Question about 2003 Yamaha YZ 125

1 Answer

Yz 125 99 won't run

New top end, new plug, carb cleaned, good spark, grey gearbox oil so changed crank seals, fresh fuel getting to plug, it won't fire HELP PLEASE

Posted by on

  • 1 more comment 
  • pearhead Jun 17, 2009

    Do you mean the crank seal fitted properly?

  • pearhead Jun 22, 2009

    My chassis no is JYACE10C53AOO8555 can you confirm this is a 2003 machine Thanks

  • Anonymous Mar 30, 2014

    Cranks good, good fuel pressure .



1 Answer

  • Level 2:

    An expert who has achieved level 2 by getting 100 points


    An expert who has answered 20 questions.


    An expert that hasĀ over 10 points.


    An expert whose answer gotĀ voted for 2 times.

  • Expert
  • 90 Answers

You need to ensure for the Carburettor Needle fixed, so that the fuel injected out properly, also if the Crank Gasket should be fitted properly.

Posted on Jun 17, 2009

  • Puneet Jain
    Puneet Jain Jun 17, 2009

    Yes need to check this also



1 Suggested Answer

  • 2 Answers

SOURCE: I have freestanding Series 8 dishwasher. Lately during the filling cycle water hammer is occurring. How can this be resolved

Hi there,
Save hours of searching online or wasting money on unnecessary repairs by talking to a 6YA Expert who can help you resolve this issue over the phone in a minute or two.

Best thing about this new service is that you are never placed on hold and get to talk to real repairmen in the US.

Here's a link to this great service

Good luck!

Posted on Jan 02, 2017


Add Your Answer

Uploading: 0%


Complete. Click "Add" to insert your video. Add



Related Questions:

1 Answer

1989 yamaha banshee no start

no you cant put them in upsidedown if they are not indexed to fit one way then you can run them either way.we need to consider a few things first spark if we have spark havve we checked the flywheel to make sure the key is not sheared and it is tight. next compression i assume since we did a top end compression is good but what about crank seals if they have never been done and are leaking transmission oil will get on ththe plugs and foul them. next fuel if gas is in the float bowls is it getting though the jets take the air filter off and spray starting fluid in the carb throat kick it if it fires for a second the carb jets need to be cleaned all that is left is air and i know you have that covered i hope this helps these 4 things are what make engines run so if you get all 4 its gonna run good luck dirt bike dan

Apr 18, 2013 | Motorcycles

1 Answer

Aprilia rs 125 won't start!!

right you done quite a bit, so whats left, fuel seems ok .. so ht lead ht cap, spark plugs dont always come with right gap, any leaks with airflow either side of carb, remember the filter often acts as a restrictor too. try the putting a small amount of fuel in cyclinder after cleaning plug, should atleast get a backfire, is choke setup ok, carb mix if not factory sealed is generally 1 and 3/4 turns out from tight,

Feb 13, 2013 | 2005 Aprilia RS 125

2 Answers

I have a 1998 yz 125 while it is running gas is pouring out of muffle

The only way that can happen is if gas is overflowing in the carb and running down the cylinder wall and into the exhaust port and / or into the crankcase. Gearbox oil is separate from the crankcase. The crank gets lubrication from the gas/oil mix. Be sure to turn off the gas valve at the tank when the bike is not in use. If you can manage it, pull the head off, (or at least remove the spark plug ), then, with the piston at bottom of the stroke, turn the bike upside down to drain the gas from the crank. I would then remove and clean the carb to be sure the float is not sticking open. Be sure the overflow line is not blocked. Install an in-line fuel filter. Please rate my answer. Thanks.

Jan 10, 2010 | 2003 Yamaha YZ 125

1 Answer

Bought a 2002 Rm125 about 2 months ago, with a fresh top end....First ride was great with impressive power throughout. About two weeks later I noticed that it was missing some about half throttle , and...

My first thought is low compression... which leads to a few questions...
What fuel to oil ratio have you used?
What do you mean by 'fresh top end'? To me a fresh top end includes piston and rings and cylinder bore, gaskets and crank seals. Anything less on a 2-stroke is an incomplete job and usually leads to premature failure.
Have you followed break-in procedure on your fresh top end? Double check the head bolt torque.

Do a compression check first then go from there.

Dec 28, 2009 | Suzuki RM 125 Motorcycles

1 Answer

1992 yz 250 won't start

A couple of things.1.Check the fuel oil mixture is correct.It seems rich.2.Check that the carby is not running to rich.With new reed valves may need to be set back to the original manu. specs.With older parts it may have been retuned to make it run with the old parts.(carby jetting etc.)3 make sure the fuel oil mix is using a good quality oil.It does make a world of difference.I hope this is a start to get you going.

Aug 24, 2009 | 2003 Yamaha YZ 250 F

2 Answers

YZ125 won't start

yeah something you wanna check next, compression. if you can get your hands on a compression tester.

Aug 09, 2009 | Yamaha YZ 125 Motorcycles

2 Answers

My 04 blaster smokes and idles poorly,dies pushing throttle

Hi I am vortash .. firstly 32 - to - 1 may be a tad high I would say ... it would be fine at the same as the ducati ratio 20-to -1 with a good quality oil , you should check that your sump is not filling with oil as this will cause performance problems with backpressure .. but maybe the best thing to do would be to replace the oil pump and run it as it was designed to do ?. I am sure you will get one off the net cheaply or from a local bike breakers .... Regards Vortash

May 18, 2009 | 2003 Yamaha YZ 250

2 Answers

Dosent start

sounds like crankcase seals may be bad

Apr 07, 2009 | 2001 Yamaha V Star 1100 Classic

3 Answers

Oil is a grey colour in the engine of my yz 125 2001

Your bike is water cooled. Some of that water is leaking into the gear box. The cylinder gasket is the likely leak. I would let the shop take a look at it instead of trying to fix it yourself.

But be sure there is not an external source for the water. Do you wash the bike often? Ride the creek bed often? Leave the bike where the lawn sprinkler gets the bike wet? Leave it out in the rain? Change the oil and keep the bike dry. If the problem comes back then go see the dealer.

Mar 19, 2009 | 2003 Yamaha YZ 125

Not finding what you are looking for?
2003 Yamaha YZ 125 Logo

Related Topics:

300 people viewed this question

Ask a Question

Usually answered in minutes!

Top Yamaha Experts


Level 2 Expert

314 Answers


Level 3 Expert

1216 Answers

Steve Sweetleaf
Steve Sweetleaf

Level 3 Expert

1165 Answers

Are you a Yamaha Expert? Answer questions, earn points and help others

Answer questions

Manuals & User Guides