New CS352--tuning and muffler mod advise

[spudulike]

Excerpt from Graham Bells Two Stroke Tuning Book -

My experience has shown that the more oil you pour into a two-stroke, the harder

it runs. Just how much you should pour in depends on several factors, but it usually

works out that the longer you hold the throttle wide open, the more oil you should use.

[difflock]

Spud, is the above quote not putting the cart before the horse?

Or rather to run a saw hard and hot, more lubrication is probably advisable?

And/Or to burn the excess lubrication oil, the saw needs to be worked hard and hot?

I know nowt about 2 stroke tuning btw!

mth

[spudulike]

The excerpt is primarily about two stroke racing bikes but chainsaws are either running flat out or on idle and partial throttle is rarely used so there are many similarities.

Two strokes like to be flat out as it allows the engine to work more efficiently and allows the heat to burn off the deposits the oil may otherwise produce.

The excerpt is from a 1983 book but was added to in 1999 - some tech has changed but it remains a good read.

I have yet to find any documented technical info that says a higher two stroke oil content in two stroke fuel creates more heat in the engine!

[lurkalot]

2 hours ago, spudulike said:

I am interested in this and may use a 50:1 and 20:1 in my saw and take a thermal reading off the cylinder top and see what really gives as I really don't see an over oily petrol mix allowing an engine to create too much heat as in my opinion, right or wrong, too much oil just stops an engine revving and makes it smoke.

I'd be interested in your findings too.   I can't see why a engine with too much oil wouldn't rev, it should have the opposite effect, it should run lean and over rev.  Example, a two stroke tuned to run on 50-1 and filled with 32-1 will run leaner.  Tuned to 32-1, and filled with 50-1 should run richer.

 

A few years of racing motocross bikes taught me that.  

[Echo]

5 hours ago, spudulike said:

Have you ever experienced anyone seizing a saw through too much oil? In my experience, saws running too much oil generally don't rev properly and smoke like a pope has been voted in. I have found this over oiling mostly on home owner or farmer saws and have never shown signs of getting overly hot - most have oily deposits around the muffler and often have an oily residue in the carb.

Personally I don't see over oiling seizing a saw but do mostly see seizure through old fuel, straight petrol, air leaks and poor carb adjustment.

No oil in the fuel creates friction, creating heat and piston meltdown and too much air makes a saw over rev making too much heat thus melting the piston!

I am interested in this and may use a 50:1 and 20:1 in my saw and take a thermal reading off the cylinder top and see what really gives as I really don't see an over oily petrol mix allowing an engine to create too much heat as in my opinion, right or wrong, too much oil just stops an engine revving and makes it smoke.

Had this on another thread and interested to substantiate and prove the fact!

 

I have a 40 year old stihl 041, it has had every conceivable mix run through it,

engine oil used, oil for two stroke boats, cheap oil, it actually never seen any of

what is now considered to be good oil, and as regards ratio, very little attention

other than always over doing it, and that saw has never been opened, and still

runs, the odd time it smoked with the various mix ratios, it got its carb adjusted

a year ago after I saw my father pouring fuel into the carb to start it, it was like

this for 4 years, a slight turn on the L and it never needed another cap of fuel to

start it.

But these modern saws, with probably tighter fit, and these cats are more

particular, I would not like to treat one of the newbies like that old stihl.

I find this 352 a good saw for its size, it has done some weird things on me,

I ran it again, and it has now got rid of the junk on the piston top, unbelievable,

am beginning to think the oil in the mix is not the best choice for this saw, in that it

seems to have too much body. I would like to richen it up mix a bit to get it to idle perfect,

but as soon as I do, it starts to blacken the plug more than I like, (soot not oil).  Since the dealer leaned

the H, it takes an extra pull to start it, and nearly always two pulls if it sits five minutes

outside, this points to lean, but the dam thing is not, the tiniest screw on the L causes

black plug in no time, the H seems to tolerate riching up better. When the dealers new

tach arrives I will see what the rpm is like, for now it is at least cutting and seems to handle the revs it currently pulling.

Would love to get the idle right without sooting up the plug, that bugs me, as does the

extra pull to start it, am adamant not to let it soot up, and seem to have hit a wall with

any adjustments to the L making it do so.

Edited March 8, 2019 by Echo

[Echo]

I read that two stroke tuners paper, and others, and to cut a long story short,

more oil is generally better than too little.

Oil serves many purposes, it creates a better seal between the ring and piston,

it lubes, and it removes heat from the engine, by providing less friction and going out

the exhaust taking the heat it absorbed with it.

Some engines handle oil better than others, some tests were done on a Suzuki

bike engine on a dyno, at 15:1 20:1 and 30:1, each time the engine was tuned to put

the exact same amount of fuel through it taking into account the added flow required

to carry along the various differing amounts of oil mixed in it, the engine did great with

20:1 which Suzuki already specified from their tests, 15:1 came second, with 30:1

responsible for scoring the cylinder, 30:1 was tested second place, and resulted in

a new piston being required,  15:1 produced the most power and ran the coolest even

though it was running the barrel the 30:1 marked,

20:1 was the second most powerful setup, and again was cooler than  the 30:1

test that produced the scoring, and slightly hotter than the 15:1 mix which ran the coolest and produced the most power.

 

You can use more oil to provide better lubrication, but the engine still has to get the

correct volume of fuel to run properly, easy enough to achieve as long as some genius

does not slap a cat on your exhaust, to stop the flow of things, this essentially does away with the prospect of using more oil to both lube better and carry off heat.

 

Edited March 8, 2019 by Echo

[Echo]

12 hours ago, lurkalot said:

I'd be interested in your findings too.   I can't see why a engine with too much oil wouldn't rev, it should have the opposite effect, it should run lean and over rev.  Example, a two stroke tuned to run on 50-1 and filled with 32-1 will run leaner.  Tuned to 32-1, and filled with 50-1 should run richer.

 

A few years of racing motocross bikes taught me that.  

The adjustment you have to make from running 50:1 and going to 32:1 wont be

a big one, your going from 2% oil to 3.25 % oil, given your engine is tuned to start with, 

thats only 1.125 % of a difference, so if your engine was tuned slightly rich, then it would even cope without adjustment. though it would be the right thing to do a slight adjustment to keep things right.

But oil and cats do not work well together, heat from the escaping oil

meeting a hot cat, I just don't think the cat will remain clean for long, without a cat you stand a far better chance in every way, cooler and more lubricated engine.

Edited March 8, 2019 by Echo

[spudulike]

23 hours ago, lurkalot said:

I'd be interested in your findings too.   I can't see why a engine with too much oil wouldn't rev, it should have the opposite effect, it should run lean and over rev.  Example, a two stroke tuned to run on 50-1 and filled with 32-1 will run leaner.  Tuned to 32-1, and filled with 50-1 should run richer.

 

A few years of racing motocross bikes taught me that.  

So are we saying say a 10:1 mix will make an engine over rev and seize being lean...I would propose it would smoke, run with poor performance and foul the plug....wouldn't it? I don't get it and not having a go, just don't see the logic!

[Ratman]

Over oiling (imo) would not help ring / piston to seal better but to eventually aid in glazing the bore resulting in poor performance, sticking rings (from emulsified oil/carbon)

 

To increase oil amount would mean increasing air/fuel ratios to compensate and keep up with performance??? I’m not following [emoji848]

I say if recommendations are 25:1 30:1 50:1 whatever.... then live by it but just use the highest quality oils available to aid it. ?‍♂️

 

[spudulike]

I measure the petrol:oil to be between 45:1 and 50:1 on my mix as I find a number of saws come in with no significant reason to seize and can only put it down to slight over revving, slight mistake in mixing oil and perhaps a tiny air leak so a number of very insignificant issues making a big issue. My thinking is that a slight over egging on oil will help keep an engine protected more than perhaps making a slight mistake on the mix and risking seize.

I wonder how accurate many mixes people use actually are!