CT 70 back fire By wanderer (Read 341 times)

[wanderer]

CT-70 motor CT70E, simi auto n,1,2,3 down 1970
story
bike new to me
it started, blue smoke, exhaust rotted at clamp, backfired, no 3rd gear, but it runs
split case, changed 31 T gear, clean 47 years of sludge, reassemble lower end
install new jug, piston,rings,new head ( complete,cam rockers, valves )
set cam dot to top of head, adj valves (.03) flywheel at "T"
install new carb
Lets Ride! 
No joy! Back fires
check timing spot on ( use timing light "F" lens up perfect)
open cover on cam check dot with timing light about 10 degrees before looks about right
dot not dancing is solid ( that rules out timing chain slap / stretch, crank gear)
Relap valves in original head, put it on, set timing, set valves,
still back firing
new coil
still backfiring
new condenser 
still backfiring
change carb with one off nice running Ct 70 ( original carb)
still backfiring
set timing advanced
still backfiring
set timing retard
still back firing
see a pattern! Lol
any ideas?
no I won't sell to you! Lol
i have 7 of them
no the kenuter valve wasn't changed
muffler bearings are perfect
thanks
mike lera 

[crwford]

Is the exhaust loose or bad in general if so that's the problem

[wanderer]

Nope exhaust is good

[cyborg]

1970,,,check the points gap,,,change the condenser,,,there lies the problem

[crwford]

running to lean will cause back fire

[cyborg]

The reason I said change the condenser is I've had a few be funky right out of the box,,,also I'd be looking at the points cam lobe and as an added also I've seen points advance plate screws be too long and bottoming in the screw holes before good clamping pressure is made on the plate,,,screws tight but plate loose enough to wander around