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Thread: Tips and Tricks for non-running 90's Bandit 250's

  1. #1
    Join Date
    26th September 2014 - 17:29
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    Tips and Tricks for non-running 90's Bandit 250's

    Hello all, it's been awhile.

    I thought I would do a little write up of my experience working on two different bandit 250's I've recently finally gotten working after owning for almost 7 years now. I know from talking to way too many people that these bikes can be a total bitch to diagnose, so hopefully some of my experiences can help someone else.

    For reference, both of these are the GJ77A variety (the much more annoying variety IMO because of the lack of info and accessible parts diagrams). The Yellow one is a variable valve timing model (red top timing cover) and the black one is the non-vvti model.

    I purchased the first bike back in about 2016 from a lad who told me the bike was stolen and recovered but he wasn't able too get it working again after that. I put literally hundreds of hours and thousands of dollars in replacement parts and mechanics time into this before I finally manage to get it working with the help of an older mechanic who lives locally here on the north shore (Auckland). The yellow bike I picked up ~3 years ago after it had been sitting in a shed being leaked on for a few years. Here is what I've learnt;


    - Its probably not the carbs

    I spent hours and hours cleaning and playing around with jetting on the carburettors, and even bought a few sets of working bikes to compare. If the bike doesn't start, thats NOT your issue.

    - The ignition switch MUST contains a resistor

    When I purchased the bike it had a replacement ignition switch since it had been stolen recovered, this turned out to be from a slightly earlier model which didn't use a resistor. The CDI WILL NOT WORK without this resistor, and you will never get any spark despite changing the loom, CPS sensor and even CDI more times than I care to admit.

    - These bikes HATE plugs

    You can have all your ducks lined up in a row but if your plugs are even slightly fowled, the bike wont start and if it does it will only run on the cylinders with the working plugs. As far as I know, theres no way to 'revive' the plugs ether, once they are gone (which can happen very quickly if the bike is turned over without starting for any length of time). They might work on another bike but they WILL NOT WORK in the bandit. Replace them with a ~$25 auto light set from super cheap. I tried literally over 25 plugs in the bike before I found a set that worked (mis-matched) and once I got it working I chucked a new set it and it starts first pop now.

    - There are variations in CDIs with the same model number

    I suspect this is due to the hp limitations between generations (although why this would happen within a model that was released after 1993 I have no idea). If your bike feels like it has no power above ~12k RPM, and your SURE the jetting isn't causing the problem (try 97' mains with 4th needle position), try another CDI. I makes a world of difference when your ignition advance works as intended.

    - If the bike feels like its struggling to turn over CHECK THE MAGNETO

    This one really blindsided me, I was absolutely sure the carbs were leaking into the pots causing compression locking (again, its probably not the carbs). Turns out the stator magnets had partially disintegrated and this intermittently caused cranking to feel like it was under huge load. This also meant that on the off chance I did get the bike actually running it wouldn't idle without dying and it wouldn't rev above ~4k RPM without feeling like it was dying. If you're struggling to find a replacement, you can use the magneto off the GSXR250s if that helps at all. You will need to remove and replace the backing place with the bandit one however as the gsxr one is smaller and wont engage with the starter clutch.

    - The air filter is important, try to find / use and original if possible

    I couldn't get the bike to run right at all without the original air filter, it looks a bit worse for wear but without it the bike would buck and surge under power.

    - If the starter button doesn't work, and your sure its in natural, check the starter relay

    For some reason this little bastard would occasionally just stop working and I would spend ages trying to figure out what had gone wrong. With a multimeter the immediate conclusion is that theres an issue with the kill switch / wiring but don't be fooled! It's a little black 4 pin relay that looks a lot like the flasher relay, wired close to the fuse box. Try hitting it gently into the bike plastic as this sometimes helps. You wont get any power to the ignition system or starter switch if this doesn't work.

    - Check the gap between the crank sensor and the timing gear

    This gap has a HUGE impact on the strength of the spark, and playing around with it can help clean up really erratic idle issues. Your and check if it's improving things by observing the strength of the spark using one of the HT leads close of the engine casing. Generally I found further away was better (~1mm), but results will vary.


    - Engine start will kill your plugs

    If it doesn't start almost immediately, stop, take a step back, and double check everything else. You will kill your plugs in no time if you keep turning it over and it doesn't start (especially with engine start) and then it REALLY wont start (see above)

    - If the bike doesn't start but sometimes backfires when turning over, its ether your plugs or spark timing

    For some reason on the yellow bike, the wrong timing gear had been fitted and this meant it would 'almost' start, but never quite got there. It would kick and backfire, sometimes after you had stopped turning it over. Once the correct gear had been fitted it fired straight into life.

    - Its probably not clearances, compression, bad fuel etc etc

    If you have any evidence the bike ran before you got it, its probably not any of the above things and is likely one of the issues above

    - The hoses joining the carbs wear over time

    These little bastards can cause all sorts of running issues and leaking fuel if you dont spot them earlier enough, pay close attention to the condition of the rubber connectors between the carbs


    Good luck! Ill add anything else as I remember

  2. #2
    Join Date
    8th November 2005 - 12:25
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    Cheers for the info, while not a bandit 250 owner, I'm sure your post will help many people worldwide

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