For the last year after a total motor rebuild I have the following problem.
When riding full throttle on a nice open country road when I close the throttle to slow down there is a real sudden flat spot around 5500 Revs.
Its almost like a backfire or as if someone has suddely turned the key of with a sudden loss of power, but the motor recovers again after the flat spot.
Pinasco 177 Alu
Housing ported to match cylinder.
High compression Pinasco (central plug) head.
Mazuchelli Race crankshaft
24SI premix carb, 116 Main with BE3, hole drilled under the air filter.
Sip road 2 exhaust
The plug colour is perfect and I changed from a BE3 to a BE4 air mixture which helped a little but the flat spot is still there.
Timing is @19 degrees.
Running 3 % full synthetic Castrol oil.
Apart from this bloody flat spot when closing the throttle the Vespa runs beautiful...
Any ideas what the hell this could be?
Thanks for any tips of wisdom