Chainsaw Repair

Being as this is a 7000 rpm engine, it does not have a lot of port timing duration. But it has generous port area.

The spark plugs used in these is a NGK CM-6 Honda generator 10mm plug. It is a non-resistor plug.

You will notice that the new Husky 550, 555, 560, & 562 engines use a smaller spark plug which may be a trend of the future?.

Thats some wild looking stuff. Thanks for sharing this.

About rpm I thought something was wrong with this last blower I was working on (first one I checked rpm on). I was like 8000 rpm what the heck.
Then I started reading on them yesterday and all of them from 28cc to 75cc only go 7K to 8K max rpms. I wonder why that is, maybe because of the no load like your plane engines?

Couple things .It would almost seem to me on that engine with the induction straight into the crankcase it would have to have either a reed or be a rotary valve .My guess seeing the induction is though the blind end of the crankshaft that it's rotary . With no piston to block the crank case pressurization on transfer it would have to use some means to check the flow .

I would be curious to see the port roof angle on the secondaries /boosters or what ever you call them .It would seem to me they'd be steep blowing upwards towards the head deck else straight accross towards the exhaust port they would seem to short circuit .

Very interesting design I must say .An old gent on the west coast once had an 090 Stihl renown at one time as the fastest  on the coast .Could be true or an urban legion .

Never the less although he did not go into detail he stated it used a set of secondaries though piston  windows ,through a set of reed valves for the boosters .He never gave any specifics  of how that was done .

You can get a lot of surface area in a pyramid reed style design . As soon as that piston is heading up it's drawing all the way up 180 degrees .

Very interesting design I must say .An old gent on the west coast once had an 090 Stihl renown at one time as the fastest  on the coast .Could be true or an urban legion .

Al it's not an urban legion. I did the same with my Stihl 090 in the early 1980s. I got the idea with the 2 boost ports in the pistons intake skirt and addition of a reed valve intake manifold from a series of 1982 - 83 Chainsaw Age magazines [I even sent Weimedog copies of the magazines complete build on the Jonsered 111 project hotsaw last year.]
 
The p/c setup is very similar between the 090 and 111. The only thing I didn't do was install the cast iron liner and cut off head. I got the 090 running pretty fast though with a go kart 34mm Mikuni diaphram alky carb.
The kart reed valve manifold and carb I bought from Russell Karting out of Kansas City, I don't even know if their still in business. The 090 I sold many year ago and don't have a clue where it is today.
30 year old mod techniques are still very repectable today.