f80 motor loseing power or pinging on full throtle when warm

[steptoe1111]

hey guys ive been rideing my 26 inch mountain bike with the f8o kit on it for about 3 weeks now, and im haveing a problem at full throtle or (wot) im actualy loseing power and then when i back it of to three quaters the motor seems to catch up a bit and starts winding out, im running a 44 tooth rear on a 26 inch rim so full revs say about 5.5-6 thou rpm id be doing about 45 kmh , i weigh about 70 kg and i have been rideing on the bike paths (dirt) from a to b, wich is about 10 k each way,. and sitting on mostly 30-35kmh then giving a bit of (WOT) from here to there, now when im giveing it (WOT) high up in the rev range its sounding like i got a litle exaust leak around the manifold but i checked it its not leaking i alredy have installed an o ring in the carburetta (wich is an nt type by the way ) and done all the joins up where it bolts on with some gasket glue (it also makes for good locktight) and i have done all air leak test by coating it with some wd40 and looking for bublles and i have none there its all air tight,, now i thought it could possibly be a small head gasket leak so i have taken the head of and given it a good mill down on some glass with some grinding pase and actualy ended up takeng the small raised ring of the botom side of the head that helps seal the cylinder hopeing to raise compreshion a bit but dident notice much reinstalled it and went for a ride and its still doing the same thing almost but it seems to do it more after its heated up a bit on long strait rides could it posibly be pinging from the heat or could it posibly a jeting problem in the carb if its jetting why wasent it happening in first two weeks of rideing any sugestions or help any one..... it is greatly apreciated as i said this is my first bike engine and id like to get it right.... apart from that im hooked on these things they are awsome

 

[2door]

Check your spark plug color. The best way to get a good reading is to shut down the engine after a good WOT run, allow it to cool a little then pull the plug.

Do a little research and read about plug color and how to get the best performance based on your fuel to air mix. A light color, white to light tan can indicate a lean mix, more air to fuel. A darker color, dark brown to black means too much fuel to air. It sounds to me like you might be a little lean at the top end.
The reason it ran better before is that the engine is getting broken in and running better. Now it might need a little more fuel.
You didn't say where the 'E' clip on the needle is but you might try lowering it one notch at a time to see if you get any improvement. Keep in mind that the needle only controls fuel flow from about 3/4 throttle down to idle. The jet size determines fuel to air mix at WOT.
Your location doesn't tell me anything about your altitude. That will effect the way the engine runs and can be helpful in diagnosing problems.
Tom

 

[steptoe1111]

ok guys after lots of trial and eror i found that the problem was a blocked air filter it was full of oil and either running to rich at WOT or restricking the air flow at WOT one or the other but i got my top end back(so far anyway) i think a better up grade to avoid this in the future may be a velocity bell or an air filter upgrade for the stock nt carb thanks guys