New member new saw

[pinhead]

Thanks for taking the time to reply 

Yes the saw does behave just like it always did with the original pot on before it died (possibly my fault trying too hard with tuning to make it right possibly split fuel pipe) that is why I think it could be something else 

The 251 is basicaly a brand new saw if its had 5 tanks through it I would be surprised yes I think it runs a bit rich too its as it came from the factory 

The chain on my saw is as new and the saw was the same when it was new untouched i have probably sharpened it a couple of times thats all 

I did try and compression test but the tester had been repaired with a jubilee clip instead of the proper swaged end and wouldn't hold over 90 psi 

I have bought a new tester but won t be able to test until next weekend as I am away 

On another note I have just bought a 036 for £100 supposed to be perfect runner I checked eBay and it had just been listed with that as bin so I clicked it before anyone else could think it was lucky timing or I may have another problem saw lol

[spudulike]

I missed the fact that both pots have ended up with the same issues as the thread has been going on so long and it is also damn difficult to compare two saws performance on a vid where the camera falls over. A couple of things to try - have you tried a new plug? I always thought it not worth it but have had a few bits of kit in recently with plug issues.

The other one is that often the kill wire can wear on the top AV mount (the one that screws in to the air box) and cause the saw to misfire when it earths on the metal washer on the mount.

The issue here is that you may spend out on an OEM pot and find the thing still isn't right due to a simple issue - it may be a coil breaking down - they can sometimes act like a rev limiter kicking in early!

Just read the thread again - if the gauze strainer filled and stopped the saw working well, the fuel tank probably has pulp debris in it and it will need flushing out until 100% clean. The split fuel line will have helped fill the carb with crap. The fuel filter doesn't always take out all the crap in the tank so check again and make sure the strainer comes out completely and is inspected with a magnifying glass.

Have you checked the flywheel to coil gap? That may knock off a fair bit of performance! Is the oiler working OK? Had many saws in "Lacking Performance" only to find faulty oilers!

Good luck with the new saw.

[pinhead]

The oiler seems spot on i have set it on high output and it does send plenty out 

 

The tank was cleaned while it was off it may not be surgically clean but it wasn't bad 

The carb has been apart again a few times to check things and looks clean still 

I have noticed some wear on the wires but they don't look like the insulation is breached and when I put the coil back on I gapped it with a business card 

 

You may have something with the coil as my tach kept acting weird with fluctuating no.s I just put it down to me not wrapping the induction wire very well on the HT lead as I could get steady reading some times 

[bmp01]

You might get some weird numbers at max rpm even without a limiting coil - if the saw is 4 stroking the real rpm will be all over the place anyway. But upto 10000 (let's say) rpm should be pretty stable. 

With the age of saw it's quite possible the spark plug lead is past its best too. Expect you can you change the lead by itself on this coil.

Thing is, from your video sound track it didn't sound like there were misfires during the cut, just low power....

What about spark advance - i don't know if these coils have an advance curve built in or fixed timing but a retarded spark would considerably reduce power.  Same would happen if the flywheel has lost its timing or been messed with. 

[spudulike]

The 026 coil in NOT limited, the thing should spin up to silly revs if allowed to. It may be worth starting at a lowly 10krpm, rev the saw up, get the tach counting and wind the screw in and see where or if it goes loopy. Only limited coils will bounce all over the shop, an unlimited coil will hold revs and the tach will display them.

Is the coil OEM? Some Chinese coils are pretty shyte and that is being polite!

You can do a rough test on HT integrity by taking an old plug and opening up the electrode gap to 5-7mm and seeing if it still sparks OK - it should be able to jump that sort of distance.

 

[bmp01]

3 hours ago, spudulike said:

The 026 coil in NOT limited, the thing should spin up to silly revs if allowed to. It may be worth starting at a lowly 10krpm, rev the saw up, get the tach counting and wind the screw in and see where or if it goes loopy. Only limited coils will bounce all over the shop, an unlimited coil will hold revs and the tach will display them.

 

Yeah you're right, my comment was incorrect,  my intention was to keep away from max rpm while checking the coil (to avoid any misleading behaviour) which is still the right approach I think. 

Worth noting: In and out of 4 stroking due to fuel mixture does cause engine speed to oscillate somewhat but with an electronic tach which averages several revolutions you get a sensible speed reading. Compare that with an rpm limited coil dishing out spark cuts, counting sparks with electronic tach to determine rpm just don't work.  (Ironically though,  the engine speed is precisely controlled by the electronics at that stage and the mechanical bits are seeing a constant rpm ).

Spud - any idea if the 024 coil has an advance curve in it or fixed timing? 

 

[spudulike]

I am not sure on the 024, I would think that there is an advance on a saw that late. One way of telling is to line up the coil with the magnet, take the top cover off, paint one of the top flywheel fins and then use a Xeon strobe on the thing and rev from idle and it should stay static if the ignition is fixed.

Simple eh

[bmp01]

45 minutes ago, spudulike said:

I am not sure on the 024, I would think that there is an advance on a saw that late. One way of telling is to line up the coil with the magnet, take the top cover off, paint one of the top flywheel fins and then use a Xeon strobe on the thing and rev from idle and it should stay static if the ignition is fixed.

Simple eh

Pretty straight forward..... takes me back to the days of setting the timing by rotating the distributor back and forth. .. remember them ???

Back to the present,  that strobe test would be worth while. But you need to know what the spark advance should be in the first place before you can draw any conclusion. 

 

[spudulike]

Grew up with contact breakers and distributors!

The question was to find out if a coil has different levels of advance and if the spark moves when you rev the engine then it proves there are different levels of advance present.

Advance would typically be around 26 degrees before TDC.

It would be relatively simple to put a timing wheel on the saw and produce a graduated scale to run over the top of the flywheel and then line up the white fin on TDC with Zero on the scale so when you start the saw, you will be able to read off the advance using the strobe, the white fin and the graduated scale. It should start at near zero and go to around 26 at 9500rpm and then retard a bit flat out - typical two stroke advance.

[bmp01]

Ok, that's it then, sorted.  Quicker and easier to do  -  than to explain it ..... again.