250-500cc WR 300 rattle noise

Are you sure it's not the floating rear brake rotor rattling?

I am 100% sure.

Yes, I'm pretty confident that it's jetting, the new digital ingnition, or a combonation of both. Since there is no TPS, the ignition is going to go through it's map just as it would if you are wide open even though you may only be 1/4 throttle. There may not be enough fuel at that throttle position to handle the load and map advance at that setting. Adding some more fuel at that setting should stop it.

The reason I ask about the gears was to make sure you hadn't added a huge amount of load to the motor, which could agravate the situation.

My 250 wanted to detonate at approx 1/4 throttle when I tried dropping the needle one notch so I put it back and it was fine. This was while the main was too rich and trying to foul the plug. Work on one circuit at a time and make one change at a time or you can easily get lost and frustrated. No matter what carb you have you still have to jet it one circuit at a time and make one change at a time if you want to get it spot on.

I just raised the needle one notch. (lowered clip) The problem is still present. I guess I have to dig deeper. If I'm going to get into re-jetting it would I have a easier time with a PWK? I found the current jet settings...Main 430 pilot 45 Not sure on the needle except that it's the one that comes with the spare jets, not the one thats in it from factory. clip is 2nd from bottom. I'm around 500 ft. elevation. Does any of this seem way out before I drive myself crazy?

I just read through all the posts on this topic again and thought I would suggest to check for an air leak around the reed to manifold connection. I have heard this to be a sometimes occurring problem on WRs. BMP resealed mine before they shipped the bike to me new in the crate to it never had a chance to leak. It would have to be a very slight leak or the symptoms would be much worse but it's worth a look especially if you have the carb off for any reason. Also how many turns out is the air screw? That would indicate how close you are on the pilot.

I will certainly check for an air leak, It can't hurt to check! I will check on the air screw when I get home tonight and report back.

Well....I sprayed all around the air boot with carb cleaner and no spikes in idle. I'm guessing I don't have a leak. I also checked the air screw which was 3 turns out. Now I'm really puzzled! Would'nt that imply that my pilot is too rich? So much for my lean theory

Three turns out may be why it's lean.

Your air screw should be 1 & half to 2 turns out at the most if you have the correct pilot jet. As stated above that is in a very lean setting at the moment.

I rode it again tonight. I turned the air screw to 1.5 turns out. Seems very rich now. Plug is black. lots of burble at lower throttle opening along with my dreaded knocking noise. I then went to 2 turns out, same problemo...Seems that since I raised the needle I get burble and knock. It never ran smooth from the bottom since new, The idle screw is flush with the jamb nut and still barely idles. (was this way when I bought it) Does that sound abnormal? Is it possible that the pilot is actually too rich?

Hey man, my wr250 is/was making a noise like you are describing. It really had me worried because I had split the cases and put a 6speed tranny in it. Thought I had it shimmed wrong or something. I went as far as tearing it back apart to check it out but all was well. I put it back together and the noise was still there and it still sounded like it was coming out of the tranny. I tried moving the kick start lever. no difference. Finally figured it out. At a certain RPM the chain would slap up ad down real fast on the swing guard and rattle like crazy. Still sounds like tranny noise but what a relief it is only the chain rattling. Hope this helps.

Dave

OK, not getting to hear this noise I can only guess at it. It is possible that it's a very rich spot that's causing some of the scavanging charge to ignite and you can get a knock from the crank case. But, it's a deeper sound that I wouldn't call a rattle.

From what you've said, and assuming that it is an engine noise, try going down one size on your pilot jet and start at two turns out on the air screw and see how it acts.

What you need to do is make a mark on the grip flange and some on the throttle housing so you can tell what position the throttle is in when it makes the noise. Then you can nail down what circuits are in play at that point.

It could still be in the ignition. The timing could be slightly advanced from the factory.

It is a deep sound. As far as throttle position goes it is at 1/4 throttle and less. I can get it to do it everytime I hold it at a steady position right after the burble. Any thoughts on the idle screw being all the way in? Any chance that points to a rich mixture as well? I'm going to drop to a 40 pilot tomorrow and see what happens.

It's common for WR's to use a lot of idle screw.

Try the pilot and see what happens.

Try something even if it's wrong you will know to go back the other way. We had an old saying when we got one tuned just right "If it was any closer it would be farther away".

I just pulled the carb to rejet it. While I was in there I thought I would double check the reed block. The bolts seemed a little loose and I found a little gas/oil along the bottom edge between the reed block and carb boot. If gas and oil can seep out I'm sure air can suck in! Gonna reseal it and see what happens!

Well boys and girls.....Problem solved! I'm a happy camper! Thanks alot for all who chimed in and offered advise!

Was it the reed block leaking causing a lean problem?

I believe so. I did'nt notice any spikes when I sprayed it the other night but when I took it apart you could see that fuel was leaking between the carb boot and the reed block. It must have been sucking a little air. It idles better now and is much cleaner off the bottom. Glad It's better!