the all aussie dribble thread!

[tdi-rick]

Walbro's were run in much the same range, and the ultralight blokes run much the same pop off pressures too.

I have found a reference for somewhere between 15 and 25psi for OPE stuff, they don't seem to really care much.

 

[Terry Syd]

Maybe my testing wasn't up to snuff, don't think so, but could be.

On the other hand, perhaps we need to get some data/tuning principles for chainsaws that we all can use.

My impressions from reading the various threads was that my POP was high. The readings (right or wrong) that I had seem to support that impression. I wish I had more to go on, but unfortunately I don't - there is a paucity of information related to chainsaw carburetion and testing methods.

I'll keep dropping the POP and let everyone know what I experience. - After all, I've still got the stock spring to put back in the carb so nothing is lost in the experiment.

Hmm, although, maybe I might just keep this stuff to myself... never know when I might attend a GTG.

 

[tdi-rick]

[snip]

Hmm, although, maybe I might just keep this stuff to myself... never know when I might attend a GTG.

hahahaha, a racer still.

 

[tdi-rick]

Did I mention that the C3M carby has a casting in the leading edge of the venturi for (what I assume) is for an emulsion/air correction drilling ?
It's aimed straight at the main discharge nozzle and fuel drilling from the HS screw.

 

[Terry Syd]

No you didn't, that sounds like a sophistication reserved to slide carburetors.

It may be a 'mixture correction' circuit that prevents excessive richness from the main discharge nozzle by having having extra air (and less fuel) drawn in through the main circuit as the pressure drops across the venturi - in other words, a flatter fuel delivery as velocity increases through the venturi.

It would be interesting to read what the designers intended.

 

[masculator]

No you didn't, that sounds like a sophistication reserved to slide carburetors.

It may be a 'mixture correction' circuit that prevents excessive richness from the main discharge nozzle by having having extra air (and less fuel) drawn in through the main circuit as the pressure drops across the venturi - in other words, a flatter fuel delivery as velocity increases through the venturi.

It would be interesting to read what the designers intended.

I reckon that you might be better off posting something about this in the general chainsaw forum or the race saw section Terry, I think that more of the guys in the know would see it then! most of us just cut wood and tweek the screws!

 

[Terry Syd]

I tried a thread over at ########, but other than drilling a carb out for alky, nobody had much input. On this site I've asked questions and commented on the topic, but other than Rick, there hasn't been any input. I actually get more information off of the Kart and aircraft forums - and some of the sites they link to. Like you said, seems people just cut wood and tweak screws over here - although you would think some engine builders might be interested and have some input. Or, maybe they just want to keep the information to themselves.

I think I've figured out why some of the changing of metering lever height goes on, but I have to test it.

I'll take your point and won't clog up this thread anymore with a topic that nobody seems to care about.

 

[tdi-rick]

I would have thought here's the ideal spot as only us two are dribbling on about it

I had the die grinder out tonight playing with the carby, I'll post some side by side differences when I'm finished.

 

[tdi-rick]

Terry, you'll tend to find that anyone that posts here is treated with a certain suspicion over there in case info leaks back, so not a lot may be shared at times.
If someone tells me not to share, I'll keep my trap shut, that's just common courtesy, but if I find something and decide to share I'll post it where I damned well please.

 

[masculator]

Terry, you'll tend to find that anyone that posts here is treated with a certain suspicion over there in case info leaks back, so not a lot may be shared at times.
If someone tells me not to share, I'll keep my trap shut, that's just common courtesy, but if I find something and decide to share I'll post it where I damned well please.

That really gets my goat and at the end of the day those who have the information obviously learned it somewhere, be it from trial and error or from someone telling them, I think we should all try to share at least the basics we learn along the way. For the greater good it ensures that the information and technology are not lost and having to be re discovered again later on! Never know sharing may lead to even greater discoveries and realisations!

 

[masculator]

Using my work laptop at the moment cause my PC died the other night while i was trying to put up a post (graphics card poohed itself!)

What I was trying to post was that on the weekend I came to 3 realisations.

the first Is that the MS660 is one hell of a saw!

the second is that the filtration is crap, which we already knew

and finally that there is only one substitute for a big saw.




















A BIGGER SAW!!!!

 

[billyj]

and when that bigger saw isnt big enough?

 

[Terry Syd]

Rick, I guess you and I can continue to dribble on about bits of information we discover. Other Aussies can dribble on about things that interest them. We could have a dribble thread of a dozen different topics going on at the same time.

As far as the metering lever height, as near as I can tell it is primarily used as a way to fine tune the POP pressure. The act of raising the lever decreases the POP a little and lowering it increases it. The other purpose was to increase the reservoir of fuel so that when sudden opening of the throttle drains the metering chamber, there is an adequate reserve on hand to keep from bogging.

The static POP is what we can test and re-set, however, there is the running POP which varies with a number of things, such as the local air pressure. That's why you see Karters re-setting the POP for different tracks at different altitudes or a change in barometric pressure. Essentially, you have pump pressure of say 7-8 lbs working on the metering needle and the local barometric pressure working on the diaphragm.

It's raining agan here, so maybe in a couple of days I'll get to test the saw. I'll keep changing the POP until I think I have a better running engine. Then I can put the stock spring back in as a control and see if I'm just fooling myself.

 

[masculator]

and when that bigger saw isnt big enough?

build a bigger one!

 

[tdi-rick]

That really gets my goat and at the end of the day those who have the information obviously learned it somewhere, be it from trial and error or from someone telling them, I think we should all try to share at least the basics we learn along the way. For the greater good it ensures that the information and technology are not lost and having to be re discovered again later on! Never know sharing may lead to even greater discoveries and realisations!

I understand where the reluctance to share too much comes from, I was a hard core racer once, any gains came at a high cost in both time and money but there were certain 'general' things that I'd happily pass on to anyone as I suppose I had enough arrogance and ego to think I could outdo my competitors anyway, but there are still a couple of things I learned that are still 'secret', if only because I haven't been near a race track or race workshop in something like twelve years

Back them, some of my peers wouldn't pass on anything, not one skerrick of info to anyone, including the newbies as they were all a potential threat on track and off to the established 'guru's'.
There's also the point that some people do blab badly, a tweak that may have taken years to evolve can be lost to the opposition quickly with an indiscreet slip of the tongue, but what we are mainly discussing here is pretty general in nature, not any specific numbers, more sign posts pointing a direction rather than map co-ordinates.

 

[masculator]

Rick, I guess you and I can continue to dribble on about bits of information we discover. Other Aussies can dribble on about things that interest them. We could have a dribble thread of a dozen different topics going on at the same time.

As far as the metering lever height, as near as I can tell it is primarily used as a way to fine tune the POP pressure. The act of raising the lever decreases the POP a little and lowering it increases it. The other purpose was to increase the reservoir of fuel so that when sudden opening of the throttle drains the metering chamber, there is an adequate reserve on hand to keep from bogging.

The static POP is what we can test and re-set, however, there is the running POP which varies with a number of things, such as the local air pressure. That's why you see Karters re-setting the POP for different tracks at different altitudes or a change in barometric pressure. Essentially, you have pump pressure of say 7-8 lbs working on the metering needle and the local barometric pressure working on the diaphragm.

It's raining agan here, so maybe in a couple of days I'll get to test the saw. I'll keep changing the POP until I think I have a better running engine. Then I can put the stock spring back in as a control and see if I'm just fooling myself.

Yes you could but I think that what you guys are discussing would be worth creating a thread of its own for. It would make it less disjointed and easier for interested people to follow. And I guarantee that there would be guys out there interested in this that are not coming into this thread. I for one find am finding it interesting, and would even more so if it was strung together.

 

[masculator]

I understand where the reluctance to share too much comes from, I was a hard core racer once, any gains came at a high cost in both time and money but there were certain 'general' things that I'd happily pass on to anyone as I suppose I had enough arrogance and ego to think I could outdo my competitors anyway, but there are still a couple of things I learned that are still 'secret', if only because I haven't been near a race track or race workshop in something like twelve years

Back them, some of my peers wouldn't pass on anything, not one skerrick of info to anyone, including the newbies as they were all a potential threat on track and off to the established 'guru's'.
There's also the point that some people do blab badly, a tweak that may have taken years to evolve can be lost to the opposition quickly with an indiscreet slip of the tongue, but what we are mainly discussing here is pretty general in nature, not any specific numbers, more sign posts pointing a direction rather than map co-ordinates.

Exactly so surely they could say "yes if you widen your ports you can use a stiffer or softer spring...etc.etc." some things could be made to benefit the greater good if from that someone has the knowledge to work out even finer nuances good on them!

 

[tdi-rick]

[snip]

As far as the metering lever height, as near as I can tell it is primarily used as a way to fine tune the POP pressure. The act of raising the lever decreases the POP a little and lowering it increases it. The other purpose was to increase the reservoir of fuel so that when sudden opening of the throttle drains the metering chamber, there is an adequate reserve on hand to keep from bogging.

[snip]

That's the way I've always looked at the lever height, rightly or wrongly, the alteration in pop off pressure was secondary to the fuel volume available.

 

[Terry Syd]

Looks like Rusty has started a thread on tuning carbs with modded engines -

http://www.arboristsite.com/chainsaw/175400.htm

It will be interesting to see who jumps in help out and what information is given.

 

[tdi-rick]

[snip]

The static POP is what we can test and re-set, however, there is the running POP which varies with a number of things, such as the local air pressure. That's why you see Karters re-setting the POP for different tracks at different altitudes or a change in barometric pressure. Essentially, you have pump pressure of say 7-8 lbs working on the metering needle and the local barometric pressure working on the diaphragm.

[snip]

Funnily enough my old kart engine builder back in the mid-late eighties hardly touched the pop off, we'd just check it occasionally to make sure it was still ok.
His son, my team mate was a multiple state/national junior champion and we'd race one weekend at Oran Park and the next at Orange, a difference in altitude of 2500' and I never once recall Col altering the pop off to suit the track, but maybe he was leaving something on the table ?