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1997 CR250 Jetting for Altitude, having problems!

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Hi Guys!

 

After leaving my bike totally the way it came for 2yrs with jetting, I decided to try and tackle rejetting it.

 

The last rides the bike would start on the first kick and ran really great (other then Major splooging and smoking, full throttle rips left a cloud 30ft x 30ft in the air).  Oddly though when I disconnected the ignition after 3 kicks fuel would pour out of the vent tube.  Cleaned the carb out, turned out the main jet was full of dirt, after cleaning the bike runs WORSE! it is much harder to start now and is sometimes bogging down low. (perhaps the leaned out main and pilot full of dirt was helping?)

 

Now the 1997 Keihin PowerJet jetting is different then the later AirStriker, it lists 55 pilot and 180main as the factory, my bike had a 58 Pilot and 180main, 2nd from top clip, air screw 2 turns out(its from California).

I ride starting at 4200ft and usually are around 5000-6000ft.  I switched to a 52pilot and a 170main, but it still splooges and smokes as much as it did on the other Jet.  It still runs well mostly, pull well mid-range and top end (just did a full rebuild last year) but the Starting is hard again, it ran better with dirt in the Jet!

 

I know that with cars our base altitude in Calgary is 3600ft and thats 14% less oxygen here, does anyone have an idea on what jetting to run? I've spent hours and hours looking through every forum I could find, but the PowerJet wasn't sold for too many years and a lot of people ride Sea-Level so I have had a hard time finding jetting info.  We Ride woods mostly, pretty low RPM and I don't even open it up that much in the top end.

 

I just want it to smoke less like those fancy new 2-stroke pumpkins I see all over our local riding place and maybe start first kick again, that'd be nice (better low end response and no sudden stalling would be super duper too)!

 

Help and suggestions is much appreciated!

 

1997 CR250

FMF Gold monster pipe thats-always-smashing-into-rocks, otherwise Stock

Edited by Kingsoup

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When I had my 97 I ran a 165 main jet, 55 pilot jet. This is at approximately 1100 feet elevation. Ran well. For your elevation, the service manual suggests 52 pilot, 165 main, from 5000-7500 feet at 59-80 degrees. I'd say your current settings are plenty rich.

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Doesn't smoke at all eh! thats what my goals are, I have brand new rings as of last year, I think the altitude is much too high for rich jetting!

 

Keith I appreciate those specs, I have the 2000-2001 manual for the airstriker and its pretty different, I've read that Honda specs pretty rich to avoid damaging the motor.

 

Fenmore my plug is usually a big black, I haven't lowered the needle position but I think it needs that, that article I've read a few times, I'll have to check the bowl height, its an old bike now, and although I work on it all the time, I ride it usually 100+hrs of woods a year and it likes the love!

 

I have a 165Main jet, I'll try that out and lower the needle, I've red that there can be air leaks from the choke dial as mine does some wierd idle surging, I wish I knew a reliable calculator, I've seen a few but I guess you don't want to be lean and its suddenly cold out and you're in trouble, as can happen here in the mountains (I saw light snow the other day at 6000ft)

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is the plug oil fouled (wet, black, and oily) or carbon fouled (black with dry sooty deposits)?

The later can be fuel mixture to rich, spark plug range too cold, faulty ignition component, prolonged idling, clogged air filter, poor compression.

Oil fouled could be incorrect fuel/oil mixture, incorrect jetting, prolonged idling, spark plug range too cold, ignition component failure, worn rings.

 

Also, if you go by the Honda manual, it says to replace piston and rings every 7.5 hours....which sounds crazy to me, but if you ride 100+ hours a year and replaced your rings last year you could need rings.  I would do a compression test just to make sure and do the air leak test like explained on the other thread.

 

I don't remember a o-ring on my idle knob and the manual doesn't show one either.  The air screw has one though.

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Also, I got a complete carb rebuild kit off of ebay for $30.....everything was brand new.

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Oooh carb kit from Ebay, thats a good idea actually, I haven't redone the parts in there yet, seems like I've had to rebuild the entire bike since I've gotten it!

 

Honda manual  for this bike is also written for people who race the bike, I could imagine that for peak compression if you'd been racing it for 8hrs you might need rings, but I'm gonna guess that 8hrs of full throttle banging off the limiter racing is equivelant to about 500hrs of my puttering around the woods, although it is food for thought.  I've read some threads that people who woods ride have gone a very long time in between doing rings and pistons, a lot longer then the Racing standard anyways.

 

I found a Excel sheet calculator online that lets you plug in altitude, humidity, barometric pressure and your baseline settings to get a correction factory.

 

Essentially it says that at 4400ft and 70f I should be running a 150main and 48 Pilot with a mid level needle which sounds about right given the lack of oxygen at said altitude, which gives an estimated 50hp about 37hp, I've never run this bike at sea level, seems pretty fast with just 37hp, what the heck is 50hp like!  I was at sea level with my '12 Ford Focus a month or so ago, I could not believe how much harder it pulled then at altitude, then I was at 8000ft a week later and holy moly was it slow!

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