Stihl compensator Intellicarb caused lean scoring?

[cambl]

Working on a MS460 that had a very dirty air filter with fine sawdust packed in. An extreme case. The piston is scored on both sides of the exh port but not seized tight.

The compensator carb on these saws leans out the mixture as the filter gets dirty, so is it possible that that the metering diaphragm was just barely moving and caused a very lean condition? That is my theory. User saws he was in a big log running it hard when it happened.

 

[blsnelling]

Highly unlikely, IMHO.

 

[HuskStihl]

Isn't "intellicarb" just a rubber tube?

 

[Chris-PA]

Isn't "intellicarb" just a rubber tube?

It's a very smart tube.

 

[blsnelling]

Isn't "intellicarb" just a rubber tube?

Instead of the metering diaphragm just having a hole in it like normal, that hole is connected to air inside the air filter.

 

[HarleyT]

Working on a MS460 that had a very dirty air filter with fine sawdust packed in. An extreme case. The piston is scored on both sides of the exh port but not seized tight.

The compensator carb on these saws leans out the mixture as the filter gets dirty, so is it possible that that the metering diaphragm was just barely moving and caused a very lean condition? That is my theory. User saws he was in a big log running it hard when it happened.

Does the guy like to fiddle with his carb adjustmewnts?

 

[cambl]

Does the guy like to fiddle with his carb adjustments?

No I don't think so.

 

[pioneerguy600]

Does the guy like to fiddle with his carb adjustmewnts?

Most likely scenario right there.

 

[tickhound93]

What pioneer guy said, maybe. If the filter was packed tight with dust, were the cylinder fins also full of dust? Something to consider. Also you said both sides of exhaust port were scored, well 2 sides if a circle (bare with me) at roughly 90 degrees to each other may yield same scoring on intake side= 4 corner seizure. Saw got hot too fast.

 

[Spectre468]

Doesn't Intellicarb make the saw run richer as the air "leans out", ie packed air filter?

 

[Justsaws]

Working on a MS460 that had a very dirty air filter with fine sawdust packed in. An extreme case. The piston is scored on both sides of the exh port but not seized tight.

The compensator carb on these saws leans out the mixture as the filter gets dirty, so is it possible that that the metering diaphragm was just barely moving and caused a very lean condition? That is my theory. User saws he was in a big log running it hard when it happened.

Grab an intella carbed saw and block of the air filter while it is running, use tape, do it in stages. When it stops running check out the piston. Then without changing the taped air filter, get it running and keep it running, this will cause damage, so use an appropriate saw.

 

[pioneerguy600]

I have yet to see a chainsaw engine spool up if it cannot get air. I have seen saws come in with airfilters so packed up with dust that they couldn`t get past 3,000 rpm, did an 026 this week exactly like that. I doubt that the airfilter was ever cleaned but the piston still had its machining marks on it. Lean condition usually scores up just the exhaust side of a piston but a lean condition coupled with a poor filter can score both sides. Running a saw on straight gas can score both sides of the piston if the saw is not being pushed really hard, if the saw is being loaded heavy at the time of straight gassing the piston swells very quickly and usually seizes in the bore sticking the rings, many times there will not be scoring on the intake side.

 

[lone wolf]

Working on a MS460 that had a very dirty air filter with fine sawdust packed in. An extreme case. The piston is scored on both sides of the exh port but not seized tight.

The compensator carb on these saws leans out the mixture as the filter gets dirty, so is it possible that that the metering diaphragm was just barely moving and caused a very lean condition? That is my theory. User saws he was in a big log running it hard when it happened.

Pics would help diagnose.

 

[Chris-PA]

In theory Intellicarb could cause leaning, but in practice I'm skeptical.

The theory part: Chainsaws carbs deliver a much richer mixture as air velocity increases through the carb. If you reduce air velocity from the point you tuned it at the mixture gets a bit leaner (pushing harder, etc). Conversely, a very clogged filter acts like choke and makes the mixture richer, but reduces air velocity which tends to make the mixture leaner. The two effects somewhat balance each other out.

With Intellicarb the blocked air filter does not enrich the mixture as much, but it still reduces air flow which leans the mixture some. The two effects don't counteract each other any more. Maybe if the mixture was borderline lean to begin with, then a clogged filter would reduce air flow (velocity) and lean the mixture further.


The practice part: Intellicarb is nothing more than a diaphragm vent placed downstream of the air filter like almost every other carb in the world does (other than a lot of all position carbs). It's effectively exactly the same as on my McCinderblock where the entire carb is placed in a sealed box below the air filter, which was done on lots of older older saws. I wasn't into chainsaws when these were popular, but if they didn't have known issues with it then it's unlikely to be a problem in practice.

 

[cambl]

In theory Intellicarb could cause leaning, but in practice I'm skeptical.

The theory part: Chainsaws carbs deliver a much richer mixture as air velocity increases through the carb. If you reduce air velocity from the point you tuned it at the mixture gets a bit leaner (pushing harder, etc). Conversely, a very clogged filter acts like choke and makes the mixture richer, but reduces air velocity which tends to make the mixture leaner. The two effects somewhat balance each other out.

With Intellicarb the blocked air filter does not enrich the mixture as much, but it still reduces air flow which leans the mixture some. The two effects don't counteract each other any more. Maybe if the mixture was borderline lean to begin with, then a clogged filter would reduce air flow (velocity) and lean the mixture further.


The practice part: Intellicarb is nothing more than a diaphragm vent placed downstream of the air filter like almost every other carb in the world does (other than a lot of all position carbs). It's effectively exactly the same as on my McCinderblock where the entire carb is placed in a sealed box below the air filter, which was done on lots of older older saws. I wasn't into chainsaws when these were popular, but if they didn't have known issues with it then it's unlikely to be a problem in practice.

Makes sense to me. I'll dig in a little more and see what else I can find.

 

[Justsaws]

Just cause it's not reving up does not mean it won't keep getting used. It is amazing the amount of attention and money sent on bar oils and mix oils compared to what people do to air filters. The intella card system works well but is not people proof. I picked up a 460 with extra holes drilled through the top of the air filter, not the cover the actual air filter, big ones, presumably for the extra power that extra holes in everything makes.

 

[lone wolf]

Just cause it's not reving up does not mean it won't keep getting used. It is amazing the amount of attention and money sent on bar oils and mix oils compared to what people do to air filters. The intella card system works well but is not people proof. I picked up a 460 with extra holes drilled through the top of the air filter, not the cover the actual air filter, big ones, presumably for the extra power that extra holes in everything makes.

I dont think it does anything for performance at all.

 

[Philbert]

Could the scoring be caused by ingesting saw dust if the filter is that plugged?

Someone posted a STIHL failure diagnoses book, on another site, and a lot of the failures were attributed to dirt, water, even snow (!) sucked into the cylinder.


Philbert

 

[SteveSr]

Someone posted a STIHL failure diagnoses book, on another site, and a lot of the failures were attributed to dirt, water, even snow (!) sucked into the cylinder.
Philbert

Could you share the link to that book?

 

[Philbert]

Could you share the link to that book?

Sorry, competitive site - not allowed. Maybe it would show up in a search.

Philbrt