Question about 2003 Yamaha YZ 125

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I have a Yamaha yz125 and when trying to start it fuel just runs out of the exhaust pipe any ideas would help.

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  • Anonymous Mar 30, 2014

    hard start and once it runs fuel is just leaking from exhaust pipe



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Turn off the gas. Take the plug out. Kick it over 10 times with the plug out to clear out the gas from the cylinders. Put in new plug. Start. The float may be stuck in the carb. P. S. Check for spark while the plug is out.

Posted on Feb 08, 2010

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Have u checked your piston rings same happened to mine.

Posted on Feb 08, 2010


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I have a 93 yz125 and it wont start, I got fire, fuel, and 120lbs of compression and ideas?

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Yamaha xt225 serow front exhaust pipe glows red within 5mins of starting also running rough

Fueling issue running far to lean, choke makes the circuit richer so it will run , lean running causes over heating and serious engine damage if its running red hot, check the plug for white burnt or blistering will show lean running. Compression test to make sure the piston ring and barrel are not damaged over 110psi. Is the exhaust blocked restricted or dented ?

Mar 31, 2012 | Yamaha Motorcycles

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R6 engine starts then runs and if u keep it running it wil run fine but if it stops wont restart again when u pull the choke its as if it is about too run but wont any ideas

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is it a straight thru exhaust, or is it just a head pipe with nothing attached? If it's just a head pipe, you need to get some sort of muffler on it or you'll burn your valves out from a lean condition. The backfire is due to the vaccum fed carbs that yamaha runs. They work wonderfully, but under heavy deceleration, the vaccum still feeds the bowl, and it builds up excess fuel, which eventually burns off as a backfire. If it were fuel injected, you could have the fuel map adjusted to lean it out under deceleration.

Jun 22, 2010 | 2001 Yamaha V Star 1100 Classic

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99 yz125 burning off piston edge at high rpms

Higher octane fuel is needed from what you describe. Without knowing where you are located and how hard you ride the bike, it's impossible for anyone to offer any jetting advice. Higher octane fuel will likely help, but if you (or a previous owner perhaps) have shaved the head for higher compression, you might have to run higher octane racing fuel.

Also - check to make sure the pipe is sealed well at the head pipe connection - if not, it will **** air at high RPM and can cook your piston.

Check also for leaking crank seal on the flywheel side (left) which can also **** air but will normally be accompanied by a very irradic idle.

Apr 12, 2010 | 2004 Yamaha YZ 125

1 Answer

Glowing RED exhaust pipe

try a bigger jet or its going to cause some damage. You can pull the choke on to get some more fuel in to cool it .
Check that the cam timing hasnt been played with, some change the exaust cam by a tooth to copy yz specs, on top dead centre, there is a little arrow on each cam that lines up with the rocker cover surface

Mar 09, 2010 | 2003 Yamaha WR 450 F

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Hi i was riding my yamaha yz125 2001 and it cut out now it doesnt have bareley any compression what so ever ! IT WILL NOT START PLEASE HELP :( WHAT DO YOU THINK THIS IS ?

make sure the float did not stick open and flood the cylinder. turn off fuel supply and remove exhaust pipe from cylinder. Does expansion chamber have fuel in it? It shouldnt- drain it. Place a towel over rear of front fender and on floor under exhaust port and kick motor over. Does fuel spray out? If so motor is severely flooded. Keep kicking untiul all fuel is purged from motor. Motor will likely start and run for a second once the fuel is reduced to a level the motor can handle. Reinstal exhaust and fix carb/ float problem. Hope that solves the problem.

Nov 23, 2009 | Yamaha YZ 125 Motorcycles

1 Answer

I have a v star 650 when i start it the top pipe gets red hot sounds like it running on 1 cylnder help

red pipe is an indicator that the cylinder is getting too much fuel. The fuel is actually burning up in the exhaust pipe. I would hope it is something simple like a vaccum hose came off, but I would try spraying starting fluid around the carb while it is running(still cold though). If the engine revs up, it has an air leak somewhere. Hope this helps...

Sep 19, 2009 | 1999 Yamaha V Star Classic

1 Answer

2001 yz125 exhaust

if you have any friends that weld. ive had this problem myself and have found it cheaper and less stressful to fabricate yourself than to search any further

May 10, 2009 | 2003 Yamaha YZ 125

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