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Idle issues

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I can't get this thing, (08 drz400s) to idle right. Just got it a few weeks ago and it doesn't have a steady idle. When letting go of the throttle sometimes it will idle down to around 1800, most of the time it will hang around 3k, if I blip the throttle a little it will then go down to 1800. I've verified that the throttle isn't binding or rubbing on the frame, When it's idling high I have looked and verified that the throttle wheel is sitting on the stop. I've replaced all of the clamps and sprayed brake cleaner and can't find an air leak anywhere.

When I first got it, it wasn't as bad, after playing with the fuel screw and setting it to 1/2 turn out it was hardly doing it. Took the carb apart to clean it and it's been doing it ever since without much change. Right now when messing with the fuel screw, it won't die until the screw is all the way in. Seems to have the highest idle around 1 turn out, but also backfires a lot and the more the screw is turned in, it seems like the worse the idle problem is. Right now it's at 4 turns out, has no backfiring, and the idle problem isn't as severe. Before the last adjustment I had a cemn needle with the clip in the 2nd spot and a 45 slow jet. swapped in the red JD needle in 4th position with a 42 slow jet and it didn't really make a difference. Should I try a 48 slow jet? I think it's lean, but I can't tell. Needing the screw all the way in makes me think it's rich, but it running better with the screw all the way out says just the opposite. If I pull the choke, the idle increases. If I pull the hot start, the idle drops. If it's already at 1800 the engine will die, if its high, pulling it quickly will cause the idle to drop down to normal. This is the most difficult carb I've ever messed with as far as getting it running decently and I had a sport bike with 4 of them on there.

Here is everything else that's done for reference. It has a new spark plug, did a leak down test that was good. Valves are at 0.14/0.15 for the intake, and 0.22 for both exhaust. Completely disassembled the carb and cleaned it. Swapped from an aluminum fuel screw to the JD one, (spring,washer, and gasket) are good. Replaced the clamps with band clamps. As far as mods, it has the 3x3 and a full Yoshi exhaust.

 

I'm not sure where to go next

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How did I not include the most important piece of info.....it's a fcr39mx

Forgot to mention that, I did check the float height and it's at 8.5-9. Checked it several times. It's hard to get it in the perfect position without compressing the spring and it would change slightly everytime, but was always around there. Another thing I noticed concerning the float. If its on the kickstand (leaned over), with an empty carb, it get some out of the overflow when I turn the petcock on. No sure if it's just the initial rush of fuel going in or what. it stops after a second. If it's sitting straight up that doesn't happen.

The first time I pulled and cleaned the carb I removed the paj and it ran like shit, so it's been in ever since. Jetting is 100/42 on the pilot circuit and 200/165 on the main.

 

Edited by soupnutz

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Not with an open flame. I have used it on my atv and car to find vacuum leaks though and it worked fine.

Put the 45 back in, no change. There is something screwy with this carb. If I tap on it while its running the idle jumps around all over the place. That's tapping on the fuel bowl and the body.

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So as it turns out, I may be retarted. Bought and swapped in a stock carb and the bike ran like a top. Steady idle and no problems whatsoever. Since it's narrowed down to the fcr, I give it another look over and 5 seconds into my inspection I see the vacuum plate is upside down. I don't feel like swapping it back out as of yet. I'm going to get at least one good day of riding before I take anything apart again. The stocker isn't bad, but even with the fcr running crappy there was a huge difference on the throttle response.

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Don't you just love spending hours on something , pulling out hairs , throwing things across the garage , pounding your head against the wall , looking something over 5 times and not seeing a thing out of place and then coming out in the morning with a hand grenade and a shitty grin only to easily see something stupid like the stop switch turned off, or as you found, a plate upside down that sticks out like a sore thumb ?

 

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Edited by jjktmrider

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