Jetting for high altitude-2003 EC250

[sanderjavant]

I’m preparing my new to me 2003 EC250 for the Colorado 500 and want to be in the ballpark for jetting.


It has a 178 main in it and starts and runs well, I’ve only started it 3 times and ridden down the street twice. I would like to be close when I get there since I won’t have much time to get it dial in when I get there.

I’ll thinking about starting with a 170. Any suggestions?



As far as altitude-My buddy says:

We spend more time at 9,000 or 10,000 than at 7,000.

Taylor Pass, 12,330;
Cinnamon, 12,620;
Engineer, 12,800;
Black Bear, 12,840;
Stony, 12,588;
Hurricane, 12,407;
Corkscrew, 12217;
Gunsight, 12090 (not sure if it is open any more);
Ohio, 10093 (about the lowest we'll see.)

 

[widebear]

I have direct experience on this matter, but if you are like most of the guys on this forum, A you will either (A) dismiss this as outragous or (B) Be afraid to try the setup. (C) get sucked into buying an aftermarket needle. So , go to the dealer and get 140 to 155 mains, and when your bike runs like crap at 10k, put them in .Its ok you can thank me later.P.S. try and get some avgas if you can, it will help

 

[AZjg]

I see a lot of jetting questions here with many well thought out analytical responses, which is what makes this such a great site. Over the years, I have found, believe it or not, that the folks who make these bikes actually have a good idea on what makes them run well. So let us take the guesswork out of this.
LTR jet kit or not (if not order one)
Refer to your GASGAS manual, if you don’t have one, refer to the manual section and print one out. Find the jetting section.

You must establish a base for your bike. For instance, my 05 DE250 @ sea level would be set up with a 185 main and 48 pilot, needle in the middle, 1.25 out on the airscrew.

The jetting chart shows that at 68 F and at 9600 ft the correction factor (multiplier) would be 0.92. Remember my base for the main was 185, so 185 X .92 = 170.20. I would go with a 170 or most likely a 172 main jet.
Lets look at the pilot, my base was a 48, so 48 X .92 = 44.16, so I would go with a 42 or 45, most likely I will go with 42.
Per the chart, if your correction factor is .94 or lower, raise the clip one and back out the air screw 1 full turn.
So you’re all set, looks like you were right on going with the 170 main, have a great time in Colorado. I will be making my 10th annual trip the last week of August from Arizona to Taylor Park Co. and will be riding most of the trail you referenced.

Just a note, sometimes it can be hard to determine your base at sea level, so if you have your bike spot on at a particular temperature and elevation, use the chart and work the math backwards to determine what your base would be. Example, my average elevation is 1800 ft at around 86 F. Here I run a 180 main. To determine what I would be at sea level or what my base would be, I just played with the math. If you look at the chart, my correction factor would be 0.97. So in my case I take the 185 main base X the factor of 0.97 and what do you know, it tells me to run a 179.45 main which is spot on with the 180 I run.

 

[widebear]

gasgas shows a 185 main as a baseline for unleaded fuel and 160 with leaded. as well 38 pilot unleaded ,35 leaded plus one step leaner needle. one set of parameters for racing the other for utilitarion transportation. I do have to take exeption on the point of the factory jetting being close, if thay were the case this jetting forum and the aftermarket tuners would have no reason to exist. I.M.O i think. the reason that they come jetted pig rich is because they are a (world market bike) sold in a lot of places where the fuel quality may be suspect at best, remember that this bike is sold as a street bike in a lot of places where it may be the sole means of transportation for the owner, fuel price and quality will factor into the whole economic picture. As a manufacturer you try to mitigate your liability by recomending a large safety buffer zone where your product will not self destruct through detonation or the likes.All the same no matter what you do your bike will not run as good as it does at sea level. A correction chart is handy but its really air density and temp that are the key .

 

[sanderjavant]

Update

I started with a 168 main as the only change staying with the air screw 1 1/2 turns out and the needle at one clip from the bottom.

Then went a half a turn out on the air screw, then another ½ turn out.

The next day I lowered the needle one clip position. And the next day I lowered the needle one ore clip position.


I stopped there; I know I should have change the pilot.

My Standard
Main 178
Clip 2nd from bottom
Air screw 1 ½ turns out
Pilot


Colorado
Main 168
Clip 2nd from the top or up 2 from standard
Air screw 2 ½ turns out
Pilot


I never did check, change or foul a plug and I had to mix the gas in the tank at gas stations. I got a tip to turn the petcock to the off position when adding oil.

It ran great but I did get some dribble and spew out of the silencer but that was mostly on the highway.

If I just would have had more time….

What a great bike!