Hi Troy,

Have finally recieved a 170 from YS for Adam to take to Argentina, but having some fun getting it to running properly.
At first would not go over half throttle with out going lean and throwing prop, pulled pump apart and found internals differant from the 160.
Found pump body and pump plate were not machined square so diaphragm was not seating properly and the pump valves were binding on the pump gasket. After repairs were done I received the next day from YS new pump valve springs which were shorter and heavier coils than the old ones which are the same as the 160, and a new pump gasket which was now the same as the old one I just modified.
Tried assembling the new springs but they were too short and the pump valves would not close off properly, so I streched the new springs to suit.

Ran the 170 again tonight and now it will go to full throttle with out throwing the prop, 8200 rpm on 17x13 (is this a smick too big?) with 30%, but it is still on the lean side, richened top end back to 7800 rpm and tried to reset bottom end, best I could get was 2250 rpm with a semi steady idle but could not richen up bottom end, went in 3 turns of the regulator from flush with virtually no differance, I feel I should be able run the bottom end richer than what it is.
I will try swaping over the complete pump assembly with one from a 160, if that does nothing will then try swapping the carby housing assembly and then the black check valve.

Knowing how the pump and regulator works with the front vent tube, I have found that a good DZ will run on about 2 to 4 inchs of vacume at idle (2000 rpm or lower) at the vent tube, but this 170 runs a whopping 8 inchs of vacume at 2250 rpm.
I feel that this high vacume may also be affecting how the diaphragm is behaving, this could be why I can't richen the bottom end.

And this brings me to another question, any idea why YS have drilled the 1mm hole (approxmatly) in the crankshaft disc just below where the crank ring runs, is this to do with pressures/vacume in front and behind the crank ring?
Apart from the pump internals, I can see the benifits of the other changes, but putting a heavier valve spring on the inlet valve only had me thinking for a while.

Will

TEAM XMAN