Spuds Porting and Tuning Thread

[spudulike]

On ‎14‎/‎03‎/‎2018 at 11:38, kcstevens said:

What size hole is best in the 201tcm exhaust Mr Spud?

Sorry, missed this, usually 10mm although I don't drill holes nowadays, have a neater solution!

[Wonky]

On 11/03/2015 at 22:22, spudulike said:

The saga of my ported 066 Red Eye continues, a very old coil gave an ignition advance of 20 deg with no change on revving it. In the cut it had as much go as a bog standard 50cc old saw on its 20" bar so pretty crap. Technically a two stroke with a set advance should be around 25 - 27 deg which will make full power but lots of kick on start up.

 

The lack of power I assumed was lack of ignition advance and the following backs this up.

 

I have tested a standard MS660 and it has circa 30 deg at idle and 22.5 deg around 7-8k revs so this coil has a built in advance and retard circuit which I already knew but wanted to find out what and when it kicked in.

 

I have now fitted a MS660 aftermarket coil to my saw and it is now idling with 22.5 deg at idle and this drops right down to 5-10 deg flat out. This sounds a lot but having done a lot of research on the subject, a good curve will be near zero for ease of starting, rising vertically to around 29-32 deg at idle and then down to 20 deg in mid range and dropping at max revs to 0 -15 degrees to protect the engine from pre ignition, the curse of ignition modification.

 

Soooo - the answer is to take the flywheel off and position it ten degrees clockwise of where it is now giving a few degrees extra advance on standard to give the engine extra wallop but not enough to cause pre ignition.

 

Anybody still following the train of thought:001_rolleyes:thought not......guess I do too much thinking:lol:

 

In laymans terms - I now know where I need to be, why the saw isn't right and what I need to do:thumbup:

 

Oh - I have learn't a lot about ignition timing advance as well!

Umm I guessing I’m a bit late to your porting thread,, but it’s an everlasting/ongoing thread, and I’m learning,  learning lots..   but what you say here is just can’t understand what your sayin, to what I’ve read. Else where,

,I think it’s pprolly time for a picture as it’s is a 1000 words and it’s. Better than me trying to ask the teacher the question

 

cheers

[spudulike]

On ‎23‎/‎04‎/‎2018 at 23:44, Wonky said:

Umm I guessing I’m a bit late to your porting thread,, but it’s an everlasting/ongoing thread, and I’m learning,  learning lots..   but what you say here is just can’t understand what your sayin, to what I’ve read. Else where,

,I think it’s pprolly time for a picture as it’s is a 1000 words and it’s. Better than me trying to ask the teacher the question

 

cheers

That graph pretty much says it all and is a curve from a relatively modern coil/saw. Earlier than that, the coil had a fixed ignition advance, no "soft" ignition start like on most modern machines so the manufacturer set them to around 27 degrees as a 30 - 34 degree advance would probably break bones on start up!

Two strokes need an ignition that advances rapidly and then falls off mid to high revs unlike a four stroke that advances more and more through the rev range! 

Anyway - the saw is set to just over 30 degrees which is slightly more than a standard 660 - been some time since I did it but that is where I believe it ended up!

[spudulike]

Interesting conversation with one of my customers today. I had recently ported his 395XP, he had taken a big tree down and had a 28" bar on the 395XP and a 30" on the MS880 which was standard. He was somewhat surprised to find the 395 outperforming the 880 with ease on ringing up the same timber - not bad considering the weight and engine CC difference!

It is good to get a bit of feedback as it is rare I get the chance to run the big saws I port through big wood and it gives me good information about the improvements my adjustments make.

[spudulike]

Lets say that someone decided to do a muffler mod on a 560XP but didn't comprehend where the hot gas would end up, this may happen.......

[spudulike]

So....in response he may end up with this......

[spudulike]

The only bit I have done is to modify the baffle plate and spray it black, the rest of it is someone else's work!!!!!

I am calling it "up Periscope"!

Edited March 12, 2019 by spudulike

[htb]

Nice welding, would have been nicer if brazed.

That was a quick disclaimer steve.

I left the spark arrestor screw out on an aftermarket muffler on one of my 346's and had a similar but much smaller hole in the top cover

[spudulike]

Even my Mrs could see something wasn't right....some of the stuff I get in....shocking!

[spudulike]

Just to clarify, none of this "modified" exhaust outlet is mine, I would have preferred doing the job right in the first place! What you see is a bad job being modified further....badly!