RPMs on older machines with no proof meter ?

Bruce Covey · Sep 23, 2018

Trying to adjust linkage and carb to get 400 and 2200 at both
ends of the throttle quadrant. What do people use on the
machines with no proof meter to set the rpm? My FO-4 manual says what to do, but no suggestion on how to read the rpms.

Bruce (VA) · Sep 23, 2018

Just get it as low/fast as you can.

Or buy one of those tiny induction takes on eBay for $15.
75 Tips

DeltaRed · Sep 24, 2018

'Ear'

Bruce (VA) · Sep 24, 2018

I love autocorrect.

TACHS, not takes.
75 Tips

Bruce Covey · Sep 24, 2018

You guys are killing me! Don't you know that I worked in an electronics calibration lab and have done 30 years worth of precise electronic adjustments?

I did have one of those TinyTachs at one point, but it didn't do too great.

I'll assume the WOT stop on the Governor is likely close enough to correct, and adjust the new linkage to hit that point at WOT on the quadrant. I'll then keep backing down the throttle to the low end of the quadrant while adjusting the idle speed screw on the Carb until I get it as low as she'll handle. Does this sound like a good plan? This mixture screws seem to be pretty good as I accelerate smoothly.

BTW... One other question. I see about 4v at the top of my front mount coil with the ignition switch on ( 6v pos ground ). I assume this may vary a bit depending on if the points happen to be closed? I do have the OEM ballast resistor ( likely original ). The FO-4 manual only says a .3v drop, but surely that is with open points to prevent any possibility of current flow through the ballast resistor...

Thanks all.

HFJ · Sep 24, 2018

u should see battery voltage at the top of the coil with the points open, and ~ half that with them closed.

Skipper_488 · Sep 24, 2018

https://www.harborfreight.com/digital-photo-sensor-tachometer-66632.html

If you really need to know your RPM. I'm one of those that likes to have an actual number. I blame it on being an engineer.

John in Mich · Sep 24, 2018

I do "ear" even with my tach equiped 8N's and Jubilees. Then, I look at the tach to see what it reads. I may try to tweek it more but not likely.

Tim PloughNman Daley RIP · Sep 25, 2018

Yep, I agree! I'm retired from 35 years in auto/truck mfg. My motto was always, "...show me the data...". Don't rely on word of mouth or what someone said. Documentation is the key. I use a hand held RPM device that gets a close enough reading at the PTO. Prior to that it was basically just going by 'feel' or in this case, by listening. These N's aren't NASA rockets so being absolutely dead-nuts on target isn't as crucial as many believe.

Tim *PloughNman* Daley(MI)

Farmer Dan · Sep 25, 2018

[I use a starett speed indicator. but you really don't need to get that picky about it. Just make it idle as low as you can and call it good.

http://ids.si.edu/ids/deliveryService?id=NMAH-AHB2012q05947&max=1000

RPMs on older machines with no proof meter ?

Bruce Covey

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Bruce (VA)

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DeltaRed

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Bruce (VA)

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Bruce Covey

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HFJ

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John in Mich

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