Chainsaw won’t start driving me nuts

[Herman Melville]

Hi

I’ve got a Husqvarna 435 - 4 years old

It won’t start.

fires but only for literally half a second then dies and makes a bit of oily smoke

the spark plug (brand new) is oily and oil comes out a bit through the spark arrestor

I consider myself good with engines and maintain a year old 15hp outboard and a 20year old Toyota landcruiser

I have so far: (in this order)

changed the spark plug,
checked that there is a lovely fat blue white spark,
changed the air filter,
Changed the fuel filter,
changed the fuel out for fresh new fuel that makes the outboard run like a train so I know it’s good,
Taken out the plug and left it for a day to let any flooded fuel evaporate,
Taken off the spark arrestor,
Changed the carb out for a new one,
Carefully made sure the L and H on the carb are set to allow a start

I am VERY careful with my mix - I have proper measuring containers and I use a syringe to put in the correct dose of oil. I use the proper expensive Husqvarna oil (like an idiot)

I think that the oily cylinder and plug is a symptom of me pulling it over and over to try start it pumping fuel and oil in rather than the cause

apart from the coil I don’t know what else to try

So I’m not wasting your time I’ve really put in the hours before asking around

cheers

 

[Andrew Finley]

Check flywheel key by removing flywheel, remove muffler and see if piston is scored, check fuel lines and pick up tube in fuel tank

 

[Herman Melville]

Cheers

flywheel off - jetway fine

mufffler off - piston looks literally perfect

fuel lines all ‘“look” fine - no splits no kinks and smoothin appearance - are they more complex than simple tubes? I have not changed them so far

I have taken off the spark cut out connectors and taped them up to make 100% sure that they can’t be operating by mistake

I had a suggestion that pressure may be being lost downwards out through the crankshaft bearings - I’ve looked at them but don’t know how to test them - they look clean as a whistle

I am at my wits end - maybe I will get the sledgehammer on it....

 

[Leeroy]

Impulse pipe

 

[DannytreeLLC]

What I have done is ran Canola oil in the tank with mixed fuel. This will loosen up the valves and it will run shaky for a minute then the idle will smooth out.

 

[Deleted member 117362]

Impulse pipe

Agree, impulse, fuel line. Pull your fuel line and blow light pressure with line plugged, check for leaks. Cracked impulse line can look fine, need to be tested also.

 

[Deleted member 117362]

What I have done is ran Canola oil in the tank with mixed fuel. This will loosen up the valves and it will run shaky for a minute then the idle will smooth out.

What? Loosen what valves?

 

[DannytreeLLC]

Trust me. I’ve been in this position with multiple saws that weren’t under warranty

 

[Deleted member 117362]

Trust me. I’ve been in this position with multiple saws that weren’t under warranty

That is crazy talk, period!

 

[Herman Melville]

OK thanks I agree impulse line make sense
The workshop manual is highly unhelpful and seems to want to pretend that the impulse line doesn't exist

I have 3 lines on the carb
1) comes into the bottom bringing fuel - that's where the diaphragm is.....
2) comes back out the bottom up to the air purge
3) comes out of air purge and seems to go back to the fuel tank...

So where does the impulse line come in? Number 1 ?

Workshop manual attached if anyone interested

 

[Herman Melville]

OK found it going into the inlet manifold.

 

[Herman Melville]

Ok stripped it down again.

it defo does not have an impulse tube. Photos attached. For peoples info and for future readers experiencing the same problem.

what it has is a pipe that seems to run from the crank case through the inlet manifold and connects to a tiny hole in the bottom of the carb. See pic. This must be where the on off pressure to move the diaphragm must come from

it’s clean as a whistle.....

I didn’t buy a new OEM carb it’s after market. I suppose it is possible that it is faulty but I also have the original carb that I’ve cleaned out - the chances of them both being bad is not high

 

[Deleted member 117362]

Aka, impulse line. Can be internal or external.

 

[sean donato]

You need to pressure and vac test the engine. This will eliminate any seals and the case covers/bad sealant or gaskets in the body of the engine. I have had to replace the intake boot on the 435 I had years ago, from getting a crack in it and causing a lean run.

 

[Herman Melville]

Thanks all I have to say you have all been really helpful:

the intake boot looks pristine. The inlet manifold too, it was so well sealed to the piston case that it had to be gently levered off with a soft plop sound

this is a very low hours engine - I’m not a tree surgeon. It can’t have more than 25hours it’s whole life and has never been dropped. it can’t be that crank cases and things are cracked or bearing seals are shot.i know the compression upwards is good because it’s hard to crank and then very easy with no plug - because it’s all pretty much pristine...

I am coming back to the aftermarket carb....

I haven’t yet changed the fuel lines but the bulb pumps fuel like a train and no fuel leaks of of the hoses and when you take them off the carb they spill the fuel so it seems like they are doing their job just fine.

I have not changed the coil because there is a visible spark when grounding the plig

The symptom is that it won’t start. It burns fuel feebly while the starter rope is doing the work for it- enough to make some smoke and then maybe the TINIEST blip on its own then nothing

.it would be easier to buy a new cheap one - I thought Husqvarna was suppose to be a good make

 

[Herman Melville]

I should add that I picked it up 3 months ago, it started first time and ran strong

It’s like its been possessed

 

[Andrew Finley]

I had a crank seal pop out and once it was re-seated the engine ran fine. It had me chasing my tail for a while though. Husky is a good make as a general rule. All makes have their issues...just don't give up and you will find what the issue is.

 

[Herman Melville]

I have not seen the crank seal under the clutch only the one under the flywheel so its possible that the one under the clutch is duff somehow

 

[holeycow]

What I have done is ran Canola oil in the tank with mixed fuel. This will loosen up the valves and it will run shaky for a minute then the idle will smooth out.

don't listen to this moron. It's just another troll. This site is full of them and I will probably just leave. It's tiresome. No great loss I know.

 

[Herman Melville]

yes thanks I will avoid Canola oil