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Dwell/Tach meter questions

dirtwagon

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I bought an old penske dwell/tach meter to accurately measure my rpms and adjust my pilot screws. Can I use the tach function on a bike without points? Where do I hookup the clamps? IMG_20160527_213520401.jpg
 
Ground the black to the frame or engine and hook the red to the positive side of a coil.

CB750 coils fire twice per revolution though so that tool would read 1/4 the actual RPM.
 
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Where is the positive side of the coil? Between the coil and the plug? And how would I hook up to that? Thanks for helping out a dude who is clueless with electric stuff.
 
The wire between the trigger unit and coil. There is one wire per coil, one is blue the other is yellow. You'll probably have to pull the tank to get to them.

That's really the wrong type of tach to be using. You should get one with an inductive pickup. (A clamp you clip onto the #1 spark plug wire.)

And I got the math wrong in my previous post (So I edited that post) as I forgot to consider that is a car tach with only 6 and 8 cylinder settings.

A common 8 cylinder car ignition will send 8 pulses per revolution so the Tach will divide by 8 to get the rpm. 8000 pulses per min = 1000 rpm.

Hooked to your bike it's only going to get 2 pulses per revolution so you'll need to multiply the reading you get by 4 with the tach set on 8 cyl.

In short this means that tach is useless for your task as your looking for 50 rpm differences when adjusting the pilot screws and on that tach that = 12.5 rpm. Your stock tachometer is far more accurate then that.

PS Just my opinion, if you have to ask where the hot side of the coil is, you probably shouldn't be messing with the carbs. But hey, I learned a lot of things by making my own mistakes ;)
 
8 cylinder cars send FOUR impulses per revolution not 8 with a single common coil. In 720 degrees (2 revs) all 8 will have fired. Only a 2 stroke engine fires every revolution, 4 strokes need two revs for every single ignition point.

Waste spark system so no distributor and two coils. Each coil will fire once per rev. Not a 2 stroke though so how?? It fires each plug twice as much as normal. One time is wasted, hence the name.

You can't measure true 4 cyl. impulses on waste spark since it would require adding both coil switching events together, that would short the ignition out. You use one coil only and getting only half of them. You're reading a twin, in essence.

Use 8 cylinder range and multiply result by 4 or 6 range and multiply by 3. The 6 reading will range slightly highly and slightly more accurate. Really need a dedicated rpm device there. Where's the bike tach?
 
BAH! I still screwed the math up. Otto is probably laughing at me right now. At least I got the answers right, AMC's math is correct though.
 
Forcing you to think, huh? It hurts doesn't it? I know it dang sure did me when I was working that post out. I hate looking like a dumb-ss, but sometimes it's just in the cards.

My time's a'comin'. I just hope I can be gracious enough to accept it when it happens............fat heads hit the ground so much harder when they fall to earth LOL.
 
Once again, your questions indicate a skill level that is not adequate for the task you are asking about.

I strongly recommend you get a shop manual and read through it before making any adjustments to the fuel system.
 
If good enough you would have been able to already without us.

Presync first then set screws then sync again, this time for engine condition. You can presync using 4 very small drill bits of equal size. The problem being, as soon as the engines get used some, the valve seal moves around to not be dead even and then you are syncing to engine condition rather than true 100% identical sync and two separate conditions there. Bike tach really not accurate enough to set idle, you do it more with ear than anything else. I listen at pipe outlet a bunch doing it. You have have 3 cylinders in such a way that they support the 4th and idle speed does not change but idle quality DOES. Like all 4 idle perfect at 1000, then you yank a plug wire and idle speed screw up to 1000 again but only 3 running now. Give that some thought. Tach is worthless there. You MUST listen to exhaust tickover to be able to tell if the engine is idling smoothly.

A plea on behalf of the smartass ones of us.........................

It never fails that overly sensitive persons get all bent out of shape when they don't get treated like we are dressing little children going to school. The problem seriously is YOU not us, yes we are bitches, yes we pretty much know everything and yes you gotta come to us if you haven't a clue as to what you are doing, which the more you get bent out of shape the more you will fit in that category. A DNA thing, the less you know the more you get bent out of shape and quicker than lightning. Blame your parentage for that, not us. We are dead sorry that happened to you but at the same time when people ask questions without even so much as thinking things over before doing so, the questions often get pretty stupid, and it gets very old dealing with that all day long. We WANT TO HELP, but WHY do you want to make it so DAMN HARD????

This is NOT directed at the OP here this thread at all but the response at some point got me thinking about another thread here again going the same way on me. Ergo, people getting terse when they think they didn't get what they should have. Hey, it's FREE, you didn't pay a cent so where is even the right to gripe in there? You who do it didn't pay a cent for that and on any site I frequent and that's a few of them. Yet you want others to give you potentially hundreds or thousands worth of $$$$ in experience again for NOTHING. We WANT to help but by no means do we HAVE TO, give that some thought.

I spent years in parts doing this and in no way was I EVER paid enough to put up with all the utter crap people who cannot heat their own hair oil gave when they were incapable of say following the most simple of instructions. Why I quit 3 separate parts places when I could have easily managed any store at any chain I was at. The PEOPLE are what put me off there. Why I buried myself for 35 years in printing and presses with much smaller groups of people to deal with so that very hardcore relationships could be created to work as a finely honed team. MOST PEOPLE cannot fit into one of those, they prefer to have others take most of the load including all brainwork. I used to run through approximately 30 people to get a keeper back then and when I got him I also got him raises on a more than regular basis to keep him and rest of crew happy. It paid off bigtime.

I by no means have had every single type machine out there. Could care less. They all work the same and I can tear down any machine on the planet to have it up and running with virtually no issues at all. I do all my own home repair as well, I pay for virtually nothing and never have my entire life, I figure I'm entitled to be just as bitchy as all you people out there that want to be 'dressed like little children'. More actually. I too will look around in research on things but when the final plan gets laid out it is all on ME not what others told me to do and commonly something I have never done before. So why does the outcome always work out so well? I THINK before I DO a thing.

So, bitch if you dare, but DON'T complain about the answer you may get back.

Again, nothing here against the OP intended or implied, and I'm sorry I jacked the thread to post this.
 
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