Question about Yamaha YZ 250 Motorcycles

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1988 yz 250 wont start

New plug clean carb has spark and gas

Posted by Anonymous on


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  • Yamaha Master
  • 43,836 Answers

Hi, Anonymous and the usual suspects are:
1. Fuel tank empty.
2. Fuel supply valve/petcock turned off.
3. Fouled spark plugs.
4. Engine flooded as a result of overuse of the enricher.
5. Vacuum hose to the fuel supply valve/petcock disconnected, broken, cracked, or pinched.
6. Fuel valve/petcock or filter clogged.
7. Fuel line to carburetor or throttle body pinched or kinked.
8. Carburetor float stuck.
9. Fuel injectors clogged.
10. Severely discharged or damaged battery, you need 12.5 volts or better and be able to pass a load test if necessary.
11. Check battery terminals for damage or corrosion, check the battery cables at "BOTH" ends for loose, corroded, or broken connectors, "INSIDE" and outside the cable harness, perform connector wiggle test and check cables with an ohmmeter if necessary.
12. Loose or corroded wire connection at the coil, battery or plug between ignition sensor and module.
Spark plug cables in bad condition and shorting, cable connections loose, or connected to the wrong cylinders.
13. Ignition timing incorrect due to a faulty ignition coil, ignition module or sensors (MAP, CMP, CKP, O2, TPS, ETP, IAC,or BAS).
14. Faulty neutral, clutch lever, or kickstand safety switch.
15. Faulty fuel pump or fuse or relay.
16. Faulty CDI box if applicable.
17. Tilt sensor needs a reset.
18. Security system not disarming alarm needs a reset.
For more information about your issue and valuable "FREE" downloads that you will need please click on the links below. Good luck and have a nice day.
1986 yz250 wont start help
Dirt Rider Magazine
YAMAHA YZ250 LC Owner Service Manual
OEM parts for Yamaha

Posted on Jul 25, 2016


6 Suggested Answers

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Posted on Jan 02, 2017

  • 3567 Answers

SOURCE: my 1974 250 2 stroke will not start. I have a new

With a bike that is 35 years old lots of things could be the problem. I will list what to look for in a "most likely" sequence but with a mind to some of the easy things to check first.

  • Got gas and is it turned on? Clean air filter?
  • Have a buddy kick the starter while you look for spark.
  • Assuming no spark, How good is your battery? Fuses good? Kill switch on or shorted to the bars or elsewhere?
  • carb, head, intake manifold and carb mounted tight?
  • Does the carb intake manifold have reeds? What condition are they in?
  • I don't recall for sure, does the bike have CDI? If so, have the dealer test it and the coil.
  • If no CDI, when was the last time the points and condenser were replaced or points filed and set? Get the coil checked.
  • Remove the flywheel cover. Take hold of the flywheel and, without turning the wheel, lift the flywheel up and down then left and right. Any movement or was the flywheel rock solid? If movement then the crank bearings need replaced along with the crank seals.
  • Speaking of crank seals, how old are your seals? The bike ain't gonna run with bad seals.
This is a pretty good list of things that should keep you busy for a few hours. Wish I were there to help. It's been a long time since I serviced an old Yamaha 250. I was a shop mechanic for ten years.

Let me know what you find out.
Please rate this answer. Thanks Brandon!

Posted on Apr 02, 2009

Fix it Out
  • 90 Answers

SOURCE: yz 125 99 won't run

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

  • 677 Answers

SOURCE: 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.

Posted on Aug 24, 2009

ollie reece
  • 1167 Answers

SOURCE: i have a 1991 yamaha yz 250 it starts then shuts off

change the pkug first buy a br8eg plug off ebay and see how this goes get back to me also are you using the choke on start up

Posted on Sep 29, 2009

  • 3 Answers

SOURCE: i have 1974 yamaha dt 250 enduro the bike sat

clean contacts on points with sandpaper (800 grit). located behind flywheel, will gurantee a fix. you can remove the side cover and get to contacts through holes in flywheel without removing it.

Posted on Nov 16, 2009

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I have a yz 250 Yamaha layed it over on it side and now can't get it to start put new spark plug in has spark but won't fire

fuel problem take out the carb and clean all the jets and the bowl also put a high flow fuel filter in as a precaution incase there is debree in the tank your problem is that you are not getting enough fuel or any at all.

May 11, 2012 | 2003 Yamaha YZ 250

1 Answer

It back fires when i let off the gas and will run for about ten mins then just quite and it will start i thought it mite be that i have bad gas or the spark plug faled or my valves need adjusted do you now...

the back firing is normal on a fourstroke and try cleaning your carb the carbs on those bike are a regular maintenance item if they set for any period of time they need to be cleaned

Mar 27, 2011 | 2004 Yamaha YZ 250

1 Answer

Ok so i have a 07 yz 250f it wont start i rode it a few months back no problem now it has set in storage and wont start it not the gas its all new could it be the plug or old gas in the carb

If you think it's the gas in the carb, use the carb drain screw at the bottom of the carb, and let it refill with fresh gas. You can also force a fresh fuel draw by covering 90% of the intake and turning over the bike. The suction created by the piston will force a fuel draw from the main jet. Verify that you are getting fuel to the plug by checking to see if it's wet with fuel after attempting to crank it over. IF that is true, then verify spark. Let me know the results and based on what you say, I can guide you on what to look at next.

Dec 08, 2010 | 2004 Yamaha YZ 250 F

1 Answer

Starts hard and wont idle, no low end power, has been sitting i'm told, cleaned carb, fresh gas and new plug.

The starting hard and Idling problem sounds like carb needs cleaning. If this bike has moved from a different area it might need different jets in the carb. I might have jumped the gun the gas/oil mix ratio is very important check that first. your spark plug should be a golden brown when mixture and right jets are in. This might resolve the low end power if the oil mix is to rich or you might need piston rings. GOOD LUCK

Aug 09, 2010 | 2003 Yamaha YZ 250

2 Answers

My yamaha yz 125

if your getting spark than i would take the carb off and clean it you could have a cloged jet.( just because your getting fuel from tank to carb dont mean its getting from carb to jug) i would try that first......yz-maniac.

May 14, 2010 | 2004 Yamaha YZ 125

1 Answer

My Bear Tracker 250 would not run well. It was cutting out and seemed to be starving for fuel. I took the carb off and cleaned it with carb cleaner and put it back on. Now it will not run at all. Fuel is...

Are you sure it has a good plug and spark? If not you might have bent the float when you cleaned the carb, try spraying starting fluid in the intake and crank the motor, if it fires the problem is fuel, one of the Jets in the carb might be clogged also make sure you have no water in your gas.

Mar 01, 2010 | 2004 Yamaha YZ 250

1 Answer

My 2005 yz 250t started ran a few feet and died. i changed out the the spark plug and still wont kick over what do you think

Could be heaps of things.

Check spark at plug.
Check clean fuel is getting to carb.
Check air intake is actually "sucking" air.

Jan 03, 2010 | 2004 Yamaha YZ 250

1 Answer

Yz 125 wont start

Hi,the fuel bowl is the bottom of the carb,take that of and make sure the little holes in the jets are clean.does it have a spark,have you fitted a new plug.

May 19, 2009 | 2003 Yamaha YZ 250 F

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