Air temp changes affects how bike runs???

Could this be a problem? I ride to and from work about 30 miles each way. I leave in the AM and the temp is about 55F. I come home in the afternoon and the temp is about 85F. My bike runs great in the morning but seems very sluggish at hi RPM's on way home. Is this possible with only mild temp changes? Traffic conditions is about the same both directions. Maybe it's all in my head. Maybe just anxious to get home for cocktail hour and bike just seems to run slower. Thanks, Jim

Both of my bikes run better in cooler weather. when it drops below 50F, it is very noticeable. I just accept this as part of riding a non-fuel injected vehicle. Climate changes, and elevation changes, can be noticable in the engine performance.

I've been riding all summer here in Phoenix where it is always hot. Didn't notice a difference before. I guess when the temp changes from 100 in morning to 120 later in the day, then there is no cooler temp. Maybe next summer I'll make some adjustments so it runs like it is now, if there is any. Thanks for input...Jim

Most of the jetting calculations I know of take ambient temperature into account. Hotter means leaner in general. The problem is, you are not really changing temps all that much going from 55 deg. to 85 deg. I think there may be something else at play if you performance deteriorates...

Tindevil wrote:

Could this be a problem? I ride to and from work about 30 miles each way. I leave in the AM and the temp is about 55F. I come home in the afternoon and the temp is about 85F. My bike runs great in the morning but seems very sluggish at hi RPM's on way home. Is this possible with only mild temp changes? Traffic conditions is about the same both directions. Maybe it's all in my head. Maybe just anxious to get home for cocktail hour and bike just seems to run slower. Thanks, Jim

This is a very known, and noticeable, phenomenon in the variable climate I live in. And there is an explaination for it. Colder air are more compressed than warm air, and you get a much better filling of the cylinders. Secondly the colder air stream will cool down the engine more than hot air.
You should check the spark plug colour after a ride in hot weather. My guess is that since your bike is running better in cold mornings than on warm afternoons, it is running a bit rich.
But it's just an estimated guess. The only way to tell for shure is by reading the spark plugs.

Cold ambient air expansion versus hot air expansion in the cylinders, IE: volume of air expanded/compression.

This is easier to explain by how a torbucharger works.
The amount of power which an engine can produce is limited by how much fuel it can burn, and the amount of fuel it can burn is limited by the amount of oxygen in the cylinder. The amount of oxygen in the cylinder is limited by the amount of air in the cylinder. So, if more power is wanted then more air is needed, how do we achieve this? Well a large engine has more air, so it can produce more power, or we can compress the air before it gets to the cylinders.
This is what a super-charger or turbo-charger does; they are a simple air compressor.There is one problem with compressing air, it gets hot and hot gas is less dense and therefore has less oxygen in it, so you lose a little bit of the advantage you would expect, unless you have an intercooler.
An intercooler is a simply a heat exchanger mounted between the turbo-charger, or super-charger and the inlet side of the engine. Cold air is blown through it to cool down the hot, compressed air inside; this makes it denser and gives maybe another 10% more power.

I'll check the plugs when I get home tonight. I looked at them last night and they seemed ok, but I just looked to see if one of them were fouled and didn't notice the color(wasn't black though). I cleaned the carbs this past weekend and the bike runs the same as last week. It always idles ok, and runs good at steady speeds. Just sluggish(very noticable) when I increase throttle at higher RPMs. Didn't notice this problem during the summer and before. Thanks

Ive noticed this also. It came on suddenly though, even though it wasnt "cold" yet. I would have to really struggle to keep it going at stops. I played with it a few times (idle air screws) and pretty much left the bike sit. Tonight I went for a quick trip in 45* temps and it ran like a dream. I cant wait to get it back to work tomorrow

Your carburetors are Keihin CV are they not? How are they jetted? What elevation are you at?

You write:
"Just sluggish(very noticable) when I increase throttle at higher RPMs"

Could you be more specific... What does higher RPMs mean specifically. Are you talking about not being able to pull redline? Above 7K rpm? Or are you talking about when you pass a semi on the highway and are going 70 mph?

How fresh is your fuel, I only ask because I've had a few problems with the fuel in the Phoenix-Glendale area. Don't forget that the blend of fuel here changes 2 times a year. if you need a hand with it or just a different veiw point on-site. I'm around the I-17 and 101 loop.

Thanks for the offer. I'm located over by the new Cardinal stadium in Glendale, not far from you. The fuel is fresh, or at least I just filled the tank this week. The plugs look good and I do have Keihin CV carbs. I don't know how they are jetted. I'll have to check this weekend. The PO wrote the settings in the service manual, but it is still packed away at this time. Phoenix is close to sea level,I think.

What I mean by sluggish is when I'm traveling at about 55 or up and I jump on the throttle, it just doesn't take off like it does in the AM. I thought maybe it could be a fuel problem, but why would it seem to act like this just at certains times when it's warmer out? Like I said earlier, I'm fairly new to riding and this could just be in my head.

Thanks again for the input. Jim