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Saw dies when choke is opened

Started by kyvet, February 25, 2011, 09:52:40 PM

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kyvet

I have a Husqvarna 36 cc chainsaw that dies when the choke is opened after warn up. I have tried a lot of things.  Fresh gas, new spark plug, cleaned muffler, tank vent is clear, fuel filter in tank is clean, rebuilt carburetor and checked again that parts were installed properly, adjuster H and L to 1 1/4 turns and increased in 1/2 turn increments, put sealant on all carburetor  gaskets.  I start saw using a shot of starter fluid with the choke closed and it runs fast.  I let it warm up and when I open the choke the saw dies. If I remove the fuel line to the carburetor and tip saw on its side the fuel runs freely so I think it is getting gas to the carburetor.  I am out of things to try, any suggestions other than scrap it.

tyb525

Sounds like your idle jet could be clogged
LT10G10, Stihl 038 Magnum, many woodworking tools. Currently a farm service applicator, trying to find time to saw!

kyvet

Thanks for the reply.  When I had carburetor apart to rebuild I blew air through both the high and low ports.  There appeared to be no obstructions.

tyb525

LT10G10, Stihl 038 Magnum, many woodworking tools. Currently a farm service applicator, trying to find time to saw!

DonT

Try cleaning the spark arrestor screen.

fuzzybear

check your manifold between the carb and jug. I just had the same problem with my saw. If it has a crack, even a small one it will suck air. When the choke is on it restricts the air and will allow it to run "normal" but as soon as you open the choke it has to much air.
FB
I never met a tree I didn't like!!

shinnlinger

Crack the gas on a propane torch but don't light it and movieit around the saw while it is running.  If it runs better when you are in the manifold area, you have found your leak.
Shinnlinger
Woodshop teacher, pasture raised chicken farmer
34 horse kubota L-2850, Turner Band Mill, '84 F-600,
living in self-built/milled timberframe home

kyvet

I have already wire brushed the spark arrestor screen, it was sooty but not completely clogged.  The fuel line on this saw is a short tygon tube is easy to see and it looks ok, I am getting plenty of fuel when choke is closed and fuel runs freely if I disconnect the hose and tip saw on its side.  The saw will only run at full speed with choke closed so if I used the propane test I don't think I could tell any difference, when I try to slow the saw down the choke opens and saw dies,

When you say there may be a crack between the carb and jug, I don't know what the jug is.  I have put gasket sealant on the gasket between the carb and manifold.

Thanks for the input but I am still searching for something I haven't tried.

ladylake

 Does this saw have a separate line for the impulse or does the impulse come through a hole in the base of the carb. If the impulse comes through the carb base you could have it clogged with sealant.   Steve
Timberking B20  18000  hours +  Case75xt grapple + forks+8" snow bucket + dirt bucket   770 Oliver   Lots(too many) of chainsaws, Like the Echo saws and the Stihl and Husky     W5  Case loader   1  trailers  Wright sharpener     Suffolk  setter Volvo MCT125c skid loader

Barebuttminer

Quote from: kyvet on February 26, 2011, 11:41:53 AM
I have already wire brushed the spark arrestor screen, it was sooty but not completely clogged.  The fuel line on this saw is a short tygon tube is easy to see and it looks ok, I am getting plenty of fuel when choke is closed and fuel runs freely if I disconnect the hose and tip saw on its side.  The saw will only run at full speed with choke closed so if I used the propane test I don't think I could tell any difference, when I try to slow the saw down the choke opens and saw dies,

When you say there may be a crack between the carb and jug, I don't know what the jug is.  I have put gasket sealant on the gasket between the carb and manifold.

Thanks for the input but I am still searching for something I haven't tried.
Is there a vacuum passage hole between the carb and manifold that may have gotten plugged with sealant? I don't use a sealer on this gasket because sealant tends to squish out and plug the small passage ways.
Wood-Mizer LT15, John Deer 450C Dozer, Husqvarna 455 Rancher, Stihl 009

fuzzybear

Quote from: kyvet on February 26, 2011, 11:41:53 AM
When you say there may be a crack between the carb and jug, I don't know what the jug is.  I have put gasket sealant on the gasket between the carb and manifold.

Thanks for the input but I am still searching for something I haven't tried.
I'm sorry for the confusion, I mean the manifold itself. It runs between the carb and the cylinder. They are made of some type of rubber and they are a vibration point. they are made to flex a little and when they get older they dry out slightly. When it gets cold they are more prone to crack.
Quote from: ladylake on February 26, 2011, 12:00:44 PM
Does this saw have a separate line for the impulse or does the impulse come through a hole in the base of the carb. If the impulse comes through the carb base you could have it clogged with sealant.   Steve
I'm not sure on your model saw if it has a seperate impulse line or not but if it does it will be behind the carb next to the manifold. Check this out carefully also.  Good call Steve.
  I hope this helps.  There is nothing more frustrating than a saw that won't run.
FB
I never met a tree I didn't like!!

Saw Dr.

I have a couple of those saws here.  They're all scored and failed crank seals killed them all.  If tipping the saw on it's side changes the running of the engine, your seal(s) are probably bad.  there are two different types on those.  The "improved" one has the crank bearing encased by the seal.  you have to replace the entire bearing assy when the seal fails.

If you had the carb apart, make sure the pump diaphragm is flush with the carb body and then the gasket goes on.  If the carb is correct check for air leaks in the intake.  Otherwise, I'd suspect crank seals.
I don't try to explain to others why I play with chainsaws.  For those who already know, no explanation is needed.  For those who do not, no explanation is POSSIBLE!

Super 250

kyvet

Where are crank seals and how do you check them?  I have had the carb apart three times checking to see that all ports are open and that all the parts are in the proper order and alignment.  I really don't think that the problem is in the carb or fuel supply.  I don't know what a crank seal or if it could cause this problem but I do believe it is something unusual like a crank seal.  Can you tell me more?

sharkey

Whats up is the engine is running lean.  Try opening the L jet another half a turn and see what happens.  The low jet will be the one closest to the cylinder when the carb is attached to the cylinder. 

The other thing that happens is the carb diaphragms harden from exposure to the ethanol which is laced into our gas these days.  You may need to replace the diaphragms which should cost about $10.  Pay particular attention to the orientation of the gaskets to the diaphragms when you put the carb together.  On the metering side of the carb the gasket goes below the diaphragm up against the carb body.  On the pump side, the gasket goes on top of the diaphragm.  While you have the covers off the carb, check the height of the metering lever, it should be flush or just below the edge of the metal when laying a straight edge across the carb body.  Too low will also run lean.  Check that intake adapter for leaks and cracks too while you have it apart.

If you would like a copy of the 36/41 Husky shop manual send me your email address through a private message and I will forward it.   

Al_Smith

It's usually a leak on the manifold or "boot " side of the carb that causes these conditions . Think about it .

If the boot were torn or in the case of a rigid mount the carb  gasket it would not get enough pressure drop across it to suck gas unless the choke were closed .If it were a blown crankcase seal it would have be ruptured badly to cause the choke to be fully on to get enough fuel to run .

If it were the diaphragm or impulse it could not get enough gas in  it to run,choke or not. It just plain would not pump it out of the tank .

Now believe it or not I've seen a partially torn boot run at a saw at around 8,000 rpm with the thottle completely closed sucking  fuel only though the idle or low speed jet .The saw could not power though unless the choke was partially on .


ladylake

 

Any luck getting it running yet?    Steve
Timberking B20  18000  hours +  Case75xt grapple + forks+8" snow bucket + dirt bucket   770 Oliver   Lots(too many) of chainsaws, Like the Echo saws and the Stihl and Husky     W5  Case loader   1  trailers  Wright sharpener     Suffolk  setter Volvo MCT125c skid loader

kyvet

I still cannot keep the saw running.  It will start on about the third pull but if I open the choke it dies.  I have tried many different H and L settings and a time or two I got the saw to run with the choke open but it soon died like it was not getting fuel.  There must be a special tool to adjust the needle valves since there is no screw driver slot on the stems.  I used my Dremel and cut slots in the stems.

Since I can get the saw to run for a short time I don't think that it is crank seals.  If it is I will trash the saw since I was quoted two hours labor, $120, plus parts to replace seals.  I have replaced the gasket between the carb and manifold and by looking at the imprint on the gasket I think it is sealing.

I am about to spring for a new carb, $25, and if that doesn't work maybe I can resell carb on ebay.

I have had a lot of good suggestions on this forum and I thank all who tried to help.

SwampDonkey

How is the idle set on that saw? Is it a spring locked screw? Turn it out so it's not touching the throttle lever, then turn it in so it's barely hitting it and then a couple more turns. Start it and adjust so the chain is barely spinning and then back it off so the chain is idle. You might have turned that idle screw in too far. There is a point to which you turn it in too far and the saw will behave like your describing.
"No amount of belief makes something a fact." James Randi

1 Thessalonians 5:21

2020 Polaris Ranger 570 to forward firewood, Husqvarna 555 XT Pro, Stihl FS560 clearing saw and continuously thinning my ground, on the side. Grow them trees. (((o)))

1270d

I would follow the suggestions and get a replacement diaphram kit for your carb.  On the older solid mount carbs the needle and seat and fuel pump diaphram would only last about one year at steady use.   this is an easy fix.
  if the crank seals were bad, i think that it would want to run at very high rpm's, with a high tone.   you should be able to get the saw to run with 1.25 turns on the jetting screws.   

the impulse line is very important.   If it is a rubber line, take it off and stretch it.  If there is any checking or cracks, it needs to be replaced.  if the impulse comes through the carb mounting block, check the block for cracks.  Also check both gaskets (carb and cylinder side)   when re assembling make sure the impulse hole in the cylinder lines up with the gasket, block, gasket and carb.     

good luck


joe_indi

On the carb, take off the cover of the metering chamber (usually held in place by 4 small screws) and remove the diaphragm.
Also, remove the metering lever and needle.
Mount the carb back on the saw and tighten it down with the two small nuts.
Connect the fuel line.
With the plug removed and the switch in 'STOP', crank the saw.
Fuel should be pumped out as tiny spurts.If that doesn't happen, the reasons are :

:-[Blocked strainer in the pumping chamber
:-[Faulty Impulse probably from clogging.
:-[Worn oil seals.
:-[Partially seized piston
:-[Stuck ring(s)
:-[Worn out piston, rings or cylinder

Joe



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