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1989 Yamaha Moto 4 sputtering after new carb

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  • Admin changed the title to 1989 Yamaha Moto 4 sputtering after new carb

Yeah that sounds like sh**, but without seeing what you are doing with the throttle, and whether it will come right with more throttle, and stuff like that, it's hard to say what's wrong with it.

Was it like that before you put the new carb on ?

Does it start easy ? Will it rev if you coax it past that misfiring ?

Is the spark, and spark-plug good ? Pull the plug out and check it  has a nice blue spark, and at the same time check what colour the tip of the plug is. It sounds like it's flooding.. But that's a guess.

You could try turning the fuel tap off and see if it comes right as it runs out of fuel in the carb.

You need to give us more info.

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Sorry i couldnt see your video just got a black screen with a pointer and a line through it, maybe i have a setting wrong, i havent been having this problem.

I think my first question would be which carb did you put on. Regardless, you might be able to adjust it out, without seeing the video, im guess it may be running lean, you can try adjusting the mixture with the adjusting screw, first turn it all the way in and see how many turns it is out, and then start adjusting from there, keeping in mind your original setting. If that doesnt work you can check against you old one to see if the jetting is the same, but that might not matter if its an aftermarket carb, the fuel and air jets have to match up, so could be different on aftermarket.

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  • 2 weeks later...

There should be two idle adjusting screws, one for idle speed and one for idle mixture. You need to get it to idle as slow as it will using the speed screw, then adjust the mixture screw to get it at it's middle position between going rich and slowing and going lean and slowing., then adjust the speed screw again to get it at it's slowest steady idle and then readjust the mixture screw again to get it to it's middle position between going rich and slowing and going lean and slowing. Keep doing that until it's idling slow and steady in the middle of it's mixture range, then, if it's too slow you raise the speed slightly using the speed screw but don't adjust the mixture any more. If everything inside the carb is right, that should work. If it seems you need to readjust the mixture, it's probably because something's not set right or worn in the carb.

The speed screw is on the side of the carb near the slide, and the mixture screw is underneath near the front of the carb and probably up a recess. .

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