Motorcycle carburetors at altitude

In My Humble Opinion
1

I just posted this on a more specific motorcycle site, but I know there are a few bikers here, so I thought what the hey.

I have a 2004 Kawasaki Ninja 250.The bike idles great. But after sitting at an idle at a stop light, when I open the throttle, the bike often dies. In the intersection: EEEIIIAA! The various solutions I’ve heard of are: re-jet the carbs (I’d rather not do that yet), synchronize the carbs, adjust the valves, do something about the float level (I can’t remember what), clean out the slow (idle) jets that might be plugged, add half a bottle of Techron, add a K&N filter. I live at an altitude of 5200 ft.

I’d rather try the easier/cheaper fixes first, of course. Checking if the low speed jets are clogged makes sense. The guy in the front of the bike shop suggested I throw on a K&N filter and see if that doesn’t solve it, because the bike is probably running a little rich at this altitude and that would “lean it out.” This made sense to me, but when I talked to the guy back in the service dept. (a more conservative guy who I think is leery of anything that isn’t stock on a bike), he said no, “The Ninja has a &^%$ carburetor (can’t remember what he called it) that adjusts itself. This altitude shouldn’t affect it. A K&N filter will make it run too lean.” One thing that makes me distrust the service guy a little is that this problem seemed to get worse after he did the 1000 mile maintenance tune up. I’m not sure.

How would you guys, using a matrix of cost/ease/likelihood to be effective, prioritize these interventions? And is the service guy (who also criticized me for changing out my stock Dunlop tires for Sport Demons, which turned out to be a really good move) full of bull?

Okay, back to work. Thanks for any suggestions.

2

Well, I’m no authority on motorcycles, but I do know a little bit about carbeurators and altitude. If your carbeurator was originally set for sea level and it’s now trying to functionat 5,200 feet yeah, I can see where you’re having some troubles.

Problem is, I don’t know jack about your carbeurator. Does it really adjust for the local altitude?

I’d seek a second opinion to the one you already have. Problem there, of course, is trying to get a good second opinion.

3

He probably said “Constant Velocity”*, and if that is what the littlist Ninja has, he is correct.

As for your problem, well, it could be a lot of different stuff, so I can’t help you too much. I’m more of a 2-stroke guy.

Okay, cut out the funny remarks. :wink:
*CV carbs, as they are known, have a diaphram and operate somewhat differently than non-CV carbs. Its how the vaccum is drawn, and from where, but I really don’t know that much about it, obviously. I recall reading a very good article in Cycle World about it recently. Maybe you can find it online. It was in the letters to the service department department. Is that redundant?

4

I ride an old 650 Kaw and I too live at altitude and I found that I had a somewhat similar problem but by adjusting the valves I didn’t have that problem again.

It’s easy enough and it is a good start.

5

Is the bike from that altitude?
How long up there before it started messing up?
Total mileage on the engine?
Riding frequency?
Grade of fuel normally used?
Additives normally used?
If Denver, you should have more than one shop to chose?
Know anyone with a similar bike locally?
Does sound like a rich mixture but can be several things…

More info needed…