048 flooding

[Robert Raven]

Hi all,

 

Was milling with my 048 today which is normally good as gold. Paused during a cut, and instead of idling, it died. Was hard to restart, had to hold throttle open to get it going. Finished my cut, ran nicely flat out. At the end of the cut, I let go of the throttle, again it died without idling, and now I can't get it to fire, just floods like crazy, fuel coming out of air filter (saw lying on it's side in the mill). These were long, long cuts, so I wondered if the idle needle had shaken out and made it too rich at idle, but I reset it to one turn out, and still floods even without choke. Gave up when it got dark, any pointers as to what to try tomorrow? Really want to finish this log!

 

Thanks

[spudulike]

The most likely cause of this is a needle valve that is stuck open in the carb, also possible is sawdust lodged between the diaphragm and the cover but less likely.

 

You will need to pull the carb off - a quick check is to attach a tube to the fuel inlet and see if you can blow down the tube - it should hold pressure!

[Robert Raven]

Hi Spud,

 

I pulled the filter out of the tank and blew into the fuel hose from there, fuel came running out of air filter. So I took the carb off, and blew through it again, this time it did hold pressure. Reassembled, pulled it over, flooded again. Blew through tube and now it leaks again. I removed the needles and reseated them again in case there was muck holding one open, but got the same result. Seems to leak for a bit when you blow/suck on the tube, then seals. Could it be a diaphragm? I did notice a little sawdust inside the air filter when I cleaned it, not what you want to see. What's my next step?

 

Cheers for the advice,

 

Rob

[spudulike]

I think from your posting, you are getting the H &L screws mixed up with your needle valve. The needle valve regulates the fuel pulled up from the tank and held in the metering section of the carb above the diaphragm, to check the needle, the metering arm, spring and needle needs to be removed and this can only be done by removing the diaphragm and diaphragm cover!

 

I would say that your needle either needs a clean or replacement, I recently had one where the metal part of it had corroded and the plating was stopping the thing moving properly.

 

Put a tube on the fuel pipe, suck it and seal the end with your tongue, if it holds pressure then it is probably OK, if it doesn't then the needle is faulty. This is a very basic test as this circuit operates at a higher pressure but can find faults in this area.

 

Yours are classic signs of needle valve problems - also check for muck behind the diaphragm cover - much less likely but a possible problem.

[Robert Raven]

Ok great, I'll take off the cover and diaphragm and have a look at the needle. You were right, I have so far only touched the H and L needles. Does the metering needle move in and out as the throttle is opened and closed, like on a motorbike carb? Are we expecting it to be stuck wide open, given these symptoms?

 

When I reassemble it (assuming I get that far), does the metering needle have to be set at any particular number of turns or anything?

[spudulike]

Ok great, I'll take off the cover and diaphragm and have a look at the needle. You were right, I have so far only touched the H and L needles. Does the metering needle move in and out as the throttle is opened and closed, like on a motorbike carb? Are we expecting it to be stuck wide open, given these symptoms?

 

When I reassemble it (assuming I get that far), does the metering needle have to be set at any particular number of turns or anything?

 

The metering ARM does need setting but to be honest, be careful with it and reassemble as it is - if you don't damage or bend it, it should be ok.

 

The diaphragm moves up as fuel in the metering section is depleted, this puts pressure on the metering arm and allows more fuel in to the metering section - it is like a switch/valve for fluids and is triggered by the diaphragm.

Find out what manufacture the carb is and google the manufacture and download the maintenance info - it will help.

If you have had the H&L screw out, these will need setting up again, make sure you don't lean the H screw out too much or you may seize the saw:thumbdown:

 

Carb should be a Walbro WS series!

[Robert Raven]

Ok It's running great now, took off the cover to find a mugful of sawdust, thanks for the pointers!

 

This begs the question, how the hell did this lot get in here?

 

Again, thanks for pointing me in the right direction, didn't want to take it to bits without a bit of backup!

 

Browsing similar posts I got some tips on tuning so I'm pretty sure its not too lean, I leaned the high needle till it revved free, then made it richer till the engine note dropped noticeably and the firing rhythm is disrupted- I guess this is 4-stroking? As for low needle and tickover, I just adjusted them to run nicely and pick up revs well. Sound about right?

[spudulike]

Sounds about right but always adjust the idle first and H setting after as adjusting the idle on some carbs disrupts the H setting but apart from that - well done, nice pic and you should be chuffed:thumbup:

[Robert Raven]

Yes very chuffed, always nice when the fix is instant and complete! Cheers for the help.

[miker]

that is one truck load of crud in there !!