Can anyone identify this finger mower please?

Interesting, the engine is a Tecumseh (aka Aspera/Tecnamotor) wonder if the machine is an Alpina?

Not sure of the manufacturer of the entire machine, but the engine is either an AV520 or AV600 Aspera engine. The diaphragm in the carb is not controlled by the fan, but the throttle is. The diaphragm is controlled by the engine suction, when the reed valve, that the carb is bolted to, open, the suction from the engine pulls the diaphragm up, pressing the valve in the centre and allowing fuel into the carb. the rest of the carb then works normally i.e. the diaphragm and valve take the place of a float and fuel needle & seat. The engine may be fitted with a primer bulb instead of a choke system, this will be fairly obvious, is there a rubber button screwed into the airshroud and a small pipe leading to the underside of the carb? If it is a primer system, then when you press the primer whilst looking into the airfilter housing (with the filter etc removed), you should see a firm squirt of fuel hitting the top the venturi. If you don't get the this, check the diaphragm, the fuel valve and the one way valve in the fuel elbow fitted in the side of the carb, on an engine of this age, it will most probably be a small ball in a tapered seat, so watch out when you remove the elbow.

Also your machine is probably older than what you think, it was most likely made sometime in the  80s

A definitive answer regarding the speed control will only be settled if we can see the flywheel and carb with the blower housing ( engine shroud) removed. I think that this will show a fixed speed air vane governor operating a throttle butterfly which will be wide open with the engine at rest and will then react to air pressure generated by the flywheel fins.

As has been said, the diaphragm regulates the fuel flow and is not sensitive to engine orientation as would be a float. The advice regarding the non return ball valve is good but if it is an early engine it won't have a ball valve but a little "poppet" valve . These were a bit prone to getting stuck and if squirting with carb cleaner wouldn't clear them had to be removed ( which destroyed them) and replaced with a new one . Unfortunately they are no longer available and are not directly replaceable with the later type ball valve . I have several machines with the early valves and am experimenting with a solution. This is not as straight forward as it might first appear as although the later inlet elbows and balls are obtainable there is an issue with the casting of the carburettors  differing.

A non functioning no return valve will result in difficult, or impossible, starting  as in conjunction with the primer button its function is to inject a squirt of fuel directly into the carb throat ( venturi).

Now tell us that your engine does not have a primer button but a manually operated choke - some applications did!

Thank you Wristpin and Hortimech,

Very thorough replies and extremely helpful.  Yes, the throttle assembly does have a baffle in the fan housing to govern the throttle opening.  Unfortunately the spring connecting it to the throttle arm is missing and I haven't found a suitable one yet.  

I understand the system now and the tube that I thought was what opened the diaphragm is, of course, the primer tube which is missing the bulb. The diaphragm seems to be in good condition but the engine vacuum does not seem to allow fuel to go through.  I will have another look at the carb when I get a chance and see if the airway is blocked.

The throttle lever seems to be cut off so it is a little awkward to operate but with a spring it should be ok.

I can get it to fire by putting a small amount of petrol down the plug hole but it does not keep running which is what made me suspect the diaphragm mechanism.

I will check out the valve and get back when I have found out anything.

I don't think the valve is pumping petrol into the engine as the problem seems to be a lack of petrol in the engine.

I might try and make some time to try pumping the primer with a syringe or something and see if I get any life out of it.

Thank you both again for you very helpful information.

Richard.

Looking again at the picture of the machine, I 'think' the big blue bulge, that the engine is fastened to, is a centrifugal clutch, if it is, you seem to be a throttle lever and cable missing. This is backed up by the cut-off throttle lever at the engine end, this was fairly common on engines that used the Aspera 2 stroke engines. Without a governor spring the engine will shut down to a tickover as soon as it starts and if the stop screw on the carb isn't set correctly, the 'tickover' could be totally off.

I think you are going to have to remove and clean the carb, I doubt if it will have the earlier type of non return valve in the fuel inlet, this was replaced before the AV engines came out.

Without a primer bulb starting will be difficult. Bulbs and their bases are hard to come by; it's possible that there is more chance of finding a scrap Flymo with a primer assembly than obtaining just the needed parts. 

Once you have a primer bulb or an improvised substitute it's possible to check its operation as follows. Remove the air filter and hook out the perforated screen so that you have an unobstructed view up the carb throat. Then with fuel in the tank press the primer sharply and you should see a jet of fuel erupt from the floor of the carb throat with enough volume and force that it nearly hits the roof of the throat.  If no fuel appears try opening the adjust able jet *and repeating the test. 

* The carburettor may have one adjustable jet and one fixed one or two adjustable ones,  Looking straight at the heads of the jets it is the one on the right that may be fixed , if it is it will be brass and screw in almost flush with the carb body. The jet on the left is proud of the carb body and has a friction spring below its head to hold the setting. 

If the priming test fails to produce a squirt of fuel in the carb throat try removing the right hand jet and see if operating the primer produces some fuel from there. If it doesn't the problem lies with the non return valve in the carb inlet. If you get fuel there but not in the carb throat  you have a blockage within the carb - another problem for another day!

Thank you for all that.  I tried using a syringe to work as the bulb and fuel was going through but I will check if it is coming out of the right place.  I can't see if the ball valve is intact but will have a look at the technician's manual that I downloaded.  It shows an adjuster where the fixed  jet is but otherwise looks similar.

I am going on holiday shortly so will not have a chance to try it out before I get back so will report back then.  Hopefully I will have sourced a spring for the throttle mechanism by then.

Thanks very much for all the information.

Richard.

Thank you both.

I have checked and, using my syringe, petrol does indeed squirt right across the ckoke of the carb. As I said, putting petrol direct into the cylinder results in it firing for a few seconds but it won't continue.

If it squirts when priming does that mean that the diaphragm is OK or is it worth getting one anyway?

Did I understand correctly from the manual that it uses a reed valve? Could that be damaged?

Sorry to bombard with questions.

Thank you for all your help

Richard

If you remove the carb there is a block with four reed valves ( pieces of spring steel) . They should be lying flat with no gaps between them and the block when at rest. 

The diaphragm controls the fuel flow by opening the needle valve so  while the carb is off check for wear by removing the diaphragm and gasket and placing a straight edge across the face of the carb. The tip of the needle should just touch the straight edge. If there's a gap the diaphragm may not be opening the needle valve enough to sustain a fuel flow.

As far as I know new needle valves are not available from regular sources in th UK  - I've just bought a couple of pattern ones from Italy and they are also on some on U.S. websites. If the needle is worn you may be able to raise it with an extra washer between the valve body and its recess.

Also, while you have the carb off remove the two jets and with a thin nozzle tube on an aerosol of carb cleaner or even WD40 squirt right  into  each jet recess and see if there's fuel coming up into the throat of the carb. With the diaphragm removed you will see that there's a small welch plug . This covers a small jet and ball valve supplying the idle circuit. This can block but the fuel squirt test will show whether or not it is. Back in the day when replacements were readily available we would drill into the plug and the jet and pull them out  but here again, you will be lucky to find one. A further complication was that depending on the age and carb spec there were two sizes of jet.