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250r muffler


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The most frequent cause of loud popping on deceleration is an air leak at the header pipe connection to the motor. Even a very slight air leak can cause the deceleration popping. This is usually harmless, but can be annoying. As the pipe develops carbon/soot, the popping usually reduces with ride time.

The jetting can be adjusted richer at idle to help reduce the popping in most cases. A lean idle mixture can cause popping on deceleration, but the deceleration popping is usually more mild. Try turning the fuel screw on the bottom of the carburetor outwards by 1/4 turn steps up to 1 turn. The next option would be to switch from the Red marked needle (if currently being used) to the Blue marked needle in the same clip position (or 1 step leaner) to make the low-end jetting richer and keep the mid-range unchanged. Be aware that richening the low speed jetting excessively will reduce mileage and make the motor more difficult starting when hot. If your motor doesn't need the choke at all when cold starting, then the idle may be on the edge of a rich condition when hot.

Note that all the Japanese motorcycles have a bolted header flange and gasket to prevent exhaust air leaks. Yamaha WR450s and WR250s have a air-cut coast enrichener to reduce the same deceleration popping too.

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Depending on the year of your bike you probably have the emission control system still installed on the bike. The system takes air from after the air filter and injects it into the exhaust stream. The reason for this is to burn any unburt fuel that has made it into the exhaust. Without removing this system completely to a certain extent the bike will always pop on decel. They do have delete kits on the market if you want to get rid of it. The popping is most likely more noticeable to you know because your bike is now effectively running leaner which in itself can cause the popping sound as well.

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Did you rejet your bike after adding the 250R exhaust? If not, that's the cause of your problem...you need to rejet when you affect the flow through the system.

Bingo! Of course check for air leaks, but i suspect it's the jetting. Aytime you change the air flow you need to rejet.

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When i first bought my 2004 crf250x I had somebody install the JD jet kit and do the airbox mod which i now regret paying someone to do because of how easy it is. If I am running the full 250R exhaust system should I replace the main?

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Well, it depends. The JD Jetting kit has several different jets, 2 needles with 5 different clip positions per needle. The only way you can tell if it needs to be rejetted is if you check what is in your bike and compare them to the instructions that come with the kit on what is recommended for your level of mods. If the incorrect jets and needle/clip position are being used, then yes, you need to rejet. If not, you don't. That's the problme with paying someone to do something...you have no idea if they did it right...if they did anything...or if they did it wrong.

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I dont have any instructions with the jet kit but i do have all of the left over parts from it. How do i find out what the main should be at for the mods i have? I have the 250R muffler/header and the airbox mod.

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What elevation do you ride at? Did you do the standard 4x4 airbox cut? I'll give you the settings but I need the info first.

Since this is my little bro and we had our bikes jetted at the same time, I will answer for him. We have the std 4"x4" airbox cut, backfire screen still in tact, and jetting includes:

red needle, 5th position

#158 main

fuel mix screw 2 1/4 turns

Typically we ride at 1000-2000 feet elevation. I also have the boysen quickshot, pink wire mod, and complete 250r exhaust. My bike has been running great over the last year but I bumped up the main to 165 since I was probably a tad on the lean side.

With the 250r exhaust, see any changes needed with our jetting? Does the 165 main sound right? Also, see any benefits in cutting out the backfire screen?

Thanks!

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I pretty much agree with Markey....

You should be running the 42 pilot jet, red needle on 5th clip, and a 160 or 165 main. (I think a 162 would be best but doesn't come in the new JD kit). I would stick with the 160 main unless you have went with a less restictive air filter...but you might be able to get away with the 165. The fuel screw will vary...I run at 2 1/4 turns in the summer also...2 3/4 in the winter. You need an adjustable fuel screw if you don't have one already.

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I pretty much agree with Markey....

You should be running the 42 pilot jet, red needle on 5th clip, and a 160 or 165 main. (I think a 162 would be best but doesn't come in the new JD kit). I would stick with the 160 main unless you have went with a less restictive air filter...but you might be able to get away with the 165. The fuel screw will vary...I run at 2 1/4 turns in the summer also...2 3/4 in the winter. You need an adjustable fuel screw if you don't have one already.

got it, thanks codeman! :banana:

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Codeman00 is right on again! I run a 165 mj with the full R system, but I'm also in California at sea level to 3,000 without a lot of humidity so I can get away with a little bigger jets I think. If you ever have any questions you can e-mail JD himself and you'll get an answer. I had a question about high altitude jetting and recieved an answer from him in a couple of days....with that said I think Codeman00 is right on.

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