Suzuki's GN series, is there any love for 'em out there?

Discussion in 'Old's Cool' started by DoubleBit, Jun 18, 2010.

  1. DoubleBit

    DoubleBit Been here awhile

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    I've been buzzing around on my '82 250 quite frequently lately and I've come to appreciate the light, nimble, simple little thing alot.

    At first I had this stigma about it, felt compelled to tell everyone it's my wife's bike... Yes, yes,, very silly... Anyway, I've gotten over that.. And, really it was s'posed to be for her, but after one crash, she's done with,, at least for now.

    It's also come about that I might have a chance at picking up a well preserved GN400. Things I do know are it's kick start only, 6 volt, also has the "mini chopper" styling and should be at least a little more powerful than the 250.

    Are these bikes worth messing with?
    Any noteworthy pluses or minuses?

    Thanks in advance.

    Attached Files:

    #1
  2. deerslayR

    deerslayR Spodely Adventurer

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    There's a reason that New Jersey's rider safety course used them.

    They are durable, easy to maintain and were quite inexpensive when new.

    Never be embarrassed by your ride. It's part of who you are and deserves

    the same respect all civil adults extend to their peers.

    Enjoy!
    #2
  3. eric123

    eric123 Gott Mit Uns

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    I have several GN400's...Let me know if you have any questions...They are great bikes.
    #3
  4. DoubleBit

    DoubleBit Been here awhile

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    That's good news.
    I haven't seen mine yet, but am wondering about using a battery eliminator.
    Have you tried one on any of yours.
    Sitting so long, this one will surely need the battery replaced anyway.
    #4
  5. chopperito

    chopperito aka dirty dave

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    the gn400 has had success racing flattrack in the past. some people can make those things mooove.
    #5
  6. eric123

    eric123 Gott Mit Uns

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    They don't need a battery, they have a magneto...I made and posted a stripped wiring diagram on the Yahoo GN400 owner's group...
    #6
  7. eric123

    eric123 Gott Mit Uns

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    Bike looks different now, I've lost 50 pounds :wink: etc, but you get the point...They start pretty easily once you learn the drill...


    <OBJECT width=480 height=385>


    <embed src="http://www.youtube.com/v/Oju2ExjAYHk&hl=en_US&fs=1&" type="application/x-shockwave-flash" allowscriptaccess="always" allowfullscreen="true" width="480" height="385"></embed></OBJECT></P>
    #7
  8. eric123

    eric123 Gott Mit Uns

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    My street tracker GN400 went on a diet and is quite a bit quicker than my XS650, not that the XS is a speed demon...Bike is re-jetted, shorty megaphone muffler, Uni filter, no battery, gutten wiring, Omar's flattracker tail piece/seat(That I bought used for $25, Woo Hoo), etc...In its current form it is very light and flickable...
    #8
  9. bones_708

    bones_708 Been here awhile

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    I picked one up, 81 GN400, that I got back on the road and gave to my brother. He loves his. Simple, fun and easy. Whats not to like? Will go over 70 so you can drive it anywhere my brother uses his to drive from Houston to Austin without a problem. Parts can be a bit hard to find tho
    #9
  10. DoubleBit

    DoubleBit Been here awhile

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    Thanks y'all... This input is helping... We'll have to see what my work mate has to say about the 400 after he scopes it out this weekend. (It's at his friend's in his neighborhood. :clap
    #10
  11. sgtgeorge

    sgtgeorge n00b

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    I had one about 4 years ago. Great bike with only 900 miles on it. My wife thought it was brand new when she saw it. Mine was a 1981 also.
    #11
  12. DoubleBit

    DoubleBit Been here awhile

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    Well, as it sometimes happens, the guy that knows the other guy with the bike finally relayed to me that the guy he knows traded the GN400 for a cb/cl175. Sucks for me. I'll keep looking. Thanks y'all.
    #12
  13. Mark Manley

    Mark Manley On my way

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    I have had about 30 medium sized Jap commuters in the last 30 years and rate the GN400 as the best of them. It was a bit of a wreck when I bought it but a new set of rings and a cam chain sorted that out.
    The longest trip I made on it was from my home here in the SW of England to Amsterdam in the Netherlands and it did about 85 mpg, that is UK gallons, 4.5 litres not US gallons, 3.9 litres and did the 700 mile round trip without a hitch.
    The handling on my 12 mile commute along twisty coutry roads was great and the seat comfortable on a run. If I could go out and buy a new one tomorrow I would seriously think about it. I cannot remember the last time I saw one on the road.
    #13
  14. Andyvh1959

    Andyvh1959 Cheesehead Klompen

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    Da frozen tundra eh? 1.5 mile west of Lambeau
    My ice bike is a converted GN400, stripped down to look like a flat-tracker, with a Fastglas seat/tail and 18" rims front and rear, a Supertrapp muffler ($20 Ebay find) and some other minor mods.

    Great fun,.....when it runs. Right now its a garage piece because I am pretty sure the stock CDI is shot. I can kick, kick, kick, KICK for as long as I can stand and nothing. I have spark (fat, blue/violet, it'll jump a 1/4" gap), I have compression (just ask my right leg), it has gas (even if I spray fuel into the plug hole, no go), carb has been gond through many times. New plug and plug cap, all connections checked and clean. I'm not new at this, been self-wrenching for 30+ years. Also not new to thumpers, I can kick start my XL600 w/o a decomp release, so I know how to kick a thumper.

    I suspect its a spark timing issue caused either by the CDI or perhaps the 6v magneto/alternator. The bike has no battery, no lights, only electrics on it is to run the ignition. It used to run on the stock CDI, but got progressively harder to start, until nothing at all. My checks of the CDI with my VOM indicate most values off scale, indicating a failed internal connection. I have tried a Chinese aftermarket CDI (ebay) but so far no luck. Anyone else have experience replacing the stock 30-yr old AC fired CDI technology with something newer that works?
    [​IMG]
    #14
  15. eric123

    eric123 Gott Mit Uns

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    We've been talking about that on the GN400 Yahoo group page. So far, not much luck in coming up with an alternative. And from what I hear, the SP370 points setup does not fit...
    #15
  16. Andyvh1959

    Andyvh1959 Cheesehead Klompen

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    Da frozen tundra eh? 1.5 mile west of Lambeau
    Well I actually HAVE found success with a Chinese $21 aftermarket NEW Racing CDI, the one on ebay for an AC alternator application. Its a neat looking little unit in a blue anodized finned casing. I made some wiring changes on the installation I was struggling with, and now I have easliy started the bike five times. It warms up quickly and idles steadily. And it seems to rev up real quick compared to using the stock 30 year technology CDI unit. Too bad the ice is all gone for me to test it on an ice track.

    I may have to spoon on some street tires for street testing the bike (no lights, horn, etc).

    Especially since I also have a Mikuni 36mm VM series round slide carb for it. That may work well with the Supertrapp muffler and foam air filter (no airbox) I have on the bike. Also, I took a die-grinder to the air dam in the intake manifold, and ground it out entirely, to improve high rpm airflow. If this all works out I may consider installing a Wiseco piston from a Honda XR400. The 3rd oversize piston for a XR400 is the same 88mm bore as the stock bore for the GN400, and it has the same 20mm piston pin size. It raises the compression ratio to 10:1 (assuming the pin to piston head distance is ok for valve clearance).
    #16
  17. nanno

    nanno Been here awhile

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    the biggest issue with the DR250 and GN250 is the head, because the cam-bearing is very often knackered or beyond hope. Engine parts are best bought in China (HK) and there's also a 300cc bigbore piston for it which costs about 100 USD incl. cylinder to match. A new head is around 150USD and cams and followers are about 50 to 60 USD.

    All in all a very cheap bike to keep alive.

    Cheers,
    Greg
    #17
  18. eric123

    eric123 Gott Mit Uns

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    Do you happen to have a link to the Chinese CDI please?
    #18
  19. Andyvh1959

    Andyvh1959 Cheesehead Klompen

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    Da frozen tundra eh? 1.5 mile west of Lambeau
    The "NEW Racing CDI" is commonly available on ebay from many sellers. It is the five-pin AC style CDI meant for use on a bike with no battery. It is the fancy looking (yeah, it suckered me in) blue anodized finned housing CDI unit many sellers have for about $25. Easy to find on ebay, just search "NEW Racing CDI". I bought mine from seller named "1800Coolparts". Shipped quick, within five days or paying for it.

    I have started my GN on this CDI many times. Sometimes four kicks, sometimes ten kicks. It idles fine, a bit stumbly, but that may also be caused by the Mikuni VM36 carb I have mounted, which is jetted too rich on the pilot circuit. I found that out by checking the plug color after five minutes of idling, black and sooty. It does rev up quick and high, though it pops at near WFO. That too may be caused by the carb. More to come. I'm mounting rims with dirt track tires so I can test it this summer.

    Here is how I wired the NEW CDI to the old wiring on my GN:
    NEW CDI GN400 wiring
    BLACK to Black/White, chassis ignition or kill switch, this is the switch ground for the CDI
    GREEN to Chassis gound
    YELLOW to Black/Yellow, coil primary, this must go directly to the coil input
    BLUE to Blue/Red, P1 pulser wire, for the 10 degree BTDC pulser, for idle signal
    RED to Black/Red, this is the stator power output to the CDI

    The Red/Green wire from the P2 pulser is not used at all, same for the Black and Black/White from the stator. The NEW CDI is an auto advance style, that sets to a retarded ignition timing (10 degree BTDC) if it gets a signal from the timing Pulser.

    I am also going to test a CDI from a Honda CH250 (Helix scooter) as I have heard that is a good match. It is the five-pin retangular style CDI from the CH250. A Honda (Nippon-Denso I assume) may be a better name brand than the generic Chinese replacements.
    #19
  20. Andyvh1959

    Andyvh1959 Cheesehead Klompen

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    Da frozen tundra eh? 1.5 mile west of Lambeau
    Some updates on the GN400 CDI replacement:

    The Cheapo NEW Racing CDI I think is fried, perhaps it could not handle the non-regulated output of the 6v stator on my bike. I got no more spark with it. So either it needs the regulator in the circuit, or I need a better CDI. One thing about it though, when I'd kick the bike over using a spark tester, it was a smaller less robust spark than the stock 30 year old CDI.

    So I have moved on to testing the aftermarket CDI for a Honda CH250 (Elite) scooter. This is the older AC fired style CDI with the 5-pin green connector. I wired it into the Suzuki harness like before with the NEW Racing CDI. Spark produced is nice a fat, strong, easily jumped a .250" gap. Once I got it fired up the bike settled into a nice idle, and the throttle response is real good. I have street tires on the bike now, so down the road for a test ride I go. Easily up through the 5 gears and it seems to max out about 7,000, a bit shy of the 8,000 rpm limit. I have no speedo on the bike, so I guess with the 54 tooth rear sprocket I may be getting about 75 mph. The CH250 CDI goes to full 27 degree BTDC advance at 6,500 rpm, so it does limit the bike. Also, normal Suzuki full advance would be 35 degree BTDC, so I bet the bike is running hotter than it should.

    But wait,...there's more! When I try to kick start the little beast, most often it kicks back REAL hard. Please no "try starting it this way" or "use the decomp lever like this" because I have tried them all and it kicks back hard most all the time. When I try to bump start it in 2nd gear, most often it just locks the rear tire and slides. So I assume I have some strange timing issue which has advanced the timing for starting. Next step is to pull the magneto rotor and check the timing for the rotor, cams. valves, all of it. Because these GN400s are actually supposed to be an easy starting bike. But not mine!

    Umm. what else. Oh! I have mounted a round slide Mikuni VM36 carb, 130 Pilot jet, needle on the 2nd notch from the top (needle low) and stock main jet (I think is a 420). This carb is a good match for the bike, and is more tuneable than the stock CV carb.

    I am also working with a supplier for a new CDI/Coil/Plug wire combo unit, that is adjustable for high rpm ignition advance. The price on the AC fired CDI/Coil unit (all one piece) is $143 which is pretty good considering it includes a matched, new coil and is adjustable. So more testing to come folks!
    #20