090AV running 9/16 chain

[bulletpruf]

gasket delete will help but muffler are wide open dont you think ?
my 090 had gasket delete, real sumbich to pull the recoil

Robin - The inside of the muffler is indeed wide open with no baffles. I'm talking about the outlet - it just seems to be quite small compared to what is necessary. And it's the same for a 106 and 137 cc saw.

Metallichg - The number that's thrown around here is that the muffler outlet should be 80% the size of the exhaust port. You can measure this by putting uncooked spaghetti in the port and the outlet and then counting how many fit into each. No shortage of threads on the topic - here's one:
http://www.arboristsite.com/communi...-modified-mufflers-on-stock-chainsaws.246018/

Don't forget that you will need to re-tune after a muffler mod - the saw will likely be running leaner.

As for the gasket delete, yes, you're removing the paper gasket to gain more compression. Most folks recommend you check clearance before you remove the gasket to ensure the piston won't contact the cylinder. You can do this by using play-do or soldering wire on top of the piston and then rotating the piston so it compresses it. Measure it to ensure you have enough room. If you still have room to go after a gasket delete, you can cut the base of the cylinder to increase compression even more.

You use liquid sealant instead of the paper sealant between the cylinder and case. There are a few different sealants that folks here use.

Scott

 

[bulletpruf]

Just measured the exhaust port on one of my 106 cc Contra's - it's 1.224" x .695" or about .85 square inches.

And the Contra muffler (likely the same as the 090) has 6 outlets that are roughly .158 x .795 or .13 sq in. And multiply that by 6 and you get .78 square inches. And doing the math, you find that the exhaust ports are 91% of the size as the exhaust port.

So on a stock Contra 106 cc, it doesn't look like it needs a muffler mod.

As for the 137 cc 090, I didn't dig up a 66 mm jug to measure, but I'm thinking you'll still be in the 80% ballpark, so maybe a muffler mod wouldn't make a lot of difference. I still plan to try it.

You could also try the redneck method and just open up the metal slits on the exhaust a bit more with a screwdriver. They sell reproductions of the metal piece for about $5 on eBay.

 

[Metallichg]

Robin - The inside of the muffler is indeed wide open with no baffles. I'm talking about the outlet - it just seems to be quite small compared to what is necessary. And it's the same for a 106 and 137 cc saw.

Metallichg - The number that's thrown around here is that the muffler outlet should be 80% the size of the exhaust port. You can measure this by putting uncooked spaghetti in the port and the outlet and then counting how many fit into each. No shortage of threads on the topic - here's one:
http://www.arboristsite.com/communi...-modified-mufflers-on-stock-chainsaws.246018/

Don't forget that you will need to re-tune after a muffler mod - the saw will likely be running leaner.

As for the gasket delete, yes, you're removing the paper gasket to gain more compression. Most folks recommend you check clearance before you remove the gasket to ensure the piston won't contact the cylinder. You can do this by using play-do or soldering wire on top of the piston and then rotating the piston so it compresses it. Measure it to ensure you have enough room. If you still have room to go after a gasket delete, you can cut the base of the cylinder to increase compression even more.

You use liquid sealant instead of the paper sealant between the cylinder and case. There are a few different sealants that folks here use.

Scott

very interesting! thank you Scott. so much info on this site, it's hard to find what you want unless you know what you are looking for with exact terminology. That opens a whole can of worms for me.

 

[Bill G]

I am the odd duck as always heck I run 3/8 on everything I can including the gear drives

 

[Bill G]

The ole gear drives run well on 3/8 well that is with the short bars I run......................