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Old 04-15-2010, 07:56 AM   #1
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Default Kyosho DBX problem

I have a DBX and up until the other night it was running great.

I was trying to tune it and I think I might have turned the HSN too far but having stripped it down it appears that the threads are fine.

The problem is that now it either doesnt start at all or that it starts and immediately goes to what seems like WOT. The idle, HSN and LSN have all been reset to standard (2.5 turns) but it still happens.

Have I permanently damaged my HSN? Do I need a new carb?

Another issue is that when applying the glowstarter, there is a sound like the servo's are activating. Do I have a grounding issue?
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Old 04-18-2010, 02:13 PM   #2
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Bump - any ideas?
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Old 04-18-2010, 02:23 PM   #3
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What noise does it make when it dies?
Does it die with the glow plug on?
Try turning the idle up (on your transmitter so you can turn it down again) and seeing if it doesn't cut out?
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Old 04-18-2010, 06:09 PM   #4
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The servo noise is fine; when you put the ignitor on the motor, the pressure on the car is causing some pressure on the front wheels and the steering servo is just trying to make tiny little adjustments to stay centered. If you lift the front of the car off the ground for a second then the servo will center and become quiet again.

What is your air gap? Remove the air filter and look down the carburetor. When you release the trigger on the remote, the gap should be very small, maybe .5mm. If it's much larger then that might explain it revving up.

Also with your LSN, note that if you turn it in until it stops then you're going to need a lot more than 2.5 turns out. Look at the carburetor slide very carefully. As soon as the LSN seats, it will start to push the slide out, as if you're giving it gas, but the LSN doesn't actually stop turning here. Stop turning it in as soon as you see the slide start to move, then back it out 2.5 turns from that location.
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Old 04-19-2010, 02:59 AM   #5
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The idle gap is fine - its set as per manual at 0.5mm. It has never been moved since i did the original tune.

It does one of three things:
1) Doesnt fire at all.
2) Occasionally fires but stalls within 2-3 secs ie before I have the chance to remove the glowplug or use the throttle.
3) Starts and instantly goes to high revs and tries to launch itself off the bench. Throttle position is unchanged (fully closed).

Is it just in need of a complete retune or am I needing to replace the HSN or carb?
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Old 04-19-2010, 03:36 AM   #6
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What makes you think the HSN or carb would need to be replaced? Did you crank them down super tight or something?
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Old 04-19-2010, 03:58 AM   #7
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"3) Starts and instantly goes to high revs and tries to launch itself off the bench. Throttle position is unchanged (fully closed)."

Sounds like your LSN? :S
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Old 04-19-2010, 04:28 AM   #8
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I had turned the HSN too far but it appeared to be ok once stripped down, cleaned and reinstalled (it does feel like there is resistance when turned in to reset it).

With regards to the LSN, it is stated in the manual that it is 2.5 turns - is that from fully screwed in or from moving the slide?
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Old 04-19-2010, 04:37 AM   #9
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Your manual says 2 1/2 turns out from closed according to the one I found on-line
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Old 04-19-2010, 05:10 AM   #10
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That is what i have it set to.

HSN=2.5 turns
LSN=2.5 turns
Idle=0.5mm approx
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Old 04-19-2010, 08:50 AM   #11
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With my personal DBX, if I screw the LSN in until it stops, then it requires more than 2.5 turns out. If I screw it in until the slide starts to move, then 2.5 turns out from that location is a good starting point. Try it both ways and see if either makes your situation better.
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Old 05-04-2010, 12:11 PM   #12
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Default LSN

Same issues i had as i'm a newb. I found out i was running rich, which will cause the issues you are experiencing. Returned everything to factory EVEN the idle.
Left my HSN alone and worked on my idle / LSN. My LSN ended up about 3.5 turns out from close. The idle, i had to remove the air filter and physically look at the idle setting.
I think the 5mm is too much, it should only be about 1-2mm and then adjust ur LSN accordingly. I put mine to 1mm and slowly set the LSN richer to maintain my idle. This is counter intuitive as you would think that more gas = better idle / less stalls. This however overloads the carb similar to flooding your engine.
Once you start it, rev the engine a few times (lift wheels off ground) to bring engine to temp so it won't stall. If it stalls immediately, still too rich.
When you maintain a good idle, read your temp, it should be about 150 - 175. This reading will depend on your cold plug, your nitro, air temp, etc. Im running cold plug + 30% Byrons Fuel. Then you can start to slowly lean it out by turning it in "1hr" increments. Remember, it takes a few seconds for the engine to run ur new setting so adj, be patient, throttle.
Once you get ur LSN done, THEN you can repeat the process for your HSN.
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Old 08-03-2010, 03:58 AM   #13
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Hey hello,

Also just had the same issue as the one you're describing.
However, the day before my DBX was temp gun tuned and all the settings were perfect! What I discovered the day after when I had the problem were a couple of cracks in the fuel tank . The car would only start and work (shortly) if you'd prime the engine by blowing into the fuel line directly....

So, first of all check your fuel tank for cracks and the o-ring for bursts, and then your fuel and pressure lines for cracks and bursts similarly.

Hope it helps and you get your problem shorted.
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Old 08-03-2010, 04:05 AM   #14
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maybe a O-RING has broken off a bit and got stuck in the fuel nipple or throttle slide. assembly making the thing run excessively lean
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Old 08-03-2010, 07:14 AM   #15
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As mentioned above, remove the air filter and make sure the carb side isn't open too much. Maybe the trim on your radio is set too high and the servo is holding the throttle open?

If that's not it, check the front bearing, maybe you've got an air leak. I just dismantled my DBX engine a short time ago and the front bearing was so bad I could see light through it. That said; I just swapped to an O.S. CV-R .18 engine and WOW what an improvement. If you've got the cash, it's a very worth while upgrade IMHO. There's a link at the end of the DBX thread for how to do the swap.
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