jetting xr600 AGAIN, sorry

hi guys, thanks for giving me advice about jetting my xr 600, unfortunately it's still a damn pain in the ass!!!

It's running quite hot and it's idling nervously.I'm 99 percent sure it's a jetting problem. checked the oil pump, it's working fine, and it's got fresh en pleny oil in the engine. ignition is good as well, and compression is great.

When i bought it, it had a 170 main jet, a 70 pilot jet, and needle in 4th position (so more gas than stock setting), whilst stock jetting for my bike is 152-62 and 3rd (middle position)

When i bought it, it ran like [@#$%&*!]. it didn't idle good, and with throttle half opened, it' just made a lot of funny noises and it dropped in speed. At full throttle in 5th gear it was running really, really bad. Plug was black, so obviously too much fuel. tried setup 152-70- 4th position first, wich resulted in a nice unexpected wheelie :awww:

But it was still idling bad, and the problems with half open throttle were still there. Plug was now white, so i think too much fuel at low rpm and too little at high rpm. I tried various setups after this; 65s-155-158-162-165-170, and in the end it runs allright on 65s-165 with needle in 3rd (stock) position. No problems with half open throttle either.

BUT, plug core is white and it runs quite hot, and as a result it starts idling nervously again.But worse, if i leave it idle for about a minute the oil becomes so thin that you can hear the cam tapping on the valves :devil:

i don't want to wreck the engine, so who's got a good idea besides an oil cooler :lol:

The snorkel is removed from the air filter box, muffler is stock (but removed the square piece of metal which is attached with 2 bolts on the 'bottom side' of the muffler), and i removed the exessive welds in the exhaust manifold.

Got a keihin single carb by the way.

I'm living near sea level.

thanks in advance :thumbsup:

What kind of fuel are you running? You need at least 92 octang per the manual for the XR600. I would look for an air leak and just to be sure check the valves.

If you run 87 octang the bike will run very bad and at 91 your pushing the limit. I aways ran octang boost, lead works best or mix race gas with pump gas just to bump it up to 94+. No need to go crazy like 100 octang.

Don't forget it's an air cooled engine so don't let it sit at idle on a hot day for very long. That is where the higher octang helps it slows down the burn and burns cooler.

How does it start? Do you have to choke it even when hot like I did. I had an FMF pipe than ran fast but was a pain to get jetted right. It was always lean.

What year bike is it. I think pre 96 was a 38mm carb and in 96 + they went to a 40mm like I had.

IM running a 95 628 kit, main jet 165,needle on third notch down,slow jet #62,fuel rich screw 2.5 turns.Fuel octane over 92 less then 100.valve noise might mean it needs them adjusted or you may need to change to a better oil

hi guys, thanks for the advice so far, but i'm sure it's not the fuel, i run fuel with at least octane number 95. So please keep the advice coming :thumbsup:

When it's hot i don't have to choke it.

By the way, it's a 92 engine.. so must be the 38 keihin

It sounds to me like your float may be set incorrectly. If your 600 has anything in common with my 650 it may be very sensitive to different float heights. I messed with my jetting for a long time when I first bought my 650. When I felt I had run out of options in the jetting department I took a look at the float. I had leaned the bike out and leaned it out some more. It still wasn't running clean. So I lowered the float about 1mm. Voila! I bet I gained an honest 5 HP. The engine cleaned right up and now it really rips!

Despite all of your hard work with the jetting if you adjust your float you may have to go though all of your jetting again to get it to be spot-on. Hope this helps. Hang in there. You will figure it out eventually. I spent much time to figure my bike out, but now I know how the bike responds to different pilots, needle positions and main jet sizes. It was worth the monkeying around.

Try raising you float in 1mm increments and see what happens.

Hope this helps.


I would have to agree, be sure your valves area adjusted properly, your floats are properly set and your air filter is clean and properly oiled.

I know my bike is too lean when I have an occasional backfire when starting, popping on decelleration, sometimes some detonation at lower engine speeds under load and of course excessive heat.

I ride at different elevations and may go from high country to vally areas with elevation changes as much 4-5000 feet. My aproach was to start out rich and then lean the jetting just enough to make it run and start properly. If I'm going to a lower elevation I'll set the bike up to run at the lower elevation and live with a little bit of sputtering at the higher elevations if I head into the mountains.

I found it easier to try to tackle one aspect of jetting at a time, so I tackled the main jet first since it seems to have the largest effect on carburation. Once I got close with the main then, I fine tuned the pilot and air screw.

You will know if your main is too rich if the bike sputters at wide open throttle and doesn't rev out all the way. I put the largest main I had in the carb (a 170 I think) and took it out for a spin in an area where I could pin it in high sputtered badly at WOT. I put a 168 in it and it cleaned up a lot but still sputtered a bit so I put a 165 in and it ran pretty good at WOT. I set the air screw at 2.5 turns and turned my attention to the pilot (I was having some detonation and backfiring when starting at this point).

I checked my pilot; it was a 68. I resoned it was too lean with the backfiring and detonation. I went to a 70 and my popping and detonation largely disappeared. I reset the airsrew and idle and the bike started very well (hardly ever touch the choke unless it's very cold). I later switched fuel sources and installed a cooler plug. With all that being said here's what I run with stock engine, UNI filter, FMF Power Core IV Q exhaust and no snorkel:

7000 feet elevation 165 main, 68 pilot, stock needle pos

3200 feet elevation 168 main, 70 pilot, stock needle pos

I have never ridden the bike below 3200 feet so my guess for sea level jetting would be:

sea level 172-175 main, 70-72 pilot

Once again, I found it easiest to address one aspect at a time and started out rich and leaned it out just enough to get it to run right (my plug is a bit dark, but to me that's reassuring). Also keep in mind that the all "circuits" in the carburator are affected when any one is changed (they overlap to a certain extent). Good luck, it's worth the hassle. :thumbsup:

guys, thanks you very much for your advice, it give's me al lot idea's. There's one thing that velvet hog wrote, that could be the case, but i don't really know how to check the float level. I know you can adjust it with that clip that is attached to a small pin, but do i have to set it in a way that the fuel distribution to the jets stops more early (so less fuel in the carb itself), or is it the other way around?


From your post I think you need to raise your float level so more fuel is in the float bowl. AZ is right; only change one thing at a time. Don't do multiple adjustments or you won't know what contributed to whatever results you got.

Good luck.


If I remember right to adjust the floats you need to pull the carb. With the bowl off and the carb up side down you measure the carb base to the float. It should sit 14mm above the carb base. You adjust the valve stop or tab on the float until your in spec. I can look in my book tonight and see if that sounds right. :thumbsup:

As far as your valve tapping and oil temperature problem, RUN SYNTHETIC OIL if you dont want to wreck your engine... Synthetic oil withstands much higher heat than regular oil, not to mention a lot of other benefits.

Sure its best not to get the oil to hot, but in the air cooled 600R it happens !!! Run pure synthetic oil if you like your engine... Mobil 1 Delvac for heavy trucks is best, but hard to find. Mobil one Red Cap synthetic is really good and you can find it anywhere....

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