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Old 11-04-2021, 08:12 PM   #11
Caledoniandream
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Couple of things: check if it has enough compression, when you pull it, does it seem to be a bit on the light side, or if electric start, take the plug out and plug the hole with your thumb, just to feel the compression.
Sometimes the exhaust valve get stuck, take the valve cover off, and check the tappet settings and if the valve is not sitting too deep.

Check the spark, these machines don’t have a very strong spark when you start them, it’s only a magneto, no battery power involved, the strength of spark increases with the revs.
Check if the machine hasn’t hit anything heavy with the blade (blade bend) as they can snap the key in such an occasion.
If the key snaps it knocks the ignition timing out.

If you have fuel in the tank and you have the tap open there should be fuel coming in the bowl, if you take the drain plug out the bowl, you should have a steady stream.
If not either the tap is blocked (filter in the tank) or the needle in the carb is stuck.
A quick way to check is to open the throttle, spray some carburettor cleaner, brake cleaner or electrical contact cleaner in the carb and start the motor, if everything is dandy it should run for a few seconds, if it does you have a carb problem.
If it doesn’t it is one of above.

Remember some fuel taps work on pulse from the engine, some carbs pump fuel (can recognise them on the little fuel bulb on the side of the carb) these are troublesome if the membrane perish.

But if there is spark and the valves work properly than it should start on a squirt of brake cleaner.

Last edited by Caledoniandream; 11-04-2021 at 08:44 PM.
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Old 11-04-2021, 08:22 PM   #12
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Quote:
Originally Posted by Rakti View Post
.......I'm thinking blocked passageway between the carb fuel inlet pipe and the needle valve that the float sits in. Completely forgot I have carb cleaner in the loft and also have a tin of compressed air.
just pull the hose of the carb and blow into it......soon find out if its blocked!

then pour in fresh fuel and check the bowl is filling up.

after that, you can think about sparks, etc.
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Old 12-04-2021, 04:24 PM   #13
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UPDATE (live from Mum's house)

1. Removed air cleaner housing.

2. Re-attached carb (same long bolts hold the air cleaner housing and carb to the engine).

3. Removed carb drain plug.

4. Poured petrol into tank, NO PETROL came out of the float chamber.

5. Removed carb, cleaned out carb with carb cleaner and compressed air, repeated steps 2 to 4 with the same result; NO PETROL.

Possibly a problem with the float valve seat; maybe the spring is no longer strong enough? Here's some photos;

Upside down (on a spray cap)


Upright standing on its central tube


New carb?
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Old 12-04-2021, 04:37 PM   #14
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Probably the float needle stuck / corroded, pull the pin out the float and carefully remove the float, donít bend anything.
Underneath the float and most likely fixed to the float is the float needle, if you can free that up, you get fuel in the bowl.
When you cleaned the needle and itís seat (use a Q-tip in a drill or so) and put the float back together, check if it closes and opens.
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Old 12-04-2021, 06:11 PM   #15
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Originally Posted by Caledoniandream View Post
Probably the float needle stuck / corroded, pull the pin out the float and carefully remove the float, donít bend anything.
Underneath the float and most likely fixed to the float is the float needle, if you can free that up, you get fuel in the bowl.
When you cleaned the needle and itís seat (use a Q-tip in a drill or so) and put the float back together, check if it closes and opens.
Yeah, I've had the float and needle out Cal. It wasn't stuck or corroded. At a guess, without experience of a similar float needle, I'd say the spring seems weak, and the angle of the float in that last picture suggests something's wrong to me.
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Old 12-04-2021, 06:12 PM   #16
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Have you tried to get a spark from the plug - I know youíve tried with a strobe, but if your plugs not sparking, it ainít going to fire up.

Take the plug out, connect it to the plug lead and earth the plug on the lawn mower and pull over a few times. Check to see if you see a decent spark or not ?

If you do, then you know thatís good, so itís a fuel starvation issue, so check youíve fuel in the little reservoir under the float, check the jets are clear etc.
Just for you Andy, the first thing I did today was check for spark with the plug against the engine; it was fine.
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Old 12-04-2021, 06:19 PM   #17
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With the float bowl off, still as it is in the pic, right way up, if you blow into the petrol hose inlet, does air come through?

I know some of these carbs can suffer with the float bowl becoming compressed due to a missing washer or similar or over tightening - this stops fuel coming in with the float bowl on!
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Old 12-04-2021, 06:21 PM   #18
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Yeah, I've had the float and needle out Cal. It wasn't stuck or corroded. At a guess, without experience of a similar float needle, I'd say the spring seems weak, and the angle of the float in that last picture suggests something's wrong to me.
I also squirted carb cleaner down the float needle valve seat followed by compressed air. Also, the other way round from the fuel inlet pipe, which I assume runs to the other side of the valve seat.
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Old 12-04-2021, 06:57 PM   #19
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The float in the last picture sits correct. You should be able to blow carb cleaner through the fuel inlet.
The spring on a float needle is always very weak nearly non existent.
When blow in the fuel inlet in the position and slowly lift the float up the needle should close the inlet.
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Old 12-04-2021, 07:35 PM   #20
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Originally Posted by Caledoniandream View Post
The float in the last picture sits correct. You should be able to blow carb cleaner through the fuel inlet.
The spring on a float needle is always very weak nearly non existent.
When blow in the fuel inlet in the position and slowly lift the float up the needle should close the inlet.
Fair enough! I'm back home now (so can't do that test) but do you agree there must be a fault with the Carb? They're only £12-£13 on ebay, so don't I just need to replace the Carb?
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