hillbillyracer
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| posted on 14/6/12 at 08:20 PM |
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Anyone know much about bike CDI ignition systems?
A mate has built an off road buggy using an old quad bike as a doner, it ran ok as a bike & he has had it running ok in the buggy but now it
starts & runs fine but wont rev past mabye 4000rpm if you use the choke (not really a choke, an excess fuel valve) it will rev higher. I've
got it to see if I can sort it for him.
I expected to find carb problems, valve timing/lift problems, a blocked exhaust or mabye an over charging fault but so far nothing.
So I've checked the ignition timing (in 20 years of fettling farmer's quads I've never had the need to do this before!) & it
would seem the timing retards as it revs up & obviously if it retards too far it just wont run & it does explain the symptoms, an over rich
mixture would be more tolerant of ignition timing retarded too far.
There has been some engine work done on the top end but all looks fine, mabye of more interest there has been some rewiring to suit it being in a
buggy frame.
The ignition advance uses electronics to work, the pickup on the crank is fixed with no mechanical advance & it somehow counts the rpm &
alters the timing to suit.
Quad bike ingnition systems which I expect are similar to other bikes tend to be fairly reliable with a corroded connection, CDI failure or sometimes
a dodgy coil being the usual problems & they tend either to work ok or not at all. This problem is so unusual I've wondered am I looking at
it the wrong way round etc but have gone through it & tested it a few times & cant see it any other way! I could be worng though, have been
before!
The doner bike was a Kawasaki KLF400, a mid 1990s single cylinder water cooled quad that wasn't the most popular thing in its day.
Cheers for any help or direction to where I may find out more.
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mangogrooveworkshop
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| posted on 14/6/12 at 10:49 PM |
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It's a single cylinder thumper they by design don't rev hi anyway.
And when you do rev them they tend to fall apart.
My quad was a good one for that.
The gn 400 Suzuki used to self dismantle.
Better take the quad engine and junk it for a four pot 650 £150 for a good one.
If its a shaft drive chuck a st1100 v motor in.
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hillbillyracer
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| posted on 14/6/12 at 11:02 PM |
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Ha ha, fitting a "proper" bike engine has been talked about! But then you lose the reverse the quad engine comes with.
Although I hear what you're saying about them not reving hard anyway it's not just that, it wont take full throttle beyond a certain revs.
Most quads will still rev as hard as any car engine, many go over 6000rpm. Quads with more than 1 cylinder are fairly rare, they're all
thumpers. Most of the problems I see are drive-line & suspension, engines seem to be the strongest part & while trouble isn't unknown
though poor running is usually dirt in the carb. Some folk can break anything though & I have seen all sorts! Never an ignition timing fault
though. Thinking about it I must try a different timing light on it.
I've wondered if something is connected wrong & the control unit is seeing a signal or rpm reading the wrong way round?
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owelly
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| posted on 14/6/12 at 11:07 PM |
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Just a thought Kev, but has it got two pick-up coils? I have played with bikes and outboards that have a low speed and high speed pick-up. I've
seen engines that will fire up and run all day at low revs but pop, fart and die if you try to rev them. Worth a look?
http://www.ppcmag.co.uk
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hillbillyracer
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| posted on 14/6/12 at 11:14 PM |
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Not that I'm aware of Owelly & I cant think of any quads that do use 2 pickups, but it's not a model I'm all that familiar with!
There is a Clymer manual with it & looking through for how to check the ignition timing it only talks of one & explains that the timing is
advanced electronically.
What the manual does not explain is that the back pressure will blow oil at you as you try to check the timing! Getting around this involved making an
oil seperator tank & connecting a vacuum cleaner to the breather!
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hillbillyracer
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| posted on 14/6/12 at 11:19 PM |
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I'll see a lad I know over the weekend that mucks about with bikes & I know he's got a timing light so I'll talk to him &
borrow it for a second check. It does seem so odd that I'm questioning what I'm seeing!
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MikeRJ
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| posted on 15/6/12 at 07:47 AM |
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The CDi systems used on these things tend to be extremely simple, no fancy digital electronics that measure RPM and no ignition map. The way they
usually work is that the trigger coil voltage has to reach a certain threshold before the coil is fired. Since the voltage output of the coil
naturally rises with increasing RPM (magnet approaches the coil faster, increase rate of change of magnetic flux) the coil gets triggered earlier at
higher RPM. There is often some kind of built in system to limit the maximum advance, such as loading the coil so it saturates at high RPM - this
could even cause some retard at high RPM.
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Peteff
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| posted on 15/6/12 at 08:23 AM |
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I had a moped here that would only run on tick over and It was driving me mad as I obviously thought it was the fuel causing the problem. In
frustration I fitted a new cdi and it was perfect straight away. What kind of ignition does it use ? If it's one like on the pit bikes you can
fit an inner rotor ignition kit and a cheap 12v cdi unit from ebay. The basic systems used on pit bikes and mopeds don't have any advance
mechanism at all, you can buy ones that plug into the wiring if you need another .5bhp but it's hardly worth what they cost.
[Edited on 15/6/12 by Peteff]
yours, Pete
I went into the RSPCA office the other day. It was so small you could hardly swing a cat in there.
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hillbillyracer
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| posted on 16/6/12 at 08:50 AM |
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Cheera for the info on how the CDI works MikeRJ, I was fairly sure they were simple enough thing & didn't have any map or electronic chip
etc to work but how they actually do work I had no real idea! I'll look into the possibilties of replacing the CDI with a one from ebay etc as
Peteff suggests may work, as these quads wern't common getting a correct one from a breaker may not be easy/cheap. Kawasaki ones on the 300cc
bikes which were more common did fail a fair bit, I know of a bike that was in an auction to sell & on starting it as the auctioneer came to it to
demonstrate it was a runner it wouldn't go & some cnut had nicked the CDI unit!
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