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300ex bogging, hesitation

19580 Views 12 Replies 7 Participants Last post by  tomgodd
Ok fellow riders. Let me explain the problem in as much detail as I can.

First 1996 300ex, completely stock. At half throttle it bogs, stutters, hesitates, whatever ya wanna call it, in neutral. When riding, 1st gear allows me to go maybe 5mph, 2nd gets me 8-10, and so on so forth.
Checked plug, it was black, replaced it, same problem.
Checked fuel, noticed a lot of junk in the tank. Emptied tank, cleaned. Removed carb, tore down, cleaned, reinstalled, all stock jets, needle clip positions, everything stock. Removed fuel petcock and cleaned it. Reinstalled all with fresh gas, same problem.
Researched 14pages on another forum and found that some say to ground the neutral and reverse switches on the cdi side of the harness. Did that, same problem.
Swapped 3 known good cdi boxes, 2 reverse inhibitors, and 2 good coils, all with the problem still happening. Everything I have tried has not gotten rid of the problem.
Also just finished replacing the cam and exhaust rocker, timing is dead on, compression is great, valve lash is set at 6, all done a couple of days ago, ran great when I finished it, now today this starts.

Now my brothers 98 300ex with SuperTrapp slip-on and .50 over piston, developed the same problem at the same time. All he did was ground both switch wires and it solved his problem, so we believe, need to test ride to verify.

Both were running fantastic 2 days ago. Help me please. I just got this bike a couple of weeks ago and have not even been able to ride it. Have a trail ride planned Saturday and would love to go. Sorry for the long post, but I believe it is better to inform as much as possible to get help over the intraweb. Thanks in advance.
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All suggestions have been done. Jets are stock, stock exhaust, stock intake. Bike is stock. Jets are all free, none are clogged. Someone also recommended that the regulator be bad or a charging system problem. Swapped a known good regulator and problem still exists.
Next step... what elevation are you at?
Not sure, I am in Lexington, KY though.

Did some more diagnostics tonight. First off, checked the charging system and all is well.
Then checked valve adjustment, its good, no tight or loose valves.
Kinda wierd. We noticed that with the air intake pipe off, that when it would bogg down it was throwing fuel out of the intake side of the carb. We did some adjustments, and with the intake pipe on it would run fine, yet with the pipe on, or the lid off, or the filter off, it would bog down at 1/2 throttle.
Now got to lookin again and pulled the main jet outta the carb, number on it is 128 with what looks like a fat K in front of the number. I am going to the stealership tomorrow and pick up a 122 main jet to see if that is the problem.
Sorry for saying the jets were stock earlier, I could have sworn I saw a 122 in there. Hope this solves the problem. I don't have anything left to check.
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