ATVForum, allt om fyrhjulingar
Märkes diskussioner => Märkesspecifikt ATV Quad Fyrhjuling => SMC => Ämnet startat av: strepto skrivet 17 februari 2005 kl. 10:58:30
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I was told to keep writing in english instead of norwegian, so Ill do that. mail me if there is any additional info you want.
I order to achive HP gains on the CBW-250 - regardless of how you choose to do that - you need to upgrade the ignition system. The stock ignition system on the CBW-250 engine is so weak, its actually too weak for the stock engine. From the first minute I started driving my quad, I noticed how the low range rpm was unstable, even at normal load. I started looking at the ignition system to see what went on there - and after getting the details from SMC in Taiwan, it was pretty clear that the system is weak - very weak.
So whats the stock system like? The service manual sent out to the distributors doesn't give any insight into how the ignition system is set up. There are no schematics telling you how the CDI unit calculates timing advance. The answer is that it doesn't. Its actually predefined and RPM based. But set up to what?
The service manual states that the CDI unit uses the following values:
0 -> 4000 RPM advance 10 degrees BTDC *
4000 -> X RPM advance 26 degrees BTDC *
* Pluss / Minus 2 degrees
So what to do? There are many great CDI system to choose from today, but none of them, at least the ones I have found so far, doesn't support 2 cylinder 4 stroke applications. You can find bunch of bolt on CDI units for the big-brand models like Honda, Kawa, Suz etc.
URL's to a few CDI systems:
http://www.yoshimura-rd.com/contact.asp
http://www.dynaonline.com/english/index.htm
http://www.vortex-performance.com.au/
http://www.duncanracing.com/atvproducts/index.phtml?id=270
http://www.procomengineering.com/
In addition to that - there is a distinct need for stronger coils. Why? Because when you increase the compression, you increase the need for a stronger and faster spark. This is extremly important when you are going with a shorter advance to keep the timing as optimal as possible - to avoid engine knock and possible failure.
If you have any interest in tuning the CBW-250, keep looking for alternative ignition solutions - coils, CDI's, sparkplugs - anything that can improve the stock spark!
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Anyone?
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I´ve got a brand new CBW-250, all original. The engine produces a weird knocking sound from low to high range rpm, but especially on low rpm on heavy load. However, this noice doesn´t appear when revving on neutral.
Can this be related to the weak stock ignition system?
Best regards, Fredrik
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Im guessing, without being certain, that your problem is related to the runin of the bike. The entire engine is set in with a fat and very greasy oil that will burn away during the first 200 km. This will steadily help the rings set, and the engine to perform better. The knock sound is, tho unsure, not related to the ignition.