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Post by ThaiGyro on Sept 20, 2021 14:34:14 GMT -5
Haha! After so many years of tuning and testing, I have a problem and need some guidance.
I recently picked up an '89 Yamaha Wave Runner. It is a 500cc 2T twin that looks like leftover TZ 500 cylinders, except it is super de-tuned to 32 h.p. Some of that is exhaust, which I am NOT going to mess with for now. (other than cleaning)
In looking at parts and tuning, I have found nothing wrong. As third owner, this thing has near new compression and runs super good. That said, it is a curious setup. Though I did get some good spares with it, I have seen some stories about CDI box failures. No big deal...except Yamaha, (Hitachi) does not build them any longer.
The big issue is having a spare or maybe even a better CDI without rev limiter, so I can do some testing. (OEM is set about 6050 rpm+/-) My new impeller can handle that and a bit more, so PLAY TIME!
My search (and therefore problem) has turned over something strange. The PWC forums have suggested to use GY6 ignitions...$15 instead of $300 for a used OEM CDI. First off, I have never used a 4T ignition on a 2T, because it was not even a close match. However, this engine is very much not a monster, so I am looking closer. They are a wasted spark setup, thus fire every rotation.
Does anyone know the approximate timing curve of a typical GY6? The stock Hitachi spec sheet is quite pathetic...1 degree BTDC at 1000 rpm, 7.5-8 at 3000, 12-15 at 5000. The PWC forum info is all old, like 2013 to '15....however the GY6 CDI's are all over Amazon/eBay.
Wet butt dyno, here we come.
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Post by milly on Sept 20, 2021 15:20:47 GMT -5
I know you can get adjustable cdi's if that might be of any use to you for fine tuning I presume.
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Post by FrankenMech on Sept 20, 2021 18:30:55 GMT -5
a standard gy6 CDI should be capable of 10,000RPM+ I have had my pokey little 4T up to 10,500RPM without problems.
There isn't much of a timing 'curve' on a Gy6, almost none. There is some info out there on the timing pulse and firing points due to rising and falling edges of the pulse from the ignition coil near the flywheel. I would just set the timing close to where it should be at the RPM you want to operate at and try it. Hard starting being a problem.
Maybe MSD has racing ignition components that may help.
Otherwise you could try programming a Arduino or Raspberry PI to run your needed advance curve. There is a lot of program info for that on the net.
Except for RPM limitations there is not much of a difference in ignition systems between 2T and 4T systems, there is a trigger signal of various kinds (points, optical, hall effect, magnetic, magneto, etc), coil driver circuit (dwell, capacitor charging electronics, etc), coil, and a spark plug. Wasted spark is common in many engines. The basic purpose is to derive a timing signal and fire a spark -igniting a fuel-air mix under compression. The higher the compression the more voltage it takes to jump the plug gap. The ignition system components must be able to withstand the voltage necessary without shorting someplace to ground other than the plug gap. The system must be able to generate and control the voltage required to jump the gap under compression, not always an easy thing to do.
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Post by woodini on Sept 20, 2021 22:47:03 GMT -5
Holy shit 89! 👀 good luck dude
At work our 2018s are for sale. How many hours does it have?
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Post by 190mech on Sept 21, 2021 3:58:30 GMT -5
A flat line around 12 to 15 degrees should be good for a tame 2stroke like that..A 4poke usually has a curve that advances which can heat the pistons up on a 2stroke,,Guess the only way to see is hook one up and see what the timing light says...
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Post by snaker on Sept 21, 2021 13:20:45 GMT -5
When Polaris and Ski Doo got into jet skis they pretty much tweaked their snowmobile engine technology to work.
That may be what Yamaha did as well?
They had a 89 Phazer 480 (485cc?).
That was a fan twin, reed valve.
Maybe that would have a similar ignition?
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Post by ThaiGyro on Sept 28, 2021 17:52:42 GMT -5
Thanks all!
FrankenMech...I am thinking that the way this power plant in engineered is uber-simple, thus the mild advance? Idle to 6000 rpm seems a good range for my Suzuki Sidekick.
190mech...same thoughts. Flat and quick off the line.
snaker...thank you for the reference. I have had a few sno-blowers, but I was young and not tuned...in...that might be a good place to look.
woodini...see below:
For more project fun---I am planning on maxing out this engine with the "improved" impeller. OK, OK...it is fun for a 65 year old, but it ain't shite, really. Thus, I will ignition tune, then carb tune, then hull, (kinda like CVT tuning+handling, but not really)
After that? I am converting this from a jet pump to a surface drive. Yes! I have enough cahones left to test a 30-40 h.p. with a REAL prop setup. My 40 mph, (wind aided) WaveDoggy should be capable of 60 or more mph. (70??)
That is the real reason for thinking ignition timing. I need to keep the low end torque and then figure out the "power-on-the pipe" thang...Because? A jet ski does not need to wheelie. It must...just...thrust and behave like a scalded ass APE!
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Post by FrankenMech on Sept 28, 2021 19:20:30 GMT -5
A real prop may make hamburger out of you at some point, an impeller may just suck the cahones off.
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Post by jackrides on Sept 30, 2021 9:50:23 GMT -5
I have (had) a Yam WaveVenture 700 from the early 90s'. CDI gave out at 50 hours. Bad, but only a couple hundred yards from shore. And, I did carry a collapesable paddle. Should have had 2. I may resurect it, so thanks for the tip! Now I'm sure I'll add a waterproof radio to the equipment.
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