Briggs and Stratton Sprint 45

[rkinsella]

So after a hiatus of nearly nine months - I went back at this. Pushing the my other mower without a self-drive provided the necessary motivation.

I put everything back together squeeky clean but the engine is not catching. When I prime the engine and pull the cord, everything feels fine, moves nice and freely - little resistance but not loose, but the engine does not start. If I over prime it a little it will start to catch, so I over primed it alot and it ran fine for a few seconds, but then cut out. They suggests to me that carburetor is not drawing petrol out of the tank correctly - how can I confirm this?

The diaphragm and gasket are brand new. I took off the carburetor and re-positioned the diaphragm and gasket three times without success, the behavour is much the same afterward. The diaphragm wet and floppy now and curling edges, needs replacing perhaps?

Before I run out and buy another diaphragm and gasket, which will probably do nothing. What are the obvious things I should be trying?

Thanks all.

 

[Burnerman]

I have to say, the genuine Briggs gasket and diaphragm lasts longer than any pattern parts.....!
Check the filter on the dip pipe is clean
Is the 'O' ring that seals the carb to the inlet manifold tube in place
Check that the diaphragm sits to the tank face
Was there any crap on the fine mesh carb filter (not the dip pipe one)
With the diaphragm off the carb face, was the fine spring still there?
On the outside of the carb, you can see where a moulded pipe turns through 90 degrees, and its corner must be sealed with a plug - could this have blown out?
If all else fails, you can get a complete carb from GHS Ltd very cheaply.
John

 

[DaveHerns]

Is there a needle valve in these carbs? Could it be sticking?

 

[Burnerman]

Not on these carbs Dave - they aren't needed as the fuel is below the carb choke.....and the fuel is pumped directly up to the venturi so no float chamber either! They are amazingly effective devices with only one none adjustable jet.
The common issues are rusty fuel tanks - which confuses folks because the top of the tank is aluminium and the bottom half steel.....glued together!
The alloy is there to give a nice flat surface for the diaphragm flap valves to seat well.
John

 

[rkinsella]

Any obvious way I can confirm I haven't stuffed up the head, when I replaced the head gasket and cleaned out the carbon. Presume the head needs to create a vacuum to suck in the fuel air mix. Any way to rule it out as the problem?

 

[Burnerman]

Its most unlikely you have made a mess there.....these side valve engines don't have much compression at the best of times. If the head gasket is intact and the valves weren't jammed open with carbon deposits then forget about it.
Here's a test.....plug out, plug lead out of the way, thumb over the plug hole and crank it over. Your thumb should be blown past with a satisfying chuff!
John

 

[DaveHerns]

I've just been given a 17" Mountfield mower with a B&S engine. What make is the carb so I can look up the rebuild procedure? I see it has no choke flap and the primer squirts fuel straight down the carb.

 

[Burnerman]

There are basically two Briggs engine designs here......the Classic (Rays engine, which has the fuel tank under the carb) or the Quantum which has the fuel tank wrapped around the engine, gravity feeding the carb with petrol.
Both squirt raw fuel into the carb choke when the primer button is pressed which does away with a choke flap. The Quantum has a round float chamber on the carb, and it is a conventional design.
Check out GHS Ltd, who supply pattern parts......but if you have a Quantum engine great care is needed not to lose the needle valve seat (red plastic) when cleaning it out.
John

 

[DaveHerns]

GHS do the complete carb for about £15 it seems .

 

[rkinsella]

What does the moulded pipe supply, it's not fuel, air or the inlet?

 

[Burnerman]

Is that the one with the rubber elbow, Ray? That one is a steel pipe from the valve tappet chamber to the carb so that crankcase fumes can be burnt.
John

 

[rkinsella]

It's alive, works great!!!!!

Cleaned out the carb one more time. This time I actually dismantled the carb and cleaned out the injector. Did the trick, works great.... And I have learned loads in the process, thanks to all.

 

[Burnerman]

Pleased you got it sorted Ray, and cheers for the update!
Do keep a look out for rust in the tank......if it gets bad a replacement is the only option.
John

 

[rkinsella]

Thanks John,

New tank looks to be €45-ish, €70 with a new carb.
It's a priority 2 problem as the deck of the mower itself is pretty rotten with rust.
I can't understand the rational of putting a briggs engine on something with a sub-standard deck.

There is about a 2x4 cm hole in the deck, its rusted through.
Currently weighting up whether Fibre glass or a small piece of sheet metal and pot rivets to fill the hole.
Is there anything worth doing, to slow down the rust?

 

[Burnerman]

Alas this is an age old problem that affects many machines, including the cheaper Honda models.....once the rust is there then its there for good, hardly surprising with the amount of mud and grass debris that sits on the deck underside all year round!
If there's some reasonable metal adjacent to the hole, I'd go for a pop riveted plate and probably a heavy coat of Hammerite or similar - you'll get another couple of years out of the machine.
On purchasing a new machine, there's a choice of steel, aluminium, fibreglass or plastic decks out there.......you pays your money and takes your choice, as the saying goes!
John