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Zeneth Carb Needs a Tickle!

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peternsomerset Thu, 30/05/2024

Hi,

I have what seems to be fuel starvation and have cleaned the carb but it still persists and suggestions what i can try next would be appreciated.

The mower is a Suffolk Super Punch 17inch 1956 and have recently cured an ignition problem and it starts and slow runs smoothly,  but:

if not touched,  it runs for about 45 seconds slightly speeds up then stops

I can keep it running (to mow the lawn) by keeping it primed but doesn't last long when using the main jet as anticipated

the idle is set to 1 1/4 turns and main to 3/4,  variations do not improve situation

the hole at the bottom of the float chamber has been carefully cleaned as has the fuel tank and petrol tap filter.

I have some old float chambers and floats that I will be tryng in the next couple of days but am running out of ideas and having to prime every time I cut a strip in the lawn is a bit of a pain ATM!

Thanks

Forums

wristpin Thu, 30/05/2024

Those carb settings are not what I would expect. About 3/4 on the slow running screw and whatever results from half way between rich and weak on the main. You don’t mention the fuel tank cap breather hole . Try dropping off the float bowl, holding s suitable container under the carb top, turning on the fuel and see whether you get a steady flow for 60 seconds. Finally, at the back of the elbow of inlet manifold, viewed from the inside with good light there’s a tiny drilling connecting with the chamber below the slow running needle . With a steady hand insert a very thin bit of wire through it to check that it’s clear .

 

sparkymike Thu, 30/05/2024

If the fuel pipe from tank to carb is rubber, then they can collapse internally especially with this modern fuel. It could also be something floating around in the fuel tank and then blocking off the outlet pipe when fuel is drawn off. As Wristpin states, check fuel cap has a breather hole. If not, a vacuum can form in tank when fuel is being drawn off. Only other possibility I can think of is an electrical component breaking down after X amount of time, however it sounds more like fuel starvation than electrical.

 

Mike.

peternsomerset Thu, 30/05/2024

Hi,

Thanks for all the info.  I had checked the hole in the cap and the holes in the carb but have not checked the fuel flow.

I then reset the slow running screw and guess what...........

it immediately ran OK without having to prime every minute!!

I have for years wrongly set it to 1 1/4 as I wrote it on my old manua,  maybe that's the reason it seemed to always running rich.

Thanks for your help.