Hunting B & S 4 stroke mower engine

[robgraham]

OK when cold, but irritating when warmed up. Is this a carburettor problem - that is dirt in the jet or something ?

Rob

[NT]

Hunting usually means a mixture problem, so almost bound to be the carb. I'd start by cleaning it out and checking float level.

NT

[Nospam]

Replacing the carb gasket should solve it.

[Dave Liquorice]

carburettor

Probably, my B&S mower started hunting. One of the flap valves in the gasket between the upper and lower halves of the card ahd managed to get itself down the hole it was supposed to cover. Put it back in the right place an carefully reassembled and it's been fine since (years). Might have to mow the grass for the first time soon...

[Jules Richardson]

Which engine and how old? I've got a 10HP and 11HP here, both mid-80s vintage, and the carbs on both are worn around the throttle spindle holes, so they suck (varying amounts, depending on vibration etc.) air in via there and hunt a little because of it. I'm not sure if rebuild kits are available, but I suspect that they don't address this problem even if they are - I think the shaft holes are bored straight into the carb body, rather than using any kind of insert. It's on the to-do list to try and improvise my own at some point...

If yours is an engine of similar size / age to mine, then check that the mounting bracket which holds the mechanism linking the governor back to the carb isn't loose; ISTR having that problem once too as the mounting bolts worked free, and the governor was no longer able to maintain a constant RPM.

cheers

Jules

[Pete Shew]

My B&S ride on engine had a solenoid in the bottom of the carb. The purpose was to prevent unused fuel banging in the exhaust when the engine was turned off.

It started to fail to hold the cutoff needle valve open when warm, so the engine would stop and couldn't be restarted until it had cooled.

Solution, remove the solenoid and replace with, IIRC, a short 5/16" UNF bolt to hold the float changer. Now no problems as long as I allow the engine to return to idle before turning off to avoid bangs.

Alternate solution, spend over £100 for a new solenoid!!!

[robgraham]

Hi Jules - can do better than that; I inherited an old cultivated and found that the single cylinder B & S engine on it had a great long serial number. Part of that number gives the date of manufacture - April 1964. I had to do a decoke recently and actually managed to get a head gasket for from a local dealer. The carburettor is as basic as they come and only works well with the fuel tank about half full.

Thanks to everyone for their input; that's now on the list of tuits.

Rob

[Dave Liquorice]

A lot of these small engines use a foam air filter soaked in oil...

[robgraham]

That was the first thing I did ! And should have possibly said so in the original post !!

Rob

[The Natural Philosopher]

My B&S all have paper ones.

[Andy Champ]

... which I always cleaned in petrol. It really needs to be dry!

Andy

[Jules Richardson]

Nice! As it's on a cultivator, I assume it's a horizontal-shaft engine? Some of those had cast cylinder liners, so they're pretty much bomb- proof... (I don't know if B&S ever offered verticals with cast liners too, but perhaps they did)

Pulling the head and decoking is on the list of routine maintenance for my pair of (newer than yours) engines - the interval's quite low, something like 50 hours (it takes me about 3 hours to mow our lawns, so I can pretty much put that on in a season).

So far I've just kept reusing the same head gasket with no apparent loss of power; they're very thick and heavy-duty on my engines and the torque for the head bolts isn't high - but I'm not sure if you're technically supposed to replace it every time the head comes off (as is the case with most engines of course!)

cheers

Jules