Briggs and Stratton Sprint 45

[rkinsella]

Hi folks,

Forgive my posting in this forum, I think this is closer to a car question than it is to a Garden question.

My Petrol Briggs and Stratton Sprint 45, has started to cut out after a few minutes.
Initially it starts fine.
Then it starts to struggle and putter.
Eventually it cuts outs, altogether.

I removed the air filter and found it was full of oil.
I replaced with a fresh new air filter and checked the oil level, which where fine.

Started here up, and got the same again ... putter, splutter and dead.
Any clues, as to what I should try next?

Ray K

 

[Burnerman]

On this engine, the fuel tank is below the carburettor, so fuel has to be pumped from the depths of the tank to a holding chamber so it can be inhaled by the carburettor.
Between the carb and the fuel tank is a gasket, complete with a very thin diaphragm that pumps the fuel up to the carb.....these gaskets/diaphragms are very prone to failure and its best that you fit a new one.
At the same time, the carb is a very simple affair but it does respond well to a good clean with an aerosol of carb cleaner.....pay particular attention to a 'dip' pipe that pokes out of the carb and rests in that holding chamber - there is a fine filter on the end that must be clear.
That should sort you, but an air cleaner full of oil means that the machine has probably been tipped on its side - rather than back on its handles. Wash the filter in petrol, dry and thinly oil the sponge filter.
Hope this helps!
John

 

[Peter.N.]

The parts can be obtained very cheaply here:

http://www.ebay.co.uk/sch/i.html?_f...0&_nkw=briggs+and+stratton+diaphragm&_sacat=0

Peter

 

[Burnerman]

That's the one!
Its important that the diaphragm fits to the tank face, with the gasket above, facing the carb.
John

 

[Nige F]

That's the one!
Its important that the diaphragm fits to the tank face, with the gasket above, facing the carb.
John

What happens if it's reversed? I may have done it wrong accidentally

 

[Burnerman]

The thinner diaphragm has 'flap valves'......looking at the thing, there are two, and they are a solid U shape.
These flap against drillings in the tank face and if the gasket is in the wrong place it will interfere with the pumping ability of the carb. The gasket at the top also gives more space for fuel to flow.
To be honest I'm not sure if this will disable the engine completely....certainly it does with Stihl machines but they aren't the same.
You may be able to see the thin diaphragm and thicker gasket in place?
John

 

[rkinsella]

I took off the spark plug and found that it was _full_ of oil.
So I took off the head gasket to see what was going on, and I found the following.



As you can see the gasket is gone in the top left corner.

And head is completely choked with carbon.
I presume this is from me tipping the lawnmower on it's side to clear out wet grass too many times.
Oil mixes with the petrol, petrols burns and creates all the smoke and residual carbon, I see here?

Part of the problem?
What should I do?

Ray K

 

[Burnerman]

Don't worry too much about this, Ray......these engines are side valve and notoriously inefficient. Hence the carbon build up - they simply aren't well enough designed to keep it clear.
The fact is, the head bolts benefit from being tightened after the first year of use - but no one does! Hence the weeping head gasket which will have been slightly leaking for ages.
So.....with the valves shut, scrape the carbon away and wipe clean with petrol or whatever. With the valves open, gently brush around the valve head with a wire brush - a soft brass one if you can. Wash the crap away.
Reassemble with a new gasket (if there's a chunk missing) and tighten down, job done!
If you want to get under your mower, always tip it back on the handles.
John

 

[rkinsella]

When you talk about the "valves", you mean the valves to the right of the cylinder/piston in the photo?
(what do these do BTW?)
Do you think the Gasket between the Carburettor and the fuel tank still needs a look?

Thanks,

Ray K

 

[Burnerman]

Yep, if you spin the flywheel, the valves will happily open and close, allowing you to clean things up.
The valves let the air / fuel mix in, than allow the exhaust gas out.
The inlet valve will have softer carbon than the exhaust one, which runs at a higher temperature.
So, make good the repair here, and then it's back to the carb if there's no improvement!
John

 

[rkinsella]

The diaphragm between the Carburetor and the Fuel Tank appears to be intact.



The Carburetor sits on top of fuel tank shown below.
Plastic tube goes through the hole on the left and sucks the fuel into the Carburetor.

There is another larger hole on the right, doesn't appear to go through to the Fuel tank.
It had a good bit of dirt in it, I cleaned it out - any ideas what this does?

 

[Burnerman]

The plastic dip pipe ( with the morsel of crap in the filter ) takes fuel from the tank and then deposits it in the other chamber, which you've just cleaned out - ready to be drawn into the carb to be mixed with air.
Your tank seems to have some grot inside?
It's really best to replace that diaphragm and gasket, because it tends to get a bit floppy and wrinkly with age. If you remove it, look out for the spring on the underside!
John

 

[rkinsella]

which you've just cleaned out

I have gotten 60% of the crud out - with kitchen roll and WD40.
Its proving tricky to clean.

Your tank seems to have some grot inside?

Yeah - the inside of the tank appears to have rust spots!
I empted out the petrol - should I clean it out with Carburetor Cleaner or similar (WD40?).

 

[Burnerman]

The best stuff you can use is a proper carb cleaner.....it's a pressurised aerosol and contains toluene, which will degrease almost anything. I'm fortunate to have a huge air line which also helps!
Wash your tank out with petrol if you can to reduce reoccurrence.
John

 

[rkinsella]

The best stuff you can use is a proper carb cleaner.....it's a pressurised aerosol and contains toluene, which will degrease almost anything.

Might invest in a can of compressed air :-p