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Discussion Starter #1
I have a 2000 Honda 400ex that’s bored out to a 440 with a yoshimura off-road exhaust. I put a 162 main jet in it and a 42 pilot. Other then that nothing motor or carb wise has been touched. The idle screw on the handlebar needs to be backed out all the way to idle and the motor spits and sputters a lot unless you are very high rpms. Not sure what it need
 

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Your jetting is WAY too low. What air filter are you running? Bumping the engine size up 40cc and most likely increasing the compression in the process requires a lot more fuel and air. If you haven’t accounted for those changes, it isn’t going to run, or will run very lean and will blow the motor in the near future. It would also help if you gave a lot more info on your engine build.
 

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Your jetting is WAY too low. What air filter are you running? Bumping the engine size up 40cc and most likely increasing the compression in the process requires a lot more fuel and air. If you haven’t accounted for those changes, it isn’t going to run, or will run very lean and will blow the motor in the near future. It would also help if you gave a lot more info on your engine build.
 

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Discussion Starter #4
Your jetting is WAY too low. What air filter are you running? Bumping the engine size up 40cc and most likely increasing the compression in the process requires a lot more fuel and air. If you haven’t accounted for those changes, it isn’t going to run, or will run very lean and will blow the motor in the near future. It would also help if you gave a lot more info on your engine build.
Everything is stock on the wheeler except the big bore 440 kit. I am running a k&n air filter and I just put 188 main and 148 pilot. It all of a sudden started surging. And cutting out
 

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How long has the 440 kit been in? Is it a new upgrade, on it when you bought the machine? It is very difficult to troubleshoot without a lot of information to go with it. Why did you change the jets in the first place?
 

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How long has the 440 kit been in? Is it a new upgrade, on it when you bought the machine? It is very difficult to troubleshoot without a lot of information to go with it. Why did you change the jets in the first place?
I did the 440 kit, changed all filters and it ran good but needed bigger jets. Put the 188 main and the 48 pilot in it and it’s still needs to be ran with no air box lid or it will not go. With the lid off as of today it runs very good. Just doesn’t have a lot of low low end
 

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Ok. The main jet and needle runs everything from roughly 1/4 throttle to wide open. Right now it sounds like you have a pilot jet and fuel mixture problem. With it only able to run with the air box lid off tells me that it is too rich. You need to get the idle and low side fixed before you can do anything else with the main jet. Before doing any of the jetting, take the carb apart and clean everything. Make sure you spray everything down with a good contact cleaner and blow everything out with an air compressor. Check the accelerator pump diaphragm for any holes or tears. Pull the fuel mixture screw out along with the spring and o-ring and clean that. Tightened it down until it stops, without forcing it tighter because you can break the tip off, and back it out 2 3/4 to 3 turns. Make sure the accelerator pump linkage is just touching the plunger when the throttle is fully closed. Turn the throttle adjustment screw on the carb all the way in. If it starts, adjust the idle to where it sounds best. It may be idling very high when it first fires. Get the low side adjustments correct before messing with the high side fuel circuit. I would try dropping your pilot jet down to a 45 and try starting from there. Try to get it to run with the airbox lid on to start with. Only make one change or adjustment at a time because each change will affect other parts of the fuel circuits. You will also most likely need a few more jets on either side of the 188 main that you have in it. I would suggest getting them before you decide to get too much further. It helps to have everything on hand so that you can make an adjustment, try it out for a few minutes, and then make another adjustment. Carb tuning takes a lot of time to get just right and a great deal of patience. Good luck.
 
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