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sactoXR

Rough Running BRP

11 posts in this topic

I bought my 2001 XR650R a year ago from the original owner. It has always run rough (when compared to my buddies 2000 that he bought new), but I had not gotten around to checking the jetting until yesterday. Yesterday I did the valves (the intakes were tight, exhausts were in spec), and disassembled the carb to take stock of what was in there and try to find any smoking guns.

Findings: The hop-up kit intake manifolds and exhaust tip are in place, the pilot jet is a 65s, the main jet is a 175, and the needle is B53F with the clip in the third position. The fuel screw was showing ~2 threads between the hex and the lock nut, but the lock nut rotated during disassembly, so I wasn't sure of its original position. The spark plug was black and oily, and there was some soot around the exhaust tip. The air filter is stock and the number plate is intact, no holes. In this condition, the bike was very rough off idle until thoroughly warm and displayed a significant stumble in the higher rpm range.

Changes: The only change made other than setting the intake valves to spec, was to adjust the fuel screw to ~2.5 turns based upon some info found in other TT threads, which appeared to move the lock nut much further down the screw than before. Following these changes, the bike was very rough off idle, exhibited the same stumbles, and began making a cracking/popping sound at high rpm/large throttle openings. The exhaust tip was cleaned before evaluation, and it didn't seem to collect any new soot. At one point, I tried running it with the air filter removed and it improved, but once it died from a rapid throttle twist, it would not run smoothly again.

Are there any expert opinions about what the problem may be, and how to correct it? My next step is to put my buddies carb on my bike to see if this improves anything. If so, then I'll copy his settings. If not, what could be wrong? I hope it wouldn't be anything too serious, but judging by the chunks I pulled off the frame oil strainer at my first oil change, it really won't suprise me.... :)

TIA for all you help!

Charlie

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First check the spark plug. Even if it looks only slightly questionable, replace it and see if this resolves your issue.

If the original owner never once cleanred the downtube screen, then it's normal to have metal and chunks of crud in there. After one or two oil changes, that screen should remain pretty clean from then on or until you install a new clutch.

If the stuff on your exhaust is black powdery soot, then your issue is from unburned fuel, not from oil passing the rings. If it's wet black and oily, then perhaps you have oil passing the rings. Even if your problem is from oil passing the rings, the fix can be pretty simple if the problem stems from improper break in (glazed bore), etc. If you're comfortable with removing the head, jug, etc, you'll be fine. Remove the jug and clean off the burned / glazed oil with 3M Scotchbrite 7447. Then wash it down thoroughly with several times with hot soapy water. Then wipe it down with a rag that has tranny fluid on it and wipe until the rag has no more black on it. If everything still measures out good, then put some rings in there and break her in.

If you have a black powdery soot on the exhaust, then you may want to thoroughly clean the inside of the carb and set the float to spec. As far as jetting goes, you can check out this web site for a 'starting' point based on your riding conditions http://www.xr650r.us/jetting

As far as adjusting your fuel screw, you ideally need to adjust it at your riding location for accuracy. First make sure your engine is fully warmed up, set your idle speed to spec and set the pilot screw to 1.5 turns out. Turn the pilot screw clockwise until the idle slows. Then turn the pilot screw counterclockwise until the idle slows again. Make a mental note of how many turns you made in between the low idle points. Then turn the pilot screw half way between the low idle points to finish the adjustment. If you turn the adjuster counterclockwise and the idle doesn't drop down, then you need a larger pilot jet. If you turn the pilot screw clockwise and the idle doesn't drop down, then you need a smaller pilot jet. After adjusting your pilot circuit, re-adjust your idle speed if necessary. Your fuel screw should now be pretty close to an optimum setting. From here, you'll want to fine tune it for the best off idle performance, which should be within about 1/4 turn of where you are if you aren't already at the sweet spot.

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I don't mean to sound stupid, but what does "BRP" mean? How does "BRP" have any relation to an XR650?

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Best not to set the fuel screw off other peoples settings but to set it to your own bike.

Get the bike warmed up and on a fast idle, then slowly turn the fuel screw clockwise till it starts to change it's idle speed, note how much you turned it. Then turn the fuel screw anti-clockwise till the idle speed starts to change. Now set the screw in the middle of these two points.

I run a 175 main jet and a 68S pilot jet. Stock needle in the middle position. Uncorked and drilled holes in the airfilter side panel. Have the HRC exhaust tip and standard air filter.

Mine runs really well and starts fine. It accelerates like a bastard and is responsive to the throttle with no flat spots or bogging.

Running 15/46 gearing and it will get from 0-80 mph pretty damn quick.

If your valves are adjusted correctly and you have no air leaks and no mechanical damage the bike should be able to be set up to run well.

Tim

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First check the spark plug. Even if it looks only slightly questionable, replace it and see if this resolves your issue.

The final step last night prior to shutting down was to pop a fresh plug in, then run it for a while. Unfortunately, it didn't make any difference in how it ran. :)

If the original owner never once cleanred the downtube screen, then it's normal to have metal and chunks of crud in there. After one or two oil changes, that screen should remain pretty clean from then on or until you install a new clutch.

The screen and the oil have been clean since I changed it the first time. :) Even after I had to drill and tap the frame oil hole because the previous owner had stripped it.... :p

If the stuff on your exhaust is black powdery soot, then your issue is from unburned fuel, not from oil passing the rings. If it's wet black and oily, then perhaps you have oil passing the rings....

If you have a black powdery soot on the exhaust, then you may want to thoroughly clean the inside of the carb and set the float to spec. As far as jetting goes, you can check out this web site for a 'starting' point based on your riding conditions http://www.xr650r.us/jetting

The exhaust soot was definitely black and powdery, not oily, and the carb was very clean internally. I was following the instructions from The Pig Pen regarding jetting, but I have yet to find a shop around here that has a 68S pilot. Is there any place online to get this?

As far as adjusting your fuel screw, you ideally need to adjust it at your riding location for accuracy. First make sure your engine is fully warmed up, set your idle speed to spec and set the pilot screw to 1.5 turns out. Turn the pilot screw clockwise until the idle slows. Then turn the pilot screw counterclockwise until the idle slows again. Make a mental note of how many turns you made in between the low idle points. Then turn the pilot screw half way between the low idle points to finish the adjustment. If you turn the adjuster counterclockwise and the idle doesn't drop down, then you need a larger pilot jet. If you turn the pilot screw clockwise and the idle doesn't drop down, then you need a smaller pilot jet. After adjusting your pilot circuit, re-adjust your idle speed if necessary. Your fuel screw should now be pretty close to an optimum setting. From here, you'll want to fine tune it for the best off idle performance, which should be within about 1/4 turn of where you are if you aren't already at the sweet spot.

I think that I've realized something here. What I was calling the "fuel screw" is labelled the "needle jet holder" in the diagram, and the "pilot screw", as labelled from the same diagram on page 5-7, was not removed or adjusted. I'll tear into it again and reset the needle jet holder where it should be, then adjust the pilot screw. Thanks qadsan!:D I feel like a doof....:D

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qadsan:- Sorry read your post again, I only read it quickly , I have repeated what you have said only you were more thorough :)

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Well, I have gone back in and reset the main jet holder to where it should be, and done the pilot screw adjustments. The idle wouldn't drop when turned ccw past the 1.5 turns out point, so I guess I need to get that 68S pilot jet. When I test rode it around the block, it still had the off idle stumble if snapped open, and still sputtered at high rpms with popping on decel.... Come to think of it, the high rpm sputtering felt like a rev limiter. Does the BRP have a rev limiter that cuts the ignition intermittently? :)

Thanks!

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Yes, the BRP definitely has a rev limiter. If you're running WOT for too long, you'll end up bouncing off the rev limiter (i.e. sputtering). This bike doesn't rev out like a CR, CRF, YZF, etc. If you look at any dyno charts, you'll see it signs off pretty early.

The 65s is definitely the culprit for the majority of the off idle stumble you're experiencing. You'll always have a little stumble there unless you install a pumper carb, but a 68s or 70 pilot jet will offer a big improvement over what you're experiencing now. Go to your Honda dealer and tell them you want to order this part number "99105-MBN-0680". They'll tell you it's just a 68 pilot jet which is how its listed in the computer, but you should get a 68s with that number. The jet will be stamped 68s instead of 68 as pictured in this link...http://www.xr650r.us/jetting/68.jpg

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Thanks for your help, qadsan! :) Once I get the 68s installed, I'll post the results.

Thanks again!

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If it runs great after installing the 68s you may find it still sputters and possibly dies specialy after climbing a steep grade. If that happens it will be your float level. The stock float level is too low allowing the fuel bowl to hold too much fuel for climbing specialy slow tight stuff. But don't worry about that until after you get every thing right when riding the flats. :)

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