Let's Talk 262 Timing and Performance

[drf256]

Now that we've learned or become confused by the transfer thread, let's talk about the Husqvarna 262 model and timing. Any performance mod can and should be discussed here, as they are all interdependent with the timing of the jug.

I feel that discussing individual models will help us gain knowledge that can be used across a wide range of saws. I also plan on starting threads on other models, it would aid with the search function and overall forum exposure through google searches.

So now for the coveted 262....

 

[drf256]

The 262 was supposedly derived from putting 60cc of displacement on a 50cc series frame.

I'm no sure if anyone has info on case volume. Does any reference exist for this?

I could be off, but it should have a tight small case if real estate was tough to find in this model.

Factory numbers are around 103 exhaust (154 duration), 115 transfers (130 dur), 69 intake (138 dur).

 

[drf256]

So we have small case volume, a nice high intake and very low factory blowdown.

Why was this done? With the high transfer duration, one would expect the loop scavenged charge to be pushed right out of the cylinder. But the 262 has a very restrictive muffler. That tiny hole under the deflector (?1/2") with a tightly woven screen over it.

I'd postulate that the saw would become a fuel hog if you did nothing but open the muffler up a bit.

 

[drf256]

Onto the intake. Why 69*?

That's 16* less intake than exhaust. One would expect a large carburetor would feed the engine better with less time/area. The intake is relatively wide from the factory though. Much wider than any Stihl jug I've seen.

I'm wondering if the move from the 87 carb to the smaller bore 120 was the factory fix for pollution. Flowing less air would prevent the higher transfers from ejecting more unburned charge out of the exhaust port. The charge in the case would be less.

This model just feels undercarbed to me. More so than other saws I've tinkered with.

The one I built was a bit rpm challenged. More than one would think with these jug numbers.

 

[drf256]

So hopefully we can have a meaningful discussion about this model.

Muffler mods, carb mods, ignition timing mods, port and chamber mods, etc....

No question or answer too dumb.

We are the OPEforum now. Free discussion without argument.

If you don't like the idea of this thread, stay out of it.

 

[Deets066]

Damn huskies

 

[paragonbuilder]

I'll be tearing into one soon! I'm looking forward to this thread!!


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[Simondo]

So we have small case volume, a nice high intake and very low factory blowdown.

Why was this done? With the high transfer duration, one would expect the loop scavenged charge to be pushed right out of the cylinder. But the 262 has a very restrictive muffler. That tiny hole under the deflector (?1/2") with a tightly woven screen over it.

I'd postulate that the saw would become a fuel hog if you did nothing but open the muffler up a bit.

I have a 1992 ..262 with a KS cylinder and the HDA 87 carb on it. The standard muffler un the UK would appear to be slightly different from what you mentioned as it has a tube outlet 11mm aprox Diameter (looking from front..top left) and no spark screen. Internally it has a crinkle side tube feeding that tube outlet.
Mine has a muffler mod now with the crinkle tube removed and a 70-80% of exhaust port ratio stub tube outlet of 19 mm .

 

[Mastermind]

Not all the 262 jugs will have such a high transfer port.....as a matter of fact, that jug is pretty rare. Normally, they are about 120° on the transfers.

On the intake and exhaust ports.....

They are the same across the years.

 

[Simondo]

Not all the 262 jugs will have such a high transfer port.....as a matter of fact, that jug is pretty rare. Normally, they are about 120° on the transfers.

On the intake and exhaust ports.....

They are the same across the years.

Were you referring to the KS cylinder being rare ?

 

[Mastermind]

Not all KS jugs are the same....

Out of dozens I've mapped, only one had transfers as high as Al's jug.

 

[paragonbuilder]

Not all KS jugs are the same....

Out of dozens I've mapped, only one had transfers as high as Al's jug.

Wonder why?
Are they stronger stock than the others?


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[jmssaws]

I would think the higher ones would run better

 

[Mastermind]

I feel so dirty now......


I went over to AS and found my 262 thread..

"OK, I've checked the timing numbers. Stock Mahle jug, with a base gasket.

EX: 103.5
TR: 116
IN: 69

That means we have only 12.5 degrees of blowdown. Cool huh? 

Case compression angle is 47 degrees.

No wonder these saws are factory hotrods."

The one jug I posted about was the one with the highest transfers.

I remember checking several more after that.......

 

[jmssaws]

12.5 degrees of blow down! Me likey

 

[drf256]

12.5 degrees of blow down! Me likey

So will the gas station if you open the muffler with that much case compression.

 

[drf256]

I feel so dirty now......


I went over to AS and found my 262 thread..

"OK, I've checked the timing numbers. Stock Mahle jug, with a base gasket.

EX: 103.5
TR: 116
IN: 69

That means we have only 12.5 degrees of blowdown. Cool huh? 

Case compression angle is 47 degrees.

No wonder these saws are factory hotrods."

The one jug I posted about was the one with the highest transfers.

I remember checking several more after that.......

IIRC, the base gasket is like .032 on these saws.

Dropping the jug that much can move the transfers quite a bit with no other machine work

 

[exSW]

Keep talking I have two of these. HDA 120 and Mahle jugs.

 

[jmssaws]

So will the gas station if you open the muffler with that much case compression.

I'm not looking for fuel economy.

 

[jmssaws]

All you can do is raise the exhaust and I wouldn't do that.