What's on your bench today?

[Scott Walker]

After a little advice ive got a 1997 husq 371 xp starts and runs great but since Igot it 5yrs ago its compression has always been abit in tge low side 120 psi checked piston and pot and all good do you think I should put a new piston ring in and if so wheres the best place to get on. Thanks scott.

[spudulike]

Does it mean that even if it holds 10psi (which is as far as i've got with this test) it could still be a malfunctioning carb if the pop off and re-seating isn't right?

 

Just to confirm (I've never pumped a carb to 20ish psi imagining that the diaphragms would break) you pump beyond the 10 to 20 - observe it pop then fall immediately back to a holding at 10psi? Is this a standard and recommended test or is there any danger of damaging dias/gaskets?

 

What are the symptoms of a carb that wont pop at 20 or wont reseat at 10.

 

I'm struggling with a strimmer carb at the moment that spits fuel out of the air filter side when I try to fire the engine (pull the recoil) - don't know if this is related to above discussion?

 

Thank you folks

 

Mike

 

On doing this test, you are checking the abillity of the carb needle valve to hold back fuel under pressure with no leakage and the abillity for the needle to reseat after opening.

Failure in this area can cause fuel to leak through to the crankcase if the tank is under pressure - for instance if the saw is left in the sun, it can cause the saw not to run if the leak is bad or to run rich and badly.

 

Just depends on how bad the carb is

[spudulike]

 

Makita DBC 4010 brushcutter

on my floor whilst i sort out a bench. Attempting my first ever leakdown test with some home made gear. Absolutely refusing to hold any pressure with exhaust and intake blocked and air pumped through modified sparkplug - i guess that means the crank case is leaking and I need to tear down further?

 

Listen for escaping air, if that doesn't do it, take the recoil, flywheel an impellor off and put a strong washing fluid and water mix around the seals and see if they bubble when air is pumped in to the engine.

[spudulike]

After a little advice ive got a 1997 husq 371 xp starts and runs great but since Igot it 5yrs ago its compression has always been abit in tge low side 120 psi checked piston and pot and all good do you think I should put a new piston ring in and if so wheres the best place to get on. Thanks scott.

 

Depends if you want OEM or aftermarket, the only aftermarket ones worth having are "Caber" ones and if you want OEM, Greenstripe or some of the site sponsors will do them.

[GardenKit]

Just a little more on 'pop testing'

 

There are several ways to use the pop tester but be aware of a few things first.

1 There is seldom an audible 'pop' and never from a dry carb.

2 Inlet valves never actually pop off when the carb is working, the test is merely to prove that they can open.

3 There are no correct pressures for pop off or reseating. Both top and bottom values can vary by more than 10 psi from carb to carb, but in general the valve should open (pop) at less than 30 psi and reseat at no less than 10psi. This is because the fuel pump operates at around 7psi, so obviously we dont want pump pressure to open the inlet valve and poor unwanted petrol through.

4 When using the tester the pop off point is often not easy to spot, so pump up slowly, allowing time between each pump to watch the gauge. If the needle remains still after each pump, then pump again, but if it starts to drop slowly back then 'pop off' has been reached.

5 Watch the needle dropping slowly back until it stops moving, this will be the reset pressure. It does not matter what it is as long as its greater than about 10 psi.

 

6 So to recap, the important thing is that the inlet needle does pop off at some point and that it reseats at 10psi or above.

 

With this said, you can use the tester in a number of ways.

 

You can connect it to the fuel pickup pipe with the carb in situ. Pump it up to about 20 psi, check the pickup hose and pump diaphragm for leaks. If it holds pressure, dont worry about trying to pop it off, just crank the engine (choke on, ign off) Each inlet stroke will cause the metering diaphragm to pull down, opening the inlet valve and you will see your pressure guage drop with each stroke, proving the inlet valve.

 

Or you can connect it to the carb on the bench via the inlet pipe. You can pump it up to pop off, and then watch it reset, or, by putting a thumb over the choke plate and sucking gently on the engine end, you can create vacuum and see the needle drop.

 

Or, if you suspect the inlet valve you can remove the metering chamber plate and drop the carb into a jar of petrol, pump it up and see the string of bubbles when the valve pops, watch them slow and stop on reseat.

 

There are loads more uses for this bit of kit, but I'm getting bored now.

 

Happy popping.

 

 

 

[mikerecike]

Thank you for these comprehensive replies - it is much appreciated.

 

When you are a little less bored rest assured it is getting read and appreciated. Testing directly into the fuel pick up in the carb is a great diagnostic tool to know about. You guys should put this stuff in a generic manual. I'm really keen to learn. Thanks again.

 

Superb forum.

 

Mike

[spudulike]

Had a small Sawfest round at Burrells yard on Saturday and created a large amount of sawdust - the ported 372XP is below - it now pulls 14,200rpm:blushing:

 

Oh - thats Burrell using it modeling the green Arbtalk T shirt:lol:

 

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[MattyF]

Sounds and looks good done about 5 tanks through the 395 so let me know when your out again for a retune !

[spudulike]

Sounds and looks good done about 5 tanks through the 395 so let me know when your out again for a retune !

 

Worth checking the plug colour but would put another 5-10 tanks thrrough before a retune. Will have some time in a couple of weeks - not as if you are a million miles away:thumbup:

[spudulike]

While we were testing the 372, we ran some comparisons with other saws through the same piece of timber - results below

 

Stihl 036, standard with 18" bar - 7 secs

Stihl MS441 - 20" bar - 5.5 secs

Ported Husky 372 - 4.4 secs

Burrells Spud ported Husky 357XP - 5.2 secs

My ported 357XP - 5.7 Secs

 

Conclusion - think my saw needs some more running in and maybe the 8 pin isn't good in larger wood as it has had more work than Burrells but was a bit slower!

 

The 372 is blistering and knocks over a second off the 441:thumbup:

 

Shows what can be done with a little tuning!