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Dies when off throttle

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So recently when I go out riding my bike has started shutting off when I come off throttle to stop for lights, and won't restart. It starts fine the first time and runs fine at idle and low speeds, and so far only happens after doing about 50mph. My road test is in the morning, I'm deploying shortly after, and I'm having fits trying to fix it tonight.

Stats on the bike:

'06 DRZ 400sm

FMF power bomb/power core 4

K&N air filter

3x3 mod

JD jetting kit:

Red needle at third position from top (due to hot humid riding conditions)

155 main jet (thinking this should be a 160)

25 pilot

Mixture screw 2.75 turns out

Idle is good and solid maybe a little high but not too low.

Kickstand switch has been deleted and carb has been meticulously cleaned several times. Peacock flows well and vacuum line is connected. Fuel cap off makes no difference.

I'm out of ideas any help would be greatly appreciated.

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Have you done any work to the bike directly before this issue started.?

Does it do it when the fuel tap is on "prime"...?

 

Most likely not related to your issue, but I would be using Blue needle, clip 3 and a 155 main jet....(Hawaii is more humid than hot?)

Edited by Craigo 485sm

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I rebuilt, cleaned, and jetted the carb. When I got it it wouldn't run at all off choke and only barely ran with it on, so this is still an improvement. I haven't tried to duplicate the gripe on prime I'll try in the morning.

I'll also try your blue needle suggestion, JD's chart called for red for over 75 degrees. Seemed like a good starting point.

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I rebuilt, cleaned, and jetted the carb. When I got it it wouldn't run at all off choke and only barely ran with it on, so this is still an improvement. I haven't tried to duplicate the gripe on prime I'll try in the morning.

I'll also try your blue needle suggestion, JD's chart called for red for over 75 degrees. Seemed like a good starting point.

 

Ok, Got ya.....I reckon you could still have some partial blockage of the pilot circuit...replace the pilot jet and get some compressed air on the carb passage ways...

If it runs good on prime you probably have a tank venting issue, also check the little filter is clear on the needle valve assembly..item 18 on this chart...

https://www.thumpertalk.com/shop/oem.php?partcategory=777397&manufacturer=5&category=5&year=2006&model=27185

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Ok, Got ya.....I reckon you could still have some partial blockage of the pilot circuit...replace the pilot jet and get some compressed air on the carb passage ways...

If it runs good on prime you probably have a tank venting issue, also check the little filter is clear on the needle valve assembly..item 18 on this chart...

https://www.thumpertalk.com/shop/oem.php?partcategory=777397&manufacturer=5&category=5&year=2006&model=27185

 

18 points to the needle valve seat.

 

There's a filter in there?  I thought it was just a hole...

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if it runs with choke on then probly the pilot is clogged. So, get it to die as you describe and then try choke on n see if it runs. If not then try petcock on prime. Do these things before taking it apart cuz its easier. Do the easy things first.

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18 points to the needle valve seat.

 

There's a filter in there?  I thought it was just a hole...

 

Yes, there is a small mesh screen on it.

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To get past the test just up then idle a bit using the adjuster screw. You may want to check the valves at some point soon because that may be an issue.

More importantly be safe out there.

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Test got rained out today so once it cleared up I went out troubleshooting, and had the same gripe under any condition (fuel on, prime, reserve, choke, no choke, even when I increased the idle).

I might check valve clearance for my own information and because I'm bored and deal with it when I get back to the states.

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So quick update.

After returning from deployment and cleaning the carb AGAIN I happened to look down in the intake and found coolant pooled on the backside of the valves.

I'll be replacing and sealing the Welch plugs, and I also found the cylinder base gasket to be exploded. Hopefully once it stops burning coolant it will run a little better.

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