jetting running lean

Hey all,

I have a 05 DR650 with all the good Mods: FMF Q pipe, DJ kit with the 160 MJ, fuel screw at 2 turns out, and the side cover off. Everything seems fine, idles well and runs great at the low and top end. My only concern is that when I check the plugs they are almost white on the ceramic. i have been playing with the fuel screw but nothing seems to improve the color of the plug. I am in Atlanta and at about 700 ft ASL. Also, if I ride the freeway for a while and then go to surface streets and stop, it dies. It will start right back up and run fine after that.

any help or suggestions would be greatly appreciated

You should probably go up to the dj170 for starters. Also, you should try and run your bike on prime and try and get it to stall after the same circumstances, sounds like your float bowl may be running dry.

To add to that good answer...

The fuel screw only applies to the idle or near idle running conditions. It won't make any difference to the mid and upper throttle/rpm ranges.

You need to richen the main up and adjust the needle height if required to get that insulator at least showing some brown. Milk in coffee is the preffered color.

I think I will start with the 170MJ first. As for the stalling, It is kinda weird. It pops and then stalls like it did when it was too rich. But like I said, the plugs are nearly white showing a lean condition. Won't rejetting tothe 170 mj just make the problem worse?

Your issue seems to be with the idle and part throttle running. Doing the main jet may or may not cause enough of a change to show up in your idle. It WILL affect it but depending on how far out of kilter your carb is it may not be enough of a difference to notice.

It sounds like you need to get back to basics and start at the beginning.

To set the mixtures using plug color you need to run the bike at the RPMs and throttle opening that puts the part of the carb you're testing for into the forefront.

For the mainjet that means some uphill full throttle or very near full throttle runs in teh higher RPM range. Find a LONG hill and hit it at the bottom and run up it at full throttle and in the upper range of the RPM for as long as you can (do try not to get a speeding ticket :banghead: That's why the hill, it'll hold you back). At the top of the hill do two things at once. With the throttle held open full reach over and hit the kill switch and at the same time pull in the clutch. Coast and brake to a stop without letting the clutch out and pull over off the road where it's safe. Now whip out your plug socket and pull out the plug. Assuming you got a good 40 seconds to a minute of running at or near full throttle and at least in the upper half of the RPM range this should be your main jet color. If it's got some brown tinge to it sort of like coffee with cream or close to hot chocolate you're good.

This is called a plug chop in the old tongue and it's how things were done before there was dynos and exhaust gas analyzers.

To test the slide needle mixture you set the main jet as above first then go out and do more riding around. This time you don't need to worry about a speeding ticket. Just ride for about 10 minutes on a highway in top gear at a steady cruise. This should see the vacuum slide running about mid range up the travel. When it's clear behind you and there's a handy weigh scale pullout coming up do the same chop with the kill switch and clutch again. If it's the same color as above then your needle height is pretty good. If it's lighter then you need to move the clip down a notch or two to raise the needle and let more gas in. Play with the needle height until you get it right.

If you set the needle as per above and then find your power tends to surge a little when riding in town at lower settings then you may need a needle with a shorter and more blunt taper to provide a little more gas at the smaller openings.

For the idle it's pretty hard to set by color. You can let it sit and idle for a while but in reality you're best off to set it so you get the most responsive pickup with no hesitation when you just crack it slightly. You're looking for a nice running and smooth idle that does not hang or slow down slowly when blipped and does not drop below the steady state idle and then recover when blipped. The first means lean and the second rich. When you get close it's harder to tell but just play with it in and out in 1/4 turn steps and ride between until the bike feels sharply responsive. with a strong pull and no hesitation or stumbling. You need to make sure you test this last bit with very small throttle openings, as in less than 1/8 of a turn and less than about 2500 to 2700 rpm. If you use more than that or let it rev more then it immediatley moves into the vacuum slide lift range and the slide needle steps in and clouds the issue.

The main jet affects everything all the way down to idle. The needle only the midrange and idle and the pilot screw the idle and the first 1/8 inch or so of slide lift. Some websites I read indicated that they are actually all independent with just a little overlap but in tuning three bikes now I have found that was not the case and that they reacted as above.

Great answer BCrider, should be a sticky .

thanks BCRider and everyone else. This will give me a great starting point. I will let you all know what happens.

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