02 XR650R Jetting question


9 replies to this topic
  • buteoridge

Posted September 26, 2006 - 08:47 AM

#1

I am considering a partial uncorking of my BRP. I don't want to alter the exhaust system in any way. (I have to keep the exhaust noise to a minimum in order to ride in certain privately owned areas near my residence.) If I remove the snorkel and plug from the air box, change the carb boot, and leave the exhaust system stock. What jet sizes should I run, how should I adjust my idle mixture screw, and where should the clip be positioned on the needle?

Thanks in advance for the input.

P.S. I have already posted this same thread in the Jetting Forum but haven't gotten a response yet.

  • Ramcc4x4

Posted September 26, 2006 - 11:24 AM

#2

Tough call. If the elevation is near sea level I would probably start with leaving the stock 65s pilot jet, MAYBE lowering the needle 1 clip, and possibly a main jet in the 165 range and see how it rides.

  • LesJive

Posted September 26, 2006 - 06:00 PM

#3

If your going to leave the exhaust stock, and not drill holes in your airbox, contact your local Honda dealer. There's a hop-up kit available for your mods..

  • Max Power

Posted September 26, 2006 - 07:08 PM

#4

If your going to leave the exhaust stock, and not drill holes in your airbox, contact your local Honda dealer. There's a hop-up kit available for your mods..


My dealer does not have a P/N for that scenario. Can you post a P/N.

  • Ferdinand

Posted October 09, 2006 - 09:15 PM

#5

Anyone else got more info or suggestions for this setup. Would like to know if anyone else is using corked exhaust with jetting and airbox box mods?

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  • Dave102429

Posted October 11, 2006 - 03:46 PM

#6

If you have already decided to keep the exhaust completely stock, then leave the intake stock too. An engine is basically an air pump; what goes in must come out. Just think, if you could only breath in trough your mouth but could only exhale through your nose, and you have a cold, and one nostril is congested, you're going to freak and pass out, or explode. Your XR650R won't be happy either, and it'll be hot too because it can't expel it's hot gases quick enough.

If quiet is a concern, use the stock header and a "quiet" silencer. The stock silencer with the HRC baffle is fairly quiet. I've even seen guys install a turn-down tip on the end of the HRC baffle to lower the DBs even more. At one time I saw turn-down exhaust tips from Baja Designs (don't know if they still sell them). Several manufactures produce "quiet" silencers. So you have many options to keep your bike quiet. Another way to keep your bike quiet is to just putt around in high gears at low RPMs. The bike's not loud below half throttle.

As far as jetting is concerned...this is what usually works for me.

2000-3500 Feet
65-75 degrees
172-175 main
68s pilot
53E needle on the 3rd clip
2.0-2.25 turns out for fuel screw
Pop out the air box snorkel and plugs
Replace the intake boot
Choose an option for the exhaust

Your results may vary.

  • HawkGT

Posted October 11, 2006 - 04:34 PM

#7

I would definitely install the HRC intake manifold and remove the airbox inserts--even if you leave the exhaust completely stock (the manifold being especially important). It's easy to imagine that the engine can only suck in as much as it can pump out, but the dynamics of intake/exhuast functions are not that simple. Exhaust scavenging, valve overlap, the momementum of moving intake/exhaust charges, and more all come into play when it comes to filling the cylinder with intake charge.

Intake and exhaust mods are not generally an either/or situation. They compliment each other--yes--but are not mutually dependent. Running hot because it can't expel exhaust gas quickly enough is nonsense.

  • Billahjack

Posted October 11, 2006 - 08:08 PM

#8

I bought mine uncorked but I believe there is also a plug in the end of the tailpipe that you can drill out with a hole saw. The smog air pump on mine was removed. It is the unit mounted to the back of the right radiator with hoses comming out of it. My bike did not sound overly loud with the baffle cut out of the end. I'm now running a FMF powercore 4 and it is way louder than the stock pipe with cut out baffle. My buddy has a FMF Q pipe that is louder than the baffle removal but yields the same power due to the Q baffle restriction. In my opinion it is not much louder, but get some opinions from others first.

Maybe you can find another stock end cap for cheap and experiment. If you remove the entire tailpipe baffle by unbolting it, you will find a mesh cage with a flat bottom steel plate. Just drill the baffled tip like the picture in the web link below and leave the plate/cage alone. Side note - The HRC end cap has a different cage tail pipe configuration that is way louder than the stock tip with the baffle drilled. In my opinion, its as loud as my Powercore 4.

One of the comments on here noted that removing the stuff forward of the engine does not help much without removing the stuff after due to the fact of the engine being an air pump. He is correct, although think of it this way. You are sucking air through a straw. Wherever there is an obstruction, then that is the limiting factor. I think you can gain a bit from removing the front end stuff without the back but not nearly as much as removing the exhaust baffle center. Jetting would probably be pretty close to stock (meaning little improvement) if you uncork the carb side.

Check out these links:

Jetting Guide - http://www.xr650r.us/jetting/
Uncorking - http://www.qsl.net/n...ing the brp.htm
Example of Hole Saw - http://www.coastalto...649a 1160721093

If you decide to uncork the entire thing, then read on:

There are kits on e-bay for the entire jet kit. This is a really good deal. Honda charges about $35 for the HRC needle jet kit, $3-6 for a pilot jet and $2-6 for a main. You can do the math to figure out what you want to do. Look up item # 280036748948 for the entire jet kit set. These guys are fast and professional. I would definitely put in the 68s pilot and then the 175 main if you drill the tailpipe baffle. You can do the pilot (idle) and main (half throttle to wide open) only. If you do the needle jet set, then that refines the mid throttle a little bit. Not really necessary though. I didn't notice much difference with my bike anyway. The pilot jet is the longer one with the holes cut in the side of one end. The main jet is the short one. The needle jet set is the needle plus the jet that it plunges into. The needle is a pain to get out because you have to take out the carb slide from the top. Make sure the keep the stock needle with the stock needle jet and the new needle with the new needle jet. The other two jets are accessible from the bottom by removing the float bowl.

The lazy way to rejet the carb just changing the main and pilot ( think I hit all the main points but I'm sure somone will correct me if I missed something):

Turn off the fuel petcock. Remove one end of the fuel line from the carb or petcock. Loosen the carb hose clamps, rotate the carb so you can access the underside from the left side of the bike. There is a key in the forward boot that keeps the carb oriented correct. Just rotate the carb and the rubber nubs will go over the key protrusion on the carb. Put a rag ontop of the engine case below the carb to catch anything you might drop. Make sure that it will catch something instead of roll off.

Remove the 5 philips screws on the bottom of the carb. Remove the float bowl carefully with out dropping the float pin pivot. The float pin pivot will fall out if you play with the float. If this pin falls out, you will need a high quality smaller phillips to remove the bent sheet metal plate so you can access the float pin pivot/plunger/spring setup. This is a pain. Don't play with the float. Just take a look at the pivot point and make sure the pin is centered and not hanging off to one side or another.


The main jet is in the middle. There is a concave cup with the open side of the bowl pointing down....kind of like an umbrella. The main jet is in the center of that. The brass cup is for fuel slosh. Just unscrew the main jet but leave the brass tube tight above it. Use a socket on the jet and a wrench above the brass cup if you can. The wrench should be 1mm larger than the socket for the jet. If you loosen the brass tube, you have to reset it. It holds the needle jet in place in the carb. To set the tube, back off the jam nut that jams against the aluminum carb body, screw the brass tube finger tight into the carb body then tighten the jam nut while holding the brass tube from rotating with a wrench. You will need to know how to set this if you decide to swap out the needle jet and needle.

Now remove and replace the pilot with a screwdriver. Button it all back up. Be careful when you put the float bowl back on. Make sure the seal and seal surface is clean. Make sure the get the brass tube into the sheet metal slot by the main jet. Be gentle, don't force it. Screw everything back together. Use firm torque but don't put the hurt down on the screws. You can tighten them and then feel a slight click as the head slides with friction against the float bowl. Too loose, they fall out eventually, too tight you can strip them. When you finally get the jetting how you want it after trial and error, I would use some loctite to secure the screws. Don't loctite your first time around since you may swap jets a few times to get it right.

If you are only swapping out the main jet, then you can unscrew the 17mm plug in the center of the carb (turn off the fuel petcock first and drain the carb). Gently remove the main jet with a socket. Make sure not to screw up the orientation of the brass cup. If you are good, you can just let it drop to the bottom of the float bowl, then put the new main jet through it.

If you want to do the needle jet set, then you need to remove the carb, disassemble the top and bottom end. This is alot more work.

The side cover mod is a good one also. This mod cuts out a portion of the left sidecover and puts a screen under the cut-out. I found that my filter stays cleaner with this mod. The bike sucks air from under the seat. The air the gets under the seat comes from the edge of the seat and sometimes under the rear fender area where it is dusty. The side of the bike behind your leg has less dust. If you get a aftermarket UFO rear fender, make sure to seal it up with silicone against the airbox and the two rear holes with duct tape to keep the dust from your back tire away from your air filter.


It is easy to tell if your bike is running rich on the main or pilot. It is harder to tell if it is running lean. To effectively figure out if it is lean you need to check the spark plug. If the plug has white haze then it is running too lean. The plug should be brown/black hazy with good jetting. If it is black sooty or black and wet, then it is rich.

Its easier for me to start rich then back off to leaner jets. The other reason why I do it this way is that you can overheat your bike in tight stuff or ruin the exhaust valve & piston over time if it is too lean. Better safe then sorry right?

As far as telling if your bike is jetted right (most probable cause):
Difficult to start without 1/2 choke when engine is warm - Pilot too small
Floods when starting (hard to start then backfires) - Pilot too large
Full throttle rolling off gas causes slight hesitation - main jet too large
Backfires when going fast and returning throttle to idle position while RPM is high - Main and/or pilot too large


I am considering a partial uncorking of my BRP. I don't want to alter the exhaust system in any way. (I have to keep the exhaust noise to a minimum in order to ride in certain privately owned areas near my residence.) If I remove the snorkel and plug from the air box, change the carb boot, and leave the exhaust system stock. What jet sizes should I run, how should I adjust my idle mixture screw, and where should the clip be positioned on the needle?

Thanks in advance for the input.

P.S. I have already posted this same thread in the Jetting Forum but haven't gotten a response yet.



  • Thunderbug

Posted October 11, 2006 - 08:57 PM

#9

Man just uncork your pig with the HRC kit, than purchase one of the baffle tips from Baja Designs.

They're very, very quiet without a big loss of power.

  • Thunderbug

Posted October 11, 2006 - 08:59 PM

#10

And buy the Edelbrock carb while you're at it, otherwise you'll forever be having problems.





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