Purpose of pivot on carburettor linkage ? ?

[Alan DonovanParticipant @alandonovan54394]

Hi All

I am in the process of reassembling the carburetor linkage on a 250 / 125 volt generator driven by an Italian Aspera engine.  The engine is a Tecumseh design licensed to Aspera – Vintage 1970’s or thereabouts.

The carburetor linkage is very similar to that shown on this diagram, and it is the lower part of the linkage my query relates to.  Please see arrow in diagram below ……….  well I hope it is still there when uploaded.

The lower part of the linkage locates on a pivot shaft with a flattened end.  It protrudes through the main body casting from the inside.  See picture of pivot shaft below,

The shaft is rotatable through an angle of approximately 235 degrees and has some form of internal stop at either end.  The flattened end is nominally vertical in its ‘normal’ working position (this is an assumption) and is only able be vertical once in its total movement.

The carburetor linkage (see photo below) is placed over the shaft diameter and is held in place by means of an rectangular integral spring clip arrangement that is a push fit on the flattened shaft end.

However when I tried to refit this linkage this shaft disappeared ‘flush’ inside the engine casting.  I have managed to retrieve it, using a strong magnet, but this is obviously not how it was meant to be.  So I am hoping there is someone who is able, and willing, to answer my questions.

These are:

1.     What is the function of this shaft, beyond being a pivot.  It does not appear to have any resistance to rotation other than the ‘hard stops’ at each end. Is that correct?
2.     Should there be something inside the engine that stops the shaft disappearing inside.
3.     Does anyone have any alternative suggestions, for a workable solution, so I don’t have to take the engine apart – as I don’t think I will be able to separate the generator drive shaft from the engine output shaft.

Additional information / progress – when trying to refit the original linkage, the spring clip feature fractured – so is no longer usable.  I have managed to manufacture an alternative that secures to the shaft and flats using opposing grub screws.  So I no longer have to forcibly ‘push’ the linkage on the shaft …….. which is some progress.

I am very tempted to run the engine anyway with the alternative linkage, but it seems sensible to ask the above questions first.Any comments would be very much appreciated.

All the best to you all, and thank you in advance.

Alan.

[David JuppParticipant @davidjupp51506]

It is part of the throttle governor – the has a 90° bend inside the engine and runs against a ‘thimble’ which has pivoted bob weights on it.  As engine runs faster the linkage try to close the throttle.

No- not usually anything inside the stop the shaft being pushed in.

You can probably find Aspera or Tecumseh parts manuals on line which show everything.

You have to adjust the angle where the screw is to get required performance – I used to do these routinely many years ago.

 

[noel shelleyParticipant @noelshelley55608]

As said it is the governor shaft, it’s many years since I’ve had one apart . It bears against the governor weight carrier and needs to be in the right position when fitted it may only be possible to assemble in one way. I can’t remember. The Haynes manual on lawn mowers may be able to help. Noel

PS the drawing shows a mixture screw in the bottom of the carb bowl. In the UK such engines as I saw had a carb drain in the bottom so that in the winter the carb could be drained to prevent water Etc causing corrosion, it was NOT a mixture screw !

[BazyleParticipant @bazyle]

re mixture screw. Depends on vintage. Old carbs where the float chamber was just that feeding the simple spray bar in a tube eg Suffolk Punch mowers it was just a drain but newer designs with plastic bits the vaporisers are quite a refined and complex shape inside the float chamber and it is a mixture setting, eg Balmoral mower. I can’t remember the details as it is quite a while since I played with either. I’ve referenced mower names as I don’t know the actual engine but probably not B&S.

[Alan DonovanParticipant @alandonovan54394]

Good afternoon.

Thank you for your input w.r.t. the carburettor linkage described above.  Your advice / comments are very much appreciated.

A catch-up ……..  I have had the engine running today.  I feel it is running far too fast, but if you drag the ‘throttle lever’ (?) back to the current adjusting screw setting it runs at a pace I would expect for this duty.  The 250 volt socket is working, it blew the bulb immediately but as the engine was running at max speed – I assume that is to be expected.

David J – the Tecumseh /Aspera parts lists I have found so-far don’t appear to show the governor parts inside the engine.  But I shall have another search looking for governor parts only.

Noel S – The carb bowl I have has two screws on the bowl.  One is a spring loaded drain, so I guess the other is the mixture screw.

Otherwise it runs, so that is good progress – I will now do some research on governors to see if I can find a way forward with that.

Again – many thanks for your input – it is very much appreciated.

Alan.

[David JuppParticipant @davidjupp51506]

When engine is stopped, the governor shaft rests on the top of the weight carrier and (if pulled by the throttle spring) the throttle can reach fully open.  Any lifting of the weight carrier due to the weights spinning round will tend to reduce throttle opening.

Engine operating speed is a balance between spring tension and the raising of the weight carrier.

Unfortunately I don’t recall which direction the governor shaft turns in, but it should be simple to work out.  The actual arc of operation will be no more than perhaps 30°, probably less.

[Alan DonovanParticipant @alandonovan54394]

David J.

Thank you for your additional input.  I found a YouTube video of a governor on a petrol engine.  Now I have a much better understanding of how they work, I will see if I can work out which end of the pivot shaft movement the governor mechanism pushes.

Next steps – The engine has been inactive for a few years before I bought it, so to my mind the governor may be ‘gunked up’ with oil deposits.  If I cannot ascertain any movement I may consider using an engine flush to see if that makes a difference, but first I will let it run at a low speed for 20 minutes or so in the hope that hot oil will free it up.

Thanks again for your continued input.

Best regards. Alan

[David JuppParticipant @davidjupp51506]

Highly unlikely that is it totally gunked up – there really isn’t much to these.  If it was so bad as to be gunked up, I’d be wanting to split the engine casing anyway to give it all a clean out

The ‘push’ from the governor weights will try to close the throttle flap, opposite to the pull from the spring which tries to open the throttle.  A quick search found a Youtube video where someone showed the workings https://youtu.be/cZWy9rNscLU

[noel shelleyParticipant @noelshelley55608]

May be it was 40 years ago, but memories ! Observe which position the throttle is in when fully open and which way the throttle must move to close, this is the direction that the spring must pull. When not running the thottle will be wide open, closing rapidly as the engine approaches governed speed. An engine like this will be governed to 3000 or 3600 rpm depending on frequency, 50Hz or 60Hz. The governor arm can not be fitted in the wrong way. It is not uncommom for the spring to be lost, it is shown behind the carb bowl in your diagram. If the governor has stuck then take the side plate off and inspect it, one thing you will see is that unlike the rather crude B&S engines this will have an oil pump, a very neat arrangement, You will almost certainly need a gasket but this you can make. Don’t waste your time with flushing oils ! DO NOT run it ungoverned it WILL go bang !

A warning ! The governing and speed control is at best not great and the output voltage may vary quite widely, fine for simple lights or motors but for electronic item could prove fatal. Sudden disconnect of a high % load could see a sudden large spike – electronics DO NOT like this.  Good Luck, Noel.

[Alan DonovanParticipant @alandonovan54394]

Hello again.

DJ – Thank you for that video link.  Brilliant – every day is a school day, that helps tremendously – thank you.

NS – Thank you for the additional information.  Its working speed is 3000rpm – confirmed by the data plate.  Thank you for the additional warning about running overspeed.

It may be a few days before I report back on progress.  Other tasks get in the way.

Best regards

Alan.

 

[David JuppParticipant @davidjupp51506]

See pages 52 and onwards in this document

https://www.mymowerparts.com/pdf/Tecumseh-Service-and-Repair-Manuals/TECUMSEH-SERVICE–REPAIR-MANUAL-EUROPA-ENGINES.pdf

[Howard LewisParticipant @howardlewis46836]

3000 rpm is the full load speed for a 50 Hz genset. Off load the governor should maintain engine speed at no more than 3150 rpm (5% run out)

When initially starting, if the engine speed is below 3000, the governor will open the throttle fully, to bring the engine upto rated speed, but close it partially as rated speed approaches.

As Noel says, check that the throttle closes as the engine speeds up.

Once upto speed, depending on the electrical load applied to the alternator, the speed can vary between 3000 (Full load) and 3150 (No load)

Trying to shorten the run out, to control frequency more closely, can make the governing too sensitive, and unstable, so that the speed is constantly varying, even with a constant electrical load.

Hopefully, any “hunting” will gradually be damped out, by mechanical and electrical inertias

The electrical control set up should limit, and control, voltage.

Usually. lacking means of applying a full electrical load, normal practice is to set the maximum speed, unloaded, to 3150 rpm. As electrical load is applied, the speed should fall until, what ever load results in 3000 rpm, will be the maximum that the engine can deliver.

If the engine is overloaded, and the speed falls below 3,000 rpm, the frequency will be below 50 Hz, with the problems that can bring.

Overspeeding can bring electrical and mechanical problems, so is to be avoided.

HTH

Howard

[Alan DonovanParticipant @alandonovan54394]

Hello all.

Just a quick note to say thank you to you all for your input.

Unfortunately other issues require my attention, so the generator is ‘on hold’ for the moment.

Best wishes to you all  –  Alan

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