The 390 won't start

Blimey, this bike is testing me! Still suffering from the same problem. I spent two hours last night cleaning out the engine and still the plug is being flooded. It runs for about 5 seconds then dies. I have adjusted the float height three times, trying it effectively lower and lower each time. I even put the flat slide back on, but it wouldn't start at all with that carb on.

So I am wondering if I am barking up the wrong tree. I have another question. Could the exhaust be causing this? The exhaust is the original and am I right in saying that it is a double skin assembly? When I first took the bike apart I found loads of bits of the inner layer floating around inside the exhaust, and now that it has run a bit, it sounds like there are quite a few large bits moving around inside. If one of these bits managed to get lodged and partially block the exhaust could that cause a problem like this? I really am running out of ideas now and would welcome any more suggestions.

If its a CR you should have a single wall pipe the WR's had double walls on some models. I would take the pipe off and see what comes out. Sounds like a carb problem letting that much fuel in the engine.

The pipe was off last night and that is when I heard the pieces rattling around inside. The pipe is originally off an OR390, so explains the double wall. The pieces must be quite big because I cannot get them to fall down to either end of the pipe. I have been focusing on the carb, although it is brand new. One of the guys correctly suggested float height but I have adjusted that correctly now and it still has the same problem.

Have you checked the needle and seat and also the floats on the pins that they go up and down freely. Try to start it with the gas tap off after the bowl is full and see if it will run for a little bit and then try it again with the tap open and see if it floods out that should give you an indication of the needle or float situation. If I had an extra carb I'd send it to you.
Bill

Murph, I have emptied my pipe out twice. Once cutting it open where the extension is to remove the big pieces. I pulled a 1x3 in" piece out the back last night. New pipe is out of budget at the moment. Try pulling the carb out of manifold and hang straight turn on gas so you can see if needle and seat are holding.
geary

Also, if you still have the stock 45 pilot jet, you might try dropping a couple of sizes to clean up off-idle throttle response.

Well, at last the bike is running and sounding great. Problem turned out to be that pesky exhaust pipe. I am guessing that one of those rougue bits of rusty metal inside the pipe managed to get lodged and block or partially block the pipe, and the motor just did not like it. Tried a different pipe and she started up, burbled a bit while she cleared out the cases again, then she sounded great. Nice crisp response with the new carb. I am riding her at Hawkstone Park on Saturday so will go up to the standard 430 main from the 390 that is fitted as I don't want her to nip up in the Hawkstone sand, but otherwsie I think she is there.

I will get some pics in the next few days and post them on the restoration thread I started a while back.

Thanks to everyone who contributed to this thread, it is really appreciated.

I better start looking for a pipe.