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  • Poxy Lawnmowers, carburettor advice welcome
  • Premier Icon spooky_b329
    Full Member

    I was going to sign up to a lawnmower forum but it seemed a bit dead, but I bet I’ll get better advice here anyway. Advice is welcome as if I resort to buying a new mower, its going to seriously hamper my efforts to treat myself to a nice new helmet light for night rides this autumn!

    I’ve got a Mountfield lawnmower with the HP164 engine, for about three years now its had a hunting problem, I pull it apart each year and for a couple of cuts I think I’ve fixed it, and then its back to its old ways. Its had a new fuel pipe and filters, carb gaskets, posh unleaded fuel, all the springs and linkages seem ok. Parts are expensive so I’m reluctant to keep throwing money at it each year.

    This time I found a top tip that there is a little washer in the carb that perishes. Sure enough, I pulled out the plastic plug and the lower o ring fell to bits. None of my o-rings fit and the plug won’t seat properly with them, it seems to be a very thin square/flat low profile o ring. I managed to bodge it by poking a hole in a tiny disc of inner tube and it ran great for the next 20 minutes so I thought I’d cracked it. Now it won’t start, as suspected the o ring I bodged doesn’t like contact with petrol.

    I’m not sure what this part is, I’ve got a suspicion its the pilot jet? A new complete carb is £40 plus extra for the gaskets, and of course there is always a chance I’ve not found the main fault. Seems mad to buy a whole carb for the sake of some tiny O rings…the carburettor part number is 118550697/0 but I can’t see a diagram or any details of the carb itself.

    Any advice on what material I can cut a tiny O ring from, or perhaps a selection of O rings for this type of application?

    Premier Icon blokeuptheroad
    Free Member

    I think nitrile o rings are good for petrol. Rubber is no good. You can get o ring sets on Amazon and Ebay.

    Another top tip to keep lawn mowers running, use fuel stabilisers. It stops the fuel gumming up the carb jets as much, as it gets old.

    Premier Icon hunta
    Full Member

    You can often buy carb kits that might have the O ring rather than whole new carbs, but I’m guessing you know that having spent some time researching already. Thought it worth a long shot though…

    Premier Icon colp
    Full Member

    That looks too big to be a pilot jet, they are tiny (the hole). Think that’s your main jet

    No start / bad idle is often the pilot jet, they do get gummed up, a guitar string will sometimes clean them.

    Premier Icon sharkbait
    Free Member

    You def want nitrile for petrol applications – easily found online for very little money.
    Problem you have now is that the inner tube has probably disintegrated/turned to goo and blocked the jets which now need cleaning.
    🤦🏻‍♂️

    Premier Icon boblo
    Free Member

    Are you sure it’s £40 for a carb? I recently bought a service/rebuild kit for Stihl hedge trimmer that was misbehaving then found a new (copy) carb was £11!

    Premier Icon Cougar
    Full Member

    You’re draining the petrol out of it and then running it dry after you’ve used it, right? The (ethanol / methanol?) in modern petrol rots rubber, you can’t leave it laid up for months.

    Are you sure it’s £40 for a carb? I recently bought a service/rebuild kit for Stihl hedge trimmer that was misbehaving then found a new (copy) carb was £11!

    I had this exact experience resurrecting a petrol strimmer earlier this year. A service kit was like £12, a replacement carb £15. No brainer.

    Premier Icon fettlin
    Full Member

    How soon do you want it?

    Carb from China HERE for less the 20 notes delivered, just won’t be here till next month.

    Premier Icon hot_fiat
    Full Member

    ^^what cougar said^^

    I have this every year on both my Hayter mower and my old KTM950. Modern petrol is rubbish in old tanks. Comma petrol magic will sort of stabilise it.

    Premier Icon spooky_b329
    Full Member

    Thanks guys, I don’t normally drain the fuel as the first three or four years it was bomb proof! Will from now on.

    The carb was £13 direct from China, can’t find any service kit so although I’ve blasted it with cleaner I’m reluctant to take the bowl off as I bet it will ruin the main seal. £37 is the cheapest although there is one ‘bidding’ auction currently under £20.

    What’s a bit worrying is I repeated my bodge last night but still won’t start, pretty sure it’s a fuelling issue though. Perhaps I’ll stump up for the carb, if it doesn’t work I’m sure I can resell it next door spring!

    Premier Icon spooky_b329
    Full Member

    Just changed my search terms (by mistake) from the part number to HP164 carburettor and found two UK sellers with carbs between £10-£16. Even better is it includes the gaskets which is another £7 I don’t have to spend.

    If you search by 118550697/0 the same product is twice as much!!!

    So perhaps it has one final chance before being replaced with a battery mower…

    Premier Icon boblo
    Free Member

    It can’t be right that you (we) can get a new carb imported from China than less than the costs of the bits to keep the existing stuff going. No wonder the world’s gone to hell in a hand cart…

    Premier Icon neilnevill
    Free Member

    Yep ethanol in petrol is a problem, although aging petrol caused problems anyway. It helps to use a premium fuel, it helps to use stabilser (I use startron) and it helps to buy small can fulls more regularly. I don’t think it’s necessary to empty the tank after every mow, if you’re expecting to mow again in a week or 3, but I do try to empty the tank and run the carb dry before leaving the mower for the winter.

    Premier Icon Nobeerinthefridge
    Free Member

    Crikey, my mountfield is 14 years old, never drained fuel or run it dry, starts first pull every year.

    I reckon the rust will defeat it before the petrol does!

    Premier Icon johndoh
    Free Member

    I have a similar issue (see my threads about this going back a couple of months) and I hope someone can help. I have a B&S engined mower which started misbehaving recently (hunting) and I noticed that it was leaking around the carb so I replaced the gaskets (with genuine B&S spares). Unfortunately it was still leaking (although running a bit more smoothly) so I dis-assembled again and noticed that the carb had warped and therefore wouldn’t get an air-tight seal. So I then replaced with a new (again, genuine B&S) carb and it fixed the leak (which should mean it was also air-tight) however it still hunts (although not as bad as it was and it gets a bit better once fully warmed up.

    All Googling I have done simply says ‘replace the gaskets and it will run perfectly’ yet I can’t get it to run as nicely as I would expect.

    Any ideas?

    Premier Icon trail_rat
    Free Member

    And here I am using a 20l Jerry can of fuel I bought before the first lock down to keep the chainsaw going…in my mountfield that’s never had the fuel drained.

    I had a stuck float in the bowl which caused a hot start issue (and fuel over flow) a couple of years ago but that was due to a pin shifting out of position and jamming it.

    If you have got the length of the governor rod wrong or bent it trying to refit it- it will hunt for ever as the guvernor constantly adjusts the throttle to hit the sweet spot.

    Common issue on DIY repaired mowers.

    Premier Icon fettlin
    Full Member

    Replace the spark plug.

    sounds daft and all experience suggests hunting is an air/fuel issue, but!

    I had the same on my Honda engined mower, wouldn’t run clean so i swapped with a spare new plug I had in the garage and hey presto! running nicely again.

    Premier Icon johndoh
    Free Member

    Replace the spark plug.

    I did that at the same time as the carb. kit came with a new spark plug so I bunged it on even though the original looked fine (if a little blackened)

    Premier Icon Cougar
    Full Member

    never drained fuel or run it dry

    Depends what it’s made out of I suppose.

    Is it 14-year old fuel too? If you look a a (newer) petrol pump you’ll see something like (E10) on it. That’s 10% ethanol, that’s what kills the squishy bits. Higher octane fuels likely have more ethanol, exacerbating the problem.

    The strimmer I did, the owner had bought it, failed to be able to start it, and abandoned it in the garage for two-three years. When I got it my initial diagnosis (after replacing the old fuel) was a fuel leak. As I fiddled with it, the fuel pipe between tank and carb literally disintegrated in my hands. I got it out in like half a dozen pieces and replaced it (and of course you can only buy the stuff in lengths of about 15 miles), still wouldn’t run. Stripped the carb and the … I don’t know what you’d call them, reed valves? on the gaskets were all shrivelled and perished. New carb and it runs like a champ.

    Premier Icon trail_rat
    Free Member

    You have essentially described a service on a 2 stroke cougar.

    you lot experiencing issues do service your equipment right ?

    While i dont drain down the fuel – it does get a service – and the supply hoses on the 2 stroke strimmer is listed as a service component with a rather short service life.

    2 strokes have short service intervals – the cheaper the engine the shorter it is generally.

    Premier Icon Cougar
    Full Member

    Right. So basically you either accept that you’re going to be replacing bits, or drain the fuel over winter.

    It was an interesting little project to be honest. I’ve never done anything like that before but figured it’s as basic as an engine is likely to get, right? Fuel goes in, spark goes bang, engine goes vroom. If the third bit doesn’t happen, there’s a problem with one of the first two.

    Premier Icon neilnevill
    Free Member

    E5, it’s E5 still i think, E10 may be coming some time.

    While ethanol raises Ron, and can be added to stock fuel to create premium, it used to be the case that the previous law about ethanol in fuel didn’t apply to premium and shell VPower was ethanol free, others like bp Ultimate often were. The current E5 law applies to premium as well. It’s still worth getting premium though I reckon although I’ll leave the reasoning to the stw fuel exoert (there is one, I forget who but there is).

    Premier Icon yeager2004
    Free Member

    The B&S carbs can warp, especially if hot water has been used to clean them with an ultrasonic cleaner.

    One way to get round this is to use two gaskets (with one diaphragm). The other thing is use genuine a B&S gasket and diaphragm. The cheaper pattern kits seem to be of inferior quality, and will either not work at all, or fail very soon.

    Make sure too the fuel pick up pipe isn’t blocked (there’s a small mesh at the bottom) and
    check the recessed part of the tank where the carb fits into is clean.

    Premier Icon spooky_b329
    Full Member

    The mower is still not fixed. Fitted the new carb and gaskets (one gasket didn’t seem quite the right shape where it meets the engine so I added a bit of gasket sealer).

    Still won’t start. Fuel flows freely through the filter to the carb and fuel drains out of the bowl when you remove the screw, and the spark plug is sparking. I can get it started spraying carb cleaner into the inlet and it will run for perhaps 20 seconds if I throttle it up and hold it there but as soon as you step back it just stalls. All the springs and linkages seem to be there, throttle works, nothings bound up. The butterfly valve in the carb is full open when starting, I assume this is correct?

    The only thing I can think of is the fuel but I bought it at the beginning of the year (posh stuff) and it just randomly stopped after the first 20 metres when my wife used it…was running fine 2 weeks earlier. I’m not convinced the priming bulb working properly but once its started on carb cleaner I’d think it wouldn’t matter. The bulb creates good pressure through the pipe that connects to the carb so I don’t think its allowing air in…

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