Sparks out of the exhaust, not flames! GL145

[Arronduke]

I have rebuild a GL145 motor with some new goodies..

CRF150 piston
XL185 barrel
1mm over sized inlet valve
Ported head
Kelford cam grind

Motor starts and idles well but bogs when opening the throttle then clears and revs all right up top.
What is interesting or scary is there seems to be sparks... not flames coming out of the exhaust..

Im thinking timming but would metal to metal interferance cause this? all the tolerances have been checked but fuck me... sparks?

[FJRider]

Dont panic ... just crud in the exaust system getting blown out ...

[sidwyz]

Cool, do you have the cam specs?

Would be interesting to compare them to what Dads got in his (and I hope to send mine off to get ground soon)

Did you work out what compression you ended up with?

Are you still using the standard pumper carb?

So will this turn up to the next meet in december then?

Luke

[Arronduke]

Luke how is the knee..?
I have given the cam timing to Gary at the 2hr..

http://www.akunar.com/STD_PISTONS.htm

the cheap bits from Thailand.

regarding the sparks etc... makes sense ... new exhaust which would be full of grinding shit... so that cool.

[JimO]

sounds like your power band is broken

[FJRider]

sounds like your power band is broken

Or just one of those yellow ones ...

[LBD]

If you are still using the old possibly carboned up exhaust then as FJ says, probably just carbon burning out of the exhaust.

Re bogging.....carbureted right? (And have you fitted a bigger carb?) If you open the throttle just a little slower and it does not bog down, then what may be happening is when you open the throttle fast it lets such a rush of air in that it loses vacume between the carb and inlet valve and therefore loses the pressure differential across the venturi, momentarily starving the engine of fuel.