Question about Yamaha YZ 250 Motorcycles

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What should my carb settings be on a 98 yz 250,all pro-circuit exhaust,living in timmins ontario,im running 91 octane

98 yz 250

Posted by Anonymous on

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  • Yamaha Master
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Hi, Anonymous it should be noted that your performance issues are not electrical ie. faulty charging system, battery condition, and connections etc. If your fuel system (gas tank, filters, fuel valve and carburetor) is contaminated with ethanol sludge, varnish, rust, dirt, water etc. or your bike has been sitting for months or years without running these components must be "PROPERLY" cleaned and reassembled "CORRECTLY" before any adjustments can be made. Tuning your carburetor is fairly simple once you understand the basic principals. You engine is a simple airbox sucking air in and blowing it out, it is finely tuned at the factory for maximum performance once you upset that delicate balance by changing air filters, camshafts or exhaust systems your performance may go down the and the engine may run poorly, you need to compensate the air-fuel mixture in the carburetor in order for the engine to run smoothly and at peak performance. If you are running multi carburetors you need to sync them first and make sure your air cleaner element is clean and dry for paper elements or lightly oiled for foam and meshed elements and properly installed. Here is how and where you compensate trouble: "TIP" if your engine "BOGS" your not getting enough fuel.
1. Closed to 1/8 throttle is managed by the air screw and pilot/slow jet.
2. 1/8 to 1/4 throttle is managed by the air-screw, pilot/slow jet, and throttle slide.
3. 1/4 to 1/2 throttle is managed by the throttle slide and jet needle.
4. 1/2 to 3/4 throttle is managed by the jet needle, needle jet, main jet, and air jet.
5. 3/4 to wide open throttle is managed by the main jet and air jet.
6. Wide open throttle is managed by the main jet.
If you are running lean, spark plug electrode color is white, engine runs hot and feels like it is starving for fuel you need to go up on the jet size or move the c-clip down one notch. If you are running rich, spark plug color is black or dark gray, engine runs cool, and bogs down when accelerating you need to go down on jet size or move the c-clip up one notch. When your carburetor is properly tuned for maximum performance your spark plug electrode will be a light tan color like coffee with cream. If you prefer fuel economy over performance you can go down on main jet sizes until a satisfactory level of lower performance is acceptable versus MPH, your spark plug color will be whiter and your engine will run warmer. These tuning adjustments will only make improvements if your intake and exhaust system have no air leaks or sealing issues and the entire electrical system is in proper working order and you have no mechanical issues. For more information about your issue and valuable "FREE" downloads that you will need please click on the websites below. Good luck and have nice a day.
Some help with my yz250 carb settings please Yamaha 2 Stroke
Two stroke Carburetor jetting How to performance tune your two stroke carb...
YAMAHA YZ250 LC Owner Service Manual
OEM parts for Yamaha
http://mybikemanuals.com/yamaha/yamaha-yz-owners-manuals

Posted on Jul 25, 2016

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Posted on Jan 02, 2017

  • 13 Answers

SOURCE: 91 kx 250 stock carb setup.

Low speed screw 1.5 turns out from bottomed. Middle position for clip #3 position.
I never rely on the factory settings for the low speed screww, set it to factory and keep adjusting it 1/8 turn at a time until idle sounds best and quick throttle blips dont sound "stumbly" the later being the most important.

The needle position is for low altitude.

Posted on Jan 26, 2009

  • 3567 Answers

SOURCE: need torque specs for 98 yz 250,rebuilding engine

Go to the site below and you can download a free srevice manual for your bike.

http://www.carlsalter.com/motorcycle-manuals.asp

Top rating due on this answer!

Posted on Apr 13, 2009

  • 209 Answers

SOURCE: i have a yamaha yz 250 98' and wont start i

coil

Posted on Apr 07, 2010

mxtras
  • 194 Answers

SOURCE: 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.

Posted on Apr 12, 2010

DJ_MAX1369
  • 119 Answers

SOURCE: how do you get 110 octane in gas when super is 91

yes they are adding boost or they are buying a race fuel of some sort or another

Posted on May 20, 2010

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1 Answer

Hi, I have a 2009 Husqvarna TE 250, spec states the engine as 12.9:1 compression ratio. The question I have, is what octane fuel rating is recommended for this bike? Thanks, Rob


91 or 95 octane is suitable for 9.5-10.5 ratios ( most engines)
for 12.9 you will find that it runs best on 98 octane
it may be good on 95 octane but generally the higher the compression ratio the higher octane rating
discuss the octane rating required with the bike service agent/service center

Apr 02, 2017 | Cars & Trucks

1 Answer

THE BIKE IS RUNNING LEAN WHAT CAN I DO TO STOP THIS JUST PUT A NEW SPARK PLUG IN AND DID TO LAPS AT THE TRACK CAME BACK IN AND CHECK THE PLUG AND IT IS LEAN I ALSO WENT UP 2 JET SIZED TO A 182 AND THERE IS...


Check a couple of things before going back to increasing jet size. First, it may sound a little strange but make sure the vent hose and gas cap are functioning properly. Yamaha has a check valve that allows air to come in but prevents gas from coming out if you tip it over. Just blow thru the end of the hose and make sure it's open. I've had this problem with my kids YZ, couldn't figure out why the jetting was all over the map and found the vent wasn't working. Bought a new gas cap and hose and problem solved. Also, check the e-clip setting on the jet needle. If someone set it towards the top, it could be lean no matter what jet size you run. Should be 1 position either side of the middle.
Also, quality of fuel and oil makes a huge difference. The book will tell you to run a minimum of 94 octane and a 24:1 mix of Y2R oil. While the oil mix is a little rich(32:1 is sufficient, and Y2R Yamaha oil is reaaly good) the octane is critical to 2-strokes. It's hard to find anything over 91 octane at the pump, and non-oxygenated fuel is critical(no ethanol!). Find a source for good race gas 102-110 octane, cut it half and half with pump 91 non oxy. and mix it 32:1 with Y2R. Once you jet for this combination, don't vary from it and you'll have no problem keeping it running strong!

Jun 13, 2011 | 2003 Yamaha YZ 250

1 Answer

Plz which fuel can i use 95 octan or 98 octan for clk 320 2002


Do you have 95 or 98 octane where you live? The airport? I'm sure it will burn just fine, most race cars use it, at $14 a gallon. I would run any gas in there as long as it didn't ping or knock. The book calls for 91 octane, and I just read an article that we are wasting our money on it, because if the lesser octane gas doesn't ping or knock, use it! Hope this helps.

Apr 14, 2010 | 2000 Mercedes-Benz CLK

1 Answer

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

My 2004 yz 250 starts and runs but cuts out when put under load. tired a new stator but no better.


Sounds like dirt in the carb, there are two sets of jets, one for idle one for load.
Strip and clean the carb.

Jul 19, 2009 | 2004 Yamaha YZ 250

2 Answers

Oil and gas mixture coming out by exhaust


first off make sure the oil gas mixture is correct and mixed very well.... have the carb cleaned out very well or even rebuilt, jetted and adjusted...

Jul 06, 2009 | 2003 Yamaha YZ 125

1 Answer

Getting better gas milage....


Hey there, well if its anything like mine(91 cressy) its pretty thirsty! but things worth checking(if u havnt already) are the engine timing, fuel filter, air filter, as they will make a huge differnce. still im getting 11L per 100 around town, and i dont exactly flog it. and about the octane, i realy wouldnt worry too much if its just the non turbo version, although sticking to 91octane or above is always a good idea. usually only costs a few extra dollars a tank for 98 octane here in Australia, so i think its worth it.

Cheers
Andrew from Queensland

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3 Answers

Rmz 250 04 model wont idal or kick start


Like I told somebody earlier to day lower the octane rating of the gas you are using....repost if you need anything futher......

Jun 22, 2009 | 2005 Suzuki RM-Z 250

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