Advice on 051 problems

[muttley9050]

HI Chaps,

Was out milling today on twin powerhead mill with two 051avs, was milling well, just before exiting one cut one powerhead cut out and wouldnt refire. Took plug out and its as dry as a bone, so thinking carb off and clean fuel system. Does this concur with your thoughts?

Also i have a spare powerhead that i went to attatch to mill, ive never used this or tried to start it since i bought it when it started fine. Now its like theres somuch compression you can hardly pull it, sometimes these saws kickback at you when starting but then free up, this one wont. Its definately not seized but wonder if anyone has any clues how to remedy this.

Im a reasonable mechanic, but dont have that much experience with saws, mainly on 2 stroke motorbikes and 4 stroke generators/gokarts. Any saw specific lingo may have to be spelled out.

Any advice greatly appreciated and thanks for your time.

James

[Rich2484]

My guess would be the fuel tank vent is blocked on the first one. Tis would stop fuel getting to the carb. Either this or fuel line broken or blocked filter.

 

But I would check the tank vent first. Remove the fuel pipe from carb and first blow down it, carefull as if tank vent is working it will blow fuel,back up pipe at you. If tank is empty then you can suck it (have a mint handy) or use a vac tester, it should allow air up fuel pipe from tank but not down it.

 

The second one, remove plug and try and pull it over, if this doesn't work remove chain cover and look at the clutch, expose clutch and try and pull over. Other one is remove pull start assembly to flywheel and then try running over gently with a spanner on flywheel nut.

[spudulike]

The first one is lack of fuel, as Rich says, tank vent, possibly crap in the internal carb gauze filter, perished/soft or holed fuel line, gunked up fuel filter, cracked impulse line, worn pumping gasket in the carb, blocked jet in the carb due to crap in the diaphragm metering part of the carb.....

 

The second one, try removing the plug and turn the saw so the plug hole is pointing downwards and pull the machine over - it is possible that the needle valve has leaked fuel in to the crankcase and is stopping the saw being pulled over.

 

Other than that, the saw should pull over freely with the plug removed, if it doesn't, you may have something binding or seized bearing etc.

 

The "Kickback" is down to the saw being old and probably having no decomp and the ignition timing being fixed rather than stepped as on later machines - it is normal for older saws to do this if not pulled over with conviction:blushing:

[agg221]

I concur with the above, however other things to note on the second one.

 

The thing that feels like compression kicking back and trying to take your fingers off sometimes when starting isn't. It's something to do with the way the ignition module is configured on older saws (ask Spud for technical details!)

 

edit: Spud has just provided technical details!

 

Anyway, it means you can't take it as a sign of good compression.

 

On the saw that feels seized - check that all the screws that hold the fuel tank and starter housing are present and tight. When they work loose, the whole thing tilts up a little when you pull the cord and it jams the starter.

 

Alec

[spudulike]

edit: Spud has just provided technical details!

 

Alec

 

 

No flies on me M8:thumbup:

[muttley9050]

thanks guys, third saw has similar symptoms to the first now! was just milling some holly with it, and managed to hit a nail at about the same time as the saw started complaining and labouring.

Think Alec hit nail on head with seized saw, 2 of the threads on the recoil casing are stripped, why it was spare saw, ordered some helicoils to fix it earlier but didnt think it would cause these problems till just reading this.

Think i have a lot to learn about tuning these saws and keeping them running. THinking of stripping carb and fuel system down on all 3 for a clean and inspection, is this sensible?

Also if you had bought these saws is there a method you would use for tuning and inspecting them all before putting into service, any advice on this would be great.

Thanks

JAmes

[agg221]

At least it looks like the problem is identified - I have a reason for knowing this one...

 

On the carb and fuel system - yes it's sensible. I would equip myself with three carb kits from Rowena, a length of impulse line and fuel hose from L&S and some replacement fuel filters. This lot should cost under £50 for all three saws with a bit of luck.

 

I would then set about the first saw - ideally with a jam jar of white spirit, a paintbrush and an airline to hand. I would at first be staggered by the amount of crud you find when you lift the flat aluminium plate off the top of the carb, then start blowing it out with the airline, painting the stubborn bits with white spirit and letting it soak in to shift it.

 

The carb on these is really easy to take off, take apart, clean and put back together if you follow the manual. You need a few small spanners, screwdrivers etc but nothing complex.

 

While the carb is off you can get a really good view down onto the top of the piston, which lets you see if it looks reasonably healthy.

 

It's easier to clean the carb with an ultrasonic bath - even a cheap one.

 

Reassembly is easy, if a little fiddly on the screw on the fuel tank side of the air intake plate. You do have to jiggle the throttle as you're putting the air intake plate back on as it has a tendency to trap the throttle linkage the wrong side, which is irritating as then you have to slacken everything back off to get it to work properly.

 

Before running hard, in an ideal world I would go for a pressure and vacuum test, followed by tach tuning, but to be honest I've never had any problems by tuning to factory settings, tweaking down the idle so the chain doesn't spin and away you go.

 

Alec

[muttley9050]

Thanks Alec, few questions if you dont mind. Whats included in a carb kit from rowena and after looking atthere website im slightly bemused as to which kit i should order. Is the fuel filter you speak of in the tank pickup, or isthere another one, whats the difference between impulse line and fuel line. Thanks mate,

James

[spudulike]

Carb kits come in two flavours, full contains the needle, metering arm and welch plugs plus all the normal pumping and diaphragm parts and the Lite kit just has the diaphragm and pumping parts.

 

An impulse line takes the positive and negative pressure of the crankcase and uses it to pump fuel up from the fuel tank by way of the pumping section of the carb and the fuel line connects the fuel tank to the carb and transfers fuel from the tank to ths carb but needs the impulse circuit as the fuel is generally held BELOW the carb:thumbup:

[agg221]

As per Spud.

 

Re. Rowena's website - erm, yes, well, not much to say about it. However, ring them up and you will get one of the most helpful people imaginable. Get the make and model of the carb first, from the saw not the manual as there could be several options. Their kits are genuine, not pattern, however they come in Tillotson/Walbro/Zama packets rather than a Stihl packet and as such cost a lot less.

 

Impulse line is ordered by the metre - a metre will do everything you will ever need. Fuel line is sometimes by the metre, sometimes per saw. Looking at the saw without doing any dismantling you can see the fuel line coming out of the tank and disappearing into the innards. When you've taken the aluminium air intake plate off you will see where it plugs onto the carb.

 

The impulse line comes from the crank case, from the other side of the carb near where the crankshaft would be, loops round over the top of the choke rod and in to the visible side of the carb.

 

You might as well renew them both while the thing is apart for the price of them. If they're old they're likely to be perished and a hole in either can cause air leaks, resulting in the saw running lean which risks seizure.

 

Alec

 

 

Fuel filter is the one in the tank pickup. Only costs pence.

Edited May 31, 2013 by agg221