Idle Problem w/ stock carb


12 replies to this topic
  • 4Takt

Posted August 18, 2005 - 08:19 AM

#1

My bike is a 2002 XR650R. It is uncorked with drilled out stock tip. 168 main jet, 68s pilot, competition needle. I'm at sea level.

I have to set the idle fairly high for the bike not to stall. Even though it still does sometimes. Or it will idle but stall as soon as I crack the throttle a bit.
All this only happens when standing still, at everything above minimum throttle the bike runs fine without any issues.

I can't seem to get the air screw to do anything. I read that your supposed to turn it in until the idle slows, then turn it out until the idle slows again, and set it midways. I can turn the screw all I want, it doesn't affect idle speed at all.

I ended upsetting it 1 1/2 turns out, but not because I noticed any difference.

What am I doing wrong?

Will an Edelbrock carb fix all these issues?

Edit to add: it was like this since it was brand new.

Thanks, 4Takt

  • Ramcc4x4

Posted August 18, 2005 - 10:43 AM

#2

Sounds like a problem with the pilot jet. With the stock 65 pilot jet installed does the problem go away? When the bike stalls does it feel/sound like it's too rich or too lean?

  • 4Takt

Posted August 18, 2005 - 02:48 PM

#3

Don't know about the stock 65 jet, I never tried. Did the uncorking before I first fired it up and the 68s was what everybody recommended. I tried different main jets before settling on the 168 though.
Maybe I'll try the 65 pilot.

4Takt

  • captb

Posted August 18, 2005 - 04:09 PM

#4

Sounds lean, pilot jet dirty or the idle passages dirty.

  • 4Takt

Posted August 18, 2005 - 04:26 PM

#5

Anybody else out there with a similarly uncorked bike and a 68s pilot:
does your air screw setting have any effect on idle speed?

I doubt it's dirt, it was like that from day one and I did inspect the carb.

4Takt

  • TimBrp

Posted August 19, 2005 - 03:14 AM

#6

Air screw can effect idle speed. However, not by much. Maybe your idle if off?(Left side of carb adjustement) Also at sea level uncorked I'd go with a 172/175 main.

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  • 4Takt

Posted August 19, 2005 - 04:55 AM

#7

Air screw can effect idle speed. However, not by much. Maybe your idle if off?(Left side of carb adjustement) Also at sea level uncorked I'd go with a 172/175 main.


If the air screw doesn't affect the idle (much), how do you know where to set it?

My idle is off (high), because otherwise it stalls.

I tried the 172 and 175 mains, the plug looked better with the 168 and it runs a bit crisper, too.

4Takt

  • Ramcc4x4

Posted August 19, 2005 - 05:36 AM

#8

The air screw will definately affect throttle response down low. Try making small adjustments with the air screw and see what works best on test runs from 0-1/4 throttle.

  • frankstr

Posted August 19, 2005 - 05:38 AM

#9

When you adjust your mixture, have your idle set low as possible...
A Edebrock will help out and you'll smile bigger when whacking the throttle :D

  • Old_Man_Time

Posted August 19, 2005 - 08:02 AM

#10

168 main does seem a bit lean for sea level. I would go with a 170 main. You must turn the idle way down before you will be able to notice the effect of the air/fuel mix screw.

Not all the XR650s respond the same to the 68s. My a buddies ran like a champ with the 68s and mine I had to go with a 70 on the slow jet. But make sure you have the mix correct before going to a 70. When you open the bikes exhaust system up the idle circuit always goes lean on you and you must go up in Idle jet size. If you go back to stock you will find the bike pops out the tail pipe on compression slowing. If it is still popping then you are still lean with the mix. Did you take all the plastic inserts out of the air box?

Did you change out the needle? There is a slightly different taper needle that you were supposed to change out with the 68s main. Make sure it is on the third clip from the top.

  • 4Takt

Posted August 19, 2005 - 08:39 AM

#11

168 main does seem a bit lean for sea level. I would go with a 170 main. You must turn the idle way down before you will be able to notice the effect of the air/fuel mix screw.

Not all the XR650s respond the same to the 68s. My a buddies ran like a champ with the 68s and mine I had to go with a 70 on the slow jet. But make sure you have the mix correct before going to a 70. When you open the bikes exhaust system up the idle circuit always goes lean on you and you must go up in Idle jet size. If you go back to stock you will find the bike pops out the tail pipe on compression slowing. If it is still popping then you are still lean with the mix. Did you take all the plastic inserts out of the air box?

Did you change out the needle? There is a slightly different taper needle that you were supposed to change out with the 68s main. Make sure it is on the third clip from the top.


Yes, I did go with the different taper needle, and all the plastic restrictions are removed from the airbox.
There is some noise on decelleration, not sure I'd call it "popping" though. It's more of a snarling, growling sound, kind of like a pissed off wild boar.
I quite like it :D.
I'll order a 70 pilot and try.

4Takt

  • Old_Man_Time

Posted August 19, 2005 - 11:04 AM

#12

After rereading your post I noticed something. You said this only happen when you crack the throttle from standing start and never when the bike is moving. When you said "Crack the Throttle" did you mean give the throttle a full twist just like you would a two stroke? If so the stall is normal.

With the stock carb you must give the throttle a couple of whacks so the the rpm is up before dumping the clutch. The stock carb works best if you roll on the power as it is needed instead of extreme twists when starting from a dead stop. You might try the #70 jet and see if it helps but I think you will always have a hesitation when you whack the throttle. It shouldn't die but a slight hesitation when you whack the throttle is normal with the stock carb.

Get an Edelbrock or some other pumper carb to eliminate that trait.

  • 4Takt

Posted August 20, 2005 - 06:35 AM

#13

After rereading your post I noticed something. You said this only happen when you crack the throttle from standing start and never when the bike is moving. When you said "Crack the Throttle" did you mean give the throttle a full twist just like you would a two stroke? If so the stall is normal.



OMT, thanks for trying to help me out. I didn't explain this clearly.
The bike will stall when I open the throttle just a bit. Basically as soon as the slide opens a crack.

I ordered an Edelbrock today, I've been curious about it anyway.

Thanks all, 4Takt.





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