300ex help

[RichM1983]

Hey all. I finished up putting my 300ex together and it ran fine. It has a 2mm over 12:1 250x piston in it. When I first started it up it ran fine through all the gears and idled great and had crisp throttle response. Well one day my brother took it up the road and all of a sudden it started bogging when you give it throttle anywhere past half and wont clear up and rev right. I put in a new plug but still nothing. Anyone have any ideas? I know when a motor is broken in the compression goes up. I did a compression test because I thought something may have went wrong so I took the motor apart and it looks great inside still and the compression is about 220psi.

Could my problem be that the octane of the fuel is not high enough? The only thing I can think of is that I need higher octane fuel but I dont get why it ran fan and then just stopped. I definately need some things to check out. Thanks to everyone for the help.

[bwamos]

Clean the Reverse and Neutral connectors for the indicator switches at the bottom of the clutch case cover.

They will be located behind a black sheetmetal cover right next the the rear brake pedal.

The rubber caps/connectors will pull right off. Clean them up with some contact cleaner.

If they get oxidized and have any resistance the CDI thinks the quad is in Reverse and the Rev Limit gets dropped down to something like 5000 rpm's.

Outside of that, make sure that your mainjet didn't back out and fall out in the bowl. ;) Happens more than you'd think.. lol.

THose are the 2 thing's I'd check first.

[RichM1983]

Thanks for the reply Ill check those things out. Anyone else have any other suggestions especially concerning the high octane gas.

[2muchquad]

Make sure the 2 screws didnt come loose that hold the needle in place on the carb slide,i have seen that happen especially when one has been doing some fine tuning,they forget to tighten them all the way.;)

[bwamos]

Yep that too.

12:1 in a 250x should be fine on premium pump. If you used regular pump would be detonating.

I'd imagine it's one of the things mentioned above though.

[RichM1983]

Thanks for the replys guys. Ill check that stuff when it clears up outside. I hope its something like that because Ive been working on this thing forever and havent been able to get it fully up and running. I feel bad because Ive been doing it for my brother so he can ride with me and I just keep running into one problem after another.