Question about Yamaha DT 125 R Motorcycles

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I have a dt125r and need to re jet my bike think i have standard 210 jets have fitted dep pipe and not getting much power what sort of jets do i need to buy to make a difference ??? can you help me please

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  • Yamaha Master
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6ya6ya
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Posted on Jan 02, 2017

  • 2712 Answers

SOURCE: Re-jet the bike

than it was the day before you can actually go back to your sea level jetting a 260 main jet! If you don't rejet you can kiss your assets goodbye when you rebuild the seized engine. Air temperature makes that much difference! Our final example will deal with something often overlooked. We are still up in the hills enjoying our NEW riding area when we notice the old fuel supply getting shorter. No biggie; there's a little store/gas station just down the road. A short trip a few bucks change hands and we are ready to go again. Out on the trail the bikes are running funny sometimes pinging and running HOT. What happened?!?! When we changed jets to compensate for altitude and temperature we were still using SEA LEVEL gasoline. Gasoline sold at higher elevations have a different blend of additives to compensate for the altitude. Generally high elevation gasoline is less dense to compensate for less available air going into the engine and to aid starting. The lighter specific gravity of the high elevation fuel actually leaned out our mixture! A 1 to 2 sizes bigger main jet will get us back into the hunt. If you ride in vastly different areas try to bring enough or your normal fuel along to last the entire ride. It will save you hassles and grey hair in the long run! PILOTS NEEDLES, MAINS: So far we have only talked about main jet changes to compensate for altitude, temperature and fuel density. As most of you know there is a pile of jets in a carb. While main jets are the most critical for ensuring full power operation and engine longevity, the other jets are equally as important for a good running engine. Let's run through them quickly. Pilot jets control the low-speed and idle mixtures. Many times an adjustable jet is used in conjunction with the pilot jet. The adjustable jet allows a precise setting of the idle mixture. If the adjustable jet is located to the rear of the carb and usually on one side it is a AIR adjustment. It controls the amount of air that mixes with the fuel coming from the pilot jet. If the adjustable jet is to the front of the carb, on the side or bottom, it controls the amount of air/fuel mixture going into the engine. In either case if adjusting the mixture screw won't improve the low-end running speed it's time for a different pilot jet. Throttle valves (the slide) control the off idle, to 1-quarter open ,mixture. Some aftermarket carbs have replacement slides available with different cutaways. Changing the cutaway changes the mixture. More cutaway is lean, less cutaway is rich. Some carbs do not have different slides available, so you have to compensate by changing the mixture on the idle circuit or needle circuit. Partial throttle hesitation or rough running can be caused by the slide cutaway. Needle jets control the amount of fuel going by the needle and into the engine at low to mid throttle. There are 2 types of needle jets used in a carb. One is a primary type that has a very precise hole hole drilled through the middle of it, along it's length. The size of the hole relative to the size of the needle determines how much fuel goes into the engine. The other type of needle jet is constructed essentially the same except for a bunch of holes drilled into the side of the jet. These holes allow air to mix with the fuel before it's metered into the engine. Either type of needle jet works well in most cases but there is power to be gained on HIGH PERFORMANCE 4-STROKES by going to the needle with the holes in the side. These are called bleed type needle jets and produce more midrange power in a 4stroke. In any engine going to a leaner (smaller) needle jet is the easiest way to rejet the midrange running when going to higher elevations. Changing the needle jet leans out the mixture evenly at all the midrange throttle settings moving the needle clip doesn't. Jet needles more commonly know as the needle control the fuel mixture throughout the midrange. The shape or taper of the needle dictates how much fuel goes into the engine at a given throttle opening. The needle must work in conjunction with the fuelling requirements of the engine relative to slide position. If you have an engine with a strong hit in the midrange the needle will probable have a noticeable reduction in size the the slide is half open. Remember it takes fuel to make power and when the engine makes power it needs fuel NOW! If it doesn't get the right amount of fuel it pings or misses. You many have cleared up a little midrange pinging by moving the needle up a notch but at the same time you may have overrichened some other areas. If the problem isn't too bad you won't even notice the rich condition. If the machine stutters before it comes on the power that part of the needle's taper is too small and the only way to cure it is to get a needle with a different taper. Finding the right needle can be difficult so hopefully moving the clip will do the job. Finally the good old mainjet comes into play at 3-quarters open to full throttle conditions. Most of you already know a bigger mainjet has a bigger hole so it lets more gas into the engine! Pretty simple!! As simple as it is the mainjet is absolutely CRITICAL to high-speed engine operation. Not only does it meter the gas into the engine, it can aid in cooling the engine as well. A properly sized mainjet will let the engine make good power for a long time. A one size smaller mainjet may make greater power for a while. A slightly rich mixture burns cooler than a lean one so be sure the mainjet is big enough! One final note on jets. All of them and the carburetion functions then perform tend to overlap into some other jet's territory. If you mess with one jet, you may have to mess with a few of the others. My best advice is to not change more than one jet at a time. Slowly work out the correct jetting and keep notes on what you are doing. If you get totally fouled up at least you can go back to where you started. SIGN, SYMPTOMS AND CAUSES: How would you know if there was something wrong with your jetting? If you listen, your engine will tell you! All you need is an interpreter. Since I speak and understand several different engine dialects, I will give you a hand. Let's start with lean conditions because they can cause the most damage. In a lean condition the engine will surge and sometimes ping under acceleration. The engine will also be cold-blooded (hard to start and keep running) but will run better when hot. The spark plug will look bone white or burned in extreme cases. The engine may spit back or sneeze thought the carb once in awhile too. If the engine is running rich the throttle response will be fuzzy and not too quick. The engine will burble, miss and blow black smoke. It will start easy but will run funny when fully warmed up. The plug will be dark, wet or fouled (possible all 3!). Ok so what do you do first to cure the problem? The very first thing is to check and adjust the float level. If it's off one way or another it can throw the jetting off too. Set the float to the specs and retest the running. The next item is to determine a rich or lean condition. Let's say the engine gets hot and doesn't pull well. This is a lean condition so the engine wants more fuel. Stick in at least a two size bigger main jet and try it again. If it's better but still not right go even bigger on the jet. and try it again. Bear in mind that drastic or sudden changes in jetting usually mean an air leak has developed somewhere in the engine. Find it and FIX IT!! When the engine burbles on the top end come down 1 jet size at a time until it winds all the way down. Don't drop and more sizes! If the engine seems sluggish and lumpy or want to load up on the bottom end the mixture is TOO RICH. Adjusting the low speed mixture screw helps a little but doesn't cure the problem completely. What you need now is a new pilot jet. Go 1 size smaller and try the adjustment again. When the engine runs smooth with the adjustment screw about 1 and a half turns out from the seat you have it!! IS THAT ALL THERE IS TO JETTING??: There's a lot more to jetting than just stuffing jets in holes and hoping the problem goes away. If you can understand what your engine is trying to tell you when it runs funny you will have a better chance or correcting the problem than someone who doesn't have a clue. When you rejet, go slowly and carefully until the problem is solved. As a final thought let me remind you that jetting is a lot like life, if you have a choice it's always better to be a little rich!!,,,

Posted on Nov 10, 2008

  • 311 Answers

SOURCE: Which size Jet Kit for 800 Vulcan Classic?

general rule of thumb is to go up about 10 jet sizes,unfortunately it is a bit of trial and error,and you may have to swap out diferrent sizes to get the bike running right,(jets are quite cheap though)but first step about 10 sizes from standard,your local dealer should be able to tell you what jets are in it and supply replacements,if you change to a hgh flow aftermarket air filter you may have to change jet sizes again as changing the filter may effect the mixture ratio in the carbs,,hope this helps

Posted on Jul 10, 2009

  • 47 Answers

SOURCE: hi their what size is a standard jet in carb for

phone any Yamaha dealer, dealer list on Yamaha website, the standard jet size is always shown in the parts list, and they all have parts lists.

Posted on Aug 09, 2009

Benimur
  • 6966 Answers

SOURCE: WHAT SIZE MAIN JET AND PILOT JET ARE STANDARD WITH

Hi and welcome to FixYa,

On a 2003 Kawasaki KLX125, these are standards:

  • main jet - 145
  • pilot jet - 17.5

Good luck and thank you for asking FixYa. Happy Holidays.

Posted on Dec 18, 2009

pugwash814
  • 377 Answers

SOURCE: My Sabre has Cobra pipes and a Jet Kit, but I can

its also recommended to increase the main jet by 2 sizes for every change,( filters, pipes etc )so your main jet needs to be 4x bigger than it was standard..

Posted on Apr 04, 2010

Testimonial: "Thanks for the information. We did use the recommended Jet Kit and settings per Cobra, but just can't seem to get it to stop popping/backfiring. "

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1 Answer

Main jet size


Bigger jet is not the problem. More fuel would be put in and you said that it runs well at the top end. So it is not a fuel shortage issue.

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1 Answer

Hi i brought this bike in the summer and its never run right,its fine on tick over but when the revs get up it starts jumping like its lacking fuel, ive cleaned all the jets but it didnt help, it has k and...


Hi... if you have vacuum cabs... Have you checked to see if the vacuum on the fuel tap is working correctly.. Take the fuel pipe of the carbs, put the fuel tap to on.. If its a vacuum tap there should be no fuel coming out. Put the pipe in your mouth and suck on the pipe, if fuel comes out then stops it seems to be working. Also check the diaphragms in the top of the carbs are not split or have any pin holes in them. You can do this but holding the diaphragm up to the light.. (If they are vacuum carbs).. You can aso check to see if the carb rubbers are leaking between the carbs and the engine.. You can do this by starting the bike up and leave it ticking over. Get some carb cleaner or WD40 and spray it onto the rubbers between the carbs and engine. If the engine pics up speed (revs go higher) then the rubbers need to be changed.. Hope this helps you out...

Good luck.. Tony.

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1100 Dragstar Fitting Straight Pipes


We have changed a few bikes from standard pipes to drag pipes. Their is a few considerations here, sea level or at what altitude, how much back pressure. so my suggestion rather take it before fitting the pipes to someone with a dyno, run and record the test, then have the pipes fitted, and let the same shop to the test again on there dyno, they will then know what to do with the jetting, because you should achieve better results with your new pipes.

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My Sabre has Cobra pipes and a Jet Kit, but I can not get the bike to stop popping when I let off the throttle-Any Help?


its likley to be running a bit to week,, try opening up the fule mix screw just a bit to let in more fule

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WHAT SIZE MAIN JET AND PILOT JET ARE STANDARD WITH THE BIKE


Hi and welcome to FixYa,

On a 2003 Kawasaki KLX125, these are standards:
  • main jet - 145
  • pilot jet - 17.5

Good luck and thank you for asking FixYa. Happy Holidays.

Dec 18, 2009 | 2003 kawasaki KLX 125

1 Answer

Hi their what size is a standard jet in carb for dt125r 2004 mod


phone any Yamaha dealer, dealer list on Yamaha website, the standard jet size is always shown in the parts list, and they all have parts lists.

Aug 09, 2009 | 2004 Yamaha DT 125 R

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Which size Jet Kit for 800 Vulcan Classic?


general rule of thumb is to go up about 10 jet sizes,unfortunately it is a bit of trial and error,and you may have to swap out diferrent sizes to get the bike running right,(jets are quite cheap though)but first step about 10 sizes from standard,your local dealer should be able to tell you what jets are in it and supply replacements,if you change to a hgh flow aftermarket air filter you may have to change jet sizes again as changing the filter may effect the mixture ratio in the carbs,,hope this helps

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hi remove the front down pipe take out the washer that restricts the hole will invole drillng or grinding

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