What in the redneck heck am I doing!?

Rigged up an action camera to record the tachometer.  Hopefully it’s secured well enough.  We will see…

The idea is to video record the tach and capture times:

1) 3rd gear from 4000 - 6500 rpm
2) 5th gear from 3500 - 5000 rpm

This is stealing a page out of DBM’s playbook in “Evolution of a Hotrod”.  Once I’ve captured the video, I can play it back on a PC and use a stopwatch to measure the times.

I want to optimize the carb tuning without dropping a small fortune on real dyno testing or relying on my butt dyno.

Wish me luck!

EDIT: I’m going to use different parameter's.  It won’t match with DBM’s parameters, but they work better for me.  I don’t take 3rd gear up to 6500 rpms even when I’m getting on it (shift around 5800-6000).  And I want to keep speed down a tad and test 4th gear and not 5th.  I’ll use DBM’s parameters a couple times, but for what I want I’ll use the following:

3rd Gear: 4K-6k
4th Gear: 3.5K-5.0K

zevenenergie wrote on Yesterday at 09:29:21:


Thank you!  The camera stayed secure on a test ride this morning.  Step 1 good.

I need to work on my technique to try to replicate the way DBM suggested - a running start into the test rpm range.  For example, if the test starts at 4K in 3rd gear, hit WOT at like 3k.  The throttle will be wide open when the tach reaches the 4K rpm data point and no chance the throttle action will affect the time.

Any comparisons to Mike’s results will be subjective (bike set-up, rider weight, conditions. etc).  My results will be used to compare to my results to find the “optimal” tune for my carb and setup.

For me JOG, it's about learning and knowing I've tuned the carb as good as possible for my setup.  It's also fun to do all the WOT pulls.  

I installed the PWK38 carb because I literally broke the stock carb.  I added a 5” UNI foam filter to accommodate it and get it breathing better.  I installed a Dyna muffler because I like the look, sound, and slightly better breathing.  Just all the low hanging fruit stuff.  I've only spent about $150 on performance enhancements.

I'm not going for 50hp with an aggressive cam, bigger valves. porting, and big bore high comp piston, etc... Yes,  I have thought about it, but I've decided against it. I may try to do a little exhaust porting that really won't cost me anything except time.

I’m trying to use the stopwatch as a tuning tool; not to illustrate superior power or performance.  Tuning this PWK38 carb has gotten to a tricky point and I want to see if some data can help.  My biggest issue right now is when slightly closing the throttle from WOT.  It’s just not as clean or smooth as it should be (surge, pop, stutter, I can’t really describe it).  I can’t tell if it’s a lean surge, main jet too big - going from a 130 to 128 helped but did I give up some performance?, or should I move the clip on the needle richer or leaner?  The stopwatch can’t detect those “hiccups”, but once I find the right recipe, I want to know if I’ve tuned or detuned the carb to get there.  Before I installed the Dyna (with the stock muffler installed), I had to move the clip on the needle leaner to alleviate the issue.  

That said, when I had a PWK40 on a different S40 with a more open pipe (Jardine) and I was using a flat panel air filter in the air box, I was using somewhat larger jets and the clip in the 4th groove on the needle (richer).

On that bike, I had a PWK40 - stock air filter set up and Jardine muffler and ideal jetting was around #38PJ, #138MJ, clip in 4th groove (richer).  I thought that was good.  In 20/20 hindsight, I could have used a smaller PJ - like a 35 or 32.

With this current S40, I have a PWK38.  I’m at #32PJ (2 turns out on A/F mix screw), #128 MJ, clip in the middle groove and it ain’t quite right when slightly rolling off WOT.

These tunes aren’t reconciling for me…. I’m a bit baffled.  I could just leave it as-is and just not run it WOT, but that’s no fun.  The bike is running great except for this little pesky deceleration issue.

Well, look at you Paul.  Ready for action.  I predict you're gonna have a lot of fun with that camera.  Tell us more about the camera.  Where did you get it?  What did it cost?  How easy is it to download the vids to your laptop?

Regarding the timing routine.  Not only do you want to start your run well before the start point, you also want to stop your run well past the stop point.  If you want to time 3500 to 5500, go WOT at 3000 and close the throttle 6000.  That way you are WOT steady state at both data points.  

The camera probably isn't gonna help you with needle clip position, needle taper, or pilot jet.  It's a good tool for main jet size.  I find that changing two sizes initially helps to get you headed in the right direction.  For instance, you currently have a 128 installed.  I suggest you do four or five timed runs with the #128 over a wide range in 5th gear.  Since the engine is close to stock, try to use start/stop data points around 3000/5500, so you will have to go WOT at 2500 and chop the throttle at 6000.  Then go up two jet sizes to a #132 and see what it does.  If it runs faster, you were too lean.  If it runs slower, you know you were close to optimum so you can zero in one size at a time.

Depending on your circumstances, you may need to use a lower gear, but the higher gears are better.  The tach swing is slower and it's easier to collect consistent and repeatable times.  Resist the urge to will it faster.  If you develop trigger finger, take a break and try again when you calm down.  If you find yourself anticipating the data point and hit the start/stop late/early, you are only cheating yourself.  It takes a bit of self-discipline.