i have a briggs 35,thats 3.5 horse power not the 350 hp twin turbo V8 model,after it has been running for about 15 mins,the engine starts to run a bit rough,like it,s flooding,puffs of black smoke from the exhaust etc,had the carb and air filter to bits,all looks ok.
any ideas peeps ?..

yes, it's knackered.























spark plug?

How old is the petrol, fresh?

choke stuck on, running too rich, needs a rolling road and re-map?

Is it rich or oily smoke John? The B&S engines have a breather pipe that runs from the crankcase to the air intake which means if you tip them on their side when you clean underneath you get a carb/air filter soaked in oil. I usually tip towards the back of the mower, this seems to be ok.

Overfilling with oil can give similar issues, you need to check the level with the dipstick screwed in, not just resting on the top of the threads.

Usual problems with the carb are the diaphragm, or blockage in the pickup pipe that dips into the tank - these usually cause fuel starvation though, doesn't sound like your problem.

Sounds like an excuse for a BEM to me. ZX6 should see you round the garden pretty quick.

I had one that did this - then it started to not want to start, then it wouldn't start........ bought a new cheapo electric one and haven't looked back

To be fair I never looked after the Briggs engine (10 years old) but I messed about for ages with it when it broke and everything works as it should according to a manual I found but it still runs like a bag of sh*te - life is too short and grass doesn't stop growing at this time of year

cheers guys,no choke so cant be that,new petrol,ill have a look at the breather pipe as i do turn it on it,s side to clean out,as for BEM.....dont put ideas into my head
garden is too big for a lecy one anyhow,i know i would run over the lead and chop it....just like i did with my hedge trimmer

[Edited on 30/5/14 by theconrodkid]

Does it start to run normally when it's about to run out of petrol? mine did which (along with a compression test) told me it was the carb. Took that to bits and cleaned it (and the breather pipe) in a proper ultrasonic tank and........ no better. I wasn't buying a new carb 'just in case' so I left it to be honest

quote:

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,i know i would run over the lead and chop it....just like i did with my hedge trimmer

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never run it out of petrol,it,s fine for the first 15 mins or so then starts to play up and geoff....you know what i mean

breaks and scrap'em

[Edited on 30/5/14 by ste]

Mine did something similar, put a new carb on it for £15 off eBay sorted it.

It also stopped running if half empty on fuel and if it started struggling if I tilted for a couple of seconds it would sort itself out.

I could not see anything wrong with the old one, it may have just been a knackered gasket.

Know nothing about the engines but if its always after 15 mins could it be heat related?

Mike,thats what i am thinking, i start at one end and when i reach the same point every time it starts playing up.ill have the carb apart again but if it,s something too complicate it may be time for a new one

Tried a new spark plug?

I wnder if pouring water or placing wet cloth on just thr carb being careful none gets inside to cool it down makr a difference

Does aound like hrat related,

Does it cut out when idling?

Does winding up the speed makr a difference?

new plug on order,changed the oil,washed air filter and it runs better now,i think the problem may have been the govenor springs....pinkies crossed :-)