Setting Idle Speed using a multimeter

[Rob E UK]

recently bought a multmeter with an RPM function on it.

The motor is my 62 1200 6v motor, bone stock.

Ive warmed the motor and its come off choke, set the multimeter to 4cylinders and used the red probe on the - side of the coil and grounded the black probe, and i am getting a reading of 160 ish on idle.

It says you have to multiply the reading by 10 to get the correct figure, but thats still too much, as i believe the idle should be set to 800-850RPM.

So the multimeter should be reading 80....is it reading 160 as its for 12v motors? should the figure on the multimeter be halved to get the correct reading for 6v?

thanks in advance

[glutamodo]

No, it doesn't work that way... firing pulses per minute are the same no matter what base voltage the coil has. No need to double or halve anything, it's got a 4 cylinder setting. The decimal shift, that's different, and to be expected. What brand of meter is it?

I must say, I've used a few different digital tach/dwell meters over the years, and not many of them would read VWs worth a crap... 6V or 12V. I end up using my old analog tach/dwell meter instead, which always works.

-Andy

[Rob E UK]

this is what i have.......

http://www.gunson.co.uk/item.aspx?cat=663&item=1855

so are you saying its not reading correctly?

[glutamodo]

It could be. 1600 RPM is pretty darn fast for idle on a warm engine.

What happens when you put it on 4-cylinder dwell?

[Rob E UK]

Will try that. What should the Reading be?

Oh and if I slow the idle right down so the generator light starts to glow the multimeter still only reads 100ish

[glutamodo]

Dwell should be in the 44-50 degree range if your points are adjusted right.

[Rob E UK]

yup 45-46 so thats ok.

tested the rpm after and it still reads between 150-170

im thinking this maybe faulty......

i tried this also on my other beetle and got no readings at all!?

totally confused now

[glutamodo]

Well, I've found that usually, but not always, if they read dwell OK they should work OK on tachometer as well.

The no readings at all thing... I've got 5 different digital tach/dwells, and I think only one of them works very well... they either don't read, or the numbers go all over the place. The one that does work halfway decently, and the one I've had the longest, like 20 years now, the tach always reads too fast until I smack it on the dial with my knuckles... makes no sense but it's always been like that.

[Rob E UK]

found this.......

http://www.thesamba.com/vw/forum/viewtopic.php?t=223927&highlight=multimeter+rpm

maybe too much 6v "noise" for the multimeter to read properly?

[glutamodo]

Yeah, could be. It's been so long since I did anything 6V that I can't remember how well my old Metex meter did with them, I think it was OK though.

Whenever I have a meter that doesn't work, I just get this out instead.

[Rob E UK]

just tested the multimeter on my 72 camper which is 12v and it works fine on the RPM and Dwell.......so i guess it is the 6v system.

bummer

[Rob E UK]

reckon i should get an analogue tester like that instead??

[Rob E UK]

also found this........

http://www.1966vwbeetle.com/Forum/viewtopic.php?t=487&sid=bb0c7e245bca11425c6f9c4b8852197c

a guy on there posts this-

[glutamodo]

Doubling numbers is for analog meters with an 8 cylinder scale. Digital testers with a slot for 4 cylinders don't need that. My analog meter doesn't need it either, as it's set up for 4 cylinders, with the note saying you have to halve those numbers for 8 cylinders.

[Rob E UK]

gotcha. thanks for all your help.

guess i will just have to resort to setting the rpm by ear.

[Rob E UK]

do you reckon this will work?

http://www.amazon.com/Actron-CP7605-Tachometer-Voltmeter-Analyzer/dp/B00062YUUS/ref=lh_ni_t

[kombiboy]

[Rob E UK]

you dont get an 6v "noise" through it? my digital multimeter reads too high and erratic on my 6v, but fine on a 12v.

[glutamodo]

Since I needed to check my dwell/timing on my (12V) 62, and since this is a current topic, I thought I'd go and compare all the meters I had around at the moment. I don't have my Metex though, that's in storage.

All of these can get VERY flaky if held next to the engine, with numbers shooting all over the place. So for this test, I used a jumper wire with alligator clips on the ends so I could lay them all out on the ground behind the engine.

The yellow one, I got like 12 years ago from one of the tool trucks, but it's not a name brand.

The Sunpro CP7676, that one is one my Boss had in the mid/late 90s and worked good, so I bought myself one later on, but I never found it to be as good as the one we had back years ago.

The Blue "Sincmeter" I dont know where I got that one, I think maybe it was an addon from an electronics parts order or something. This one sucks, even away from the engine it still shot numbers all over the place, I was lucky that when I took my photos the nubmers sometimes were close, most of the time it was just random numbers.

The black Cen-tech, that's Harbor Freight. It also has a clip on inductive lead for RPM, which is totally useless.

The analog Suntune, I have two of these, both I think I found at different times at antique mall type junk stores back in the 90s.

Here's RPM with the 4 hooked together and the black one clipped to plug wire number one near the spark plug as the instructions state. The black one reads way too low, this is not a doubling thing either, as going to the 8cylinder scale dropped the number in half.




Here they are with the throttle up a couple of steps on the fast idle cam.
Again, the Cen-tech is way too low.



Then I went to hook the Cen-tech up for dwell, which means using standard leads, and I notices that when I hooked the ground up, and I was still on tachometer, it was reading about right... depending on where I held the read lead in proximity to my other leads... Go figure. Here's two shots, one showing how wild that blue meter is.




And then lastly, the dwell. Again, if I have these closer to the engine they won't read for crap, but I was surprised how well they read a couple of feet back.



The only one that really was decent was the no-name yellow one.

I did want to do a higher RPM test, as I've often found that a lot of meters just quit reading after 2000RPM or so, but then I discovered my analog meter doesn't work on the High RPM setting anymore.

-Andy

[b4thea4]