Briggs & Stratton engine will not run with air filter on

[fivebellies]

I took a petrol lawnmower off of a friend who said that there was something wrong with it, got it home and found that the head gasket had gone, so I got a new one and put it on and changed the spark plug, put it back together and tried to start it and nothing, took the air filter off and tried again and it started and it runs, a bit lumpy, but it runs just sounds like its drowning itself in petrol. So I took the carb off and changed the diaphragm, put it back together and still the same problem. So I changed the gasket on the inlet manifold. But still the same problem, if I start the mower with the air filter off and as soon as the air filter gets anywhere near the carb the mower dies, the air filter 9 times out of 10 doesn't even get to be placed on the carb. I checked the spark plug and it was black, so I gave it a clean. It has no choke or any adjustment screws. Has any got any ideas, as I'm running out. They will be greatly received.

 

[seco services]

The fuel is new and not old.
Checked all the filters jets are clean.

 

[fivebellies]

Fuel is new, will check jets tomorrow. When air filter is off there is a lot of petrol splashing out. What's the best way to check the jets?

Thanks

 

[seco services]

Strip the carb and clean in petrol and blow through the jets etc.

 

[fivebellies]

I have put the carb in a bowl of injector cleaner, leave it in there for a few hours and get it back out and dry it off.

 

[fivebellies]

Still nothing, can hear the engine popping but that's as far as it goes, even with the air filter off, for me to get it to tick over at least twice I have to push the prime bulb, then it starts and then dies. Am lost, maybe the carb is knackered?

 

[JohnD]

if you have to prime it to make it start, then either it needs the choke and/or air filter because the mixture is weak; or for some reason insufficient fuel is getting through, e.g. the jet is now blocked or the needle is too low or the float is stuck (if it has one)

your previous fault (will not run unless air filter removed) suggested that the mixture was too rich. Unless there is some way of altering the mixture adjustment on the carb, this is commonly because the jet has been damaged, e.g. someone trying to clean it by poking a bit of wire down it. The clearance between the needle and the jet is very precise.

Have you had the needle out, and does it have mutiple rings notched into it so you can fix it at varying heights (in which case, higher means richer, since the needle will be tapered)?

carb jets often block with sediment if they are not drained before being put into storage. Slow-running jets, in particular, if you have one. I would not have thought you could clean a jet by immersing the carb without at least partial dismantling.

If it has a fuel system like a fairly modern motorbike, there will be a suction tube from the inlet that opens the petrol tap when the engine is running. If the engine is not running it will not deliver fuel. You can test by sucking on the pipe at the end that should be attached to the inlet manifold

 

[fivebellies]

The carb is one piece with no adjustments on it, it's the diaphragm type carb, I took the carb off, it's only small so that's how I submersed it. it didn't help, the carb looks clean and when I blew through it, all was clear. Maybe compression is a problem? Will try and test that tomorrow, would that stop it from starting?

 

[enyam]

One thing with these engines is that if it has a foam air filter then it should be clean but have been soaked in new oil and then squeezed clean,this prevents any fine particles from getting into the carb.

 

[JohnD]

I haven't had a B&S engine, but I used to have an engine with a diaphagm fuel system, where the suction of the inlet pulled the diaphagm down according to the volume of air passing over it, against a weak spring, and the movement of the diaphagm metered the amount of petrol, by moving a needle in a jet. Is yours like that? mine had an adjuster in the centre of the diaphagm cover allowing the needle to be adjusted (slightly) up and down to calibrate it.

I wouldn't be suprised if the B&S ssytem in a "use-once, throw away" item with no provision for adjustment or servicing

 

[fivebellies]

The air filter is sponge and isn't that dirty and has been oiled. There are no adjustments on the carb or under the diaphragm. I might try buying a new carb and see how that goes, if still the same, then it has to be something with the valves, this is my reckoning anyway.

 

[enyam]

Still nothing, can hear the engine popping but that's as far as it goes, even with the air filter off, for me to get it to tick over at least twice I have to push the prime bulb, then it starts and then dies. Am lost, maybe the carb is knackered?

Sorry didn't see this earlier,when you say push the prime bulb,if its like mine then it has to be pushed four or five times to start from cold,it was in the instructions which I now can't find.Have a look in the FAQ's on the Briggs site there maybe an answer or solution there.

http://www.briggsandstratton.com/support/frequently-asked-questions/

 

[fivebellies]

Yes I do push the prime bulb 3-4 times before trying to start. Just sort of mumbles a bit but never gets going, if I take the air filter off, I can get it to turn over twice by itself then it dies again and won't turn over again unless I push the prime bulb. I had it sort of running without the air filter yesterday, was rough but still ticking over on its own, but today, doesn't want to know. The diaphragm does go down with gasket on petrol tank, then diaphragm on top then the carb?

 

[enyam]

The diaphragm does go down with gasket on petrol tank, then diaphragm on top then the carb?

I haven't got a diaphragm on top of the carb on mine.Watch this although American its relevant.

http://www.youtube.com/watch?v=C5nzigcNTwo&feature=related

 

[fivebellies]

Thanks, I watched that video after I put the diaphragm on myself, and according to that video I had put the diaphragm on the wrong way, that's why I asked if the gasket went onto the petrol tank first? Because I had the diaphragm first then the gasket and the lawnmower seemed to work a bit better, but have changed it to the way that video said. Thanks enyam.