# Lawnmower - non-starter



## Rakti (Nov 11, 2019)

Maybe not the right forum to post on but there's so many knowledgeable people on here I thought I'd give it a try.

Machine is a self-propelled Champion petrol mower with the Sumec SV150 engine (also used in Mountfield's I believe).

The mower's been gradually getting more difficult to start over the last 2 years.

I managed to start it 2 weeks ago and it ran long enough to cut a small lawn before stalling and wouldn't restart. I checked the throttle cable adjustment and it seemed ok, removed the carb and took out the main jet; again visual inspection didn't reveal anything. Then, as I was replacing the filter body (two very long bolts hold the filter body and the carb to the engine) looking downwards I noticed a gap between the filter body and the carb with a gasket in between.

I thought sure that must be the problem as any gap there would allow excess air into the carb (effectively bypassing the air filter) and weaken the mixture. So, last week I ordered a new gasket and filter body (plus a few other parts).

Fitted the new filter body and gasket today, but still no joy. After several pulls the engine did briefly start but quickly stalled and wouldn't re-start. After that, I thought I'd better check for a spark (plug only replaced 2 years ago), so I attached my old strobe light, pulled the starter cord and confirmed there was a spark (though not the quality of spark I guess). A new fuel cap also made no difference (has a breather 'pipe' in it).

The only other thing I could think of was when I removed the screw holding the main jet 2 weeks ago, the jet fell out before I could stop it, so today I reversed it in case I'd put it back the wrong way, here's a photo, numbered 11 in the top picture (10 is the screw that holds it in). Does the larger diameter end fit next to the screw or the other way round?










That still didn't work and I'm now at my wits end. Guess I'll probably have to take it in for repair. I'm convinced its a fuel starvation problem but can't identify the cause.


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## grunty-motor (Aug 11, 2016)

Is the plug dry after a few starting attempts? that would suggest fuel starvation? Is there a float with a needle valve? that would often be the starvation point - but if float boal has fuel in it, then its not that.

spray some wd40 down the plug hole and see if there are signs of life.

Have a look here about 19mins


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## Rakti (Nov 11, 2019)

Thanks for this GM :thumb:

When he replaces the main jet and says "with the thinnest part at the top", I assume he means the thinnest part should be at the top when the carb is back on the engine? If so, I think mine was right the first time and now it's the wrong way round.

He doesn't mention the gasket that goes between the filter housing and the carb. I can only assume his was stuck to the filter housing.

If I remove the carb drain plug (with a tray underneath it) and put petrol in the tank, anyone know if the petrol should drain straight out of the carb, i.e. does the petrol live in the float chamber?


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## bigbrother (Jun 30, 2011)

Sounds like you have exhausted all fuel issues apart from a new carb, sometimes its better to bite the bullet and buy a new part, i'm sure there are some cheap Chinese parts flying around.
Did you leave fuel in over the winter with out an additive as tis will affect the internal of the carb.

Also a sure sign of starting when cold but won't start when hot is the coil/ magneto have a punt and buy one.

http://https://www.magic-parts.co.uk/cgi-bin/sh000008.pl?WD=18550126%2F0&PN=118550126%2D0%2DIGNITION%2DCOIL%2D118550126_0%2Ehtml#SID=272

I know this is expensive but there might be cheaper versions


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## grunty-motor (Aug 11, 2016)

Rakti said:


> Thanks for this GM :thumb:
> 
> When he replaces the main jet and says "with the thinnest part at the top", I assume he means the thinnest part should be at the top when the carb is back on the engine? If so, I think mine was right the first time and now it's the wrong way round.
> 
> ...


The float works a bit like the systern/ball**** in your toilet. The bowl holds the fuel and the "float"......floats when the fuel fills up. When that happens it lifts the needle valve and this closes the fuel supply.

In short, when you remove the drain plug, fuels should come out.

If that is not happening, thats your problem


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## Andyblue (Jun 20, 2017)

Have you tried to get a spark from the plug - I know you’ve tried with a strobe, but if your plugs not sparking, it ain’t 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 that’s good, so it’s a fuel starvation issue, so check you’ve fuel in the little reservoir under the float, check the jets are clear etc.


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## Tykebike (Mar 27, 2016)

Is this a problem after winter storage or does it happen all the time? It amy be that the fuel has lost its' oomph over winter, one does even though it has the Briggs and Stratton fuel additive in it. I've taken to using Bradex to get it started in the first few weeks. 
Now all I have to do is summon up courage to get the hedge trimmer out and give that a damn good Bradexing!


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## Rakti (Nov 11, 2019)

Tykebike said:


> Is this a problem after winter storage or does it happen all the time? It amy be that the fuel has lost its' oomph over winter, one does even though it has the Briggs and Stratton fuel additive in it. I've taken to using Bradex to get it started in the first few weeks.
> Now all I have to do is summon up courage to get the hedge trimmer out and give that a damn good Bradexing!


Well, I've had the carb off 3 times in the past two weeks (and disposed of the old petrol), so no old petrol left in the carb or tank. Pretty sure I drained the carb last autumn any way.

I will try pouring petrol in the tank with the carb drain plug removed next. 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.

The mower's at my mum's 8 miles away, so can't do anything until I go.

I found this excellent video (looks like the same carb) that clear's up which way the jet goes in, at around 4:14;


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## blademansw (May 23, 2011)

Watch this guys channel for a bit for a master class in getting recalcitrant machinery to run
https://www.youtube.com/channel/UCcSeeATlWJJbXpOZRYOfaDg (Mustie1).

There is a process to follow which is laid out in his videos. Basically, air, spark, fuel. If all those things are present and correct barring a mechanical issue the engine must run.

The carbs on these things are so small you can generally fit the bits in an Aldi (or similar) ultrasonic cleaner - this will clear out any hidden ****.


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## bigbrother (Jun 30, 2011)

Rakti said:


> Well, I've had the carb off 3 times in the past two weeks (and disposed of the old petrol), so no old petrol left in the carb or tank. Pretty sure I drained the carb last autumn any way.
> 
> I will try pouring petrol in the tank with the carb drain plug removed next. 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.
> [/url]


Ok looks like you have definitely exhausted all fuel related issues and you are sure it's not the spark plug, any petrol fuelled engine 2 stroke or 4 stroke if the engine starts from cold then won't start when hot it's a very good chance it's the coil, if they are faulty when they get warm/hot they will not work, there is no reason for them to go they just die.


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## Caledoniandream (Oct 9, 2009)

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.


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## grunty-motor (Aug 11, 2016)

Rakti said:


> .......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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## Rakti (Nov 11, 2019)

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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## Caledoniandream (Oct 9, 2009)

Probably the float needle stuck / corroded, pull the pin out the float and carefully remove the float, don’t 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 it’s 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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## Rakti (Nov 11, 2019)

Caledoniandream said:


> Probably the float needle stuck / corroded, pull the pin out the float and carefully remove the float, don't 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 it's 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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## Rakti (Nov 11, 2019)

Andyblue said:


> Have you tried to get a spark from the plug - I know you've tried with a strobe, but if your plugs not sparking, it ain't 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 that's good, so it's a fuel starvation issue, so check you've 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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## blademansw (May 23, 2011)

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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## Rakti (Nov 11, 2019)

Rakti said:


> 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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## Caledoniandream (Oct 9, 2009)

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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## Rakti (Nov 11, 2019)

Caledoniandream said:


> 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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## grunty-motor (Aug 11, 2016)

you have checked that fuel is getting to the carb??? (i.e. not a blockage in the petrol tank or hose)


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## Rakti (Nov 11, 2019)

grunty-motor said:


> you have checked that fuel is getting to the carb??? (i.e. not a blockage in the petrol tank or hose)


Absolutely! First thing I did when no fuel came out of the bowl drain plug was place a bowl under the fuel pipe and remove it from the carb. Fuel flowed freely.

If Cal is right that the float angle in my 2nd photo is correct, I can only assume that my cleaning of the fuel inlet pipe was unsuccesful and there is still lots of crud blocking it.

Just wondering if maybe I didn't wait long enough for the float chamber to fill up. I thought it would be pretty much instant but maybe it takes a few minutes?


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## Caledoniandream (Oct 9, 2009)

For £12 it is worth a go, there is definitely a blockage, assuming that the fuel flows freely out of the pipe when you open the fueltap.
The bowl should fill instantly and relatively flow fast for the size of pipe. 
So open the fuel without anything attached and it should come out, if not than you have a problem there.


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## grunty-motor (Aug 11, 2016)

As above, just buy a new one - and an inline filter.


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## Rakti (Nov 11, 2019)

Fitted a new carb today. Engine fired up first pull. Great £12.59 spend which included a new gasket (filter side) and sealing washer (engine side) that I'd already paid £3.24 for. It also included a new fuel hose that was half the size of mine.

Many thanks for all your help:thumb:. What a great forum this is.


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## Andyblue (Jun 20, 2017)

That’s great news :thumb:


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## bigbrother (Jun 30, 2011)

bigbrother said:


> Sounds like you have exhausted all fuel issues apart from a new carb, sometimes its better to bite the bullet and buy a new part, [/URL]


Ha told you so, pleased you to my advice LOL :lol::lol:


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## Rakti (Nov 11, 2019)

bigbrother said:


> Ha told you so, pleased you to my advice LOL :lol::lol:


Yes, well done, you were right. Wish I'd just done it straight away. TBH though, I didn't realise they were that cheap. Thought maybe £45-£50.


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## kartman (Aug 2, 2012)

This will be a rubber seal somewhere in the carb being eaten by likely E10 ethanol content in fuel. It may have broke a bit of rubber off and blocked somewhere. Either use super unleaded as this is currently capped to E5 or drain mover and carb off fuel over winter.


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## Caledoniandream (Oct 9, 2009)

kartman said:


> This will be a rubber seal somewhere in the carb being eaten by likely E10 ethanol content in fuel. It may have broke a bit of rubber off and blocked somewhere. Either use super unleaded as this is currently capped to E5 or drain mover and carb off fuel over winter.


The other problem E10 has it is hygroscopic (attracts water) and causes aloys to corroded, causing blockage.


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