Engine tuning: timing and ignition

[eagle]

Hi folks!

I'm currently working on my ZS155 engine (runnning a oko28 flatslide). Got a akunar cam (midrange) and HD valve spring set on its way. In the meantime I'm flowing/porting the head. Carb is set up pretty much spot on for current setup.

Now I thought the next thing to optimize would be igition and timing. I'm using the ZS' stock CDI and rotor kit and think I'll keep that. Or are there affordable CDIs with tuneable ignition courves? I guess no...
I however saw camshaft sprockets with 40degrees of adjustment to tune valve timing... this should help to control where the engine produces most power what cought my attention since I would be interested in generating most power in midrange...

Can anybody give me an understanding or guide (or link) of how to correctly tune valve timing? Would this even make sense without a dyno to check setup?
I heavent read much about that yet, it seems to be something of the more advanced tuning stuff I guess but I'm not afraid giving It a try.

 

[The_GDFP]

IMSLTHO, the mini industry is crap when it comes to that specific detail. Even the lamest $59.95 16-lobe camshaft for a V8 has a cam card with it. In their defense, not too many "builders" have a clue how to read one or use the information Takegawa at least posts the opening and closing points of some, with the included paperwork. Email Ranuka to see if he has specs, if none come with the cam. Pre-slotted cam gears? Awesome! Who has them?

If there are no specs available, you can measure it out yourself. It's well worth the effort. I've seen cams installed, dots aligned, 20 degrees from where they "should be". Production tolerances are all over the place.

There's a million articles on the web aboot it, so I won't bother posting the several cam-degreeing techniques, but will add my pair-O-pennies on a few points

I like using just the inner valve spring when dialing in a cam. It saves some fighting stiff outers.

You'll need at minimum a degree wheel, pointer, dial indicator and a fixture to hold it securely and inline with the valve. Two sets is more better, and quicker.

First, you need to verify TDC on the motor accurately. I use the piston-stop method, at least 15-20mm down the bore. Go up to the stop, check degree number, back 'round the other way to see number, adjust as needed.

The least you'll want is to find the I&E lobe centers and adjust from there(method I use). A little advance for low end, retard for revs. More or less. Look at Web or Megacycle sites and see what engines of similar displacement/cylinder use for a rough idea on what is good for your needs. 1970's Honda 750 SOHC, 350 twin, XR185/200, etc. Sadly, our one-cam/two lobe setup have factory-determined lobe seperation. That varies among YX and Zonger motors, too, of course. BBR has cams that fit, too. Proud of them bastids, they are.

Ignition timing is similar. You need to verify a true TDC and work from there. I like to mark the flywheel every 10 degrees, 20-30-40 so the timing light is useful. Take the diameter, multiply by Pi to get circumference. Divide by 360 to get the distance per degree. Multiply by 20-30-40 to get where to scribe your marks. Different colored Sharpies are good if you're of an age or eyesight to need an easy method of telling what mark is which. lol Don't use a caliper, unless you math-out the arc of the flywheel and how it changes distance. Steel ruler/scale is fine.
Figure out what it is, stock, and go from there. Static timing at idle is nice for starting and smooth idle, but without an adjustable curve, tune for max advance and let the idle fall where it may. A small-bore hemi chamber really only needs 27-28 degrees total, max. Any more and the piston is fighting it on the way up. An hour meter/tach combo is the least you'll need. More accurate tach helps if really fine-tuning.

Now you know every thing I know, more or less.
Others may have varied opinions, but Hell if I can figure out why:action-smiley-035:

 

[eagle]

Nice! Thanks! Thats more info than I expected.
However I guess I have to read a few articles before getting started...

So this cam cards tell me when intake and exhaust is opened... reference point is TDC I guess. By installing dial indicators at one valve and check flywheel mark or play safe and install a second one at the spark plugs hole I can verify the position of the cam, right? But how do I know at which spot it works best at a certain rpm range or produces most overall power without a dyno? Or would it be easy to "feel" when riding? And how much is "a little advanced" ? ^^ 10deg?

Ignition point can be advanced or retarded by moving the "sensor" clock or anticlockwise, right? Unfortunately my rotor set has no adjustable one... is there a rotor kit for 155 zongshen engines that would allow me to tune that... a rotor with a spinning mass to best suit midrange torque?
And also same problem here... might hard to tell a difference without dyno?
Or is ignition point tunded differently by moving the wheel insteat of that "sensor" (can't remember right term) with reading the position of the mark with one of those ignition synchronisized strobo lights...?
What do I do with that meter/tach combo? Go out and ride and compare speed at a certain rpm ? So for example if I'd like to have most torque in the midrange at about 7000rpm I go out and ride the bike in forth gear at exacly 7000rpm and read speed and compare this to other timing settings?

Oh, and here's the link to the sprocket... its from OO-Racing in UK:
OORacing - performance monkey bike, pit bike, madass, zoomer, dirt bike components - Cam sprocket YX 150/160/170 4V VVT40 Adjustable valve timing (Powered by CubeCart)

 

[The_GDFP]

A degree wheel will be needed for accurate setting of valve timing. The Double-O sprocket is slotted aboot 35 degrees more than you should ever need. Easy enough to just drill the holes larger and use a washer and Loctite. Ignition timing can be varied some by slotting the pickup mount and sliding it in the direction needed.

Decent degree wheel, should be 8" or bigger:

Sample cam card. Good luck finding one for a Chinese engine, but you can make your own:

Home made piston stop:

 

[The_GDFP]

Web Cam Inc. - Performance and Racing Camshafts / Honda XR 100 (81-03) SOHC 2v Timing Card

Sample of Web Camshafts card info, the one I run in my XR100's with stock head.

 

[sean01]

one thing id like to add that hasnt been said yet...

some/most aftermarket cam grinds have advance ground in them, most the time they wont tell you too..
use the degree wheel to find out if it has...

as for ignition timing/tuning, buy yourself a lifan 150 adjustable outer rotor kit, you will need to machine 3mm of the backing plate to allow for the slightly shorter crank in the yx/zonger

 

[The_GDFP]

Like this?

 

[eagle]

What do I do with that meter/tach combo? Go out and ride and compare speed at a certain rpm ? So for example if I'd like to have most torque in the midrange at about 7000rpm I go out and ride the bike in forth gear at exacly 7000rpm and read speed and compare this to other timing settings?
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Haha, wait... that won't work ^^

So how do I test the setup? Acceleration? Measure the time I'll need from zero to a certain speed? I saw some Koso speedos that do that.

I'll contact akunar for specs... only thing I know right now is that it's got 280degs open duration and a higher lift than their 330deg top end cam.

Thats what my rotor looks like:

This might sound a bit stupid, but how do I mount those degree wheels to the cam and what do I use as reference?

 

[The_GDFP]

I use a flywheel puller to hold the degree wheel. mount to crank.
The pickup bolts on yours can be removed and slot the bracket to move it a few degrees in either direction. Up/retard, down/advance. Offset f/w keys exist, too.