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Help Bandit 250 problem.

Discussion in 'Suzuki 250cc In-line 4's' started by Alibongobingo, Mar 18, 2018.

  1. Alibongobingo

    Alibongobingo Member

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    Hi.
    I am currently rebuilding a 1990 250 Bandit for a friend.
    The bike was all in bits and i cannot find a manual so i am guessing.

    I have the bike up and running but am experiencing trouble.

    It will start and run and sounds fine. It will idle no problem and rev up in neutral.

    When put in gear and attempted to move, the revs will drop to idle and the bike will only idle only at WOT. Letting go of WOT will stall it.
    It will idle like this for maybe 30 seconds with the throttle open then seemingly fix itself and rev up.

    The bike can then be ridden for maybe 2 minutes and seems fine except for bogging between 6k and 10k rpm.

    Then the revs will die again and the bike must be put in neutral with the throttle open wide or it will die. It will idle like this for 30 seconds again (throttle open) and then you're off again (with the bogging)

    It seems like intermittent fuel starvation but why?

    I have stripped and thoroughly cleaned those carbs, fitted a small inline filter.
    I had to guess pilot screw settings and put them at 2.25 turns out each.

    Im also not sure i have the carbs plumbed in properly.
    The two highest outlets are obviously fume outlets so i connected them to the fume canister. The lower, central seemed like the fuel line so it's connected to the tank.
    There's another 2 connections slightly higher. I assume these are overflow drains so i haven't currently connected them to anything??
    Although the float bowls have their own overflow drains in the form of those little tubes inside??

    Somewhat confused.

    Any help?

    Thanks.
    Al
     
  2. Linkin

    Linkin The Apprentice Premium Member Dirty Wheel Club Contributing Member

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    The bandits have Mikuni BDST carbs. Blair has a rebuild guide here:

    http://litetek.co/Guide_MikuniBDST_Rebuild.html

    The central t piece facing the rear of the bike is the fuel line one. IIRC all the rest are vents or breathers.

    I'd be removing the filter for troubleshooting purposes.

    And I'd also check the air filter as well.

    We have manuals in our resources section, a small donation will get you premium membership so you can access them.
     
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  3. Joker

    Joker If you want me find Club250 on facebook. Premium Member Contributing Member

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  4. Alibongobingo

    Alibongobingo Member

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    Thanks. I just read through that.
    Pilot one turn out? Really? I'll give it a go.
    I'll also try without the fuel filter. Btw, the petrol tap is working fine, I tested it.
    I've got the vac tube for the petrol tap on cylinder 3. Looks like it's on number 4 on others. I can't think this would matter though?
     
  5. Joker

    Joker If you want me find Club250 on facebook. Premium Member Contributing Member

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    I tried a number of things, I found it a very difficult bike to deal with so don't take anything I did as gospel. I was messing with everything trying to make sense of it but admit I was pretty naive at the time. I reckon if I had another crack now... well nothing can be worse than a fizzer surely lol

    I would start with two turns out, ensure your vacuum hose is connected to cylinder #1 (I'm pretty sure that's where the only connection point is on the rubber between the carbies and the engine) and ensure your fuel tap is OK. I had several problems with the fuel tap because it is gravity the condition of the diaphragm inside is pretty important for it to work. I assume you've done a good carby clean and such, if anything take the bowls off the bottom and give it a good clean. I'd also take each of the jets out and clean them with compressed air (if you have it) and a strand from a wire brush just to remove the crap. You should get at least some life out of it if the carbies are in reasonable condition.

    If all that is good you might also have weak spark from the coils, I was struggling with that as well now I reflect on it. So unscrew them, snip 10mm off the lead and screw them back in. I don't know if you attempted/messed with the timing... without information that was a pain in the bum but the GJ73a manual helped me (in resources for premium members).

    On the carbies there is the main connection point for fuel in the centre, two breather hoses come out the top they don't do anything provided they aren't blocked so don't worry about them.

    I eventually got mine running (albeit relatively poorly) but by that stage I had enough so I wrecked it and bought a fizzer which I thought was going to be easier... hindsight is a funny thing!
     
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  6. Bab

    Bab Active Member Premium Member Contributing Member

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    Looking back I think I was lucky with my Bandit, as it started the minute I changed out the TDI unit. I did pull the carbs and cleaned them all out, but did not mess with them in any way, and the bike ran quite well as it was found. I still need to do some fine tuning and change the oil and filter. Based on my observations, is it possible the fuel tank is not venting properly to allow the fuel to run through the petcock?
     
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  7. Alibongobingo

    Alibongobingo Member

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    Yep ..so update.....
    I decided after checking everything else, that I hadn't cleaned the carbs properly and it needed redoing. (?)

    So, carbs off, fully taken apart, cleaned and put back together meticulously via the guide.

    Now it won't start at all! Zip.

    I can get one cylinder to cough (#2) by throwing starting fluid down its throat. That's it.
    All other exhaust pipes clap cold, no cough with starting fluid, nothing! (Air box off)

    I have a spark at all 4 plugs. The plugs are fine. No other changes from running. I only took the carbs off and cleaned them, didn't touch anything else.

    I am dumbfounded.

    I thought perhaps the CDI has gone mad, so I rode a 5 hour round trip into Brisbane on my 600 kwaka, braving rush hour morons and pouring rain to retrieve a CDI from a bike being wrecked.

    No joy. :(

    The new CDI must be fudged or the wrong one as it only fets intermittent sparks and attemping to start the bike with that CDI causes huge backfires but nothing else.

    So inside the bikes original CDI looks all goid. No melted circuits, no obviously fried components. It looks new in there. And I get a spark at all 4 plugs!...but the right sparks? Has it gone mad and is sparking at all the wrong times? Is that possible? Am I barking up the wrong tree??

    I wish i had a friend with a working bike like this one so i coyld borrow the CDI and at least rule it out. I'm at my witts end!

    Compression ..check
    Carbs all good...check
    Spark....check
    Fuel....check

    Runs....Does it f*ck

    This bike ows us $1000 so far and it's not my money. My mate and I were supposed to be selling for a small proffit once up and running.

    I could just put it in the flipping trash can and forget it.

    So yea...lol.. stumped.
     
  8. Murdo

    Murdo The Good Doctor Staff Member Premium Member Ride and Events Crew Contributing Member

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    Have you opened the drain screws to make sure there is fuel in the carb bowls? Does it have a vacuum tap and have you put it onto 'prime'?
     
  9. my67xr

    my67xr Bike Enthusiast Staff Member Premium Member Contributing Member

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    Is the firing order right, plug lead's on the right spark plugs ?
     
  10. Alibongobingo

    Alibongobingo Member

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    Yep, all 4 bowls have fresh fuel at correct level. But even if it were bone dry, it 'should' still fire with startyabastard down the throat of each carb. It doesn't even cough :( (except cylinder#2)

    Tank/petcock is off for testing. Line connected direct to plastic bottle of fuel raised up.

    I just dont get it.
     
  11. Alibongobingo

    Alibongobingo Member

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    I should hope so. Lol

    I haven't moved them from where they were when running.

    Besides, this must be a sort of wasted spark system, or wasted in pairs as the two coils fire 2 pots each and they only have a live and an earth. I'm no electrical genius but seems to me it must spark in pairs and waste a spark.
    Also this makes sense when the firing order is considered and which lead goes where.

    Firing order 1.2.4.3
    Left coil 1 and 4
    Right coil 2 and 3

    ?
     
  12. kiffsta

    kiffsta Administrator Staff Member Dirty Wheel Club Contributing Member

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    Sounds like you are almost there as you have spark, carbs are clean, and you have fuel can you Post a pic of your plugs , I am guessing that your Plugs have fouled.

    When you say you have done a comp test , can you share how you did it and what were the results , ie were the carbs on, if on,’did you hold the throttle full open ?

    When you are trying to start it, are you doing it with the tank or are you using an aux tank?
     
  13. Frankster

    Frankster See the World before you leave it Staff Member Premium Member Ride and Events Crew

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    I agree with @kiffsta. If you have spark, fuel and compression, the only thing that could be causing your engine not to fire would be timing or fluid in the combustion chamber (oil or fuel or both). Does the engine oil smell fuelly?
     
    Last edited: Mar 29, 2018
  14. Alibongobingo

    Alibongobingo Member

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    What the actual!....??.

    I went and got a compression tester.

    Compression test gets 30psi on all four pots, 35psi wet. Exactly the same on all 4!

    I tested the tester (if you will) on my car. No issue. Reads what I'd expect. Shot up like a good un.

    Of course the car uses a different thread attachment on the hose.
    I don't believe those results on the bike and in wondering if im not getting a good seal on my compression tester 10mm adapter.

    I took the rocker cover off and its all pretty clean in there. The valves look to be going up and down no problem when i turn it over.

    This bike has 35,000km on it. 22k miles. Not huge amounts even for a little 250 four pot?

    The plugs look a little fouled but not terrible.

    I just don't get it.
    If 30psi on all pots is accurate, there's no way it would start?? But it did before! And ran almost ok untill i cleaned the carbs . That's all i did!

    And what could cause exactly 30psi on all 4 cylinders?

    In my experience, rings/valves wear non uniform and a worn engine will get different results on different cylinders. A blown head gasket will show really bad compression on one or two (depending on where it blew).

    I just don't know.
    Compression test results inaccurate?
    Cdi really is the problem? How to test?

    Something else??

    I've no money to give up and take it to a shop. :(

    I appreciate the help and suggestions. Thank you. :)

    I'm not holding much hope right now.

    Al
     
  15. Alibongobingo

    Alibongobingo Member

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    Compression test done with carbs off btw.
     
  16. kiffsta

    kiffsta Administrator Staff Member Dirty Wheel Club Contributing Member

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    Wow, 30 psi is not good, these should be around 180 PSI when new, the manual states that the use limit is 8kg/cm2 which equates to 115 PSI

    I have a cheap Chinese comp tester and I have had running engines report 30 psi, I will one day buy a quality compression gauge. Do you have access to a leak down tester ?
     
  17. Wozza

    Wozza Active Member

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    all the exhaust valves burnt or carbon build up and sticking?
     
  18. Andych

    Andych Well-Known Member Premium Member

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    Check valve clearances... although I doubt you would get the same on all 4 even if they were all out... which they will be.
    Plenty of spark plugs have died after being cleaned or fouled with a heap of unburnt fuel. Try new plugs or new old plugs if you have any.
    A leak down test is a better gauge of engine condition than compression test... if it holds pressure with very little leak its all good.. if it leaks down fast... check inlet or exhaust for the leaking air... (Valves) or oil filler (rings)...
    Any compression losses and fuel issues or combinations could all conspire to send you mad... high performance 4 cylinder bikes will do that to you :)
    Good luck with it
     
  19. Alibongobingo

    Alibongobingo Member

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    I don't have access to a leak down test unfortunately.

    Valve clearance not adjustable? Call me stupid but there doesn't seem to be any adjusters in there. Shim over bucket. New shims?
    Everything is clean on top and around the cams. I haven't taken the head off. I can't even figure out how!
     
  20. Murdo

    Murdo The Good Doctor Staff Member Premium Member Ride and Events Crew Contributing Member

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    No need to take the engine apart yet.
    Try some new plugs first as the either starting fluids are no good for them.
     
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