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Suzuki 1984 GSX250S "sleeved" GSX400?

Discussion in 'Technical and Troubleshooting Torque' started by beeroll, Aug 12, 2009.

  1. Hi all,

    I have a 1984 GSX 250 S (see my garage for photos of this awesome beast :wink: ). I've recently found a page claiming it's a "sleeved" down GSX 400:

    www dot rideastride dot com slash suzuki-gsx250.html

    (not five posts yet...)

    Does anyone know whether this is, in fact, the case? (They certainly share a shop manual).

    Now the bike, although mostly in very good shape (the tacho still has traces of the run-in rev limit sticker on it!), is woefully underpowered, struggles to make 100 on the M4, and in almost every way is outperformed by my girlfriend's 125cc one cylinder Bug Agility :oops:

    Does the fact that it's sleeved mean that there is an easy path to a 400c bike, if the sleeves are removed, and GSX400 pistons inserted? Or is "sleeving" a less reversible process than it sounds? And if I did get this done, should I expect to have to change other things on the bike - carbs? pipes? as a result of the increased engine capacity/power?
  2. Thanks for that. My bike isn't the GSX250E though, I think that is a slightly different model, although there are a bunch of similar bikes from Suzuki in the period.

    I'll check the shop manual tonight to see if it can shed any light on the bore/stroke question for 250 and 400 variants...
  3. If you cant milk 140km/h out of that there is something wong with what you have now. Get it seen to and save yourself a whole lot of hassles.
  4. The engines are the same, just look at them.
  5. It's just jargon rather than reality. They are mostly the same engine but have a different bore and stroke.

    The easiest path would be to get an engine off a grey importer and swap the engine. Find out from the RTA about what you would need to do to get that complied.

    It's usually not hard to get a larger capacity car engine of the same type into a car, but a bike may be different and the fact that that engine was never officially imported here may also make it harder or even impossible.
  6. So that's a "yes, you probably can get away with this"?
  7. Around about that time, Mick Hone shoehorned a GSX1100 engine into a GSX-R 400 frame, IIRC (but that was for racing, not road riding :))

    One of these. [​IMG]

    In stock for the bike weighed only 152kgs so you can imagine how fast it went with an 1100 engine in it.
  8. Ah, OK, that makes more sense. I also hadn't realised that the 400 model was never imported here. So the likelihood is that any work done will have to be custom, rather than simplified by being able to use off-the-shelf or scavenged parts.

    So my second question would be - if the engines are not really the same, does that mean that my version of the engine is not likely to tolerate being bored out to somewhere near 400cc in its current configuration?

    I'm sure it's no newsflash by now, but I'm no expert on engine mechanics... but I want to get there...

    2wheelsagain, I will talk to Scotts Motorcycles, who serviced it last (great job, too, by the way!) and see if they have any suggestions as to why it's not pulling full power in current config.
  9. I've just realisted you are talking about the earlier twin rather than the later 4.

    On the twin, the engines are quite different from the crankcase up. Most of the 400 models were 2 valves and I believe they were officially imported, so ignore my earlier comments in that regards.

    Finding a GSX400 engine is not going to be easy. Finding a piston kit is going to be impossible.

    For 7mm bore increase you would need to push the old sleeves out, bore the casting and put new sleeves in. That is if there is enough meat in the casting.

    I think the first of the gs400 engines was actually a 8 valve engine despite the x being missing.
  10. Correct.

    Thanks for that info, sounds like it might not be a realistic possibility. I'll check the workshop manual tonight to confirm, but sounds like I should settle for the bike being a slow but reliable commuter and maybe look at one of Scott's GB400s as a funky weekend machine...
  11. From memory, the GSX250S wasn't an offically imported bike, making sourcing parts somewhat of a lottery. In Japan the designation is used to describe the "mini Katana", IIRC.
  12. These numbers are borne out by the shop manual.

    So if the machine was simply de-sleeved to the diameter of the bigger piston, it would yield only a 300cc bike - 67 * 44.2 - which probably wouldn't make that much difference to performance - unless the current slowness is caused by really out of spec pistons/rings. That doesn't seem too likely, since the bike doesn't smoke, and doesn't make a whole lot of mechanical noise at idle.

    So perhaps I need to look elsewhere. I know the carburettors were in pretty crook shape from having fuel stored in them when I first bought the bike ("green" was the description of the mechanic), but they were completely disassembled, cleaned and reassembled, and a new fuel tap added. But maybe the carbs need to be revisited.

    The only other symptoms the bike displays that seem out of the ordinary are: when started up on the choke, the bike will idle at +/- 2000 revs for a little while - maybe 30 secs - then rev right up to 4000 or so and stay there until the choke is brought back or disengaged. And the headlight causes a noticeable loss of idle speed, so I assume there's an earth or short problem somewhere in there, which I intend to investigate.

    The bike is slow whether or not the headlight is on, however, so that doesn't seem to actually cause the performance lag.

    Any other suggestions I could follow up?
  13. Or just save yourself all the hassle and buy something like a Breva 750... ;)
  14. Now what kind of idiot would say something like that? :wink: (the clairvoyance gave me a start until I saw the handle...)
  15. I see a Mod has been active in this thread :roll:
  16. Um, wha? I haven't seen mod activity. The last two posts were just a mate of mine giving me some cheek, and me responding in kind... :wink: