Chainsaws and carburetors

[dpuckett]

My girlfriend's grandpa gave us a pair of old (70s) ECHO 701 chainsaws in return for clearing out the trees and brush aroudn his farm from the ice storm last week. I got one to run fine, and the other wouldnt idle, or rev up very high. I figure they need a carb kit, but got to reading on some forums that the H and L screws will change the air/ fuel ratio (carburetors are waayy over my head, and tick me off any time I mess with them beyond starting and running. How they even atomize the fuel is beyond me), and how they run. I got the one to idle, and the other just wont start. I ran the first one out of gas, filled it back up and it wont start. It sounds like it may want to start and run, then changes its mind. The owner's manual is no help- it says to run the screws all the way in and turn the adjusting screw out 1 turn for low speed operation, and 3/4 turn out for high speed operation. What does this mean?

I was wanting to cut some trees and get some firewood for next winter, and make some extra cash for clearing out brush and trees, but at the rate I'm going, it'll be July before I get a running saw.



Daniel

 

[TORQUE THIS]

The owner's manual is no help- it says to run the screws all the way in and turn the adjusting screw out 1 turn for low speed operation, and 3/4 turn out for high speed operation.

Lightly seat the high and low speed screws. Turn both screws out 1-1/2 turns.
Inside the fuel tank, there should be a fuel line with a filter in the end. If you can see it, gently pull it out and change the filter. Fill with fresh fuel and try to start.
If the saw starts and won't idle, turn the low speed in 1/4 turn. If now you can keep it running, turn the low speed screw in slowly till it races and wants to stall, turn the screw back out till it wants to stall, turn the screw back in between those 2 spots. Now go to WOT. Turn the high speed in slowly till it sounds like it gonna take off, back the screw out 1/2 turn. It should smoke slightly at WOT and not be screaming. You'll be able to tell what I'm trying to explain. Make sure this is correct or you'll burn the saw up.

If it won't start, you'll need to rebuild the carbs.

One other thing, to do a quick compression check, hold the weight of the saw by the start rope, it should fall slowly and not smooth, it should bounce on the way down. If it falls too quick, you have poor compression.

 

[Skydiver]

Clean the spark arrestor ,the spark arrestor bolts will come out easier if the unit is hot, go ahead and replace the fuel lines along with pick up strainers. A small hole in the fuel line will run you crazy trying to tune it, if it runs at all. Make sure the oil fuel mixture is correct. Too much oil is bad. More oil means less gas, which is lean.

If all fails pull the head and look at the cylinder wall and piston. Some one could have ran straight gas in it. They usually won't crank, even with a shot of gas in the carb. if they are ran with no oil.



The best carb cleaner I have found is Quick silver ( I think) from a Mercury marine dealer(I know). It foams when applied.

 

[bb218]

When it is running at med or high speed with the breather off check for fuel mist spewing out of the carb, if it is most likely it will need rings and not a carb kit.

 

[AMink]

If the spark arrestor is clean, pull the muffler and look at the exhaust port. If it's full of carbon buildup, very carefully scrape it out. My weed wacker had enough build up it wouldn't run. Then the spark arrestor was so clogged up it wouldn't run. Cleaned them both and BAM! everything is good to go for another few seasons.

 

[Skydiver]

bb218, NO pun. I'm not saying you are wrong ,but every 2-cycle I have owned spews out the carb unless it has reed valves. That's one reason they can't pass emissons test.

Comments please. If I am wrong I want to know it.

 

[dpuckett]

Thanks for the responses guys. The reason I think it is in the carb is I ran a tank of gas through it and it did just fine power- wise. It was idling fast, and I thought the H and L were fine tuning for the idle/ run speeds, not air/ fuel ratio. I backed off the L screw, and it died. Cant get it going now. I know for a fact it was never run without oil, as the guy they came from is meticulous about maintenance- his farm tractors look showroom new, complete with no leaks of any kind- and he got them new. They have just been sitting a long time.



I got the second one going last night, Have to feather the throttle coming off idle, but other than that, it's fine. Idles well, no chain movement at all.



What are reed valves? These saws were made in Tokyo in the late 60s/ early 70s.



DP

 

[dpuckett]

Lightly seat the high and low speed screws. Turn both screws out 1-1/2 turns.

Inside the fuel tank, there should be a fuel line with a filter in the end. If you can see it, gently pull it out and change the filter. Fill with fresh fuel and try to start.

If the saw starts and won't idle, turn the low speed in 1/4 turn. If now you can keep it running, turn the low speed screw in slowly till it races and wants to stall, turn the screw back out till it wants to stall, turn the screw back in between those 2 spots. Now go to WOT. Turn the high speed in slowly till it sounds like it gonna take off, back the screw out 1/2 turn. It should smoke slightly at WOT and not be screaming. You'll be able to tell what I'm trying to explain. Make sure this is correct or you'll burn the saw up.



If it won't start, you'll need to rebuild the carbs.



One other thing, to do a quick compression check, hold the weight of the saw by the start rope, it should fall slowly and not smooth, it should bounce on the way down. If it falls too quick, you have poor compression.

They both have excellent compression- 'bout jerk my shoulder out of socket if I start on the wrong part of the stroke, and there is a noticeable jerking/ notching when pulling the rope. Filter in the non-running one is clean; the one I got to run had orange paint clogging half of it. Scraped it off and all was well (sa far).



I should have added that I drained the old gas, removed the old spark plug, sprayed PB Blaster (what I had) in the hole, and pulled the rope a dozen times or so. New gas/oil mix. Cleaned the air filters, and the saw overall. Put in new plugs. Some off brand, but it's the style where you can remove the end and have the threaded part for the boot to go onto, and I get a nice blue spark.



I'll try turning the screws out a little more and see what I get. Is there any danger of flooding it?



Thanks again,



DP

 

[dpuckett]

TORQUE THIS- I tried your method. It sounded like it wanted to start a time or two, but then died off. I ended up with fuel coming out the exhaust, so I think I flooded it. I assume I need the choke on for the first few pulls, right?



I went to start the one I got giong yetserday, and the cord broke right as I pulled on it. I think I am going to try to find a shop to fix them both. They run on the wrong fuel type, anyway.



DP

 

[TORQUE THIS]

If you flood them, just pull the plug and blow it dry, and then pull the saw over about a dozen times to clear the cylinder. Always hold WOT when starting also.

Yes, the carb will mist fuel when running.

 

[TORQUE THIS]

TORQUE THIS- I tried your method. It sounded like it wanted to start a time or two, but then died off. I ended up with fuel coming out the exhaust, so I think I flooded it. I assume I need the choke on for the first few pulls, right?

I went to start the one I got giong yetserday, and the cord broke right as I pulled on it. I think I am going to try to find a shop to fix them both. They run on the wrong fuel type, anyway.

DP

It would be best to have someone experienced check them. They will also check your idle and WOT RPM's as they are very important. Make sure you use good quality 2 stroke oil also. I also mix a little stronger on the oil.

I have worked in a mower repair shop for quite a while when I was younger. I would love to get back into it. It was a lot of fun!

 

[fest3er]

... What are reed valves? These saws were made in Tokyo in the late 60s/ early 70s.

DP

You need a short lesson in 2-smoke engines. The following may not be technically correct, but it should capture the essence.

A 2-smoke fires on every revolution. The gas-oil mix is drawn through the crankcase and the oil in the mix lubricates the crank and rings. The engine fires near TDC. The piston is pushed down and exposes the exhaust port, out of which the exhaust gas flows. When the piston moves down, it should pressurize the crankcase; this pressure will force fuel/air into the cylinder when the intake opens. This is where the reed valves come into play. The reed valve closes off the path back to the carb, preventing fuel/air from being pushed back out the carb. If the reed valve is worn or weak, you'll have lower power and less efficiency.

That's it in a nutshell. If you want to know more about 2-smokes and reed valves, check out almost any snowmobile, dirt bike or personal watercraft forum; you should find just about everything you'd want to know about 2-smokes there, including high-performance mods. The performance mods (like super-duper reed valves, et al) might not apply to, or be available for, tiny appliance engines such as chain saws, weed trimmers and leaf blowers, but the operational principles are nearly identical. Performance mods include tuned intake and exhaust, stronger high-performance reed valves and other slick stuff.

And for what it's worth, a good synthetic 2-smoke oil (like Amsoil) is very good for keeping crud, varnish and other deposits from building up in the cylinder, especially on the piston. They'll also provide good lubrication at closer to 100:1 fuel-to-oil ratios, as compared to the typical 50:1 ratio most appliance engines want when using dino oil. And as we all well know, less oil means less smoke. :}

N

 

[dpuckett]

Hey, thanks fest3r. That explained the reed valves.



I dont know what is coming out of the carb, as I have the air filter on it, and cant really tell what I'm looking for anyway. The raw fuel/ oil of which I spoke is coming out the exhaust. I looked in the cylinder when i took the spark plug out, and saw the intake ports at the bottom. Looks just like an old 12V92 Detroit block I saw in a shop one time..... Walls looked good, with some marks, but no apparent scoring.



The book calls for a whopping (I'm not kidding) 20:1 fuel/ oil mix. I am using Stihl brand oil. It's actually convenient- they sell it for 2. 5gal @ 50:1. Mix that bottle with 1 gal, and you have 20:1. Had to get a second jug. But, when it can cut through an old dead oak like hot butter, it is kind of nice.



I found a local guy who is about as old as the saws are (comparatively, that is), who is quite familiar with them. I will let him check out the one and get it running, then take him the other to let him fine tune it if needed.



DP