+2..exactly as you said..and a 155ho does not have a decomp or you got one of these fancy +Rheads with the cam in the pictureThe cam above is anti-kick back, auto decomp holds one or more valves open when a engine is spun over slow, when the engine comes to live centrifugal forces hold this particular lug in place (which is the same od as the cam) and allows to fully close the exhaust valve(s)
Simpleset way I can explain it
Well that's how it works on my Honda anyway
decomp works off the exhaust valve not the inlet, so it wont really make it back fire or anything like that. would be down on power and maybe slightly pop out the pipe..This PSTO I have is a weird one. Some times when it starts it runs rough, back fires when I rev it and is a dog. I hit the kill switch and re start it and it runs smooth. Sometimes it does it 4 or 5 times before it clears. I have tried changing all electrics and it still does it so I was thinking the decomp plays up.
pull the cam cover off and shoot us a pic...The 155z does have decomp. Im sure as poo about this.