XR600 help with acceleration problem

I have a '98 XR600R. It has been running fine until a recent ride when I started getting acceleration problems. When riding at lower RPM's and you want to quickly accelerate (3/4 to full throttle) the bike has a large hesitation. It is also noticed when the bike is idling and you snap the throttle wide open it also hesitates(it will sometimes stall when you do this). If accelerating by slowly rolling the throttle open there seems to be no notice of the problem.

Today I have removed the fuel petcock and cleaned it. I also removed the float bowl on the carb, pulled the jets and cleaned them with carb cleaner. I also removed the air cutoff valve to inspect it and it looks fine. These procedures have not helped at all. I am now wondering if it could be an igintion problem?

Anyone else had a similiar problem. I would really, really appreciate the help. The weather has cleared and I still cannot RIDE!!!

You did not mention the air filter. This sounds like either a filthy or over oiled air filter to me. If it were an ignition problem I would think it would come about if you romped on it or rolled it on. Just an idea. Ryan

I did wonder about the air filter. One thing I did do was remove the filter in the garage to see if it would make a difference but it didn't. It really seems confusing to me...

what is your idle jet, main jet, air fuel screw adjustment and needle jet position?

If the temp has dropped and/or the moisture content has dropped you may need some richer jetting. Before I did that though I think I would check my valves for clearance.

Usually an ignition problem shows up as a miss that continues. There is one thing that might cause your hesitation and that is the mechanical advance mechanism, It could be stuck in the retard mode.

I had a friend whose 83 XR500 had an exhaust system that slowly plugged and caused a similar hesitation along with loss of high end power.

Matt, I didn't see what the jet sizes were when I had the carb apart. I bought the bike last spring from a Honda sponsored desert racer. He had the bike set up and it ran fine all summer long. This new problem just started recently. It really seems like an airjlow problem (carb or exhaust) to me because it only happens under 3/4 or more throttle and runs fine when holding the RPM's steady anywhere in the RPM band. I could very well be wrong though. Thanx for all the input guys!!!

Check the complete intake and exhaust system for blockage.

The exciter coil (I think that is what it is called) is known to go on these bikes. Baja designs has some info on checking it.

I had a problem with the automatic de-compressor on my 600. Symptoms were a bit different, but you might want to check if all else fails. The de-compressor is a very difficult problem to troubleshoot.

Sounds like your pri.curcuit or your valves, have you checked your plug lately.

Another thing don't sit in garage and snap the throttle expecting it not to go flat because it will. Now going flat while in gear on the roll is another thing. The pri jetting sounds to lean. If it's cold out you might need to raise the needle one notch.

Thanx for all the input guys. I called Baja Designs and talked to Tex today. He said the first thing he would do would be to adjust the valves and then check the decompression system. I hope that fixes it!!!

The 87 and and the 91 I had needed resetting pretty often at first,,by 5000 miles it stopped on the 91. In stock form none of mine were too senstive to jetting (xr500's and xr600's). FYI moving the needle didnt seem to do much for the top on mine and changing the main(s) was easier anyway. Good luck.

Sounds like the inherent XR6 "cough then stall" problem that basically gets worse as the bike gets older. Several methods are available to fix but essentially it is carb problem, in that the vacuum is too low at low revs. One popular solution is to fit a Mikuni flat slide carb of 38mm or 41 mm size. You totally lose the cough then stall problem and you get far better fuel economy. Another solution is to drill a hole in the slide of the standard carb. Call Ballards in Australia for more info as they know XR600's better than anyone.

[ January 23, 2002: Message edited by: hrc600 ]

that bike was probly jetted crisp for summer...so when the temp droped the jetting went leaner. just drop the clip a noch(i read that dropping the clip a notch will compensate for the leaner jetting in a 1965 honda trail 90 manual) try that.

I think I'm getting closer to the actual problem. I finally ruled out an ignition/spark problem. I moved the clip up 1 position yesterday thinking it may be too rich - wrong move 'cause it made it worse. Took it apart again and moved the clip down 1 from the original location - now it's at the very bottom position on the needle.

Still has the hesitaion when you give it full throttle. This is fully warmed up. Then for the heck of it I decided to put the choke on half way and guess what.... it ran perfect - no hesitaion at all.

Now I'm curious - the needle already has the clip in the very bottom position so I cannot adjust it any more. It cannot be the main jet as the bike has always ran fine before - even in similiar weather. I already cleaned the carb out (maybe I missed something).

Now I'm thinking a bad needle jet. Is there a way to test, measure or identify problems with them or do you just replace it and hope? The tip of the needle is currently very sharp and almost looks like it has been wearing that way (very shiny compared to the rest of the jet). I did pull the other jets and cleaned them already.

Thanx again beforehand - you guys are GREAT!!!

I had the same problem when I put my FMF pipe on. In fact I would run with the choke on 1/2 way when it was cold, and you know what? I sucked that choke plate threw my engine 63 miles out in the Mexican desert. Let me tell you, when you pull the plug, sitting on some trail and it looks like someone took a hammer to it. You know your in deep crap.

Anyway, I fixed the problem with jetting. I tried 4 different pri jets until I found the one I liked.

I lowered the clip 1, and went up 1 pri size. Adjusted the air screw for best lean idle with the engine hot.

You might check out the carb, and mount for air leeks.

It just sound like your too lean. Bikes change as they get older and so does jetting as HRC600 points out.

If you have to engage the choke to run, you need to increase the pilot jet 1 size.

DH, you may need to buy a different needle or needle jet if you are bound and determined to change your lean condition that way. It would be cheaper and easier to try a little richer main jet though,, you might consider that first,,even though you state that it "cannot" be the problem.

so how did you get out of the desert. 63 miles is a long walk.

Well Highbeam that's a long story.

I was on a Tour with Trailboss tours over by Luaguna Hanson south of Tecate coming back from Mikes Sky Ranch when it happened. Trailboss (Chris) towed my behind his XR600.

We started out with a 12' rope and we kept getting crossed up and snapping the line. After a while we got everything moving smoothly and started shifting gears. He would look back in a panic when we were going too fast for a turn so I started hitting the brakes. Soon things were beginning to click, we were hiting the cattle grates and geting air at the same time. At one point we passed the group at about 50 MPH.

When we got back to Santa Veronica my forks and front rim was sand blasted because now we had only a 6' rope. It was so dusty I had to stand up the whole way so I could see.

I've been on 16 rides with Trailboss now and I ride sweep for him everytime I go. In fact I'm going to Baja Thursday for a 3 day Mike's Sky Ranch ride.

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