lack of chain speed/ power

[nuggsy]

i have a komatsu zenoah 621, its a 62 cc saw and i think it could be nearly 9 year old.

i have ported the saw which made a difference, the sparkplug is the cookie brown like it should be but it still seems to lack a bit of oomph so if anyone has any ideas that i could try (cheap) then it would be greatly appreciated.

the saw only cost me 50 quid so if its a case of run it till its dead thats what i shall do lol but obviously i want to get a year out of it so only 10 months to go ha ha

[skyhuck]

You could change the drive sprocket to increase chain speed, but you may find this makes the lack of power worse.

[geoff]

does it reach max revs under mild load? if not check throttle linkage/carb opening full for a start.

[evo0001]

Take the exhaust off and have a look at the piston for any scoring and if the chain is slack is there much resistance when you pull it round sound like it could have some crap around the crank clutch area draging

[nuggsy]

carb could be an option, i had to modify the linkage arm slightly when i first got the saw as it wasnt returning properly due to is being over long. it hits max revs but it just doesnt seem cut like it should, had it in running against a 341, simeler sized saw etc and it was pissing all over my saw lol, had the clutch out and there doesnt seem to be any problems there although it could do with a grease up. i had to change the feuling slightly aswell as it wasnt idling properly, seems to cut out when its hot or when the chain brake is applied, resistance maybe ? cleaned the air filter out also but it could be cleaner so possible new air filter aswell ?

looked at new drive sprockets yesterday but the company didnt have the small centered 1 in stock so i have replaced the old for a new standard 1 with small center

Edited June 10, 2009 by nuggsy

[Al Smith]

I can't say much about the saw because I've never heard of one let alone even seen one .

 

That said more times than not a restictive muffler will hinder greatly the engines ability to produce power and speed .

 

In this part of the world we just gut the mufflers and retune the carbs .

 

Oh,if that thing has a fixed jet carb,that could be a problem also .

[Al Smith]

I can't say much about the saw because I've never heard of one let alone even seen one .

 

That said more times than not a restrictive muffler will hinder greatly the engines ability to produce power and speed .

 

In this part of the world we just gut the mufflers and retune the carbs .

 

Oh,if that thing has a fixed jet carb,that could be a problem also .

[coolie]

The first things I would look at are

1 Make sure throttle valve fully opens.

2 Low and High speed mixture adjustments.(first,your 2 stroke mix)

3 Check muffler is not coked up or air filter is not clogged(run without filter)

4 Rings(compression)

5 Is there a lower ratio sprocket available(if you are running a longish bar),or a higher ratio sprocket,which will increase chain speed at the cost of torque.(if you are running a shortish bar)

Edited June 10, 2009 by coolie
spelling

[nuggsy]

they are basicly a cheap husqy saw, good wee saw like, air filter has been cleaned and the muffler has been ported but im gonna strip it down again 2night and make sure ive not missed anything, maybe the muffler mod isnt done correctly ?

[nuggsy]

ok popped into my local small engines clinic and he gave me a list of things to do, strip carb out and down to clean, put high n low screws back in and turn bk out 1 full rotation and wind the idle screw right in. done all this and mucked about with it for a bit n it was fine, then it changed its mind n started to rev higher, ive checked the piston and all looks fairly well in there, no pitting but some slight scratching on the outlet side but only for like a 10mm section then the rest is fine, its also cutting out after idling for abt 5 mins.

 

any ideas ? oh and ive re cleaned the air filter with petrol this time instead of warm soapy water which took a fair bit out again