hi can someone shed some light on this. Bike runs fine until I hit 4500rpm and the. It breaks down like its missing. Any ideas on what this could be and what to check. 

what year and model would help.

plugs
leads
type of ignition
carb or EFI

Sorry fellas its a 92 softail. Stock ignition. Ev27 cam carby has 45 pilot jet and 180 main if that helps. New plugs today replaced the leads about a month ago with 8.8mm accel brand new ignition pick up sencer. 

Plugs and leads have been eliminated then ?

would have to suspect the coils next,

Did this happen gradually or start to break down all of a sudden ?

More likely to be spark rather than fuel, but if main jet is partially blocked it could cause RPM limitations.

Thanks rider I'll pull the carb tomorrow and clean it then see how it goes if no better then I'll replace the coil and see if it is that. It's not long started doing it I can work on the bike no worries but can't diagnose problems well.

Good luck Wazza, sometimes diagnosing is about eliminating what you know it isn't, then that leaves a smaller list of possibilities of what it may be.

One other thing to consider, does it start to breakdown when it's relatively cool, or is it more so when it warms up a bit.

If it is doing it from the word go then it could be a fuel blockage/restriction.

If it takes a while to start playing up it would be more like the coil breaking down when it heats up.

 

(don't want to make it too complicated, but, seeing as you have made some recent changes, keep in mind that it's possible for new parts to be faulty sometimes,,, if the problems started at the same time as the new parts were installed it's worth thinking about.)

Thanks rider for your info. I'm just about to pull the carb and strip and clean the fuck out of it. I hope it's a fuel blockage.

Goes without sayin, but check fuel filter and air cleaner for blockage while ya there.

if she goe's ok down low in da rev's but no good mid range & up throttle i would look @ the rubber dia in da carb , easy way to check is to rev her up  look @ da carb slide with a torch & make sure da slide goe's up as it would be conected to da throttle cable , if she only goe's half way up & flutters up & down  its da carb slide  dia

Thanks daddy racer I haven't checked that yet. I pulled the carb down and clean every thing and blow it out I also moved the needle clip down one and went for a ride and it's stopped as far as I can tell it let me hit the limiter. Not that's I want to do that to often.

This bike is doing my head in now its poling in the rear xy kinder again and running rich as hell. Does anyone live northside who can and is willing to show how to tune these bikes. I haven't got the cash to send it to the shop.