Topic: My bike runs great and then losses power HELP!!!!!!!!

[unixgnuru]

So here is the situation. Just had a new chain and sprockets installed, a 400.00 dollar tune up 6months ago. So I go for a ride. She runs great, then at around 30 miles she starts losing power like she is getting no gas. I move the petcock to reserve and I check the tank. Still plenty of gas. I give it throttle and she accelerates extremely slow. Going from a stopped position she takes forever to get to sufficient speed, like she has no power. At a stopped position if I am not giving her gas she will shut off. After about 4 miles of this she recovered.

Does anybody have any idea what I could look at. I already had someone check the fuel line and petcock for clogging. It is intermittent and only happens after she has been running a while.

[flybox1]

vapor locked tank?
clogged fuel supply....check - tank filter, petcock screen, fuel line/filter, idle and main jets, bad float height setting...time for a DIY carb cleaning/synching my friend.  
getting good spark, battery good?
clean your points...if you still have them.
check your plugs.

[Hush]

Sounds like a blocked gas cap vent, makes the carbs suck hard to get any gas, clean out your gas cap.
Could also be coils breaking down, they work great until they heat up then deliver bad spark.
Has it happened since or was it a oncer?

[Duke McDukiedook]

It is a fuel related issue, check it from the tank to the carbs, be thourough.

And look at it yourself, as long as you have some simple tools, this is stuff you can so yourself instead of depending on someone else to screw it up.

[scottly]

Sounds like a blocked gas cap vent, makes the carbs suck hard to get any gas, clean out your gas cap.

1+ to a blocked vent.

[madmtnmotors]

Fuel restriction. Either blocked cap vent or in-tank filter screen. Run a longer fuel line from the petcock to a clear, plastic container and check the rate of flow. Does it flow or just trickle out? Remove the fuel cap and see if the flow improves. If the fuel still trickles out with the cap removed then the in-tank filter screen would be the culprit. Earlier models might have a filter screen in the petcock, my 78' CB750K has the screen in the tank. It is accessible from the petcock opening (with the petcock removed).

I had a similar issue when my filter screen became clogged. Essentially the motorcycle is running out of gas. The fuel flow cannot keep up with the demand.

[unixgnuru]

Thank you all for the ideas. I will check them all. Oh the bike is a 1975 cb550four.