Huztl / Farmertec ms 440

[BuckthornBonnie]

So I went to run the 440 again the other day. Filled it with fuel and oil, checked and adjusted the chain, put a piece of old carpet in the back of the Landcruiser, and put the 440 next to the farmertec 372 I just built. It didn't like that at all, when I got to the wood pile it had filled the cases with fuel again!
So the 372 got more work and the 440 went back on the bench.
And my brain went to work.
Most other chainsaws don't run pressurised tanks as far as I can see,.just good vent systems, and the carb on the Stihl copy obviously doesn't play well with pressure..... So I modified the old tank vent I had so that it doesn't seal either way, but slowly let's air out. Then I put it back together and started it up. Once it was warm I had to retune it but out seems to run better, the dead spot has gone and it transitions better to high rpm. I know it will dribble fuel when it's upside down but that's better than emptying it's guts all the time.
Isn't it?
Will doing this cause any other problems?

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Well, it's probably not good to have any fuel leaks due to a fire risk, but I don't think it would cause any running issues.
Bed T is right--- got a different vent?
Also--- how's that needle look in the carb?

 

[BuckthornBonnie]

Well my AM440 test vid must have got deleted.
Here's pulling the seal out the real 440 last week.

Gotta love using those pullers...nice vid!

 

[TimTaylor]

Well, it's probably not good to have any fuel leaks due to a fire risk, but I don't think it would cause any running issues.
Bed T is right--- got a different vent?
Also--- how's that needle look in the carb?

This was the second farmertec vent and the third carb. Although I tried an old genuine Stihl carb , it ran very well on the first carb but for this problem. The second carb was a non runner and the third one fixed the problem for a couple of weeks. I have rebuilt the second carb and I will try that again with a Stihl vent but the farmertec vent let air in and not out just like the Stihl one. I think you are right and its a problem with the needle in the carb but the pressure in the tank gets really high, and its the only saw design I've seen that let's that happen......unless I'm missing something?

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[Bedford T]

You may want to fix the vent first and then look at the problem again.

 

[TimTaylor]

I think that's what I have done, hopefully, by getting rid of the pressure in the tank.

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[TimTaylor]

Problem for me is that I like old saws. This design is the most modern I have apart from a couple of ms200t s . I looked at the vent system they have and although it's more complicated, it let's pressure go both ways. Pressure doesn't build up in the tank. I'm curious about if a genuine Stihl ms440 builds pressure inside it's fuel tank?

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[Bedford T]

When I test the fuel circuit. I expect the tank to hold pressure and release slowly on vacuum and I know that all is well on the tank. Testing the pulse is part of that routine but has nothing to do with the tank.

 

[TimTaylor]

How much pressure? Surely it should let it out above a certain pressure. I'm wondering if our crappy fuel is partly to blame, shaking the saw builds pressure, even on a cold day, greater than 5 psi, and that has got to be rough on the carb needle surely?

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[Bedford T]

Stihl manual says 10pounds. I will double-check that and correct if it's wrong. There is a warning about going too high. I will go read it now and refresh

 

[TimTaylor]

Good point actually.
Funny how I never thought of getting the original Stihl manual, but it's the first thing I did for the 372xp.
If it's 10 psi then I guess I still don't have a good carb. I'll do some pressure testing today and see what pressure the rebuilt carb resists.


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[Bedford T]

Put some pressure on it and put in a bowl of water and look for bubbles

 

[Bedford T]

Looking over the different carbs 8# might be safer in general.

 

[TimTaylor]

Put some pressure on it and put in a bowl of water and look for bubbles

Will do.

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[TimTaylor]

Looking over the different carbs 8# might be safer in general.

Sorry, don't understand.

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[Bedford T]

pounds of pressure. check your messages in a few minutes

 

[TimTaylor]

Ok, well the carb blows bubbles at 4 to 4.5psi plus or minus the accuracy of my gauge. The others are close to that figure. That is pressurised through the fuel line. The fuel line itself leaks at 6psi ish around the carb pipe, depending on how I hold my tongue. And the tank holds pressure to above 10psi with a genuine Stihl vent, pressurised through the fuel delivery line.

I've gone back to the modified vent, (I just cut a tiny piece of the green rubber seal) and the tank holds zero pressure. Filled the tank and shook the saw then left it in the sun(not hot today maybe 14deg c) and it seemed fine.

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[Ozhoo]

Ok, well the carb blows bubbles at 4 to 4.5psi plus or minus the accuracy....

You need to get the carb to hold pressure. 7psi at a minimum. With fuel in the carb, start adding pressure and drop it in a bowl of water. You'll likely have leaking around the diaphragms so pull it back out and tighten the screws. Retest... if you see bubbles in the carb throat, you need to check the inlet needle/spring/metering lever. Keep fixing and testing till you get the carb to hold pressure.

If the fuel line leaks at the carb under 7psi, replace it. Reinstall an unmolested vent.

 

[Mac&Homelite]

I've been chasing my tail with the same problem on my ms361. I eventually concluded that something is either wrong with the carb, but more likely the kit and my solution to the flooding was lowering the metering lever to quit a bit below it's "normal" position. So far it has solved my flooding problem. It no longer floods when sitting after being run. I think I lowered it around 1/16 or so below the carb top. Give it a try, I bet it will solve your problem.

 

[Bedford T]

The carbs can be troublesome. I have been chasing a problem with my ms380. I am on 5th carb. Once I get it running right I will be able to go back to orginial carb and determine excatly what the problem is. That means 3 bad carbs looking for a good one. I think #5 will be the charm the seller seems helpful. The last carb the jet was not drilled put. I found problems in all 3

 

[TimTaylor]

I've been chasing my tail with the same problem on my ms361. I eventually concluded that something is either wrong with the carb, but more likely the kit and my solution to the flooding was lowering the metering lever to quit a bit below it's "normal" position. So far it has solved my flooding problem. It no longer floods when sitting after being run. I think I lowered it around 1/16 or so below the carb top. Give it a try, I bet it will solve your problem.

Looks like I'm going to be learning more about carbs. Thank you.

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