I just purchased a 93 honda 300ex. It is bored .50, uni filter, holes in air box lid, and dg exhaust. It has been sitting for about 2 years. With the choke on I can rev it up to half throttle fine, after that it starts to break up and back fire. When I take the choke off it breaks up no matter what throttle position and it is very harb to keep running. I drained and replaced the gas, new plug, and I tore apart the carb and cleaned it. It had the stock main jet in it(122). i replaced it with a 130. After all of this there is very little to no change. What should I look at next. Thanks for the help.

 

After sitting so long, you probably have some dried fuel varnish in a passage,you will need to soak the carb in a good cleaner, then take carb spray,and use the straw on the nozzle to blast out all the tiny little holes and ports, then blow it all out with an air gun. Even the tiniest bit of crud can restrict fuel, but we also need to look at your intake/exhaust set up, you have a bored out motor with higher flow filter, modded air box lid, and free flowing exhaust. The fact that it runs to half throttle with the choke on tells you it needs more fuel, how does the plug look after it runs a while? if it is whiteish,you will need to jet up more,if it is dark or black, you have other carb problems. Also, it may have some bad connections in the ignition circuit, make sure the plugs to the cdi and grounds are clean,weak voltage can cause problems too. Start with a plug reading, that will get you started, keep posting results, there are lots of people here that can help you. And - Welcome to the forums.

 

I have already tore apart the carb. I sprayed it all down and then used the hose to spray in all the jets and holes. I did this twice before I put it back together. I tried putting a bigger jet in it. it made no difference at all. The plug is very black, but I don't think this is a very good reading because I can only keep it running with the choke on. I also checked for spark (holding the plug against the motor and hitting the starter). It seems to have plenty of spark.

 

I have also forgot to mention that the upgrades were done before it sat for 2 years, and I was told that it ran fine before they left it sit. That was even running it with a 122 (stock) main jet.