Valve adjustment questions

[shipsscoot]

I had problems with my gy6 150 idling so i finally got around to adjusting the valves. Turns out the exhaust was closed with no play at all.. My specs under my seat state .03mm intake, .018mm exhaust. I have done this before and the scoot ran great. I know some say .003in and .005in but again my scoot specs are stated under the seat. I dont remember what I adjusted them to last time but....... my question is.
it starts up and idles much better and at a lower rpm but now when i accelerate it backfires through the carb. does that mean my intake is to tight and its allowing the combustion up through the partially opened valve. Nothing was done with the card or fuel at all. this is a valve adjustment issue

[shipsscoot]

sorry specs state .03mm intake and .18 exhaust not .018exhaust

[scootnwinn]

Most people set 150 gy6 to .004 or .005. Not sure why your specs are so different

[Terri "Bunny" Lee]

but then again the .004 & .005 are just good starting points
correct?

are his in mm or inches?

[woowilly]

0.001181102 inches = 0.03 mm <---- intake valve only, have to check more often to make sure some clearance is still there as valve head and seat wear.
Will give slightly better performance in theory due to more intake valve open duration, probably mot enough to measure though.
This is tighter than I would be comfortable setting intake valve for.

0.004 inches = 0.1016 mm <---- reasonable

0.005 inches = 0.127 mm <---- reasonable

0.007086614 inches = 0.18 mm <---- slightly loose. the looser you go, the louder the clicking gets and power starts going down due to reduction in valve open duration.


valve clearance for intake is typically set slightly tighter than the exhaust due to
less heat expansion and slower seat wear rate than intake valve.

I set mine to 3 thousands ( inch ) on the intake and 5 thousands on the exhaust with a light drag on the feeler gauge.