Husqvarna 435 infamous air leaks

[Dellirium]

Hello everyone,

First of all nice to meet you. I’m from Romania and i dabble in chainsaw repairs.
I come to you for an idea, or an advice because i’m kind of stuck on a strange situation with a Husqvarna 435

Long story short it has idling racing issues.
I have checked/repaired/changed the following:
Bearings
Piston ring
Seals on both sides
New base gaskets
I’ve repaired the threads on the cilynder because after reinstalling it 2 of them broke when i torqued them down to 9 Nm
I have installed a brand new carb (aftermarket) on the saw since the old one was mangled by the previous owner because he didn’t had the splined adjustment tool.
With all of the above done. I have a difficult time adjusting the carb, and i suspect an air leak between the carb and the intake boot. I find the clamping design to be poorly engineered in my opinion.
However i have encountered this leak with brake cleaner on other 435 saws that ran just fine and didn’t develop any changes in rpm or had any issues with heat, and this situation really screws with my head.

My idea now is to add a 235/236/240 carburetor gasket between the carb and the intake body, do you think it’s a good idea? Or maybe someone who encountered this issue may give me a clue on what’s really going on here, because after a few hundreds of chainsaws repaired this saw is about to defeat me.

 

[Vintage Engine Repairs]

Start with a pressure and vacuum test - if you don’t own one you can get one very affordable from eBay. If that shows you a leak you can resolve it. If it doesn’t then start methodically diagnosing. We can address that roadblock when it comes to it.

Edit: Here is how a p&v is done:

 

[Dellirium]

Thank you for your reply, i failed to mention it but i already did that . I used the test pressure plate which mounts directly on the intake boot. No i haven’t blindly swapped parts, i swapped parts that were toasted, and found during the pressure/vacuum test.
As for the junk stuff, unfortunately it’s what my client can afford, even if i already told him that the saw is not worth repairing anymore since it’s the mark 1 (2008), and a brand new one is about 300-350€, but he insisted on bringing it back to life.
I will check the face of the chinesium carb to see if it’s warped, because through your reply you gave me an idea for which i thank you

 

[Vintage Engine Repairs]

What were the reasons the parts you mentioned, were replaced? Also, what was the psi of the compression test you did that warranted a change of piston rings? What were wrong with the bearings?

 

[Dellirium]

0.5mm radial play on shaft in the clutch side (cold)
80 PSI compression, and slight wear on the piston ring on the exhaust side, with no scratches or scoring on the cilynder.
Piston showed that was losing compression on that side.
I cleaned it, checked the roundness of the cilynder and i decided to swap the piston ring for that
Base gaskets were replaced because the big one ripped in half while taking out the cylinder.

For the base salary in my country unfortunately an oem carb is quite expensive for some.

And no offense taken, i thank you for your feedback. It just helps, and i’m not gonna be angry over true facts.

 

[Vintage Engine Repairs]

Hmm 80 psi of compression is a false reading, a 2 stroke chainsaw won’t run with 80 psi, it’s got to be at least 120psi. The cause of this is generally the lack of shrader valve in the spark plug adapter on the end of the tube, that makes the tube act as cylinder volume. It’s an easy mistake to make, but it’s important to use a small engine compression tester.

Either way, it’s not your issue.

I’d suggest cleaning the oem carb and putting a new oem kit in including any gaskets that go between that and the manifold as well as testing the fuel lines and fuel filter. Then take the h and l screws out and cut flat clean slots for your screw driver to slip in and then adjust the carb correctly:

Edit: This is Stihls process, but it applies to any 2 stroke OPE.

 

[Dellirium]

Already did the thing with the oem carb unfortunately but as you see in the picture it’s in a pretty messed up state. The l and h screws were both forced past the limit clockwise. I can’t do anything for it anymore (this is not my work of art) i own the carb adjustment tools

And for the main reason of my thread. I repeated the test after i replaced everything i said, and no more leaks were detected
The compression went to 115-120 psi
And, yes the chainsaw was brought with a no start condition.

Sorry that i didn’t include all the facts previously, as i said it screwed with my head, and i thought it would be obvious that i checked the values, but in the mean time i browsed the forum and you are totally right to jump on me based on what others post around here

 

[Vintage Engine Repairs]

They’ve certainly been having fun there with that carb!

Can you remove the screws from the new Chinese carb and put them in the oem carb?

You’ve tested the fuel lines and they’re not kinked or damaged? The fuel filter is good too?

Edit: just make sure the screws match up with the old oem screws in length, pitch and taper.

 

[Dellirium]

I’ll try that thank you.
The fuel lines are pressure tested, and the fuel filter is brand new. I’ve changed it after i saw the frankenstein type carburetor.
I will also check the face of the “new” carburetor to see if it’s warped. The finish on it looks sketchy, and i fear that is not straight (couldn’t find the correct term, but you surely understand)
I’ll come back in 6-7 hours with what i’ve got.
P.s. I saw that someone posted that they’ve fixed this issue by replacing the insulator wall, which surely is wonky on the saw, but i highly doubt it will solve the issue. Got any knowledge on that?

 

[Vintage Engine Repairs]

I don’t I’m afraid, but doesn’t hurt to give it a go! Update the thread with how the H & L adjustment screw swap goes.

 

[Dellirium]

Will do, but i don’t have high hopes for it.
I’ll swap the insulator too just to see if it’s fact or myth

 

[Dellirium]

So, i’ve managed to fix it.
I’ve tried to replace the screws on the old oem carb, but no success, the threads in the carb body were messed up, and the needle seat was mangled.
I have replaced the insulator but that didn’t alone fix the issue.
I straightened the am carb on some sand paper placed on a piece of glass and with the new insulator i’ve managed to ensure a proper mating surface with no leaks.

Thank you for your help, and i’ll lurk around here from now on, either with advice or help, or with another tricky question.

A friendly advice for anyone encountering this issue: DON’T use chinese c1t type carbs with 3 screws. It isn’t worth the hassle and the head aches!

 

[lone wolf]

Already did the thing with the oem carb unfortunately but as you see in the picture it’s in a pretty messed up state. The l and h screws were both forced past the limit clockwise. I can’t do anything for it anymore (this is not my work of art) i own the carb adjustment tools

And for the main reason of my thread. I repeated the test after i replaced everything i said, and no more leaks were detected
The compression went to 115-120 psi
And, yes the chainsaw was brought with a no start condition.

Sorry that i didn’t include all the facts previously, as i said it screwed with my head, and i thought it would be obvious that i checked the values, but in the mean time i browsed the forum and you are totally right to jump on me based on what others post around here

That compression is way too low if your tester is accurate!

 

[Dellirium]

That compression is way too low if your tester is accurate!

Yeah as vintage repairs said, mine is not equipped with a shrader valve on the adapter. I will buy a husqvarna oem one since any other alternative in my country is the cheap chinese ones

 

[lone wolf]

Yeah as vintage repairs said, mine is not equipped with a shrader valve on the adapter. I will buy a husqvarna oem one since any other alternative in my country is the cheap chinese ones

Or calibrate it against a newer saw with good compression and get an idea if it's close to that one.

 

[Captain Bruce]

Will do, but i don’t have high hopes for it.
I’ll swap the insulator too just to see if it’s fact or myth

This entire exercise seems to be repairing a Husqvarna 435 saw with a value of $125 all day, in running condition. Fuel lines aren't pressure tested beyond blowing thru them. ALL chinesium carbs are a coin-toss given that they are ususally lacking specific drilled passages, and a couple of plugged channels as well. This is a rabbit hole post, about spending money, again, and again....

 

[dsell]

I hope I never work on another possessed strato saw. One thing to keep in mind, your new fuel filter could be bad. I disconnect the line at the carb and connect a syringe to draw fuel through the filter. That also tests the tank vent.