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Old 11-22-2007, 12:10 PM   #1
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Default Stall when braking

Hi guys,

I'm fairly new to this sport and am trying to help my 12 yr old son who has now raced a season with MADRRC. We are running a second hand hobao engine in his Mugen MBX5 and our problem is that it stalls when he is hard on the brakes during a pit stop. It only seems to happen when the engine is warm. It doesn't stall at all when he is on the track. The stall is immediate in the pit lane - as soon as he stops. The car will idle fine if he just lets it roll to a stop. Any help would be appreciated as I have no idea what would cause this problem

Thanks

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Old 11-22-2007, 12:32 PM   #2
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Quote:
Originally Posted by Coopertrooper View Post
Hi guys,

I'm fairly new to this sport and am trying to help my 12 yr old son who has now raced a season with MADRRC. We are running a second hand hobao engine in his Mugen MBX5 and our problem is that it stalls when he is hard on the brakes during a pit stop. It only seems to happen when the engine is warm. It doesn't stall at all when he is on the track. The stall is immediate in the pit lane - as soon as he stops. The car will idle fine if he just lets it roll to a stop. Any help would be appreciated as I have no idea what would cause this problem

Thanks

Coopertrooper
im as new to this as you are so dont take my word for it, but i wanna try answering.

from what ive read, the car doesnt stall when its sitting there, but when he applies the brakes it shuts off??

well maybe the LSN needle is too far in, and when he applies the brakes, the LSN goes into the carb and blocks all fuel coming in, hence the shutdown??

maybe?
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Old 11-22-2007, 12:39 PM   #3
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I'd also check the clutch shoes/clutch bell make sure its not hanging up...
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Old 11-22-2007, 12:40 PM   #4
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It's gotta be soemthing in the clutch. Most likely the bearings.
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Old 11-22-2007, 01:09 PM   #5
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common problem this; take off the air filter. does the carb close when you apply the brakes? if no, its the clutch, if yes set your idle higher, prefferably to where neutral throttle is. then it should go

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Old 11-22-2007, 04:34 PM   #6
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also check the flywheel nut some times it backs off, if you have remove shims on the bell, also check linkage on thro servo (not running pull WO to nurtal, then hit the brake (pay close at this point) any carb movment when hitting the brake, ajust spring and re tune
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Old 11-22-2007, 05:50 PM   #7
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Since it is only happening under braking conditions, I definitely think it has something to do with the carb adjustments. Try raising the idle just a little and see if it continues to happen. If not, I would guess it is LSN and or something to do with the clutch in that order.
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Old 11-22-2007, 06:08 PM   #8
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doent over analyze things guys, its most likely just the idle out of adjustment...just turn up the idle...im sure this will fix your problem...
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Old 11-22-2007, 06:40 PM   #9
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thats right jason, thats what happened with me, adjusting that did the trick.
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Old 11-22-2007, 06:46 PM   #10
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oh and make sure the carb opening stays at 1mm...
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Old 11-23-2007, 04:14 AM   #11
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Thanks for the advice. After reading all the replies I am now thinking it is probably something to do with the clutch. Before I put this motor in the car I pulled the clutch apart and replaced all the bearings. I will pull it apart again and check that everything is in the right place. We're racing on Sunday so I'll let you know if the problem was fixed.
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Old 11-23-2007, 04:23 AM   #12
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Just bump the idle up a little first just to be sure it's not that. No point rebuilding a clutch if it only takes a 1/4 turn on the idle speed.
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Old 11-23-2007, 07:24 AM   #13
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start it up and let it idle. lift it off the ground and give it a tiny bit of throttle. set it down on the ground while the wheels spin, keeping a hold of it. you want to stop the wheels from moving when it hits the ground. if it stalls, it's the clutch...check the shoe springs.
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Old 11-23-2007, 07:53 AM   #14
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Turn up the idle first, then maybe turn the LSN needle out slightly and check it again to see if it stalls. I assume your engine is good, as a worn one will not hold a good idle hot & cold.

Usually, the clutch will cause the engine to stall after if you accelerate on the ground for more than 2-3 seconds, then when you brake. If so, check the clutch shoes and see if the tips are mushroomed. This will jam the shoes against the flywheel holding the clutch engaged. Just file off the edges if this is the case.
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Old 11-24-2007, 01:11 AM   #15
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Smile Throttle spring and clutch was the problem

Thanks for all the advice so far. The problem was solved today. I pulled the clutch off and filed down all the shoes to ensure they sat flat. I then checked the idle adjustment and noticed that no matter how far I backed the idle off, it kept idling until I applied the brakes whiched killed it. I then looked at the condition of the throttle spring and it seemed a bit dodgy. I replaced it and readjusted the idle and all problems were fixed. The car idled perfectly and braked without stalling.

Everyones advice was great appeciated

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