Too rich or not

Hi everyone

I`ve been reading the post for the last year.Have learnt a lot about the bike and set ups but now I need some help.

I`ve got a break down in power at about 3/4 throttle,I don`t know whether it is fuel or electics

The bikes uncorked 170 main 68s pilot 53e needle middle pos.exhaust drilled out 38mm and I`ve just had the tappets done.I`ve tried 160 main 65s pilot and needle in the 4th from top but still the same. It revs to 3/4 then starts to breakdown and blow black smoke.

p.s. I`m at sea level but do ride up to 2500 ft in mountains.Thanks in advance

Have you tried the simple stuff first?

1) Replace the plug.

2) Remove the gas tank and look at the High Tension lead wire for insulation breakdown. Possible wear at a weld joint on the frame.

3) Check the carb for cleaning or possibly the main jet not seated firmly.

4) Old gummy gas. How long has the bike been sitting?

5) Dirty or over oiled air filter.


Just pulled carb apart replaced top cover o`ring, but did find that the pilot screw o`ring had cut in pieces and part of it was stuck in the carb body took a bit of blowing with compressor to dislodge it.

Changed plug had BKR5E11 now got std BKR7E11.

Put new rush aircleaner foam last week (after jnr undone side cover in garage came off 110k`s in traffic in dark found side plate complete with tyre mark but no element .Always check before starting now.)

Put a piece of fuel hose around sparkplug lead as per earlier post.

I`m a daily rider so I don`t think it is fuel and have tried premium unleaded but still have problem.

Here are a few more things to check in the following order:

1) poor seal (fitting or clamping band) on either side of the carburetor (airbox or manifold side)including cracks in the rubber.

2) valve adjustment (seating over time)

3) ignition control module (a unit swap test, do you have a friend with a XR650R?)


Thanks for your feedback I rubbed grease around the rubber manifolds but no might need to explain point 2 will I have to do a leak down test? I`ve looked in the manual and going to do the testing on the ICM as the friends have those magic buttons KTMs Yamaha`s VORs

Thanks Steve

No leakdown test yet. Valves seat over time and the result is that they don't open as much as they should. If the seating is pronounced then this will affect top end performance. A simple valve clearance check is all that I am recommending.

Is there a difference in full throttle application in the various gears? For example, does winding out 3rd gear vs 5th gear make any difference?

Needsprayer sorry I haven`t got back but here`s were I`m at when twe tested the ICM we found the plug and terminals corroded we cleaned them up and that made a big difference easy to start will now run on full choke instead of firing then using half to get it going, bit stiil a hint of a stutter at 3/4 throtle in all gears as well as free reving ,we`ve removed air cleaner element no change we were wondering if we had a problem with the rev limiter but will go through all electical connections on my days off.So being the second owner unsure what previous owner has done or wether the bike has gone under but do know that he cleaned with gerni, Just one more thing if the needle was changed is there a difference between needle jet sizes with it sort of loading up would it let too much fuel possibly explaining the rich smoke when it starts to breakdown.Sorry about the long winded story but I`d really like to fix it.

Thank you

Steve B


Thanks for responding to my PM. Since you found some corrosion there may be more. Buy some dielectric grease (auto store will have this). After you check and clean all connections, use a little grease to prevent any additional problems with moisture.

I looked up "gerni" and see that it is a high pressure cleaner. If you haven't already done so, you should tear down the bike and grease the steering stem, swingarm bolt, all wheel bearings and shock linkage bolts.

The jet needle affects 1/8 to 3/4 throttle. Too rich will cause a blubbering nosie and smoking. Raise the clip (lowering the needle to make it leaner) one notch at a time (making no other changes). If you get to the top and the problem still exists its time for another needle.

Most of us run: Jet Needle B53E , Part# 16012-MBN-641 with the clip in the 3rd/middle position.

You should visit "The Pig Pen"

The jetting guide is excellent.

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