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Running lean

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SQL
World Chat Champion



Joined: 09 Aug 2012
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PostPosted: 21:32 - 09 Oct 2013    Post subject: Running lean Reply with quote
Bike has been playing up, Derbi 125 4v engine no mods.

If the bike is difficult to start and holds back (Laggy) under acceleration is it running too rich or lean? (I have heard these are lean from factory to pass emission blah blah too.

the bike runs sweet inbetween 7-10.5k

I would do a plugchop but its not very practical as no kill switch and I can't get plug out without lifting tank up and out of place.

Anything I can do to confirm this?
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Ariel Badger
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Joined: 02 Dec 2006
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PostPosted: 22:57 - 09 Oct 2013    Post subject: Reply with quote
New plug and clean the carb.
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SQL
World Chat Champion



Joined: 09 Aug 2012
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PostPosted: 23:22 - 09 Oct 2013    Post subject: Reply with quote
_Iain_ wrote:
Plug chop or go see the dyno guy & get him to stick an A/F ratio sniffer up the tailpipe.

Place near brands does three power runs for £25 apparently, myself & paddy were going to take a trip up there soon as he's got a power commander on the TL & I'd like a baseline dyno before fiddling with the H100 so as to judge the effect my tinkerings had. Welcome to come with? Mr. Green


gonna richen it see if it improves ill be up for dyno, time to unleash my 15 horses Twisted Evil
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SQL
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Joined: 09 Aug 2012
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PostPosted: 23:23 - 09 Oct 2013    Post subject: Reply with quote
Ariel Badger wrote:
New plug and clean the carb.


Been done I have 2 new plugs and a iridium too, carb is clean as a whistle.
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Kickstart
The Oracle



Joined: 04 Feb 2002
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PostPosted: 00:13 - 10 Oct 2013    Post subject: Reply with quote
Hi

Try lifting the needle a notch in the carb (or if not adjustable, just a small washer under the clip for the needle to lift it a bit).

However does sound like it is a bit lean, but it might be lean at some revs and rich at others. And it can be lean for other reasons (blocked fuel filter, blocked fuel tank breather, kinked fuel hose, split fuel tank vacuum hose, etc).

All the best

Keith
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temeluchus
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Joined: 01 Oct 2008
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PostPosted: 06:32 - 10 Oct 2013    Post subject: Reply with quote
If the bike has previously been fine and is stock, look for air leaks/splits in all the rubber bits or if anything has dropped off somewhere.

Could possibly also be a failed oring, gasket, choke assembly or float needle in the carb.

Might be worth replacing the spark plug as a matter of course, that will also give you some indication of what's going on.
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