Question about 2000 Yamaha XV 125 - S

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Engine cutting out when open throttle. YAMAHA NEOS 50cc MOPED

The engine will start ok and tick over fine. However, either soon after starting to set off the engine looses its revs and cut outs, OR will run just for a few minutes then again when open the throttle (loading engine) to accelerate or go up incline, it starts to splutter then cut outs.

Either way immediately after breakdown the engine will not start again. Only after awhile will it start again.

After taking spark plug out immediately after engine cuts out is 'WET'. Either the engine is over fuelling or i am losing my spark. PLEASE HELP. I bought this bike being told that the bike just had a new barrel, piston and exhaust fitted. Bike has only done 5 miles since rebuild. Reason for replacement parts was due to corroded exhaust to cylinder head.

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I had a simuler problem with my honda cr 250 moto-x bike it would start fine and you could keep it ticking over with the throttle(i have deliberatly unscrewed the tickover in case i come off,it will cut out) when i got on it,it would go for about 400-500 metres then splutter and die and not start again for around 5 mins. i immediatly knew it was a fueling problem. so after stripping the carb and giving it a good clean out i was baffled when i got back on and it still done the same. i then dismantled the fuel tap cleaned it all out and put it back together and tested it,it was very very slow so i unsrewed my fuel cap a little and was greated with the familur gush it should deliver. problem solved! the vent in my fuel cap had crystalised up,so the fuel was coming out but the air was not getting in,causing a vacuum and slowing down the flow and basically emptying the carb quicker than it can fill back up!!! clean your carb,fuel tap and any vents in your cap or tank. if this does not work then your bike must be over fueling or low on compression.

Posted on Sep 18, 2009

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Hi, Try checking if the air inlet on your fuel cap is blocked. There should be a small hole in the fuel cap; if this is blocked, after a while a vacuum forms in the fuel tank and the engine cannot get any petrol. No petrol, no go.
This happened on my mate's Vespa. Sometimes the most simple is the most difficult to find.
Good luck.
SHINY SIDE UP is best.

Posted on Feb 26, 2010

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If your spark plugs are wet there are a few reasons for this: 1. Carb jets are not properly set. 2. Carb floats are sticking letting in too much fuel. 3. Air/fuel set screw is not adjusted correctly which will either let in too much fuel and too little air, or the other way around.

Posted on Jun 06, 2009

  • Bill Chapman
    Bill Chapman Jun 06, 2009

    If your spark plugs are wet there are a few reasons for this: 1. Carb jets are not properly set. 2. Carb floats are sticking letting in too much fuel. 3. Air/fuel set screw is not adjusted correctly which will either let in too much fuel and too little air, or the other way around.

  • Bill Chapman
    Bill Chapman Jun 06, 2009

    If your spark plugs are wet there are a few reasons for this: 1. Carb jets are not properly set. 2. Carb floats are sticking letting in too much fuel. 3. Air/fuel set screw is not adjusted correctly which will either let in too much fuel and too little air, or the other way around.

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I've stumbled across the same problem recently.When I thought I would change the air filter to a non standard filter with less restricted air flow. The result was the bike would not rev the same as you described. It may be worth checking the rubber tube that connects between the carb and the air box to see if it is leaking or dislodged. Hope this helps.

Posted on Jul 25, 2009

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Most small engine like mopeds ,if stored for long the carburator usually get corroded get it cleaned well ,check fuel level then try to tighten air screw.check also any blockage on the pot of the block cylinder or maybe the piston which was fitted does not hold the compression

Posted on Oct 02, 2017

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Hi i have a neos if it has had new pistons and not had a rebour is could be leakin oil into the spark plug or it could have a split in the rubber on the spark plug cap

hope this will help you ?
sam stuttard
stusamm@hotmail.co.uk

Posted on Sep 23, 2009

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I've got the same problem right now, im assuming my spark plug isn't igniting the fuel that's sucked into the piston efficiently enough, so im going to take my plug out, and either clean or replace it depending on its condition. Then pump any left over fuel in my piston out with the kick start, then im going to lower the idle screw and make sure my carb is all intact. If non of that works then i guess im losing compression maybe my piston could be in need of replacement.

Posted on Jul 29, 2009

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Jul 10, 2009 | 2000 Yamaha XV 125 - S

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