please can anyone help,
i am trying to set up an old 12hp 425 and could do with some help.
when setting timing with a strobe, how many teeth advance should i be looking for.
do the 602 rocker cover gaskets fit the 425.
are the tappet clearances the same as the 602.
does the carb need to be re jetted to run on unleaded.
any help would be great, have tried a search but not really getting anywhere.
thanks in advance.

put a 6mm drill into the hole in the flywheel, now make a mark at the flywheel and a mark on the engine/gearbox housing. Now with the strobe it should be at the same spot as you marked it otherwise your timing is off. (Do all this during iddle).

rocker cover gaskets do fitt.

clearances are the same

carbes don't need to be rejetted, (Petrol in the '50 was even worse) and there is a big safety margen build in the 425 engines.

thanks tor the help,
i will have a go in the morning.
so there is no need to check the timing at higher revs.

If it runs ok. leave it that way, I think it needs about 5 - 6 teeth extra advance at top rpm..

12hp should run 45 to 50 mph I guess...... at full trottle after about 3 minutes, no headwind, flat surface, only driver inside, 22 degrees celcius, roof closed and so on....

I think they don't pink, when the timing is way to early they only build up heat.......

thanks ipgo,
that sounds about right, its painfully slow, especially uphill.
i will try it in the morning.

Those early engines used advance curve A, which is much shorter than the later engines, so if you did drop a strobe on it, you should be looking at 4 to 5 flywheel teeth past the static timing point.

I'm not too sure that re-jetting wouldn't help, as there was up to 3gms of tetraethyl lead per gallon in the petrol being sold in the 1950s, '60s and '70s.
That did not affect the air/fuel ratio, whereas the *additives used nowadays have the (unfortunate) effect of leaning the mixture on engines fitted with carburettors.
2 steps in jet size is generally accepted to work with the current amounts of ethanol and whatever else is in the mix, so a 125 main jet would be replaced with a 130, a 130 with a 135, etc.
( The jet size divided by 100 usually gives its diameter in mm.)

For the same reason, I'd advise setting the valve clearances on the high side of the original recommendation, especially since the cam profile on earlier engines is reported to make their valve seats more prone to recession.
It's also worthwhile checking the gaps regularly, maybe at every other oil change?
http://www.ecas2cvparts.co.uk/info_page ... ebaee265c5

ken

*It's beginning to look as though there are other side effects of the switch to unleaded fuel and catalytic converters, not so much a 'green' move, but instead one from the frying pan into the fire.
http://www.independent.co.uk/environmen ... 98469.html

thanks ken, very helpfull.
my engine seems to struggle to advance anymore than two teeth,
i have taken the points box off and cleaned the advance weights,they seem ok but not really sure what to look for.
also when the motor is at higher revs when stationary it sounds as if its a bit lean, but this could also be its not advancing enough.
i will have a look in the morning and also see what size jets are in there.
thanks again.