aprilia rs125 driving me to suicide

[motoxmagician]

as stated my aprilia is about to send me over the edge.
any informationor help will be gratefully recieved.

heres the problem.
bike starts and idles fine.
warms up to 60 degrees absolutely fine.
rides off as you would expect but then .....
i get a sort of stutter between 5500rpm and 7000rpm.
the engine gets through that fine and then the power band kicks in and the bike is off all pretty normal.
when i get to about 80mph at 9000rpm the bike just bogs down.
if i drop down the revs its fine. its almost like the engine is suffocating.
i have literally done everything i possibly know to sirt this with no avail.
what i have checked and is fine.
engine getting spark
spark plug correct heat range and in good condition.
coil replaced recently as old one broke down.(new coil was from a dt125)
carburettor stripped and totally cleaned.
float valce working as it should,
air mixture set back to factory settings 1.5 turns out.
air box cleaned
engine stripped and piston cleaned (was quite carbonise on crown)
barrel cleaned.
end gap on rings checked.
compression good.
exhaust cleaned and gasket replaced.
power valve working and clean however it seems to have damage from previous engine breakdown??
oil pump working.
fuel flow to carburetor good.
breather pipes all clear and attatched.

so i have tried everything.
ive increased and decreased air flow still no change
air mixture adjusted in and out with no change.

to help my bike is deristricted 98 model
with 34mm delorto carb
and fitted with arrow exhaust
airbox is standard.

so if anyone can shed some light on this
or if your local and can help please come round.

i am about to get divorced from playing with my bike instead of my wife????
and i am tying the noose for surrender!!!
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[Ariel Badger]

As the problem kicks in twice it would point to a couple of problems in the carb, is it set up correctly for the pipe?
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[motoxmagician]

i think carb is set to pipe
carb is running main 155
and pilot 68

it was fine about three weeks ago and i was getting 95mph at 10000 rpm.

the sruggle at 5500rpm has always been there, but the cutting out suffocating at high speed is getting on my tits as i cant figure it out.
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[Ariel Badger]

What is the time scale of the problem in relation to the coil change etc?
____________________
Bikers make great organ donors, get 115 on your licence today.

[Frost]

I had something similar with an RGV250. Turned out to be oval bores and it needing a rebore.

[motoxmagician]

It started doing before my coil broke down then when my coil finally gave up the ghost and I replaced it , it has kept doing it since. Although the symptoms are almost the same except when it bogs down now it doesn't cut out the engine like it did with the faulty coil.
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[Robby]

You've done most of the fault finding and eliminated most of the potential problems, which makes this a bit easier. I can think of a couple of possibilities. I doubt that its a carb problem if it was previously behaving on the current carb setting, and is idling fine. If a carb is blocked or has water in then the idle and closed throttle running is usually the first thing to suffer.

1. Power valve. Are are where you're having trouble is where the power valve operation allows the engine to make power. The power valve position and condition is as important as the carb slide position and condition in allowing a highly tuned 2 stroke to develop power. You said that it was damaged, expand on this. If it is chipped or out of position then you'll get poor running. The expansion chamber and power valve are critical in a 2 stroke running correctly, if they aren't working correctly then you're either sucking all of the mixture out of the cylinder giving you no power, or you're pushing too much exhaust gas back into the cylinder also giving you no power.

2. Coked up exhaust. I don't think you mentioned de-coking the exhaust in your maintenance. If a 2 stroke isn't thrashed then the exhaust will coke up. If you recently rebuilt it then ran it in it will have coked up. Thrashing it a lot will help, but given your clear preference for fixing it properly, a decoke with a wire brush and/or caustic soda is the way forward. If it has an aluminium alloy end can then keep the caustic away from this, you need to decoke the expansion chamber an the baffle (if fitted).

I would also run some fuel system cleaner through the system, just for peace of mind. I have never had good result from redex, can be a good way to make a lot of smoke when you add it directly through the air intake (along with clogging your exhaust, blew a car exhaust wide open this way). Wynn's total fuel system cleaner has worked for me on the car, improving the fuel burn by 25%. Costs about £15 in Halfords. Single bottle treatment, seeing as you have a small fuel tank you should only need to use half the bottle or less with a full tank.

Also, the 5500rpm stutter is common and can be fixed by cutting a wire somewhere - search in this forum and you'll find which one.

For an outside possibility, corrosion on wiring is a possibility. The bike is 13 years old, so corrosion on connectors is a possibility. The (tedious) fix is to go over the whole bike, undoing connectors, cleaning back to clean bright metal with emery paper, and reassembling with a very light smear or vaseline or copper grease to slow further corrosion. I have had impressive results doing this on 30 year old bikes.

[Dr. Quack]

Yeah if it's not the jetting in the carb (Look up what jets and needle setting for the exaust you are using)
It will be:

Barrel re-hone and a 1/10th milli over sized piston kit.
When you say checked barel did you use a micrometre?
Did you move the piston from side to side whilst in the cyclinder because two stroke wear down the exaust port side, you need to check for piston slap. If it's not too bad you will probably need a rehone and a 10th milli over sized piston kit. Rehones are cheap like £20 to £30

These are really good. https://www.pjme.co.uk/

Speak to the engineer he will help.

[motoxmagician]

I am thinking that the power valve is the last possibility. The damage is to the blade which goes into the exhaust port. The edge of the blade is chipped and dented, it looks as though previously something had broke in the barrel and hit the pv blade. The solenoid works properly opening at the correct revs. I think I'll order a new blade and cable as they need to be replaced anyway.
When I stripped down the head I had the barrel and piston micrometered as I initially thought the problem was piston slap or blow by but all is great engine wise.
As you mention the exhaust I did decoke it when I had the bike apart there wasn't much build up anyway.
I will take your advices on fuel cleaner.
I'll keep posted on any progress
Thanks for your replies.
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couldnt think of a sig so this will do for now!!