You may have water in your carburettor. It will have collected in the float chamber and semi block the flow of petrol. I think most models have 2 bolts with xcrew heads holding on the top so easy to remove.
(My 1972 B&S 3.5hp - ex my father - is still going strong in a Hayterette rotary mower..not spent a penny on spares but cut a new air filer from foam every 3 years.Used for about 15 hours a year with annual oil changes)
madf
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Tipping, eg to clear clogged grass from the blade and body, should be towards the carburettor. If you tip it the other way it fills the silencer with oil - you will recognise the symptoms by the dense clouds of blue smoke, when you eventually get it to start again!
Most B & S I have seen - I have several in various mowers and rotavators, have an automatic choke flap working by suction. It is a pivotted plastic disc just underneath the air intake, shaped so that the air cleaner bolt clears it down a groove. If this gets clogged, eg by grass or the air cleaner bolt not in straight, then the flap doesn't open fully when the engine fires.
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Secondary question. I have about 1/2 gallon of potentially dirty fuel left in a can. What can I do with it? Will adding it to the Omega affect anything? If so how can I dispose of it???
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Keep it to light a bonfire ;)
Or, seriously, you may be able to dispose of it at your local tip, or keep it for cleaning mower bits etc.
H
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Sorry, and I realise you were joking, but never never use petrol to light a bonfire. Incredibly easy, even with great care, to finish up in a flame front of your own making.
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Update: I've changed the petrol and cleaned and reset the plug. it runs a lot smoother, except it seems to be lower on power (i.e. moves slower) than I remember it. I also still have exhaust smoke, whcih I don't recall seeing before.
I'm going to get a new plug next...
I browsed the B&S web site and had a long hard look at the engine. I don't believe there is any (useful) adjustment I could make to the carb but I don't mind being proved wrong. There is no manual choke and I can't see any adjustment screws - and the manual for teh engine says "choke - if fitted" which I guess must mean some engines don't have them. There is a primer button for starting.
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Glad you got it fixed.
Our mower which had problems starting recently (see IHAQ) has never needed the choke. The primer button should be sufficient just to flood the jet for starting from cold.
Re it being down on power. It should run at a constant speed, as you say, adjusted by the governor. By down on power, do you mean that the engine speed reduces significantly now when you take up drive? If not it's probably just your perception, or the governor's mean (mal)adjusted, unlikely if you haven't touched it.
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Mike Farrow
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It's my perception I think. Engine speed stays constant when you let the clutch out - just seemed a slow walk today...
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Could there be some power loss between the engine and the wheels? This opens up more potential problems from slipping drive to gummed up wheel bearings.
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If runs ok for few secs then runs rich, clearly carb prob. I had similar prob in a Villiers mower engine - cause was the small brass valve which the float pushes up to regulate amount of petrol entering the float chamber. [years ago I lost it while cleaning carb and had made another out of a brass screw which never fitted very well].
You probably had a bit of grit causing overfilling and rough running. The test is to turn the petrol off. Rough running will eventually return to normal as the mixture weakens, then rev slightly faster briefly, then die as the petrol runs out.
Incidentally, all four of my mowers, average age >30yrs, run better on bog standard unleaded.
Use old engine oil after 10,000m - still perfectly ok for old mower engines.
Suggest filter your old petrol with paper coffee filter.
Recently I found a firm which does spares for ancient mower engines. It's called 'Meetens' - tel 0845 634 0295.
Happy tinkering!
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I tinkered this weekend. Fitted a new plug and it's still the same - smoother but feels a bit underpowered and a little smoky.
I bought the plug from a B&S service agent. He said it's probably the diaphragm (mentioned above) which he will swap for c £55. The part costs c £9. Am I going to get in a mess if I try doing it myself?
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Plug unlikely to cause prob - mine are as old as the mowers! Sometimes the HT lead can need a bit of a trim at the hot end after 10yrs if the spark not getting thru and the points are ok.
Definitely sounds like a carburettor problem but I don't know anything about 'diaphragms' apart from when found in fuel pumps, which none of my mowers have - all gravity fed.
If it's newish I would take the carburettor to bits, clean carefully, reassemble - and see what happens! If it's black smoky not blue smoky it must be running rich and there aren't too many causes of that.
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If it's the diaphram I am thinking of then it's actually a simple fuel pump. The petrol tank is underneath the carburettor, and the fuel is pumped by some kind of process that uses the induction pressure - "sucked" in short. That is why priming is necessary to start the process.
It is a straightforward job, but I have to say when I replaced one once it didn't make the slightest difference. I just replaced the whole carburettor from a scrap mower.
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The part costs c £9. Am I going to get in a mess if I try doing it myself?
For what he's charging it may be a pig of a job, but it sounds like only a couple of hours work, if that. There's no harm trying and then taking it to him if you hit any problems. As mentioned, plugs don't really cause problems, our mowers still on it's original after 30 years.
Cliff, would the priming button also serve mainly as a cold start "tickler" since there is no choke?
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Mike Farrow
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Cliff, would the priming button also serve mainly as a cold start "tickler" since there is no choke?
That's my understanding of how it works. I think they are really pretty crude engines with rather imprecise fuel measuring systems. Even ones I have had with manual chokes only needed the choke for the first few seconds of running. I think the primer just sloshes in some petrol, it splutters into life, and after that manages to draw the petrol it needs in vaguely the right sort of mixture. The "automatic" flap (choke?) I most commonly observe is just spring-loaded. When the engine is spun on the cord it is like putting your hand over the intake, enriching the mixture (old dodge for cold weather starting). As soon as the engine fires the suction opens the flap again.
I may be wrong, and a B & S spokesman is going to claim that they are masterpieces of precision fueling and that their exhausts are cleaner than the air that went in. But I have read somewhere that mowers and their relatives are actually quite a significant source of pollution, but their engine size makes them unsuitable, or uneconomic, for fuel injection.
You can't really go wrong taking a carburettor to pieces and cleaning it out, unless you are hoping to reuse any of the gaskets and diaphrams. They tend to weld themselves to the castings, and come to pieces when opened up. A thin sharp knife sometimes prises them off intact.
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I had this problem with my B&S Classic 5, after fuel, additive etc... I removed the carb (plastic it was too) and the very thin diagphram which acts as the pulsejet pump had shriveled a bit causing the mixure to be all over the place. A new one was £2.50 from Henton and Chattel in Nottingham, put on and it's never run so lovely! The person who said that Mobil 1 is too good as the mower never gets hot enough is totally wrong! It's an aircooled engine and runs much hotter than a car engine!
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Ah, reminds me of the time I tried to stop a lawnmower by pulling off the spark plug cable. Took a firm grip on some black rubbery stuff to brace myself and grabbed the plug... Turns out the black rubbery stuff was oil drenched metal. ;-)
Rest should be self explanatory.
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Ah, reminds me of the time I tried to stop a lawnmower by pulling off the spark plug cable. Took a firm grip on some black rubbery stuff to brace myself and grabbed the plug... Turns out the black rubbery stuff was oil drenched metal. ;-) Rest should be self explanatory.
Did a very similar thing myself - mower wouldn't start - thinking perhaps flooded or no spark? Removed plug, reconnected lead, swung engine - fuel gushed out over mower body, ignited by spark plug - still has fried paint + curly plastic badge.
Only in the BR would a thread on this keep going so long!
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I had this problem with my B&S Classic 5, after fuel, additive etc... I removed the carb (plastic it was too) and the very thin diagphram which acts as the pulsejet pump had shriveled a bit causing the mixure to be all over the place. A new one was £2.50 from Henton and Chattel in Nottingham, put on and it's never run so lovely! The person who said that Mobil 1 is too good as the mower never gets hot enough is totally wrong! It's an aircooled engine and runs much hotter than a car engine!
>>
If you don't believe me that Mobil 1 is too good for a lawnmower, go to a mower shop and look at the spec of the specialist mower oil. I think it is SD or SF.
I was told by a mower repairer to use "cheap" oil.
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The important thing is to change the oil regularly since there's no oil filter on these engines. I use a standard SAE 30.
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Well having baosted above about my old lawnmower.. about a week later it had similar symptons. I replaced the diaphragm, air filter, plug and 2 gaskets for some £20 and it's all going perfectly again.
'Meetens' - tel 0845 634 0295 were very helpful. Despite the age (1974 not 1972 as above) my spares were delivered within 4 days of my order.
madf
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Makes you wonder if it's modern petrol, I know they have reduced sulphur again in diesel and not made it well know. Nayve petrol has been reformulated in the last year?
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Just to round this one off, rather belatedly I have replaced the diaphragm mentioned above (even though it did not appear to be split). It cost me £10.14!
But the mower now works perfectly again.
Thanks!
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Oh Joy! Thanks quizman. Smokie described the fault with my B&S exactly, and your suggestion ws spot on. In fact the thin diaphragm had not split, but had become slightly rucked near one of the retaining bolts. All I had to do was straighten it out and make sure it was laid well flat before clamping the carb back together. Thanks - now runs like new.
P.S My three year old mower has been abused with two-stroke oil, overfilled with oil and tipped up the wrong way to empty excess oil out. I have even had to syphon out water from the petrol tank on ocassions and it still runs perfectly well on unleaded!
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I've just bought my first petrol mower with a B&S "450" 148cc engine. There's some really good info here for future use. :-)
Good to know these are reliable. This is a cheap manually propelled mower with fixed throttle and no choke. Starts in one or two pulls though.
Cheers
DP
Edited by DP on 13/05/2008 at 23:11
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He said it's probably the diaphragm
I had a problem with the carburettor diaphragm on our Briggs and Stratton-engined Mountfield after only a few weeks of use. The service agent said it's a common occurence for the diaphragm to pull out from one or more of its clamping lands, and that even some brand new mowers need a new diaphragm. Having looked at the old diaphragm I'm sure he's right ~ the clamping lands are miniscule and I can well imagine the adjacent metal parts not mating up correctly in places. I think it's probably the result of computer aided design which allows small details to be magnified and for the designer to lose his sense of proportion ~ assuming he had one in the first place. It was much more difficult to draw details too small in the days of drawing boards and pencils.
Edited by L'escargot on 14/05/2008 at 10:21
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I have a B and S 6hp intek overhead valve on my mower. When it began to run unevenly and was difficult to start when warm I found the grub screw had fallen out of the little lever adjustment mechanism for fast running on the carb - it's in behind the priming button on this engine.
Because I realised this would be an ongoing problem I substituted a blob of Bluetak to hold the lever in place and it's been fine for three years.
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Fancy this cropping up.
I had my mower in bits at the weekend. It's a knackered old thing that needs some new parts. Briggs and Stratton sidevalve engine. It did start briefly but then spluttered to a stop. Sounds like the diaphragm.
Thanks to all for the input into this thread.
Steve.
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Mobil 1 in a mower. What viscosity Mobil 1. Most mower type engine require a monograde oil like SAE30 or 40, it is not a pumped system and the oil need to coat parts quickly at start up. Depending on your Mobil 1 it mat be far too thin on start up. Regards Peter
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My B and S engine handbook that came with the mower 6 years ago only says 'use fully synthetic oil'.
I've always used supermarket 5-30 and changed it every year as per recommendation. It always stays clean and the level doesn't drop.
Briggs and Stratton has a website, IIRC, that is quite useful.
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This website may help for spares. tinyurl.com/6agvav
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It's funny how this thread can splutter almost seamlessly from 2005 to 2008 and it all seems just as relevant as it was in the original posts. The good old Briggs and Strattons just keep chugging along. Hands up anyone who has actually changed their oil in the meantime?
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I changed the diaghram in the carb just after I posted in 2005.
Oil change every year. Tesco's finest multigrade ex ebay £1 for 2 litres.
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I have.
Still wish I'd bought a mower with a Honda 160 though...
I've been looking at bigger and better mowers recently and it's amazing to see most B and S engines are still sidevalves.
Same sort of American take on technology as Harley Davidson, I guess.
Edited by mike hannon on 15/05/2008 at 18:39
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Briggs and Strattons just keep chugging along. Hands up anyone who has actually changed their oil in the meantime?
Yes - was knocking a lot - [5hp on Ransome Hahn rideon bought second hand 1979, was ancient even then] - took head off - piston had such a thick layer of carbon it was hitting the head! Wouldn't start well, changed [original] plug, refilled with usual oil from 10,000m car change left to stand for several weeks......now works perfectly again. This is the first attention it has had since 1979.
If it works, don't mend it.
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Have a few hayter pedestrians of various ages used commercially and as a rule the older the engine the better it is... Watch for the ceramic inlet manifolds on the later models that develop cracks that also cause running problems...
Have a Hayter Ranger that is 11 months old and here we go, starts will run forever and a day and then when you stop it and go to re start no play or takes an age to get going again....
Heavily sooted plug with a lumpy running... So looks like the diaphram proble as described..
Have a spy at this site I found for briggs bits which may be a help to you guys...
www.briggsbits.co.uk/
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