Question about 2004 Yamaha YZ 250

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Piston seized in cylinder bore what might be cause ? would it benifit me to add a bigger jet in carb for cooling in heavy sand play riding.where can i get a good detailed shop manual.thank you !

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  • Frank
    Frank May 11, 2010

    lack of oil? lack of coolant? may be?



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Sounds like you ran it too lean either jetting or more oil in your gas,32 to 1 ratio 4 ounces to the gallon of a good quality oil such as bel ray ,klotz or oem oils,hope this helps

Posted on May 15, 2009


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1 Answer

Saw dies after working for fifteen minutes

Could be a multitude of issues, I however suspect the carb is in need of adjustment. The chainsaw while operating under manufacturer specs runs between 900 degrees (F) and 1100 degrees (F) if the chainsaw exceeds 1100 (which after 15 minutes of use this is possible) the chainsaw quits or what is called a lean seizure, the piston swells and scores the cylinder walls. when the piston swells too much it seizes the chainsaw, after it cools down it the piston will shrink and the chainsaw will run again. Too many times and the piston will score the cylinder causing damage and space between the cylinder wall and the piston.

Oct 10, 2016 | Garden

1 Answer

Rejetting a Mikuni 44mm carb

standard carbys will cover a .020 oversize bore
melted piston is from detonation which is lean mixture or incorrect ignition timing
the oil will be a metered amount so it will be correct for all rpm
items like incorrect float level and air filter are the suspect causes

Aug 16, 2017 | Winter Sports

1 Answer

I just bought a 96 cr80r for my son, cleaned carb, repacked silencer, drained and refilled gas tank. Kicks over but is still spitting oil, and blowing tons of white smoke. No coolant in crankcase, or oil...

Fried rings on the piston...cylinder probably scored also...need to have cylinder re-bored, get an oversized piston (same as re-bore), put new rings on and break it in GENTLY.

Jul 21, 2012 | Garden

1 Answer

We have a Suzuki 50cc quad with automatic start. When you go to turn it and nothing. husband said the piston is stuck and it wont turn , not enough power. How can we fix that

If the piston is seized up you will need to remove the cylinder head, the the cylinder, then the piston. Tank the cylinder and piston to a dealer and have them bore the cylinder and supply a piston and ring set matching the new cylinder bore. Also get a new cylinder base gasket and cylinder head gasket. Check the gas / oil ratio. I prefer the old 32-1 mix. That way I am sure not to seize up. By the way, keep the outside of the cylinder clean. Cylinder fins covered in mud do not cool the engine well.

Aug 17, 2011 | Suzuki EC 300 2T Racing Motorcycles

1 Answer

My bike is smoking a lot changed piston valves seals guides but no good result can ya giveany tips

New valves, valve guides, valve guide seals; all fine but probably not needed. When the piston was changed, did you run a cylinder hone in the bore to check for distorted cylinder walls? Was the old piston seized up at any time? Were there scratches or grooves cut into the cylinder wall from being seized? Did the new piston get new rings? Chances are you will need to have the cylinder bored then install a new 1st oversize piston and rings. Please rate my answer.

Aug 10, 2011 | 2005 Honda CRF 230 F

1 Answer

I have a Poulon pro 18 42cc chainsaw. The dealer says I ran it with oil in the gas and I did not. What can cause the same effects of the appearrance that there is no oil in the gas.

cylinders that seize around the exhaust port of the cylinder usually come uner the headind of a lubrication break down ( loss of an oil film between the moving piston and the cylinder bore ) once the oil film is lost, the piston heats up very quickly and expands in the bore, the alluminium is then scraped off the front of the piston, this will gum the piston ring in, the hot gasess from the combustion process then blows past the piston, so the machine has basically seized.
Reasons for a lubrication seizure are.
Insufficent two stroke oil in the fuel.
Poor quaility two stroke oil in the fuel.
Incorrect grade of oil in the fuel.
Lack of maintenance.
Internal bearing break down within the machine.
Over heating due to dirt blocking starter cover air vents, and choked around cylinder finns.
Over heating due to poor chain maintenace ( blunt chain )
Incorrect carb settings ( running too lean )
Blockages in the fuel system causeing over reving.
Working practice ( over loading the saw ).
Air leaks within the machine causeing lean mixture and over reving.
Stale fuel, water in the fuel, dirty fuel.
Hope this answers your question, as you can see there are many reasons for a machine to seize.

Jan 29, 2011 | Poulan Garden

3 Answers

Honda cb100 motor sezied can i rebore and fit larger piston and ifso what. Thanks

in adition to the above coment, which i must say is spot on, the posability of a used barel and piston if a new piston is not available could be worth considering, other things you may wish to check on that particular engine is camshaft seizure, in a uk bike it runs directly in the machined surface of the cylinder head, oil failure due to blocked oil filter has severe consequenses, located on the l/h side of the engine under a 22 or 24mm spaner head cap just below the gear change lever, this is a washable filter retained by a cap and spring, correct replacment is inperitive. are you located in UK? HOPE THIS HELPS YOU

Aug 02, 2010 | 1976 Honda CB 100

1 Answer

Bike siezed up.rocking it frees up and starts but locks up

The piston seize destroys the piston, rings and cylinder wall. Bad enough, and repeated seizing, can get metal bits into the crank rod bearing and crank end bearings and seals. This is serious stuff. Sorry to be the bearer of bad news.

Seizing is caused by friction. Not enough lubrication means friction that creates heat. The heat builds and the piston and rings "weld" to the cylinder. A faulty cooling system can also cause heat. Any oil will break down and loose it's lubrication ability when the heat gets too high. A water pump malfunction or plugged coolant lines, leaking coolant hoses, plugged radiator and bad gaskets can create heat.

Other sources are > timing is off, air leak causing the fuel to be too lean, incorrect spark plug heat range, carbon buildup on piston and head causing detonation, motor oil used in gas instead of 2 stroke engine oil and over revs on the engine. I have probably left a few things out but these are the usual causes. Be aware that combinations of small problems can add up to a seize.

The engine needs to be rebuilt. Normally I would just rebuild the top end but since you have had multiple seizes the bottom end is probably contaminated. New crank bearings and seals should be installed. If the cylinder can't be bored then you will need a new cylinder. New piston and rings are also required. Bear in mind, you must find the cause or causes of the heat and fix those problems also. If you don't, the new piston will quickly seize up.

Top rating for this answer! Thanks Kev...

May 06, 2009 | 2003 Yamaha YZ 250 F

1 Answer

While riding my yz 125 it just died and won,t kick up again

  • If a hole in the piston then install new piston and rings. Next, clean the carbon off the head and install a new head gasket.
  • If cylinder wall is scared the piston has seized up. Pull the cylinder off and take it to the dealer. Have them bore the cylinder and return it along with a new oversize piston and rings.
  • While at the parts counter, get a new stock spark plug and a supply of Yamalube Two Stroke Motor Oil. You need to add 4 ounces per gallon when filling up. This will be a 32/1 gas to oil ratio. NEVER ride the bike without at least the needed 32/1 mix.
Please rate the solution as a "FixYa" if able. Thanks!

Mar 23, 2009 | 2003 Yamaha YZ 125

3 Answers

How to increase speed?

You can bore out the barrel to take a bigger piston or swap barrels from a 110 or 125. I know the 110 barrel can be taken out to take a Kawasaki 150 piston. This will need a new CDI and best to modify the exhaust too (more free flowing). I've done this with my Honda C70 and gone up to a wave 125 piston. the only thing holding me back is the 3 speed gear box but I have changed the sprockets to give higher cruising speeds.

You will need a bigger carb. Honda Dash Carb is just spot on. Its a Keihin and get an original (with the heavy plunger) not a cheap fake. They can stick open causing problems!

Good luck!

Jan 24, 2009 | 2005 Honda NF 100 Wave

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