Suzuki GN400, SP400, SP370 Ignition...

[guest1526]

Hi everyone,
New guy from the USA here...
I picked up a '81 GN400 for cheap and wanted to build a custom bike using it's engine.
My goal was ultimate simplicity. (kick start, air cooled, single cyl, etc.)
I'm going "boardtrack-style" as far as styling goes. See www.kustomgn400.blogspot.com if you'd like to see my progress.

Here's my question:
Currently the engine runs fine. Before I tore the bike apart I rode it around a little, did a *tiny* bit of tuning, but overall it works ok.
I know that the Suzuki CDI is a questionable piece of engineering, and for now mine works... however, when it decides to go, I'd like to swap the SP370's points ignition to my GN400. I've heard it is easy to do, but no one can tell me how to do it. I've heard that all you need is the plate, points/cond, cam, seal and cover from the SP370 and it works great. Can this be true? what about the magneto, pulse coils, timing marks and ignition coil? Is the 370 cam the same as the 400?
Has anyone done/tried it? Seems like a cam swap and adding the points parts would be too easy...

Thanks for any help, and I'm glad I'm here!

Dan

[SteveC#222]

Hi Dan, welcome to the Thumperclub.

I used to run an SP370 some years ago and it was a really nice bike - apart from the rubbish headlight.

I can't answer your question with certainty, but I think it's quite possible that it may be that simple.

Is the SP400 6 or 12V?  The 370 was 6v but I don't know if you would need 12V to power the CDI.

There is someone on Ebay in the USA selling a 370 points plate, cover etc for not too much money so it might be worth a look.

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If you do convert to points you can get an electronic ignition kit from Maplins that uses the points as a switch and makes them last almost indefineately but, in the event of the unit failing, you can convert it back to proper point by attaching 1 wire. I used one on my old Cossack and it worked well.  It comes as a 12V unit but you can convert it to 6V by changing a couple of the diodes.

Hope this help a little.

Not many SP's around anymore, at least not here in the UK.

[guest1526]

Yep, I know it's an antique and you hardly ever see one... but, the price was right, and it's actually a cool little engine.
All these bikes (SP370, SP400, GN400, DR400) had 6v electrics. I guess the Suzuki design for the electrical system was that one could easily remove the lighting circuits and be left with the "engine running" electrics alone. Perfect for those wanting to use their bike for off-road/racing only.
In my case, because I'm building a special, all I'm concerned with are the "engine running electrics". The lights will all be run from a 12v battery. (constant-loss) I'll make sure it's charged before a ride, then plug it back in when I get home. 2 reasons for this: if the engine quits for some reason, I still have lights so I'll be seen, and running everything off a battery means that I'll have much less wiring and what I do have will be easier to conceal.
Anyway, it's a custom that I've wanted to build for years, and won't get ridden that much... just on perfect days on perfect roads. Most would think it's pretty impractical. 
I'll probably try the SP370 cam, plate, points, etc. and see if it works. I'd be tickled if that's all I needed to do!

[themoudie]

Hi Dan, welcome to the Thumperclub.

If you do convert to points you can get an electronic ignition kit from Maplins that uses the points as a switch and makes them last almost indefineately but, in the event of the unit failing, you can convert it back to proper point by attaching 1 wire. I used one on my old Cossack and it worked well.  It comes as a 12V unit but you can convert it to 6V by changing a couple of the diodes.

Hope this help a little.

Not many SP's around anymore, at least not here in the UK.

Aye SteveC#222,

Had a quick look at this for a single, but on the Maplin site it refers "Suitable for engines of 2 to 8 cylinders". I'm now doubting that it can be used on a single.     Have you tried it on anything other than the Ural?

Ta, Bill.

[johnr]

the gn cdi was an improvement on the sp points setup, as it was a completely self generating system, requiring no battery or charging system to power it. points would be a definate  backwards step, cos you would need a battery to power the ignition. iirc some dr400 models were 12volt

[guest1526]

I think the battery was only there for the other electrics on the bike, and completely separate from the ignition. As far as I know, the mag/stator provided the power to run the engine.
As it is now, the only available CDI's that work are all old and decaying quickly. Everyone on ebay is selling them for over a hundred bucks, and none of the sellers can guarantee that they work. I've been on the hunt for YEARS and even had bad experiences with supposedly *working* CDI's that would let the bike idle, but not rev past 4k. That's hardly worth a hundred dollars.
Although points may be a tiny step backward technology-wise compared to the Suzuki CDI of 1981, a points system would be maintainable for a much longer timeframe.
I think the DR500 was the 12v, 4valve model. all of the 400s were derived from the SP370 and shared heads, engine cases and most other things.

[SteveC#222]

Hi Dan, welcome to the Thumperclub.

If you do convert to points you can get an electronic ignition kit from Maplins that uses the points as a switch and makes them last almost indefineately but, in the event of the unit failing, you can convert it back to proper point by attaching 1 wire. I used one on my old Cossack and it worked well.  It comes as a 12V unit but you can convert it to 6V by changing a couple of the diodes.

Hope this help a little.

Not many SP's around anymore, at least not here in the UK.

Aye SteveC#222,

Had a quick look at this for a single, but on the Maplin site it refers "Suitable for engines of 2 to 8 cylinders". I'm now doubting that it can be used on a single.     Have you tried it on anything other than the Ural?

Ta, Bill.

Hi Bill,

Yes mate, I ran my old MZ ETZ250 on it and it seemed to work fine.  It's a neat little system and has the advantage that it's dead easy to swap back to points as you keep them in situ as a 'switch'. If you also retain the condenser - disconnected - all you need to do is reconnect the condenser and swap 1 wire and you're back on points.

[themoudie]

Aye Steve,

I think I shall be making an investment! 

Like the points and if just using them as the switch, with no current, should last well.

Thank you for the information and re-assurance.

My regards, Bill.

[SteveC#222]

Bill,

Before you buy let me have a quick look in my garage - I'm pretty sure I still have the unit off the MZ in there somewhere ( I took it off when the big end went to put on another MZ and never got round to it) - if I can find the instructions too you can have it.

Steve

******  Bill, I've just had a look and I've found the unit in my garage , I can't find the instruction sheet but you can download it from here  http://www.esr.co.uk/manuals/k2543.pdf - you'll only need it to figure out which wire goes where.  If you want it PM me your address.

Steve

[themoudie]

Aye Steve,

Thank you for your generous offer. I have PM'd you.

My regards, Bill.

[guest1526]

So, what the electronic ignition kit does is take what the contact points and condenser do and make it better/more consistent?
I know I don't need the elec. ignition kit if my points work correctly, but does it really improve low and hi rpm performance?
Do you know how big the elec ignition kit is? -seeing if I have room for it on the bike...

[johnr]

hang on, let me see if i can get this right. you have a gn that runs fine, with no problems, even after all these years. you have now decided that the ignition that has been running fine for at least 25 years is unreliable. you plan to improve on this by fitting an ignition system that requires a battery (the stock one is self generating) this will require you to change the cylinder head and camshaft and then rewire the bike. the resulting system will require the charging system to work reliably and maintain a topped up battery. despite the gn having only one known electrical vice, that being the charging systems unreliability. and you are trying your best to convince yourself that this is going to be an improvement? dont you think that if the ignition system was crap, it would have failed by now. suzuki ditched the points and fitted the cdi because the points werent reliable enough, you know how they say, 'if it aint broke, dont fix it' well this is one of those situations where you should take note of the saying.

[guest1526]

Hi John,
You're kind of correct... I have a GN that is running fine now. I've already spent the big money on a replacement CDI once. I know these CDI's don't last forever. Most of the folks who have this bike either HAVE or WILL HAVE CDI problems. The potting material Suzuki used to "seal" the unit shrinks, lets moisture in, solder connections break, etc. I'm sure you haven't looked into the various GN400 groups/blogs/forums but it's a major problem that almost all the owners face. There is a Yahoo GN400 group where some of the electrical geniuses are working on reverse-engineering the CDI to come up with a working model. Or retro-fitting one from another bike. So far, no success. This has been going on for a number of years. So, for us to be searching for alternatives is the next step. Or hoarding "known working" CDI's... which is what some of us do also. I know ebay always has a few, but the sellers generally don't know if they work or not, and most don't take returns on 30 year old electrical components.

The points ignition from the SP370 is also self-generating. No battery needed. Also, I don't think a 370 head is needed either. The 400 head has the same provisions to mount the points plate, etc. That's partly what I'm trying to figure out. I'm also not using any of the factory wiring harness. (except the 5 wires that come from the stator, to the CDI, to the coil, to the sparkplug -for running the engine).

In my first post, I put a link to my blog. It goes to the custom bike I'm building. I'm going for ultimate simplicity. It's not a daily driver, and I'm sure if you looked at it you'd probably dismiss it as being very impractical, but I've wanted to build it for ever, and now I'm actually doing it! 
If the stock Suzuki CDI was that good, I (and all the other GN/SP/DR owners in the word) would keep it and not give it a second thought. However, being intimate with this bike and it's component failure-rate, I'm just trying to do some homework ahead of time so I'm prepared in the event of another CDI failure... which a new one from Suzuki is $326.30!
Plus, if nothing else, adding points would be another "custom" element of the bike.

[SteveC#222]

So, what the electronic ignition kit does is take what the contact points and condenser do and make it better/more consistent?
I know I don't need the elec. ignition kit if my points work correctly, but does it really improve low and hi rpm performance?
Do you know how big the elec ignition kit is? -seeing if I have room for it on the bike...

Basically it gives a more reliable spark as the points don't wear and go out of adjustment. It does improve the running though I wouldn't say it was really a 'tuning' upgrade. the size is roughly 3" x 2" and can fit almost anywhere on the bike.
I think the price at Maplins is around £12. I found it very useful on the MZ where the performance drops off rapidly if the timing goes out. If you disconnect the condenser but leave it in place if it ever stops working all you need to do is reconnect the condenser and join 2 wires and you are back on points.

THere was a way of wiring the generator on the SP370 up so that the ignition coil(and circuit) ran 6v but the lights were upgraded to 12V - you used a Zenor Diode and replaced the bulbs and battery as I remember - there is something on the web about it somewhere.

THis might help  http://dr400.freeforums.org/12v-lighting-sor-sp370-t310.html

The manual is here. http://www.esr.co.uk/manuals/k2543.pdf

[guest1526]

Yep. I've seen the 12v info from that site. There's also a German GN400 forum where they use a Piaggio reg/rect and splice that in with the blue/white wire coming from the *other* (non-ignition) coil from the stator. Apparently if you disconnect the pink wire and forget about it, the blue/white jumps up to around 12v. Using the new reg/rect, you can have a normal 12v electrical system for your GN/SP/DR. -Or you can buy the re-wired coil from the guy on ebay UK. (westcountry windings).
But like johnr was saying, I'd have to power the Maplin's elec. ignition somehow though yes? Does it get it's power from the stock GN400 magneto?