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Message started by GM on 03/21/09 at 11:46:30

Title: Checking Idle RPM on S40
Post by GM on 03/21/09 at 11:46:30

How does one check the idle rpm on the S40?

Title: Re: Checking Idle RPM on S40
Post by justin_o_guy2 on 03/21/09 at 12:05:27

Not sure how to do it W/O a tach, but Ill tell you this, IF you arent sure, higher is a lot safer.Low RPM will ruin the head where the cam rides.

Title: Re: Checking Idle RPM on S40
Post by diamond jim on 03/21/09 at 13:31:52

If you've got a watch or clock that shows seconds you can get a pretty good idea by counting the exhaust notes per second. Do it three or four times and see what the average is. For each exhaust note you hear at idle, two revolutions have occurred. You should be able to hear 9-10 blips per second. More than 10 will be too hard to count but you'll already know by the sound it's too fast. 5 to 6 exhaust notes per second is easy to count and you'll know for certain it's way too low. For practice, place your hand on a flat surface and try tapping your index finger as fast as you can while counting the number per second. Most people can do it up to about 6-7 times per second. Your exhaust note needs to be a little faster than you can tap your finger. Here is the math for counting the exhaust blips:

6 blips per second x 2 revolutions per second X 60 = 720 rpms.

7 blips per second x 2 revolutions per second X 60 = 840 rpms.

8 blips per second x 2 revolutions per second X 60 = 960 rpms.

9 blips per second x 2 revolutions per second X 60 = 1,080 rpms.

10 blips per second x 2 revolutions per second X 60 = 1,200 rpms.

If someone has a good tach and can record and post audio files, they should record the sound of rpms at 800, 900, 1000, 1100 and 1200 rpms for reference.

Title: Re: Checking Idle RPM on S40
Post by Moofed on 03/21/09 at 13:53:01

We covered what jim is talking about in another thread too.
http://suzukisavage.com/cgi-bin/YaBB.pl?num=1204154431
In it I recorded the sound and then used a free sound editor to visually count the "blips" over a decent period of time.

Then again, I also just took delivery of one of these:
http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=95670
But I haven't had a chance to test it. ;D

Title: Re: Checking Idle RPM on S40
Post by diamond jim on 03/21/09 at 14:39:55

That's some great info. I've never seen that post yet. Man, I've got to go get the stuff to convert video to digital and post. My exhaust doesn't really sound like any of those. It's maybe a blend blend between the Raask and the classic HD sound. Before the new exhaust nobody ever mistook my bike for a sportster. Now it happens about every third time I ride. I guess cause of the sound. The usual first words out of their mouth is, "Where's the oil tank".

Anyhow, great info on that thread. It needs to be in the Tech Section TOC. Maybe it already is and I just missed it.

Title: Re: Checking Idle RPM on S40
Post by Moofed on 03/23/09 at 16:17:01

I finally got a chance to test the automotive multimeter from harbor freight.

I had to loosen the tank in order to reach the spark plug wire. Meaning take the two bolts out and slide it back off the rubber mounts in front. Didn't need to disconnect any wires, cables or hoses, but I do have a raptor petcock so keep that in mind.

At first I put the sensor coil too close to the ignition coil and the readings were not steady at all. Once the sensor was sitting on top of the spark plug boot and the arrow pointed toward the plug the readings evened out. On the 4 cylinder setting the reading is half the real rpm, verified by Moofed's Exhaust Audio Recording Visual Analysis™. ;D The meter read 60-61 (x10) and analysis revealed about 1236 rpm (103 exhaust notes in 10 seconds). That is just slightly above spec for idle speed.

Diamond Jim, in your kamikaze air filter endeavors you mentioned that the deturbulator tubes mitigated the rpm drop when letting off the throttle sharply. That interests me because my bike (Mac exhaust, drop in K&N filter, no snorkel) gets really close to stalling at the current idle speed setting. Not that I want to make my idle speed lower (because of oil pressure concerns), but because I've learned to give baby the throttle when letting off it. I'd rather that mental capacity be available for emergency braking than keeping the engine running.

Title: Re: Checking Idle RPM on S40
Post by diamond jim on 03/23/09 at 22:51:01

There have been times, maybe weeks between carb adjustments, where I'd find myself blipping the throttle during decel just at the point where engine rpm reaches idle speed. I guess it sort of became a minor habit as it would sometimes drop a bit too low for a sec and return to normal idle. To a point I think that is normal for a carbeurated engine but obviously stalling or stumbling is not. The Turbinator seemed to improve this, meaning the engine decells (sp?) down to 1100 and smoothly stopped there versus dropping to 800 for a sec and then back up to 1100. I guess the Turbinator reduces turbulence which in turn provides for a better vacuum effect at low rpm. That improved vacuum effect means more air in the cylinder and more fuel pulled up through the jets resulting in decel stopping at 1100 and not dropping like it did. I do know that my mixture screw sweet spot is different with the turbinator in than with the same tube/opening minus the turbinator. If it sounds confusing, well, I'm still learning about it myself. Mine was tougher to adjust because of the free flowing exhaust. The exhaust back pressure plays some role in how fast an engine decelerates. The back pressure acts sort of like an air cushion. The slower the return to idle, the greater the resistance in the exhaust. Listen to the muffler sound files in the Tech Section. It sounds like the different recordings have slightly different rates of return to idle when the throttle it let go. Mine drops faster in comparison and therefore tougher to adjust for. The turbinator seemed to fix what I wasn't quite able to get just right through carb adjustments.

Edit: Oops. Turbulator, not Turbinator.

Title: Re: Checking Idle RPM on S40
Post by Wolf on 03/23/09 at 23:31:03

Turbinator ...

Now I think I know what you are talking about, but can you put up a pic or post if there is one... Thanks

Wolf :-?

Title: Re: Checking Idle RPM on S40
Post by diamond jim on 03/24/09 at 05:24:14

467E7D77110 wrote:

Turbinator ...

Now I think I know what you are talking about, but can you put up a pic or post if there is one... Thanks

Wolf :-?

Oops. Turbulator actually. Verslagen named it that. Cool name IMO.
http://i255.photobucket.com/albums/hh128/russ_diamond_jim/withstraws.jpg

A Turbinator is the Arabic version of:
http://www.spiralpocus.com/wp-content/uploads/2008/05/the-terminator.jpg

Title: Re: Checking Idle RPM on S40
Post by sakara on 03/24/09 at 13:20:54

rofl I was thinking that myself, Jim.

Title: Re: Checking Idle RPM on S40
Post by Reelthing on 03/25/09 at 09:48:00

A ball park on the safe side way - is to watch the healight - if it dims any at idle - you're too low -

Title: Re: Checking Idle RPM on S40
Post by DrunkenDwarf on 06/14/09 at 12:43:27

5173737A79781C0 wrote:

Sorry about the thread necromancy, but I wanted to share my experience with the automotive multimeter.

I was unable to move the tank far enough with the stock petcock still attached the to carburetor to get the pickup around the spark plug wire.

I'll have to attempt Moofed's Exhaust Audio Recording Visual Analysis™ for myself.

-D. Dwarf