Jetting a modded Cr500

[Ante500]

Hi all, I've got a small problem with my 1997 CR500. The cylinder has been ported and the carb is bored out. The prevoius owner recomended me to run a 190 main and a 60 low speed jet. The bike runs very well at low, mid and top-end. The problem is with the idle. If I let the bike idle for about 20-30 seconds it often stalls once the throttle is opened. Sometimes if the throttle is open very carefully and the bike gets just past the idle-rev it runs perfect and the throttle can be slammed open without any hesitation. Also sometimes if I only blip the throttle at idle the revs drop off but and it almost stalls but after a few secs it's back to normal idle. I suspect this is not due to the 60/190 jets?

Any ideas what might be the problem, is it running lean at idle?

/Andy

 

[cr25096er]

umm sounds lean, how low is the idle? if its real low i know my xr200 would stall when the throttle was cracked at idle w/ too low of an idle.just for the hell of it try a richer pilot or lower the clip a notch and see what happens.

 

[Ante500]

The idle is pretty high. Also if I drive/engine brake slowly around tight corners with the throttle fully closed the bike kind of constantly accelerates and deaccelerates. Kind of hard to describe but it now a smooth deacceleration that you would expect it to be. I would prefer not to mess with the jets unless it is nessesary. I think a 60 low speed jet is rather "rich" anyway?

/Andy

 

[Studboy]

Originally posted by Ante500
The idle is pretty high. Also if I drive/engine brake slowly around tight corners with the throttle fully closed the bike kind of constantly accelerates and deaccelerates.

/Andy

What you are saying describes a lean condition.  I don't know what the stock pilot jet is for your bike,  but it sounds too lean.  I would check for any air leaks.

 

[Mr. Clean]

60 is big for your pilot jet however the boring of the carb. probably changed it's dynamics. The surging you described sounds like a big bore two stroke that is too lean. I owned an 87 cr 500 many years ago and experienced a similar problem while jetting it. Check for air leaks too. My 500 had a chronic problem blowing it's cylinder base gasket.

Your ridin' bud

 

[Ante500]

Thanks guys, it's probably running lean at idle then. What about the air screw and needle setting? Afaik they most affect idle. What should I aim for?

/Andy

 

[Lorin]

FWIW, my WR 500 has been modded (larger bore, head mods, pipe, etc)and runs a larger, Keihin 39.5 mm PWK near sea level and runs a 175 main, and 55 pilot. Although I am not sure what temp, sea level you are at, your CR sounds rich in comparison.

 

[DEANSFASTWAY]

Yeah sounds like a air leak or if the slide is worn out on a big bore bike it will have varying idle due leakind past the slides . On some of those older carbs the chrome would wear off also I know because I had a few of them and sometimes the throttle would stick and bite you . Reeds could be shot also .crankseals etc.If you have problems with blowing or weeping base gaskets you can get Cometic gaskets to make tou a trick tin rubber laminated base gasket that will not blow out and its reuseable and you can have it mailed to you in a few working days . Theyll also make you a .188 spacer plate and you run 2 of those gaskets under the cylinder if you want to rebuild your cranky with the newer years longer aftermarket rod kits . Older motors 86/older used a 5mm shorter rod and there is no aftermarket kit available .If you do this youll have to enlarge the top motor mount bolt holes to get a fit . If youve got a bike that blows or sucks base gaskets you should run a bead of good sealer around the base of the cyl after torquing down . Good insurance . Alot of times on microsprint motors that run alcohol Ill do this with glue . Alcohol is very corrosive and can eat and rot away gaskets . Ante500; find someone who can help you pressure or vacuum test your assembled engine . Anybody good with 2 strokes should be able to help you if they cant help you then find someone more handy to listen to . Good Luck Man

 

[Ante500]

Thanks for your help guys. The engine was recently rebulid so I'm confident it's only a tuning issue. I'll check air leaks anyway.

/Andy