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Deropke |
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Deropke L Plate Warrior
Joined: 09 Jun 2021 Karma :
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Posted: 02:58 - 09 Jun 2021 Post subject: Running rich, help me diagnose |
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The bike: Derbi Terra 125cc
Symptoms:
Running rich (black sparkplug)
Hesitates initially on throttle often leading to a stall
Sometimes doesnt start at all, not even bump start. (Now fixed, was ripped manifold intake hose)
Severly poor performance below 4k rpm
Poor performance above 7k (redline is @10k, but it struggles to reach it)
Sometimes idles at higher rpm with no hesitations saddly everytime this has happened the bike was in pieces unable to ride to test performance.
Other notes
Bike equiped with automatic choke
Carb only comes with 1 screw to adjust mixture which is slightly rounded, you can screw it, but cant unscrew, seems like it's fully screwed as despite having grip clockwise I wasnt able to move it, but then shouldnt bike not able to start at all if it's fully in
Last edited by Deropke on 21:04 - 09 Jun 2021; edited 1 time in total |
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jaffa90 |
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jaffa90 World Chat Champion
Joined: 06 Apr 2016 Karma :
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Hong Kong Phooey |
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Hong Kong Phooey World Chat Champion
Joined: 30 Apr 2016 Karma :
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Easy-X |
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Easy-X Super Spammer
Joined: 08 Mar 2019 Karma :
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Posted: 11:09 - 09 Jun 2021 Post subject: |
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Mice in the airbox ____________________ Husqvarna Vitpilen 401, Yamaha XSR700, Honda Rebel, Yamaha DT175, Suzuki SV650 (loan) Fazer 600, Keeway Superlight 125, 50cc turd scooter |
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Robby |
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Robby Dirty Old Man
Joined: 16 May 2002 Karma :
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Deropke |
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Deropke L Plate Warrior
Joined: 09 Jun 2021 Karma :
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Posted: 21:01 - 09 Jun 2021 Post subject: |
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Robby wrote: | The mixture screw only affects idle really, so that is not the source of your problems. The fact that the screw is chewed up, and that the bike is a 125, tells us what someone has fiddled with the carb before to try and make it go faster.
So, carb out, strip and clean, make sure the float height, needle height and jetting are the same as what the factory manual says they should be. Work on getting the mixture screw out and replace it, and make sure that the choke flap isn't just closed all the time. |
Yeah, bike is a mess. also perhaps any of you know where "13" hose would go to. It has been sealed by previous owner, could be potentially culprit ?https://www.fowlersparts.co.uk/parts/view/863212
It seems like this bike had air problems as airbox been drilled and I just fixed the vacuum leak (the manifold intake hose was ripped, but this only fixed bike not able to start. |
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Easy-X |
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Easy-X Super Spammer
Joined: 08 Mar 2019 Karma :
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Robby |
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Robby Dirty Old Man
Joined: 16 May 2002 Karma :
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Posted: 12:51 - 10 Jun 2021 Post subject: |
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Looks like Easy is right. Typically there is a vent hose from the crankcase (often on top of the gearbox, behind the cylinder) into the airbox. This serves to even out crankcase pressure, and to direct air out of the crankcases into the engine to be burnt. This air contains a bit of exhaust that has blow past the piston, and bit of oil vapour, so you shouldn't be venting it to atmosphere.
I'm assuming the hose is still connected to the airbox and blocked off, but not connected to the engine. Find the stub on the engine that it connects to and plug it back in.
If the airbox was drilled and the inlet manifold stub was broken, then this bike has the textbook signifiers of someone trying to "tune" it. Carb needs to come out for a proper inspection, but also inspect any hoses or rubbers that it connects to, they may also be torn and need replacing.
Chances are that it has the wrong size main jet in. That's the go-to option for children that know nothing about tuning engines. If you can find someone that sells a carb rebuild kit, it may be worth just buying one and replacing all the bits.
Other hint that the person doing it didn't know anything - they tend to try to increase fuel flow in the hope that will make a difference. With most mixture screws, you screw it in for less fuel and out for more fuel. Standard setting is usually around 1.5-2 turns out. |
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MCN |
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MCN Super Spammer
Joined: 22 Jul 2015 Karma :
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Old Thread Alert!
The last post was made 2 years, 292 days ago. Instead of replying here, would creating a new thread be more useful? |
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