hey guys/girls

did close to 1000 miles on the bike the other week and on the way to home my bike died. was doing 70 down the motorway bike started to to splutter and bog down backed off to 60 rode fine for a bit but then started again backed off to 50 same result and this kept happening to the point where i cant get the bike to accelerate and a week later of trying to fix this issue the bike wont start now well it will but barely then die.

so far myself and a mechanic have:
new petcock (manual over vacuum)
cleaned the carb twice
adjust the float
put standard spark plug in instead of the iridium one
put a fresh tank of petrol in before it gave up (used the posh stuff)

the bike is mostly stock engine wise all i had done to it was
iridium plug
oil and filter change
ryca header pipe and a shorty muffler


any suggestions of what is causeing this and if one of you lovely people know the solution please let me know. driving me mad not being on my bike having to cycle to work.

If it's not the plug ,you might look at the muffler ,a baffle could have rusted/moved and plugged the exhaust.

Assuming you don't have a CA bike, mske sure your gas cap is venting. If not, it creates a vapor lock and won't let fuel flow out. It's probably not the issue, but worth checking.

Remember, you need 3 things to run:

Fuel
Oxygen
Fire/spark

Which one of yours is missing or impeded is what you need to figure out?

If it is exhaust related (since you changed that) batman has a point...are you plugged causing a problem with your air flow? What about the air filter?

I think the decomp just relieves the compression momentarily so the piston doesn't bind on the compression stroke. If yours always spins over when you engage the starter it is all working fine.

I think the 10k mile thingy you are referring to is the cam chain tensioner.

I never touched the decompression adjustment, had 20,000 miles on it.

I brought up the muffler because I had a pickup truck that acted the same way in my case it was a plugged converter ,but a muffler would tend to do the same. drop the muffler and see if the bike will start and idle with just the header pipe (the neighbors will love you) if you rev it it'll just breakup (no back pressure).