Build alert!! Another 038 Mag

[Adamski]

Right, got it fired up first time this afternoon.. choke, then to idle, idles fine then wants to die. As if it is starving of fuel. Kinda like it would do on empty. Metering needle is the bing pre set red one. Carb is pretty clean. Actually think it is a new unit. Screws set to 1.5 on each. Have not investigated further. Seals are fine too. Tank breather is ok. Fuel hose is ok. Any suggestions before I rip it to pieces???

 

[Wonkydonkey]

what,, like revs increase then die, or just idle and die. id say, if former then an air leak ie fuel line/carb, if latter then I,d first try LA screw and see if it still died. but have you tried pop off on carb? could be sucking in air and starving but revs not increasing like its lean. just my 2pence worth
but see what others say first as I'm no expert..

 

[Adirondackstihl]

Lean the L out 1/4 turn

 

[Adamski]

what,, like revs increase then die, or just idle and die. id say, if former then an air leak ie fuel line/carb, if latter then I,d first try LA screw and see if it still died. but have you tried pop off on carb? could be sucking in air and starving but revs not increasing like its lean. just my 2pence worth
but see what others say first as I'm no expert..

No rev increase. It is not symptomatic of a lean air leak from intake boot or seals etc. So what do you mean by pop off on carb. I am a carb fool or novice. I know the standard metering lever, diaphragm, valves and welch plug and jets.. are you suggesting that the metering needle is staying stuck.. i.e. The pop off pressure. Needle seems nice, well like any other needle on carbs I have been through.. I might throw on the oem fuel hose off the super I got the other day. I will have a play tomorrow when I have more time with the carb settings before tearing to me what seems like a NOS bing carb. On the plus side it has a lot of compression..

 

[LondonNeil]

1.5 is quite rich, factory is 1 turn out in both.

Have you got the saw warm or is it dieing as it starts to warm? Does it restart ok?

I'm a total novice but would set the l and h to 1 and if necessary set the la quite fast, get it idling, throttle it if it will pick up and warm it, then slow the la down and see what happens. Also, have you checked that the choke is releasing properly and not sticking?

 

[Wonkydonkey]

two things 1st as adirondackstihl said try increase the L 1/4 OR as I said the LA idle. 2nd what I was refuring to was 'pop off' is where you pump air pressure into the fuel line to about 7 psi it should hold this, it is the meatering leaver valve that holds the fuel, but what I'm getting at is, it could be air getting sucked in thus weakening the fuel, so if it was not holding upto 7 psi(after or about this pressure the valve pops open (metering)) it would mean a carb teardown as there would be a leak. ie air
but first increase the L needle or see how it revs and how the revs pickup if fine I'd increase the LA
but like most things over the net , its hard to guess as you cant hear, see or feel it.

 

[Adamski]

two things 1st as adirondackstihl said try increase the L 1/4 OR as I said the LA idle. 2nd what I was refuring to was 'pop off' is where you pump air pressure into the fuel line to about 7 psi it should hold this, it is the meatering leaver valve that holds the fuel, but what I'm getting at is, it could be air getting sucked in thus weakening the fuel, so if it was not holding upto 7 psi(after or about this pressure the valve pops open (metering)) it would mean a carb teardown as there would be a leak. ie air
but first increase the L needle or see how it revs and how the revs pickup if fine I'd increase the LA
but like most things over the net , its hard to guess as you cant hear, see or feel it.

I'm pretty happy at tuning a carb. This is the problem with over the internet convos regards symptoms. It is literally like starting the saw, idling it for 5 seconds and then as if you have pinched the fuel line. I always tune from 1.5 on each. This has has one heck of an exhaust porting. (1mm from piston skirt edges) and a fat ass muffler mod. Usually set the L pretty high and lean it out as I tune so that it picks up sweet as. That process has never failed me. I will have another look at the carb. But the screws have never been touched and the carb I am 96% sure is brand new.

Thinking about it I recon it could be the impulse. I have had impulses before be cracked and be ok on start up but then obvs open up with the crankcase pressure and kill the saw.. I am now thinking the ends of the impulse could do with clipping as they were pretty swelled with age and pretty loose.

So check impulse, swap fuel line to oem. Then check pop off..

 

[Adamski]

1.5 is quite rich, factory is 1 turn out in both.

Have you got the saw warm or is it dieing as it starts to warm? Does it restart ok?

I'm a total novice but would set the l and h to 1 and if necessary set the la quite fast, get it idling, throttle it if it will pick up and warm it, then slow the la down and see what happens. Also, have you checked that the choke is releasing properly and not sticking?

Choke is fine, did think this as I have had problems with my first one I had. It's rich as fook atm as I have ported the intake and the exhaust and gutted the muffler. Not sure where the screws should be but they will be round this at least. Better safe than sorry lol.

I'm erring towards the impulse line being split. Exactly the same symptoms as an old Husqvarna 137 I had. That had a split impulse seal between the cylinder and the intake block.

This impulse on this 038 seemed a tad loose on the barbs but I just went with it.

 

[Wonkydonkey]

whats it like to rev after its started, ie straight away before it dies, if it don't rev properly then it could well be the inpulse, but if I were building a saw, I'd look very close at carb boot and inpulse as well as fuel line. but having said that ive skipped and tripped if you see what I mean

 

[Adamski]

whats it like to rev after its started, ie straight away before it dies, if it don't rev properly then it could well be the inpulse, but if I were building a saw, I'd look very close at carb boot and inpulse as well as fuel line. but having said that ive skipped and tripped if you see what I mean

It will rev and then instantly die as if you have pinched the fuel line or flipped it to choke. I checked the boot. It was used but in mint condition. Fuel line seemed ok. It was however AM but it did not kink etc. It holds its shape nicely. The impulse is now bothering me. If I wasn't so comfy on the sofa I would be stripping it down and clipping those impulse ends to nice fresh tube. I think there is enough over length to allow it. I'll investigate tomorrow and send back my findings...

 

[LondonNeil]

Choke is fine, did think this as I have had problems with my first one I had. It's rich as fook atm as I have ported the intake and the exhaust and gutted the muffler. Not sure where the screws should be but they will be round this at least. Better safe than sorry lol.

I'm erring towards the impulse line being split. Exactly the same symptoms as an old Husqvarna 137 I had. That had a split impulse seal between the cylinder and the intake block.

This impulse on this 038 seemed a tad loose on the barbs but I just went with it.

Fair enough, and as soon as I posted I remembered this is a Magnum not super, so factory is going to be richer.

 

[Adamski]

Fair enough, and as soon as I posted I remembered this is a Magnum not super, so factory is going to be richer.

No I think you are correct for a mag too. [emoji3]But I have a lot more flow through this than a standard mag.

 

[Adamski]

Fair enough, and as soon as I posted I remembered this is a Magnum not super, so factory is going to be richer.

When are you going to gut the muffler, drop the base gasket and advance the timing on you super? Eh???

I think you will like the increase..

 

[PogoInTheWoods]

If you need to choke it to restart it after it dies I would be looking for an intake leak weakening the impulse.

Replace the impulse line instead of just shortening it. You will need the proper length to flex with the AV. Then do a vac/pressure test with a test flange that will include the entire intake assembly (boot and impulse) to determine case and intake integrity at the same time. Once you know you're tight, then go after the fuel system beginning with the fuel line and tank vent by pressurizing the tank via the fuel line. Should hold 6psi or thereabouts with the button style vent. Will leak down slowly with the grub screw style. If you're all good there, test your popoff (which is probably fine). If all is good there, richen your re-tune starting with your L screw a little fatter. The MAGII I just rebuilt behaved similarly to what you're describing at the recommended 1 turn out. Sweet spot ended up at around 1 1/2 ~ 1 3/4 (without a muffler mod).

Good luck with it!

 

[Adamski]

If you need to choke it to restart it after it dies I would be looking for an intake leak weakening the impulse.

Replace the impulse line instead of just shortening it. You will need the proper length to flex with the AV. Then do a vac/pressure test with a test flange that will include the entire intake assembly (boot and impulse) to determine case and intake integrity at the same time. Once you know you're tight, then go after the fuel system beginning with the fuel line and tank vent by pressurizing the tank via the fuel line. Should hold 6psi or thereabouts with the button style vent. Will leak down slowly with the grub screw style. If you're all good there, test your popoff (which is probably fine). If all is good there, richen your re-tune starting with your L screw a little fatter. The MAGII I just rebuilt behaved similarly to what you're describing at the recommended 1 turn out. Sweet spot ended up at around 1 1/2 ~ 1 3/4 (without a muffler mod).

Good luck with it!

Turns out I may have found the problem (I should be asleep but I am half watching TV) it seems the oem tuning screw block does not quite fit the AM tank. It holds the idle adjust skew wiff and when tightening the filter leaves a slight gap. This is both the boot and impulse.. so I am hoping tomorrow it will start to behave ok. Btw it would need to be choked to start it again.

 

[Adamski]

Cheers everyone for the ideas. Hopefully I have the issue sorted. Maybe. Well it's all together now. Bed for me..

 

[LondonNeil]

Gut the muffler?! There's fook all in there! I'm actually wondering if it's been gutted as I've no reference. I'll have to get photos but basically after removing the torx holding the outer half on and pulling that off I found an empty can bar one plate over the port, held in by 2 further torx. That was it. I would have thought there's nothing to gut bar maybe drilling a 3rd outlet in the side (Magnum has 3 I believe). As for base gasket delete, if I decide to do a permanent repair to the damaged plug port I'll remove the cylinder and get a timcert fitted, at that point I'd learn how to measure the squish and delete the gasket.

 

[Adamski]

So got the idle sorted. Seems it was the tuning block holding be carb off the intake boot/impulse flange. So it sounds pretty throaty with its big old muffler mod and exhaust porting. Haven't done anything hing else but roughly set the L and H.

On another note I need to sort out how to video with two hands. It gets a bit ropey and the saw nearly swallowed a towel..

 

[LondonNeil]

Looks good. Instant pick up, didn't see much smoke, little bit of chain creep. Almost done!

 

[Adamski]

Looks good. Instant pick up, didn't see much smoke, little bit of chain creep. Almost done!

Cheers, think the clutch springs are a bit old. Couldn't get the idle any lower than this. I will buy some new ones and see. Not too bothered about time as my 034 is far stronger than I thought it would be and was a pleasure to use today.