Husqvarna 435 won’t stay running

[kur1j]

I’ve got a Husqvarna 435 chainsaw I’m trying to fix. I was told it sat for several years without being ran and has only been ran a few times since being bought.

I got it home tonight, dumped the old gas, put new gas in it. Primed it choked it. Pulled on it a few times. It cranked up, but ran pretty fast while on choke and then died (maybe 5 seconds). Choked it again, pulled a few more times, it ran again pretty fast on choke, then died again (maybe 5 seconds again).

I looked up the jet adjustments and the idle adjustments. Turned them all tight and then turned them back 1.5-2 turns. Same as above. I spent about 15 min trying to slowly adjust the idle screw and the low jet trying to get it to do something besides running for 5 seconds, burning up the fuel during the choke and then sputtering dead. No luck with that.

I pulled the carb off and cleaned every port I could find. I could blow cleaner through the jets and every other hole without any issue that I could tell. Nothing looked all that dirty to me.

Put the carb back on and it did the same thing.

It’s obviously getting fuel when it’s choked/primed but as soon as it burns up that fuel or if i try to just give it throttle it immediately dies.

Any suggestions on what to try next?

 

[Jasonrkba]

When you cleaned it did you poke something like a paper clip into the holes? I wouldn't be surprised if the fuel line was shot also. After it cranks are you taking it off choke?

 

[kur1j]

Yeah a clipped off a wire brush bristle and shoved it in the holes I could find and then blew cleaner in all the holes including all the jets.

The fuel line seems to be okay but I guess it could have a pinhole in it and it’s sucking air? Is that what you are thinking?

When I crank it, if I leave the choke on it will run for about 5-8 seconds at about half to 3/4 throttle. If I take it off choke before that it will just die.

 

[scottr]

kur1j , did you remove the muffler and look at the piston , ring and cylinder ?

 

[Ronie]

You should do a vacuum/pressure test on it. You could have a vacuum leak.

 

[kur1j]

kur1j , did you remove the muffler and look at the piston , ring and cylinder ?

I did not. Granted it’s hard for me to believe that the saw would have piston, ring and cylinder issues as little as it’s been ran. I dont understand why that would cause this symptom though.

I’ll take a look at it.

 

[kur1j]

You should do a vacuum/pressure test on it. You could have a vacuum leak.

Wouldn’t a vacuum leak cause it to not run at all? When it’s choked and is reving when it first starts, it sounds normal. As soon as it runs out of gas it stops.

I can play with the choke and force the choke to stay on and I can get it to keep running for slightly longer.

 

[grizz55chev]

Vacuumis what drives the fuel “ pump “ , if you have a leak, you won’t get fuel. Putting it on choke will cause fuel to be temporarily drawn to the carb, so you have a classic vacuum leak symptom.

 

[Ronie]

It could be a bad fuel line/filter, carb needs a kit, vacuum leak or something else I'm not thinking of at the moment. Because it's been setting a few years I would change out the fuel line and filter, put a kit in the carb and do a vac test. It could still run with a vacuum leak.

 

[kur1j]

Vacuumis what drives the fuel “ pump “ , if you have a leak, you won’t get fuel. Putting it on choke will cause fuel to be temporarily drawn to the carb, so you have a classic vacuum leak symptom.

So essentially a leak in the fuel hose?

 

[kur1j]

It could be a bad fuel line/filter, carb needs a kit, vacuum leak or something else I'm not thinking of at the moment. Because it's been setting a few years I would change out the fuel line and filter, put a kit in the carb and do a vac test. It could still run with a vacuum leak.

I’ll try to get a fuel line and filter to rule that out.

Just curious how much is a carb kit? Seems I can get a whole carb, filter, hoses and the whole works for like 18$.

 

[grizz55chev]

So essentially a leak in the fuel hose?

Not necessarily, a vacuum leak could be from anywhere in the engine or carb, that’s why a vacuum test is advised.

 

[Ronie]

I’ll try to get a fuel line and filter to rule that out.

Just curious how much is a carb kit? Seems I can get a whole carb, filter, hoses and the whole works for like 18$.

I've got a 435 with an after market carb on it and it runs good. I think I payed $12 for it a few years ago.

 

[kur1j]

Not necessarily, a vacuum leak could be from anywhere in the engine or carb, that’s why a vacuum test is advised.

Will the vacuum test narrow down as to what is actually leaking or will it just confirm that I have a leak?

I see several vacuum test kits on amazon. Any particular recommendations? The places around here want the same price for a vacuum test as buying one of the kits. You have recommendation for one?

 

[Saw Fixr]

If a new fuel line and filter doesn’t do the trick, and you believe that the problem still lies in the carburetor, get some Berryman B12 Chemtool at your auto parts store and put 1-2 capfuls into the fuel tank, get it started, and feather the choke to try to keep it running to get the mixture up in the carb. If that helps, even a bit, let it sit for a day or so, and do it again, and again. Even though you cleaned the old gas out of he carb, doesn’t me a you got the old varnish/oil out of the tiny passages. This stuff will loosen that crud and flush it out. Has worked for me..... might be worth a try. Stuff is like $5 for a bottle. Not the spray can.
Good luck.

If this does work, and the saw runs fine otherwise, and doesn’t seeem to overrev, or run erratically (air leak) run it in wood, and see if it improves.

One other thing, maybe make sure the cylinder base bolts are tight.....

 

[Saw Fixr]

A vacuum/pressure test won’t tell you automatically where the problem is. That takes some detective work on your part. A test of the fuel line will tell you if the fuel line is good.
A press/vac test in the spark plug hole will test the rest of the engine, crank seals and the like. IF that were an issue, you’d then need to determine specifically where the leak is coming from (flywheel side, pto side, impulse port, cylinder base etc...) you’d most likely hear the air escaping during a pressure test, and could confirm with some oil around the suspect leak/seal area...

 

[Ronie]

Will the vacuum test narrow down as to what is actually leaking or will it just confirm that I have a leak?

I see several vacuum test kits on amazon. Any particular recommendations? The places around here want the same price for a vacuum test as buying one of the kits.

I use a Mightyvac. You can barrow one from your local auto parts store, I think they have them to bleed brakes. If you have a leak you'll have to pull your flywheel and clutch off. Then spray some WD40 around your seals, cylinder base and carb boot. If it sucks it in or the leak stops you found your leak. There's a lot of post on how to do it.

 

[Jasonrkba]

I bet if you do the things Ronie suggested your problems will be resolved.

 

[kur1j]

I use a Mightyvac. You can barrow one from your local auto parts store, I think they have them to bleed brakes. If you have a leak you'll have to pull your flywheel and clutch off. Then spray some WD40 around your seals, cylinder base and carb boot. If it sucks it in or the leak stops you found your leak. There's a lot of post on how to do it.

So slightly new development. I pulled the fuel lines and the fuel filter. cleaned them up some and put them back (don’t have one on hand).

So I can now start the saw on choke, get it to run and it will stay running off choke but it is running at half throttle the entire time. If I pull the trigger it will bog down and die. If i lift off the throttle it will continue running but go back to half throttle. It’s almost like the throttle is half pulled.

I never messed with the throttle and put it back the way it was when I put the carb back but the previous owner might have dickered with it.

Or could this still be a vacuum issue?

I took a video of it. Not sure if anyone else has one similar that can confirm that this is indeed correct or not.

 

[Ronie]

Sounds like you might have an air leak. I'll look at the throttle linkage on mine tomorrow and let you know if it looks the same as yours.