real, real fine) screen type, so I swapped it for a different type (brass insert) filter to see if that works better (it should).
I'm planning on doing the carb synch today and getting some riding in this weekend (supposed to get into the 40s) Can't wait!!

 

Snow for us tonight and tomorrow.. I'm ready to choke the weatherman.

 

Your relative humidity levels will be rather high..............

 

I saw the forecast. You're going to get sacked. It's almost April..I can't believe it.

 

what a lovely Oklahoma Spring we're having... AAGH! What the hell...



At least the hounds don't mind it...

 

Snowing up here in Alberta also. Getting sick of this white stuff. Every time the roads just about get clear enough that I think I might be able to test drive one of the bikes it snows again. Grrrrrrrrrrr!

 

Good looking beagle ya' got there, stereo...........

 

them be basset hounds

 

OH. Close. Fat, short-legged beagles, that's how I think of them (although, actually and strangely enough, beagles and basset hounds aren't even related.........)