Stock MS361 vs Ported MS361 with a sad ending vids

[chadihman]

I recently cut the squish band,lowered the deck and ported a MS361. This was the first saw jug I ever put on my lathe and the second saw I ever ported. I ran two tanks through the 361 yesterday and was really impressed with it's power. It was blowing a tad over 200 psi compression. I ran it some more today and then put it up against my brothers stock 361. Both have new chains on 20" bars and the ported 361 has an 8 pin sprocket. I got sick when the saw seemed to loose rpms and bog down. I gave it throttle and it cleared up so I figured it was ok and we started to video. My ported 361 beat my brothers stock 361 by 4 seconds but I felt that my newly ported 361 was not running as strong as the day before. I really felt sick when I could feel the pull cord pulling much easier.
I got the ported 361 home and tested the compression. It was now blowing 140 psi:bang:. I pulled the muffler and found a slightly scorn piston and rings that were worn also:bang: I'll tear it down monday to see how bad it really is. The saw was tuned 13,500 yesterday and then I leaned it out to 14,300 today. I guess that was where I goofed but I sure thought it was still four strokin. The rings look as if they were snagging. I think I may have made the top of the exhaust port a little to flat.
I'm planning on starting over again and thought I would try a big bore kit and port it to the same numbers. Or find a good used jug. I think this saw would have beat the stock 361 by more if we would have taken the video yesterday when it was blowin over 200 psi.
[video=youtube_share;Wc9fO3H8fhk]http://youtu.be/Wc9fO3H8fhk[/video]

 

[chadihman]

And the ported 361
[video=youtube_share;fReJgylmCYs]http://youtu.be/fReJgylmCYs[/video]

 

[wigglesworth]

And the ported 361
[video=youtube_share;fReJgylmCYs]http://youtu.be/fReJgylmCYs[/video]

Sounded seriously lean there. Did you use a base gasket or sealant?

 

[chadihman]

Sounded seriously lean there. Did you use a base gasket or sealant?

Base gasket. I fully agree, it sure did sound lean in the video. That would be the first saw I ever did damage to. Rebuilt loads of saws that were tuned by ear and checked with tach. That will be the last time I ever try to get a few extra rpms out of a saw.

 

[tlandrum]

you live and you learn. its never a good idea to lean a work saw out just for the sake of a few out of the wood rpm. it needs fuel in the cut to keep the rpm and to keep the motor cool

 

[wigglesworth]

Base gasket. I fully agree, it sure did sound lean in the video. That would be the first saw I ever did damage to. Rebuilt loads of saws that were tuned by ear and checked with tach. That will be the last time I ever try to get a few extra rpms out of a saw.

Man, I hate it for ya. Sucks puking a saw. I've been there. Flat sux.

What timing numbers u use? Can u reshape the exhaust and not throw it out of whack?

 

[chadihman]

Man, I hate it for ya. Sucks puking a saw. I've been there. Flat sux.

What timing numbers u use? Can u reshape the exhaust and not throw it out of whack?

I'm at 102 deg atdc on the exhaust so I could probably take it to 100 deg to give it a little more of a radius. That would probably give me a little more rpm also. In is at 100 deg abdc Tr are at 135 deg atdc I would probably raise them a little more shooting for 127 deg atdc or so

 

[blsnelling]

I'm assuming that you didn't raise the transfers back up after cutting the squish band?

 

[chadihman]

I gotta tell you guys. I have a heck of a time getting a nice bevel back on the ports. A round stone is what I'm using.

 

[Jacob J.]

I gotta tell you guys. I have a heck of a time getting a nice bevel back on the ports. A round stone is what I'm using.

What are you using to grind on the ports initially?

 

[chadihman]

I'm assuming that you didn't raise the transfers back up after cutting the squish band?

I raised them but not enough.

 

[blsnelling]

I raised them but not enough.

I think you'll find your missing RPMs in the transfers, rather than the exhaust.

 

[chadihman]

What are you using to grind on the ports initially?

Double cut carbide for most of the removal in the ex port then a round file to finish the ex port before polishing it. I used a 90 mini die grinder with a carbide bit for the transfers. That was a little nerve racking though. I read that some use a small wheel. I'll have to try that next.

 

[chadihman]

I think you'll find your missing RPMs in the transfers, rather than the exhaust.

I still think I'll take the ex to 100 deg so I can shape it to a nicer radius. Will 100deg be ok or will that take to much compression away?

 

[tlandrum]

you could go to 100 with no problems, i think you could stand to loose a few psi of compression from the 200. and you do need to raise those tranfers quite a bit.

 

[514mach1]

I tune it to be quite rich at WOT so it's obviously 4 stroking. Then I find a decent size hunk of wood to put a respectable load on the saw. I cut through about 1/3 of the way and fine tune the H needle so it's just a bit leaner than 4 stroking under load. If it still 4 strokes without load, I leave it at that. May not be optimal, but it seems to work ok.

 

[Spectraman]

Sorry to hear about that but can't wait to see it with a BB kit on it.:msp_smile:

 

[chadihman]

Sorry to hear about that but can't wait to see it with a BB kit on it.:msp_smile:

Has anyone used a BB kit from Baileys for the MS361? It's NiSi coated. I would port it anyway so port shape not a problem.

 

[mdavlee]

I think you'll get better results raising the exhaust a little and the transfers up with the cylinder you have. You've already done the machine work on it so raising the exhaust and transfers is a small amount of work on it.

 

[chadihman]

I think you'll get better results raising the exhaust a little and the transfers up with the cylinder you have. You've already done the machine work on it so raising the exhaust and transfers is a small amount of work on it.

yeah I spent a good amount of time with it on the lathe so hopefully the cylinder is ok.