Some help needed with Carb Tuning

[Homer6679]

Hey Y'all,

I'm new to the site and plan to be pretty active. This site seems to be an invaluable resource which I plan to use extensively. I've been doing small engine repair as a hobby/side hustle for a few months now, but I have a couple chainsaws that have me stumped. A stihl 009 and a Husqvarna 435 X Torq. Both exhibit the same problem, however I believe the husky has a leak between the carb and intake. The problem is that I will get them running good one night and the next morning/day I go to test them cold and they don't run right. They just require some carb tuning. It's almost like the carb adjustment screws don't stay put. Anyways, any help would be appreciated.

Thanks,

Cory

 

[Vintage Engine Repairs]

Hi and welcome, Cory.

They shouldn’t need to be tweaked that often, I’d suggest there is a fuel / air issue. Were you told about the history of them when you got them? Any issues mentioned? Had the previous owner done any work / repairs ?

With any 2 stroke, especially older ones, you can’t overlook the importance of a pressure and vacuum test. Along with that, an inspection of the piston through the exhaust port is also very important.

Once you’ve done those two things you’ll have a direction in which to go.

If you don’t have a pressure and vacuum tester, get it running and spray some carb spray around each seal, the intake as well as the cylinder base. It’s not as good, but works in a pinch.

Take a methodical approach to the diagnosis process.

 

[J D]

With any 2 stroke, especially older ones, you can’t overlook the importance of a pressure and vacuum test. Along with that, an inspection of the piston through the exhaust port is also very important.

+1...
Also, before tuning be sure air filter is clean, fuel filter isn't blocked, fuel is fresh & correctly mixed & the saw is properly warmed up.
In some cases it's also important to have the top cover fitted as this changes the inlet pressure on some saw models

 

[link]

Air leak typically does that, you just cant get it it tuned because it seems to change all the time.
If you need the low rpm adjustment way up at 2 turns to get it to run that's a sign.

The older saws is much easier to understand than the new such as xtorq, older saws usually should be at approx 1 turn both high and low. They are very responsive to a 1/4 turn and if everything's OK it stays that way.

Xtorq and newer saws may need perhaps 2 turns (or other) based on what it is and may not give that immediate clear and unmistakable feedback/response, but basically - if it does not seem to stay in tune and just constantly change - that's often an air leak, either within the carb or somewhere between the carb and crank house, or directly in to the crank house. May be carb rubber booth or the impulse tube or crank seals perhaps.

 

[Homer6679]

Thanks for the input, I do know the carb clean trick and that is why I believe the husky has a leak. I plan to do this hobby for awhile so I plan to buy a vacuum and pressure tester. Any guidance as to which one to buy? Any tips/tricks when testing?

 

[J D]

Buy one that does both.
There are some good threads on here on the subject

 

[ammoaddict]

Thanks for the input, I do know the carb clean trick and that is why I believe the husky has a leak. I plan to do this hobby for awhile so I plan to buy a vacuum and pressure tester. Any guidance as to which one to buy? Any tips/tricks when testing?

Mityvac MV8500 Silverline Elite Automotive Test Kit Provides both Vacuum and Pressure to Perform Engine Performance Diagnostics, Brake Bleeding, Fluid Transfer, Evacuation, Windshield Repair Jobs https://a.co/d/5OV6MTj

 

[Captain Bruce]

Welcome to the the best source of answers to questions that genuinely stump the best. The Husqvarna 435, 440, 445, and the big box store 450 Rancher.....share this issue with gusto.

Make the leap up to a 455/460 and you are here looking for wisdom as to the oil line leak. Thats a YT video on my channel. Shows the answer....but more on that later. Back to fuel issues.

I have re-conditioned 30 saws since Easter, 9 being these Mid-size Husq/Jonsereds. Same malady.
Its always the "insulator", which is a gasket that goes between the block face, and carb. It is wrapped with a ribbed rubber ring, and keeps the seal.
After 4 engines, I just went straight to the ring; if its loose, its broken.

 

[Homer6679]

I am pretty sure It is the “insulator” as it is loose. I finally got around to ordering a mityvac and it will be here later this week. I’ll let y’all know what the problem is when I test it

 

[Patrick1903]

I am pretty sure It is the “insulator” as it is loose. I finally got around to ordering a mityvac and it will be here later this week. I’ll let y’all know what the problem is when I test it

The anticipation has been killing me…
What’d you figure out? Was it the insulator?

 

[Homer6679]

Yeah the insulator was loose, the new one fixed the issue.

 

[Patrick1903]

Yeah the insulator was loose, the new one fixed the issue.

What about the Stihl 009?

 

[Homer6679]

The impulse hole was covered on the gasket

 

[Captain Bruce]

I'm back with another 440 carb question. The saw starts, and idles, but wants to bog, and stall when throttled. I've got the screws at 3 out on both sides. Its the 2nd carb, both are OEM and re-built. What am I missing?

 

[Homer6679]

The hi and lo jets should be set to 1-1.5 turns out. I’d start there. Mess with the lo jet if the throttle response isn’t correct

 

[Captain Bruce]

With the carb off, the small hole (@ 8 oclock pos) lines up with the impulse passage in the rubber manifold. I discovered an old note about a gasket, and found that one in the 1st pic. It does not appear on any IPL for this engine. I assume it goes between the air filter housing and carb, which would have no bearing, as it is ahead of the carb.

Anyone know what that gasket is for?

 

[Captain Bruce]

I have learned that the gasket is meaningless. The carb - to - intake seal is a raised rib for both ports, and the impulse passage. The intake manifold wears out, dries out, leaks. Once removed and inspected, that may be the answer to the carb issue on your 435/440, I keep a spare going forward.

Removal is a snap. Allen 4, and vise grips. The Manifold easily pushes out of the way.

 

[Homer6679]

Read post 11, the intake manifold or “insulator” was worn out and leaking. One of the black clips was also broken. I replaced that and it fixed the issue

 

[Captain Bruce]

Read post 11, the intake manifold or “insulator” was worn out and leaking. One of the black clips was also broken. I replaced that and it fixed the issue

You are incorrect. The insulator has nothing to do with an air leak, causing the carb to act up. The insualtor has no seals, fits loose, and the black tab is what locks the carb in alignment....before the screws tighten the carb, to the intake manifold. The plastic Mount and ribbed insulator, meant to hold back the engine heat, could easily be omitted from re-assembly, and the saw would run fine without it....

 

[Homer6679]

Interesting, I replaced part #504724701 which is called the insulation wall. It must have something to do with an air leak because it solved my problem. Furthermore, it was sucking air from where the clip was broken. In my experience any joint/seal past the carb needs to be correct or there will be a leak