MOPED ARMY

Nick,

Cold air = rich, I think, because high altitude = lean.

You do not mention the temperature, but the most likely problem is condensation or icing in the carburetor caused by the additional cooling effect of gas evaporation. Standing still allows engine heat to warm the carb.

If you can rig it, some cars get around this problem by directing warm air from the exhaust manifold to the air intake. I imagine that the cylinder fins would also be warm enough. You may even be able to fashion an air funnel around the carb to warm up the outside of the carb with engine heat.

Good luck,

Ron

a cold engine will always act alittle strange. i found this happens with my moped when it is cold. once the ped ahs been running for a good hour it stopps doing that totaly. or atleast mine does

Fred,

Am I backwards on my high altitude = lean?

Ron

Yes... higher altitude means less air with the same amount of fuel...which means it will be running a bit richer.

We don't need to.

Extensive testing by motor companies and racers has proven all these facts years ago.

I know people from Michigan who went on a 10 day trail riding adventure vacation to Colorado this summer...taking their own bikes... and they described the richer running characteristics they had when they reached high altitude... less HP in general though.. because of the thin air.

And you describe "less dense air creating less pressure drop..sucking less gas"

Can you show that there is LESS pressure drop at high alt than there is at low alt?

Maybe the pressure drop at both alt's is the same?

Though I have been told that this richer/leaner condition is small (few of those guys of those guys bothered to re-jet)... but the HP loss due to thinner air is more noticeable

Fred,

Thanks, I went back to my copy of Zen and the art of motorcycle maintenance and discovered that his pipes were turning blue when he left the mountains. Forgive me my transgression, it has been 25 years since I read it. Looks more interesting than I remember, I think I will read it again.

Incidentally, with my mind backwards, I was thinking of the problems aircraft have in developing lift in thin air. Obviously is different in carbs.

Thanks again,

Ron

"It just started doing this".... and it's good and cold isn't it?

My 78 Hon PA50 did the same thing on the way to the store with the 90 hp moped guy

That is 2 miles... and it was below freezing... and with the choke on it would run.. and as i went to more throttle the choke would flip off by itself... then it would run about 200 feet and bog and stall... it did that bout 8 times before it warmed up enough to run without choke... it also was still 5mph short of its normal 30mph top speed

If yours will not run without choke after 20 min then it would seem that its dirty inside like you said... restricting the air intake a little would help too.

I think many moped carbs are a little too crude for good running all the time... (mine is.. I think)

Fred,

Thanks for the response, I realize we are all running slightly rich most of the time to allow for variations which could result in a too lean condition.

As for race tuning, I liked a quote attributed to Joey Dunlop, in a obituary type piece in Road Racing World.

Apparently, at some kind of celebrity appearance in Australia, Joey was happily wrenching away on a 2-cycle race bike and the writer asked him how he selected his jetting. His response was "Lean it out until it siezes, then go up one size".

Ron

well i fixed my own problem. im just let it run longer on choke before i hoped on