What a difference the right jetting makes!

For any of you who pay attention to my posts here, you'll know that I bought a 1994 XR650L a few weeks ago to keep my other 2001 company, and to have as a spare bike when needed.  (Right now the KTM has a dead battery and the other XR is waiting a chain slider for the swingarm, so it's the only one of the three I'm able to ride.)

 

To call the bike "cold blooded" would be an understatement.  It didn't want to idle for about 15 minutes after starting it, although it ran just fine once underway.  I first checked the valve adjustment on it.  Although one exhaust valve was a little tight and all of them were a tiny bight tighter than I prefer, adjusting the valves didn't change anything.  I still had the old jets from when I rejetted my 2001, including the ones that came out of that bike which had the same markings as the replacement jets that went back into it.  I just had to find the jets somewhere inside eight boxes of stuff in my garage from when I moved two years ago.  I emptied all eight boxes and the jets were found at the bottom of the eighth one.  Wouldn't you know it.

 

So I stuck the bike on my makeshift bike stand, took the seat, tank, and side covers off, pulled the carbureator out the side (without disconnecting any lines) and opened it up.  Everything looked good enough, but in taking the jets out and comparing to the ones to go back in, it was clear that both the old pilot and main jets were quite a bit smaller.  The pilot I think had a 50 on it, replaced with a 58, and I'm not sure exactly what marking was on the main jet, but I replaced it with a 155.  The old main jet had a significantly smaller opening.

 

The idle mixture screw was also set at 1 3/4 turns, so I changed that to 2 1/4 turns.

 

Once all back together, I went through the normal starting procedure of finding neutral, fuel on, choke on, key on, then hit the starter button.  It started right up.  So after about 10 seconds I let the choke off to see what happened.  Before it would have died immediately.  But this time it just sat there idling happily.

 

The bike has been transformed.

 

This morning it was the same.  Choke to start it, then the bike ran just fine and idled right away, with no significant amount of warmup time.  I haven't ridden it enough to detect a big change under power, but it feels good to ride.

 

I guess the next step is to put the White Brothers pipe on it in place of the modified stock pipe that it has how.  Then tires and I think I'm done.  Someday, I expect to sell one of the to XR's, but I'll have to decide whether it's better to keep the older one with fewer miles or the newer one with more miles.

58 on the pilot might be a little rich Scott.......155 maion is decent.......the bike comes stock with a 50 pilot usually,,and a 52 or 55 pilot is usually good depending on ethanol...alot of people are finding 55 is a touch rich,,any more than that it`ll run good,,but wastes fuel...

 

B

I put in what I had available.

 

Can't you make up for pilot jet size, just a little bit, with idle mixture screw adjustments?

I put in what I had available.

 

Can't you make up for pilot jet size, just a little bit, with idle mixture screw adjustments?

 

ummmmmmmmm..sort of..........if you turn the fuel screw with the wrong pilot you can help the idle/start problem.......but if you have a pilot to large, once you are just off idle you are burning to much fuel and that affects power..

 

Too lean of a pilot,,same thing,,once off idle it`ll be lean till arround 1/4 throttle ....

 

Check your plug,,it`ll tell you a fair bit with it`s color........

 

B

Right now I'm happy that the bike runs a lot better.  What's a little extra gas?

 

I've had good intentions to get the 2001 tuned exactly right, but it takes me about an hour to take stuff off of the bike, get to the carburetor and open it up, fiddle with it a bit, like changing jets or needle position, then put it all back together again.  Then it takes time to verify that it's actually better and not worse.

 

If the bike is running "good enough", I'll usually choose to spend that time riding the bike instead of working on it.  I wish I loved wrenching on the bike more, but for some reason, the older I get the less I like doing mechanical work.

I put in what I had available.

 

Can't you make up for pilot jet size, just a little bit, with idle mixture screw adjustments?

I have found on my bike that fooling around with the mixture screw made a huge improvement in overall performance. Depending on what forum or who you talk to some say it only helps a bit, others say more. I have found that turning the screw in just a half turn makes this piggy start to run bad. 1+ turns in and its backfiring, hesitating ect. I am running a dynojet kit with the stock pilot jet. I know i should have gone to a bigger pilot but i have had good results with the mixture screw turned out about 3.5 turns taped in place to avoid it falling out. My pig starts up easily, idles fun, and has no hesitation or flatspots. I thought the bike always ran great, but it wasnt until i raised the needle a notch that it really shined. I am quite happy with the stock carb for now. A aftermarket carb would really have to wake things up big time for me to make the change. But i can see myself trying it eventually.

Edited by Thumper3

Right now I'm happy that the bike runs a lot better.  What's a little extra gas?

 

I've had good intentions to get the 2001 tuned exactly right, but it takes me about an hour to take stuff off of the bike, get to the carburetor and open it up, fiddle with it a bit, like changing jets or needle position, then put it all back together again.  Then it takes time to verify that it's actually better and not worse.

 

If the bike is running "good enough", I'll usually choose to spend that time riding the bike instead of working on it.  I wish I loved wrenching on the bike more, but for some reason, the older I get the less I like doing mechanical work.

 

I hear you there Scott.i hate jetting a carb,always have,always did,,,,time consuming with no apparent benefit sometimes..i`d rather spend my time drinkin beer,riding,,you know,stuff that i enjoy ;)

 

B

Edited by brianhare

I have found on my bike that fooling around with the mixture screw made a huge improvement in overall performance. Depending on what forum or who you talk to some say it only helps a bit, others say more. I have found that turning the screw in just a half turn makes this piggy start to run bad. 1+ turns in and its backfiring, hesitating ect. I am running a dynojet kit with the stock pilot jet. I know i should have gone to a bigger pilot but i have had good results have the mixture screw turned out about 3.5 turns taped in place to avoid it falling out. My pig starts up easily, idles fun, and has no hesitation or flatspots. I thought the bike always ran great, but it wasnt until i raised the needle a notch that it really shined. I am quite happy with the stock carb for now. A aftermarket carb would really have to wake things up big time for me to make the change. But i can see myself trying it eventually.

 

 

I got to the point where all the engine mods i had done just didn`t impress me.i figured it was either time to sell the pig and buy a real dirtbike.........or go through the hassle of a pumper carb.........i heard all the stories of how the FCR made such a difference and i called BS on it all..i really wasn`t buyin it :devil:

 

So.....i decided to try the carb,if it actually made a difference,,then great,,otherwise i was off to by something ORANGE ...

 

I had to eat my words on this one,i don`t like being wrong neither,,i didn`t expect the carb to make the difference it did......i think the CV carb is great if you do alot of high elevation then sea level riding,,the CV carb shines there.otherwise toss it to the curb because the difference is night and day in the way this bike works.. :thumbsup:

 

B

Edited by brianhare

I got to the point where all the engine mods i had done just didn`t impress me.i figured it was either time to sell the pig and buy a real dirtbike.........or go through the hassle of a pumper carb.........i heard all the stories of how the FCR made such a difference and i called BS on it all..i really wasn`t buyin it :devil:

 

So.....i decided to try the carb,if it actually made a difference,,then great,,otherwise i was off to by something ORANGE ...

 

I had to eat my words on this one,i don`t like being wrong neither,,i didn`t expect the carb to make the difference it did......i think the CV carb is great if you do alot of high elevation then sea level riding,,the CV carb shines there.otherwise toss it to the curb because the difference is night and day in the way this bike works.. :thumbsup:

 

B

So the carb made more of an impression on you than a high compression piston and or head work? I assume thats what you mean by "i got to a point where all the engine mods i had done just didnt impress me"?

So the carb made more of an impression on you than a high compression piston and or head work? I assume thats what you mean by "i got to a point where all the engine mods i had done just didnt impress me"?

 

Didn`t want to perform to what i thought it should with the OE carb......it was still lazy,slow in response...lofting the front wheel was fairly easy........now it`s rediculously easy,,maybe to easy..

 

These bikes need a shot of fuel in the intake when you wack the throttle,it goes really lean unti the carb slide moves and it shows..and when you put an agressive cam in it,,it needs it even more...the engine builder that ported my head said the CV carb would be fine.........he was wrong.......

 

If i would have known better,,,,,,,i would have put the FCR carb on first.........then did all the internal mods later,,then i could have seen what engine mod made a difference...

 

High comp piston,,worth it,,megacycle cam,,oh yeah,definately..

 

NOTHING wakes these bikes up like a pumper carb and high compression..

 

B

OH BOY My fcr is cleaned,jetted nossed an adustable leak jetted. done yesterday. Just gotta put in on and give it a tweek.  this carb is so easy to build it was actually fun. cant wait to try it. Thanks to all the folks with knowledge here. I'll report my results soon.                                                                                                                                                                                                                                                                                                                                                                                                                                                                        thanx guys     Dave

For any of you who pay attention to my posts here, you'll know that I bought a 1994 XR650L a few weeks ago to keep my other 2001 company, and to have as a spare bike when needed.  (Right now the KTM has a dead battery and the other XR is waiting a chain slider for the swingarm, so it's the only one of the three I'm able to ride.)

 

To call the bike "cold blooded" would be an understatement.  It didn't want to idle for about 15 minutes after starting it, although it ran just fine once underway.  I first checked the valve adjustment on it.  Although one exhaust valve was a little tight and all of them were a tiny bight tighter than I prefer, adjusting the valves didn't change anything.  I still had the old jets from when I rejetted my 2001, including the ones that came out of that bike which had the same markings as the replacement jets that went back into it.  I just had to find the jets somewhere inside eight boxes of stuff in my garage from when I moved two years ago.  I emptied all eight boxes and the jets were found at the bottom of the eighth one.  Wouldn't you know it.

 

So I stuck the bike on my makeshift bike stand, took the seat, tank, and side covers off, pulled the carbureator out the side (without disconnecting any lines) and opened it up.  Everything looked good enough, but in taking the jets out and comparing to the ones to go back in, it was clear that both the old pilot and main jets were quite a bit smaller.  The pilot I think had a 50 on it, replaced with a 58, and I'm not sure exactly what marking was on the main jet, but I replaced it with a 155.  The old main jet had a significantly smaller opening.

 

The idle mixture screw was also set at 1 3/4 turns, so I changed that to 2 1/4 turns.

 

Once all back together, I went through the normal starting procedure of finding neutral, fuel on, choke on, key on, then hit the starter button.  It started right up.  So after about 10 seconds I let the choke off to see what happened.  Before it would have died immediately.  But this time it just sat there idling happily.

 

The bike has been transformed.

 

This morning it was the same.  Choke to start it, then the bike ran just fine and idled right away, with no significant amount of warmup time.  I haven't ridden it enough to detect a big change under power, but it feels good to ride.

 

I guess the next step is to put the White Brothers pipe on it in place of the modified stock pipe that it has how.  Then tires and I think I'm done.  Someday, I expect to sell one of the to XR's, but I'll have to decide whether it's better to keep the older one with fewer miles or the newer one with more miles.

I run 58/160 with 3 turns out...runs like a beast..plug is nice...they run better rich, and cooler.

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