OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Engines Questions On Briggs & Stratton Engines GreenfieldCentenaryRide-on with 12hp B&S motor

The motor runs very well at idle & under load.It is also easy to pull start when cold.
However it is very hard to start when hot.Any suggestions pls.
Thanks fred@howlum.com (derf)

Hi Fred, it sounds as if the difference is a function of temperature. Things that change with temperature and could cause something like this are the tappet clearance (decreases when hot), vapour lock in the fuel line (could have been modified to bring it near cylinder or muffler), or a choke malfunction. How is the choke operated? If you have the Choke-A-Matic system, and you are putting the speed control in the "Start" position to restart it, you would be applying full choke to a hot engine, and it definitely wouldn't start. To get beyond those wild guesses, we'd need more information, in particular looking for modifications that have been made to the engine somewhere along the line.

Hi Grumpy,
When I bought it,the motor was not running.
It could not be turne past TDC & in fact the young fella burnt out the starter motor.I used two head gaskets & got it to turn over & run. Further enquiries revealed the young fella had got
the head shaved to hot it up.I then got 30 thou taken from inside the head to reduce the compression ratio. Valve clearances
are spot on. Choke is ok. it has A LARGE ONE PIECE FLO THRU CARBY.
My next step was to lower the float level before contacting you.
Thanks again fred@howlum.com (derf)

Fred, you might try checking the spark immediately after shutdown when it is hot, in case the coil is on the way out.

The large one piece flo-jet is a good carburetor and its choke is manual, so unless for some reason you were choking it deliberately when it's hot, that shouldn't be the problem. Lowering the float level would make it leaner: do you have any reason to think it is rich? You can check this by inspecting the spark plug colour. There is a possiblity that you have a slow-flooding situation, due to a leaky needle and seat. Problems of this kind are fairly common with an elderly large flo-jet, and it matches your symptoms quite well if you are turning off the fuel when you leave the mower standing for a long time, but not when you leave it for a short time (that is, it is still warm when you restart). You can check this in various ways, but perhaps the quickest and easiest is to compare its restart with the fuel turned off while stopped, and with it left on while stopped. Do not leave the fuel on overnight even for a test, because if it floods the carburetor it will run into the cylinder and end up in the sump, so you'd have to change the oil before you could run it.

If you turn out to have a slow flooding problem, I can explain easily what you can do about it. Also, can you post pictures of the mower and the carburetor, and give us the model/type/code information stamped on the cooling air cowl please?

Hi Grumpy,
Motor details are as follows:
12 HP Model 281707
Type 0148-01
Code 86102811
There is a picture of the carby in my 2 B&S manuals on either P21 or P42 depending on which manual you have.The mower is the 32inch Centenary model. I can't send any pictures at present.
Thanks very much for the prompt replies.
The needle and seat sounds like a good place to start.
fred@howlum.com (derf)

I don't know which manuals you have, Fred, but here is the large one-piece flo-jet:



We have had several cases here recently where these carburetors had developed slow flooding, due to wear on the float bowl seat. If you had left the fuel on when you couldn't restart, but had turned it off in the cases where you could cold-start easily, I'd just about bet that this is the problem. If you can report back when you have made the test, I can explain a couple of alternative cures, but if you have the manual you probably already know at least one of them.