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RPM, help please

Hi, I don't know if I'm asking for the impossible but I'm looking for a way to measure RPM fairly accurately but most of all cheaply. I recently bought an old piece of garden machinery powered by a Briggs & Stratton 3hp engine which runs fine, though it seems to be spinning too fast, I know how to set up the carb but it rather depends on setting the idle speed at 1750rpm. It would also be useful to know the speed at full tilt. I was wondering if there are any reasonably priced tools available or any tricks you chaps know of that might help me out. Sorry for rambling on a bit, many thanks in advance for any help or advice, cheers, Andy Hubbard

Reply to
Andy H
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3000rpm is easy, paint a white spot on the flywheel and view it after dark in a (preferably) fluourescent light, the spot will appear stationary. Variations on this can be achieved with different numbers of spots spaced equally around the flywheel.

In fact I imagine you can do much th same with the strobe light from a gunson timing light and a spark ignition engine with an accurate tachometer.

Other than that do a search on optical tachometer on ebay.

AJH

Reply to
Andrew Heggie

Thats handy- will use that method to set up my Genny after servicing it. (lamp powered from grid of course!)

Tim..

Reply to
Tim (Remove NOSPAM.

I made a mistake, 50hz gives 100 flashes/second, 6000/minute.

AJH

Reply to
Andrew Heggie

Hello. I am new to group, hope I am not speaking out of turn. I think 50Hz flourescent light would translate into 3000 rpm and 60 Hz would translate into 3600 rpm. Here in Canada our grid power is 60Hz.

If you're using an ignition triggered strobe then you need to know whether you have a 2 stroke or a 4 stroke cycle engine. If 2 stroke then its one ignition pulse per revolution, if 4 stroke then its one ignition pulse per two revolutions. If you're using an electronic timing light, it may or may not have a setting for 2/4 stroke. If not then it assumes 4 stroke and if you are using it on a 2 stroke it would show an rpm (if it has rpm display) which is two times the real number. Not a problem so long as you are aware of this.

Seems like the flourescent light method would be simpler for your purposes, just confirm whether your grid power is 50 or 60 Hz.

Sniffinvinyl

Reply to
SniffinVinyl

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