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Norton Villiers F12 Engine(BSA sloper)

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I have a Ransomes Marquis 4A fittedwith the Norton Villiers F12 engine(known as a BSA sloper I believe).  The engine runs well when hot until the throttle is closed down to tick over and then the engine either dies or struggles when the throttle is opened again.   The carb has been dismantled and cleaned,also the air filter.   The tapered needle is one notch from the top.   The petrol is fresh and there is good compression.   When the engine is first started it woorks perfectly.   Any ideas would be most welcome.   It has been a very good runner in the past, 

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redfernmowers Mon, 13/08/2012

as you've stripped the carb down, the jets, filter, everything needs a full clean and rinse to get it going again. one area to adjust is a screw next to the choke. when in idle, you should be able to increase the speed a little so that when in tick over it doesn't die. on idle it should sound reasonably rhythmical  but slow and steady so it's not driving the shaft but still able to keep on idle. so adjust the screw carefully until you get the right result.

it took a good hour to fine dial in mine and now it's a dream machine (ransomes auto certes MK6 full rig) for sale on here.

the BSA sloper is an amazing engine. just out of interest, you say your compression is great, did you recently service the engine, have the valves cleaned and where needed, ground and the shafts cleared to 6 thou? that really makes a nice difference on compression. starting this engine's a real joy. mind you, I've a cough that matches the sloper in tick over. funny but painful either way.

ed

greengrass Mon, 13/08/2012

Thanks Richard for your reply. The slow running screw is set as fast as possible without the clutch to the cutters being triggered.  I am beginning to think it could be an ignition problem

wristpin Mon, 13/08/2012

Come on Ed, give the man all the Sloper gen and tips I gave you  a couple of weeks ago!!!!!!!

redfernmowers Mon, 13/08/2012

very true angus but where would the fun be in that lol hehehehehe.

the sloper can be a temperamental engine at times.  Angus and I have conversed over a period of time over this rather sexy engine (my opinion lol) so here goes.....

when rebuilding an engine like this, it's worth remembering that the condensor, contacts, etc are most likely on their way out. Though I personally favour keeping them and reconditioning the points with 400g wet and dry paper and fine cloth to polish the contacts (replacing condensors and coils where necessary), We both recommend the use of electronic ignition which is pretty easy to install. the advantage of electronic ignition is a steady and reliable current needed to keep the engine in check. one such part as I understand it is a meco module available through Central Spares. unless there's other suppliers. (angus, chip in if you can here lol)

I've had to completely rebuild my f12 engine  which has meant a full rebuild of the carb. this cost about £100 from meetens (replacement inlet pipe was the pricy bit) this included all gaskets, main jet, needle and float, washer sets, bolts, etc as well as a liner for the choke so it was running better. The amal 379 is an interesting little carb and I have to admit to liking it a heck of a lot. 

let's assume the engine has not been rebuilt, here's some work I'd do.

1: engine bleed out. drain out all oil.

2: remove the head and check the piston for wear, scoring, etc, check the condition of the valves. is there a mass of debris there? if so, a light clean with alcohol spirit or paraffin with a wire brush helps. 

3: if the compression is reasonable, I'd check the clearances of the valves. 6 thou is fine. anything less, then it's time to grind the valves anyway and then file the stalks down carefully to give 6 thou clearance. a note on this. the springs are held in by pins (magnetic) and would be removed with the use of a spring compressor. more on that later lol.

4: a good safe bet would be a head gasket replacement just for safety sake, as well as the valve spring gasket. 

5: if the spark plug is the original one, replace it. (not sure of model. think its a champion G8 or something like that). Now it's time for a fresh oil change.

6: the ignition is always a point of concern for these engines in my experience. if you don't want to go down the route of an electronic ignition (though it would be worth doing if you're going to be using it a lot), the contacts will need cleaning. do this with the contacts closed and slide in a strip of 400g wet and dry or cloth backed paper which will polish and sand the contacts. an important factor is not to get oil or debris on the contacts. they need to be a mirror finish. the contact breaker points need an open clearance of 18 thou. 

7: clean the flywheel when removed. best thing is either an ultrasonic bath or soaking in a solvent cleaner, taking out, wire brushing, re immersing, rinsing and drying. ensure the magnet surfaces are clean.

8: your carb may require an intense cleaning cycle where it's best stripped into it's parts and left in an ultrasonic bath with a light acid to remove fuel build up. ensure you carefully remove gaskets, washers, etc. if the float needle doesn't create a decent seal at it's full point, a very light dab of fine lapping paste in the  tapered end will help to grind it into a cleaner form. rinse this off otherwise there's going to be debris which will harm the engine and carb. I'd recommend fully replacing gaskets, washers, etc the jet may need replacing if there is significant problems but by the sound of your symptoms, the jet may not need it. gaskets, etc are always best off replaced for efficiency. one place I advise is meetens unless theres other places there which can handle amal 379 series parts.

most of this you may already know so I'm sorry if it sounds like I'm advising of the best course to suck eggs, I assure you I'm not. due to new customer servicings informations I am obligings to serving you in the best way possiblings lol.

Sure there's more but it's my night off as I'm recovering from illness and stressed beyond belief with a restoration and service job in that has to go out saturday and I'm not even half way.

ed

greengrass Tue, 14/08/2012

Thanks to everybody for the excellent advice.   I stripped down the carb again and put it in an ultra sonic bath, put in a new spark plug and lowered the throttle needle one notch and it is now running like a sewing machine--hope it lasts!

redfernmowers Tue, 14/08/2012

there you go, problem solved. the trick with the float needle is to go to the 2nd stop not the first otherwise the float fails. hence the error in starting, etc. a little faith, patience, understanding and a toolbox goes a long way lol

P.S: who's richard? lol

 

ed