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Cold Weather, Carburetors, & Top Speed (?)

 
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Rusty Shackleford
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Joined: 28 Jul 2012
Posts: 238
Location: Richmond VA
2012 Buddy 125

PostPosted: Wed Oct 24, 2012 2:53 pm    Post subject: Cold Weather, Carburetors, & Top Speed (?) Reply with quote

One of the great things about the Buddy 125 is that even though it's carbureted, it idles at the appropriate RPM on its own when warming up, negating the need for a manual choke. While this convenience rids the bike of a technologically outdated step in the process, I can't help but wonder what other effects the cold weather has while riding.

For example: During warm weather, I was able to feather the throttle and get the bike to 70bmph on a flat fairly easily. Last night, I had the bike on several long 55mph roads and could only get it up to 66bmph. Why the 4mph drop? It was down in the 50's last night when I was riding. Perhaps the temperature affects the air/fuel ratio where as I didn't have this problem with fuel injection? Has anyone else experienced a decrease in top speed by a few MPH when riding in cooler temperatures? Perhaps I'm wearing more gear and the extra bulk creates more wind drag? Perhaps a little from column A; a little from column B?

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Cheshire
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Joined: 28 Jun 2008
Posts: 1995
Location: near Asheville, NC
2013 Vespa GTS 300ie

PostPosted: Wed Oct 24, 2012 3:00 pm    Post subject: Reply with quote

Do you have a wind screen on your Buddy?
I had one on mine and didn't notice a performance decrease during winter, but my first (working...I had a botch for a summer) motorcycle didn't have a windscreen initially. I noticed a definite drag effect when I pulled out the cold-weather riding gear or the rain gear. (I ended up getting a windscreen and noticed the drag disappear.)

As long as you're letting the scooter warm up before taking off first thing, at 50F air temp shouldn't be an issue for fuel mix. Generally, colder air is thicker, but rejetting shouldn't need to be looked at until the temp drop is much lower. (assuming I'm remembering things correctly: my current bike is EFI.)
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BuddyRaton
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Joined: 09 Sep 2006
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PostPosted: Wed Oct 24, 2012 3:12 pm    Post subject: Reply with quote

Temperature definatly does affect the fuel air ratio much like altitude. When it gets cold the air gets denser. This means that even though you are pulling the same volume of air through the carb you are sucking more mass of air for that same volume thus leaning out the mixture. I agree though that 50 really isn't that cold for air density unless you were jetted for summer tems of like 100-110

On EFI systems the O2 sensor takes care of this and adjusts the mixture, for carbs, if is really making a difference, it is time to rejet.

On the 2T Vespas and on Stellas there is a winter plug in the top of the air box. During warm weather you leave the plug out to allow more, less dense air in and then when it gets chilly willy you put the plug (if it hasn't been lost!) back in to reduce the volume of denser cold air. In reality most people leave that plug in all the time and either do nothing or rejet.


I think your right though...some from A and some from B...I have been told ( Mr. Green ) winter gear can get pretty bulky!

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Rusty Shackleford
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Joined: 28 Jul 2012
Posts: 238
Location: Richmond VA
2012 Buddy 125

PostPosted: Wed Oct 24, 2012 3:51 pm    Post subject: Reply with quote

I thought for a second it may also have been from the 11g Dr. Pulley Sliders, but I just went back and looked at the dates of the last time I recorded speeds for testing and it was after I got them. Pretty sure the variator is maxed out by then and relying on engine speed, but the sliders may have created enough of a slightly higher ratio to reduce pulling power a little on the top end in favor of a slightly lower RPM. Anyway, I recorded an indicated 70mph on a flat last time I checked.

I'm beginning to think this is 75% a wind drag issue from the bulkier cold wear riding gear, and maybe 25% from changes in temperature/density and humidity that come with the seasonal changes. That said, a windscreen would probably help recoup some of the loss in addition to making it a more comfortable ride during the cooler months. My GF and I went on a 100+ mile ride on Sunday and she hit an indicated 70mph on several occasions. She's much smaller than me and creates a lot less drag. I'll leave it up to her on the windshield since it's primarily her bike. She froze on the way back on Sunday, so that may play into her decision.

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rfman81
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Joined: 27 Sep 2011
Posts: 97

Vespa GTS 250ie, 81 p125x

PostPosted: Wed Oct 24, 2012 3:58 pm    Post subject: Reply with quote

I am not sure it is just wind drag. I will say that my buddys top speed is definitely affected by cold. She likes it when it is hot out. In 115 degrees we got down here in the summer she ran better than in the 95 degrees. I think the cold has something to do it. It has to idle longer to warm up... tire pressure fluctuates more in the cold. I don't know but I too notice the difference.
I run a windshield year round.
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Rusty Shackleford
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Joined: 28 Jul 2012
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Location: Richmond VA
2012 Buddy 125

PostPosted: Wed Oct 24, 2012 4:06 pm    Post subject: Reply with quote

This is part of the reason I had frequently mentioned the BBK/header. I occasionally have a little jealousy towards the 170i when it comes to holding speed without a fuss and having a computerized system to adjust to changing weather conditions. Virginia is a fairly mild state, with January highs averaging in the mid to upper 40's, so it wasn't a deal breaker, but she uses her scooter as a step-through CVT motorcycle and goes everywhere I go (barring long interstate runs). Also of note, the Buddy 125's fuel economy was only 80mpg on the longer, higher speed ride we just took. Still respectable, but 10mpg shy of her summer commuter average. Little engines work hard to keep up on those country roads. I'd say about 80%+ throttle.
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avonpirate
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Joined: 01 Aug 2012
Posts: 211
Location: Vail Valley, CO
Buddy 125

PostPosted: Sun Oct 28, 2012 2:21 am    Post subject: Reply with quote

Rusty.... I've been having tempermental problems the past days. It's been snowing and in the 30's, but I ran the scoot every day........ warmed up yesterday and GB125 was sluggish then dead.... wouldn't even kick start. Put in a NEW battery today,(which I had on the tender for 19 hrs) fired up immediately, and would kick start, then the sun came out so I was DTR. I'll share what happens tomorrow with cold temps and daylight savings gone. OBTW: took the bike path through Dowd Junction to the ski swap : no one out... no stink eye Laughing
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SYMbionic Duo
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Location: Minneapolis
'09 Blackjack; '12 Kymco Downtown 300i; '85 Honda Elite 250; '04 GB150 Stella #42; '79 Lambretta Jet 200

PostPosted: Sun Oct 28, 2012 9:54 pm    Post subject: Reply with quote

I've had both of my highway scooters not want to start in the cold (downtown and elite) due to loss of cold cranking amps. I've been thinking of either attaching battery leads that can be accessed more easily, and just jump starting in the am, or just riding the Stella or Buddy. Kickstart FTW!

With the Lambretta that I just got, I think that converting to battery-less is the way to go.

-duo

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avonpirate
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Location: Vail Valley, CO
Buddy 125

PostPosted: Sun Oct 28, 2012 10:16 pm    Post subject: Reply with quote

New battery ..... Easy start this am. Took am hour ride so we'll see what tomorrow am brings. I've been harboring the new battery 4 about a month.... There were signs.
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Rusty Shackleford
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Joined: 28 Jul 2012
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Location: Richmond VA
2012 Buddy 125

PostPosted: Thu Jan 03, 2013 4:21 pm    Post subject: Reply with quote

UPDATE: I took the Buddy 125 out on the interstate for about 20 minutes on New Year's Day (15*F colder than the test that prompted the thread) wearing a full one-piece riding suit. In a tuck, I was somehow able to hit all the same top speed marks I had previously hit during warm weather.

Untucked: 65bmph (~56mph)
Tucked: 70bmph (~60mph)
Downhill: 72bmph (~62mph)

My GF, who's a lot shorter and lighter than me can do +4bmph in each of the above conditions. ATGATT

I've concluded this is an issue of wind drag. There's not but so much resistance a 9.5hp engine can overcome. The fun part was, I followed a state trooper the majority of the way down the interstate. He got off at an exit and slowed down to look at the scooter. It's technically legal to do this here in VA, but you don't normally see it (nor would I even normally advise).

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SYMbionic Duo
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'09 Blackjack; '12 Kymco Downtown 300i; '85 Honda Elite 250; '04 GB150 Stella #42; '79 Lambretta Jet 200

PostPosted: Thu Jan 03, 2013 4:29 pm    Post subject: Reply with quote

Your gear can be a big drag, and i'm not talkin queen.

My previous jacket, was too much like a sail, i could barely keep it at 55, but if i went armor less (not the best idea) i could hit 62 no problem, and often sustain 57-60 with ease. Main reason i got a windscreen. I prefer without, but having an 80mi commute at the time, it was worth it.

Also, most of the published top speed numbers for older Vespas / Lambrettas assume you tuck.

-duo

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Rusty Shackleford
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Joined: 28 Jul 2012
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Location: Richmond VA
2012 Buddy 125

PostPosted: Thu Jan 03, 2013 4:42 pm    Post subject: Reply with quote

What I've found is that Genuine scooters will at least match the indicated top speed advertised... and will GPS the top speed if tucked. It took a lot, though. I had to have a lot of room (as an interstate certainly provides) and had my feet together, elbows in, and chin of the helmet almost resting on the speedometer. I'd like it to have the muscle to achieve the same speed without having to do that. I can't wait for the BBK this spring. It should be enough to overcome the drag and hills at top speed.

Also of note, the Buddy handles surprisingly well at (relatively) absurd speeds. It's much like a motorcycle; the squirreliness comes from having too tight of a grip on the bars. The faster a bike goes, the more it wants to stay upright, so maintaining a slightly more gentle grip allows the bike to stabilize itself pretty well considering the small tire size. The Buddy's suspension, while not firm enough to be considered "sport", is soft enough to eat up bumps at said high speeds. It's probably a more capable bike than it gets credit for. My lady takes it out cruising with the motorcycles in the country and holds 55mph GPS all afternoon, and is more comfortable than the rest of us on top of it.

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Beamster
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Joined: 07 Apr 2008
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Location: State of Confusion
Buddy 125 - Chevrolet Orange

PostPosted: Fri Jan 18, 2013 2:21 am    Post subject: Reply with quote

My air cooled motorcycle engins run better in the cold than in the summer heat, but remember that the lubes are pretty thick in the cold and need a significant ride to get thin and reduce drag.

Also, we get "winter" gas around here that cuts gas mileage down so we could assume that it could be affecting power too.
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velobuff
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Location: Boulder, CO
08 Aprilia SportCity 250, 12 Buddy 170i

PostPosted: Fri Jan 18, 2013 3:57 am    Post subject: Reply with quote

Beamster wrote:
Also, we get "winter" gas around here that cuts gas mileage down so we could assume that it could be affecting power too.


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