How to read RPM with a multimeter? - ArcticChat.com - Arctic Cat Forum

 
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post #1 of 8 Old 02-27-2012, 09:13 AM Thread Starter
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How to read RPM with a multimeter?

I have a 02 z440 that's running high RPM and when I use the choke it lowers the RPM (lean I think). I want to adjust the carbs and it should run around 1500 rpm per the manual but there is no tech on this sled. I could guess but was hoping to more accurate. I have a meter that reads hz and I heard that you can use it to read RPM's. How can I use my digital meter to read a two stroke engine RPM's? I have an EX430 meter. Any help would be great.
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post #2 of 8 Old 02-27-2012, 09:53 AM
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The problem with using a multimeter is that you need to know how many pulses your engine puts out per revolution. I found this out the hard way when I installed a tach on an '01 Z440 and on a '94 Puma 340. I bought the wrong tach and it read very low. I did a little research and found out which one I needed and now they both read correctly.

Getting back to your problem, I always set my idle up higher than the manual says. When the motor is warm and I stop and let it idle down it should idle slow enough that the clutch doesn't engage. This way when I romp on it I get instant acceleration. Also, if the idle is adjusted on a cold motor it will tend to idle too fast when it warms up. Nothing worse than having a sled walk away on it's own!
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post #3 of 8 Old 02-27-2012, 10:51 AM Thread Starter
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Great info

Yea it feels like it's about to take off without me...lol. The high idle does not bother me but I heard that if you put your choke on and then off while your idling and the rpms go down that your running lean which is what it's doing. It idles high and then I put the choke on for a second and then it drops down and idles lower. Is this lean or is it the it supposed to work?
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post #4 of 8 Old 02-27-2012, 11:01 AM
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That sounds typical. I would just slow the idle down a bit when warm. It is a bit of a challenge to get it to idle perfectly under all conditions!
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post #5 of 8 Old 02-27-2012, 12:18 PM
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When you flip the choke on for a second it gives more fuel to the engine thus causing the RPM's to drop. totally normal.

I would set the idle up to wherever your comfortable.

1998 ZR500 Carb
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post #6 of 8 Old 02-27-2012, 03:31 PM
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I inquired about this same issue with my 99 ZL500. Idles at about 3000 rpm's then hit choke for less than a sec and the idle pops down to about 1600. What exactly is going on? Why doesn't it go back to 3000 on its own? Only when I hit the gas does it go back to 3000 rpm's. Is it running lean like justkicn suggests? This doesn't seem normal as suggested. Shouldn't it just go down on its own if set properly?
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post #7 of 8 Old 02-27-2012, 04:28 PM
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After a run, the pipe is hot and it scavanges better. This results in a temporarily lean mixture. If you just let your sled sit, the idle will slowly come down as the pipe cools. If you blip the choke you give it extra fuel to richen it up. This immediately cures the lean condition and drops the egt which cools the pipe faster.
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post #8 of 8 Old 02-27-2012, 05:06 PM
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I've never had a sled do this. This is the Zl500 I got this fall and haven't run it yet besides the driveway. NO SNOW. I'm getting this without a run to make the pipe hot. Immediate high idle after first rev above 5000 rpm's. Quick choke and all better. With track lifted that is. Normal to this sled or all sleds? Hope its ok to have high jacked this post.
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