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Need a little help.

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Hello everyone, A year or so ago I put a FCR39MX on my 1991 DR 650. I used the standard tuning kit from Pro-Cycle which consists of 155 main jet, 40 pilot jet, 35 leakjet, and a EMP needle. I have bigger and smaller jets and I have an EMR needle. I also use an aftermarket fuel screw. I have ridden the bike with this carb on it but it has never ran well. Since I have owned the bike I have adjusted the valves and checked the timing chain tension. The bike is not hard to start, however after it's running the problems begin. The bike can be rode as long as the throttle isn't snapped open. If you do it responds by trying to die. If cruising at say 3rd gear, opening throttle more than 3/8 of the way will result in the bike bucking and sputtering. It acts this way in all gears. I have checked the float level, I have a Merge racing spring and have adjusted the pump timing as (Rob) described. I ran the basic jetting with the EMP 5 and have moved it from 2-7 to see if there was a difference. When I quit at dark I have the clip in the 2 spot from the top and it seems to run better here than at the other end, but not by much. I have had the fuel screw all over the place. I guessing the carb is rich but that is just a guess. Is there anyway for me to tell if I am rich or lean. The plugs are black and when you rev the bike I get a puff of something out of the exhaust. Please someone help as I contiplating pushing my bike into the river. Thanks to everyone in advance.

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This sounds like just a bit of MJ tuning is needed, then revisit the needle and clip after getting the WOT jetting correct.

If you're not sure the bike is rich (even though it sounds like it is) and don't want to inadvertently run it lean, install a 157 MJ and see if the bike runs worse at WOT. We don't care about midrange throttle response at this point.

If it runs worse, try a 152 MJ and see if that's better than the 155, and if so, try a 150, 147, 145, etc. until you find the point where the power peaks and now the bike is starting to make less power. Then go one (1) MJ rich from that point. If you can't tell the power difference between two main jets, select the richer one.

Once you get the WOT power where it should be, then go back and check your pilot circuit. You'll need both the PJ and MJ circuits tuned correctly before fussing with the needle.

Note: The fuelscrew should be set between 1T and 2 1/2T open from fully-seated. If you can't find a spot where the pilot circuit can be set slightly rich of the RPM peak at a high idle, then you need to fix the issue with the pilot circuit before working on the needle and clip setting.

Once you're this far, then move the needle 1 clip up or down and see if the mid-range throttle response improves or worsens. Pick the best clip and call it a day, unless you're at the extreme end of the needle or the mid-range throttle response is crap; you might need a different needle for whatever reason.

Once that's done, revisit the AP circuit timing and leak jet (LJ) selection to get rid of any off-idle bog when the throttle is whacked open while riding the bike. Don't bother tuning-out a bog with the bike on a stand; it rarely corrects the problem.

Check it out and post your results.

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Thanks alot davidl9999, this is what I'm looking for, an idea of where to go. Thanks again:thumbsup:. Tim

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Eddie, The bike doesn't die with the screw all the way in, so I think I'm going to a 38 pilot. My question is do I just order the 38 or should I get more. I started messing with the main jet today and I am down to a 142 main jet and still think it's rich. I have the clip all the way at the top. I need to order some smaller main jets. Also I read on the keihin website that the knob on the back adjusts idle as well as rich/lean condition at idle. I have an issue with the bike wanting to die unless I slip the clutch. Thanks for the help.👍

Timmy

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hey guys

some good info, although we all have different set ups

i am a new owner on dr650 2007 model. guy i got it from bent the slide needle?? how i dont know.

had a 140 main jet and not sure of the piolet.

has a sport bike muffler on it a M4, and a uni filter in the air box.which i removed the snorkle for flow..

i got a jet kit which has adj. needle, put a 145 jet and adj. air screw to 2 turns out. it idles good starts good, after warming up it has a deliberate hesitation on take off, like starving for fuel..? i have my needle set all the way to top.

what do i need to do? hammers down on throttle when kicked on but the take off sux!!!!

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Fuelscrew on your carb.

Anyway, sounds like a lean squirt. Check the AP timing and look at the BK mod (pretty sure that's the right one for your bike). You want the squirt to start immediately when the slide moves and last about 1 second.

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