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DJ160 too lean???? Hard to believe.

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I've read lots of posts and still can't seem to get a handle on this. With a performance exhaust, side cover off airbox and twin air filter with screen removed, will a DJ160 main be too lean at WFO?. I've got the needle in the 5th groove and the bike seems to run great. I'm nervous because of some posts I've read and because the DJ instructions say I should run the 170. I know Jesse says the 160 is the way to go. I've recently tried the DJ165 and I'd say it feels like it runs better with the 160. I know a bunch of guys run the 170 with good results and I don't want to be lean, anyone got any experience here? I think the DJ160 main with the stock exhaust is a bit rich but it still runs ok, I'm thinking that maybe with the peformance can and the twin air things are just right.

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I ran the 170 with great results,decent mileage to. my mods are identical to yours also...........a little rich is way better than lean!!

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Personally, I think most people are overjetting their DRs...especially if they've opened the airbox and have an aftermarket exhaust. I'm running a Uni filter, opened (Jesse) airbox, ISD2 pipe, no screen,...and a 155 DJ main. It runs very well, no pinging. Starts instantly, smooth mid-range, no surging...well, no more than stock. And, that's with temps in the 30-60 degree range. I'm pretty sure the DJ 160 would be on the rich side when the TN temps hit 80-90 degrees. Starts in cold temps require the choke for 30 seconds and then it's ready to ride. If you've been following MX-Rob's work with the FCR it should be clear that most people are jetting too rich. JMHO....YMMV.

MK160

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i ran a 160 with a Q2, modified airbox, stock filter, and it was too hot and smoked the FMF. :sweden: i didnt try the 5th clip :excuseme: the 170 can get hot at WFO too tho... :excuseme:

the TM40 solved the problem. :confused:

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I ran the 170 with great results,decent mileage to. my mods are identical to yours also...........a little rich is way better than lean!!

That's where I'm at,, The plugs will tell the tail...

All white and she's runnin' hot.....Keep it Kool Fool:p

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Modern pump gas burns so clean these days that a white plug isn't the danger sign it used to be.

Without a dyno or a good place to do back to back top speed runs it is difficult nail down the best main jet. Many people will end up with jetting a tad on the rich side because most bikes will run acceptably jetted a little too rich. You only give up a little bit of power and fuel economy.

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Something to keep in mind about this jetting....Unless the motor is really wound up, the mainjet may not be the limiting factor on fuel delivery. You wring the twist grip to the stop, but unless the engine is up to speed, the slide won't raise all the way, which means the needle is still the limiting factor. That's why it's so hard to nail down the correct main....the CV carb is difficult by design, but also very flexible by design. The stock needle is so long, it may never go up far enough to allow the main to deliver all the fuel it can. The DJ needle is about 1/4" shorter, and has a sharper taper, so it has a better chance of opening all the way. I'd love to have a way to visually record the slide position relative to the twist grip position.

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If you've been following MX-Rob's work with the FCR it should be clear that most people are jetting too rich. JMHO....YMMV.

MK160

I don't believe you can compare Rob's project with the DR650 with the stock carb and the dynojet kit. i believe the FCR is a Keihin carb and the jets are different from the dynojet, so you would have to convert the jet size to match or you would be comparing apples with oranges.

You can tell if the main jet size is correct you can do the roll off test.

The Roll-Off technique is the quickest and is almost as accurate as the Roll-On method. First, one gets the engine warm on the way to a safe roadway. If there is room, use fourth gear as this allows more time to assess the result.

Now, get the engine rpm high enough that it is on the cam and in its power band. This may need to be as high as 4000 rpm with some cam choices. Apply full throttle. Let the engine accelerate for a couple of seconds until it has settled in and is pulling hard. Quickly roll the throttle off to about the 7/8ths position. When you do this, the mixture richens slightly for a second or so.

If the engine gains power as you roll the throttle off, then the main jet is too small and you need to fit a larger one.

If the engine staggers slightly or has a hard hesitation, then the main jet is too large and you need to fit a smaller one.

If the bike's running this is about the easiest to do.

You can use Eddie's guide for the pilot circuit to help.

Then you just need to adjust the the needle jet.

Hope this helps some

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You can tell if the main jet size is correct you can do the roll off test.

The Roll-Off technique is the quickest and is almost as accurate as the Roll-On method. First, one gets the engine warm on the way to a safe roadway. If there is room, use fourth gear as this allows more time to assess the result.

Now, get the engine rpm high enough that it is on the cam and in its power band. This may need to be as high as 4000 rpm with some cam choices. Apply full throttle. Let the engine accelerate for a couple of seconds until it has settled in and is pulling hard. Quickly roll the throttle off to about the 7/8ths position. When you do this, the mixture richens slightly for a second or so.

If the engine gains power as you roll the throttle off, then the main jet is too small and you need to fit a larger one.

If the engine staggers slightly or has a hard hesitation, then the main jet is too large and you need to fit a smaller one.

I'm going to try this this weekend. I have the DJ needle, stock 140 main and snorkle removed. I'm super-impressed with the way it runs, but I'd as soon not run rich. Thanks for the tip.

Sarah

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I'm going to try this this weekend. I have the DJ needle, stock 140 main and snorkle removed. I'm super-impressed with the way it runs, but I'd as soon not run rich. Thanks for the tip.

Sarah

Sarah, you can't run stage 1 jetting on a 96-2008 DR650 (see DJ's install instructions). If you are running the DJ needle you must either remove the air box cover (rediculously loud) or do the full mod (way to go). The needle taper is too steep for the limited flow that a desnorkled air box provides as the throttle gets up above about half way. You will be better off going back to the stock needle with a shim. :prof:

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Sarah, you can't run stage 1 jetting on a 96-2008 DR650 (see DJ's install instructions). If you are running the DJ needle you must either remove the air box cover (rediculously loud) or do the full mod (way to go). The needle taper is too steep for the limited flow that a desnorkled air box provides as the throttle gets up above about half way. You will be better off going back to the stock needle with a shim. :bonk:

++1 :prof:

The DJ kit is designed to work with a free flowing intake tract.

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Sarah, you can't run stage 1 jetting on a 96-2008 DR650 (see DJ's install instructions). If you are running the DJ needle you must either remove the air box cover (rediculously loud) or do the full mod (way to go). The needle taper is too steep for the limited flow that a desnorkled air box provides as the throttle gets up above about half way. You will be better off going back to the stock needle with a shim. :prof:

So that's what that asterisk at the top is referring to, now that I take time to look. I'm an idiot.

It wouldn't run for squat with the DJ 150 main and needle in the 4th groove, it bogged terribly much above an indicated 70 mph or so. We dropped the needle to the third position and put the stock 140 back in and it runs better than it ever has. Doug and I are both impressed. But it's way, way rich? I sure don't want to screw my bike up. Thanks again and again.

Sarah

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