2 cycle carburetor Adjustments

[Bill Bob]

I have been told that a basic adjustment to the high and low speed screws on most 2 cycle engines is close both and open both about 1 1/2 turns to get it running, then adjust a little either way for optimum on both.  I'm workng on Ryobi string trimmer along with "Huskey" chain saw and will need a starting point.  Any advice out there?
Bill

[jteneyck]

Most carbs have at least the manufacturer's name on one of the end caps.  The model number is often cast into it somewhere, although sometimes it's underneath one of those caps.  With those two pieces of info. you can usually find the service manual for it on the internet. 

Most Walbro carbs are 1-1/4 turns open.  Your Husky saw might have a Walbro carb. 

John

[Bill Bob]

Adjust the idle before H and L??  Rather difficult to adjust that when you cannot start. 
bill

[jteneyck]

It'll start, or not, regardless of the idle adjust.  Either hold the throttle open or set the idle really high.  When, if it starts, let it warm up before adjusting the H/L screws away from the initial settings.  The manual will tell you how to adjust them properly.  Often, you have to set the idle high to do the tuning.  After you've done that, you turn the L speed screw more open.  The speed will increase, then decrease.  Note the settings.  Then turn it more closed and do the same.  The optimum setting is half way between where the speed begins to fall of in both directions.  To adjust the H speed screw pull the throttle wide open, then close the screw until it starts to reduce speed.  Now open the screw until it starts to 4-cycle.  That's the correct setting.  That's lean enough for good power and rich enough not to burn up the piston.  Better to be too rich, if anything.  After you're satisfied with how it runs, reset the idle screw where it should be and you're done. Again, make sure the engine is warm before doing the tuning.

Separate but related topic, you'll have less trouble with 2 cycle carbs if you use Stabil or 2 cycle oil with stabilizers in it.  I use Stihl pure synthetic.  Also, if you can get gas without ethanol in it you'll have far fewer problems.  Finally, at the end of the season, dump out the gas that's in the tank and run it dry (at low speed).  

I used to rebuild carbs when they eventually needed new diaphragms, etc., but the last time I bought a rebuild kit it was around $12 and a whole new carb was $18.  OK, not an OE carb, but it is an exact clone, installed in minutes, and the trimmer runs like new now.  Of course I had to tune it though, but that was all of 5 minutes.  

John

[Bill Bob]

OK,  thanks
Bill

[JosephP]

You adjust the idle before the H or L.

Are you saying you can't get the engine running at all?

[Snipe Hunter]

Be careful with 2 stroke carb adjustments. Just because you got it running well, that doesn't mean it's running right. Sometimes people tend to lean out carbs too much to keep it from stalling and that makes it burn hot. You can easily burn a hole in the piston adjusting carbs too lean. Particularly in an air cooled engine. If you can find a manual with operating adjustments, it would sure help by establishing a proper starting point.

[EricU]

what sorts of problems does a new carb fix?  My Poulan is getting on in years, and when it runs, it runs fine.  Little bit hard to start.

[jteneyck]

Sometimes varnish builds up inside the carb, and even soaking it in carb. cleaner doesn't remove it  At least I've been unsuccessful a few times.  But if yours runs fine at times, and not at other times, I'd guess you have a different problem.  Have you changed the fuel lines and filter?  Are you sure the fuel tank vent is venting?  Are the bolts tight that hold it to the engine body?

John

[tomsteve]

on the chainsaw, yer gonna want to have it adjusted so its 4 stroking .
heres a little bit on it


http://www.arboristsite.com/community/th...ng.118016/