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Jeff mc

4rt running rough

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Hiya,  my 06 4rt has started cutting out at full throttle a few weeks ago. I've changed the tea bag filter and checked the fuel flow output and it's ok. New plug, swapped the throtte body for a known good one. It now struggles to build revs at low end and top end when throttle is opened quickly. Checked resistances at 32 pin Ecu plug. Only iignition coil - primary out of tolerance. Reading 2.2 ohms instead of 2.6 to 3.2 ohms.  

I have followed as many threads as I can but hope someone can shed some light on this problem. 

Thanks

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Check the vacuum line that goes from a tap into the intake port on the head to the pressure regulator for cracks / leaks.

Don't know if that'll fix your problem, but it's something that's easy to check.

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 Hate to say check compression. We have quite a few 4rt`s with way too many hours on the original piston.

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It will be the throttle position sensor in the throttle body.  basically as they get worn the throttle sensor will go past 100% and 101% doesn't compute in the ECU so it causes the fault you described.

Easy solution is to remove the plastic cover off the side of the throttle body and put a very thin shim under the wide open throttle stop, bringing it back to with in the  0 - 100% limits...much cheaper than buying a new throttle body.

I've had this on one of my well used 4rt's and have come across it a few times.

Hope it helps,

Matt.

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25 minutes ago, mattv6 said:

It will be the throttle position sensor in the throttle body.  basically as they get worn the throttle sensor will go past 100% and 101% doesn't compute in the ECU so it causes the fault you described.

Easy solution is to remove the plastic cover off the side of the throttle body and put a very thin shim under the wide open throttle stop, bringing it back to with in the  0 - 100% limits...much cheaper than buying a new throttle body.

I've had this on one of my well used 4rt's and have come across it a few times.

Hope it helps,

Matt.

yep - done the same. Normal fault with that is only on flat out throttle (big climb etc).  If you ride on normal throttle does it run ok or is bottom end lumpy. 

As you have tried an alternative Throttle body I would be tempted to try swap tank/fuel pump assy. As maybe failing under load. Does it get worse as the bike get warmer?

Earth wire at the bottom of the coil can also corrode =- try a fresh extra earth wire from coil to engine bolt.    

Best of luck 

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Thanks for all the thoughts fellas. And no I'm hoping not to have to get a new bike Cubby.  Plenty of life in this one😜 .   I have checked the earth wire. Runs well when not on full throttle. I have taken apart all the wiring harness connections and will re seat them just in case there's a poor connection. I'll let you all know how I get on. 

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Right. It's not the earth on the coil. Not the main connections on the wiring loom. Tried the shim of metal on the full throttle stop. Checked the vacuum pipe on the fuel pressure regulator- its not split of blocked. Still misfiring and cutting out at full throttle.🤔

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Fuel pump.

see if you can swap a tank

Does  it get worse as it warms up?

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Doesn't seem to make any difference how warm it is. I checked the valve clearances a few mo the back. I can't understand why that would depend on revs. If it was valve clearances would it not run rough right through the rev range?  Starts and ticks over beautifully. 

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1 hour ago, Jeff mc said:

Doesn't seem to make any difference how warm it is. I checked the valve clearances a few mo the back. I can't understand why that would depend on revs. If it was valve clearances would it not run rough right through the rev range?  Starts and ticks over beautifully. 

If the valve clearance is supper off then yes the hole range could be rough, however if its just one side or only slightly off you can see it more at one side of the range or the other.  

Edited by jonnyc21

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Ok. May be worth checking then. I can't see them being that far off but I'll see. I guess it would be more of an issue if the clearance is not enough. That would mean the valves aren't closing fully wouldn't it.  

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Next stop will have to be swap over of tank and injector assembly to fully rule out the pump struggling under load. 

Edited by Jeff mc

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