Bandit Alley
MODEL SPECIFIC => SUZUKI BANDIT 250 & 400 => Topic started by: CrustyOreo on April 17, 2014, 08:12:51 PM
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Ok so I've cleaned and replaced the gaskets in my B4s carbs.
When I try to start it, all I get is a backfire out of the carbs. It never seems to fire through the exhaust.
What should I check next?
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a backfire that goes out through the carb is usually a sign of improperly set ignition timing, because it indicates that a sparkplug fired while an intake valve was still open.
in the case of your Bandit there's not much that could cause the timing to change from the factory settings.
the only thing I can imagine happening to a Bandit to cause something like this to happen would be if the control wires from the ignitor box somehow got connected to the opposite coils. this would have the effect of changing the timing by 180 degrees.
that's why I asked you (a few days ago) if it were possible that one of the following had happened: A. the coils or just the high tension coil wires somehow got physically swapped (don't know if this last item is even physically possible), or B. the coil control wires in the bike's wiring harness somehow got swapped out, left for right.
according to the manual the left coil is controlled by a White wire and its high tension wires go to cylinders #1 and #4. the right coil is controlled by a Black wire that has a Yellow tracer line on it and the right coil's high tension wires go to cylinders #2 and #3.
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Just double checked. All looks well on the wiring part.
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I've seen exactly this symptom with mis-wired coils and greg737 has described. better recheck those sparkplug wires.
A
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So I went through the carbs again and double checked the wiring. Same result. Back fire through the carbs :annoy: :stickpoke:
I think a compression test is in order.
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I can't see how changing the carb o-rings will have made it lose compression.
Was it running well/reasonably before you changed them?
Have you checked the plugs themselves?
It does sound like plug caps on the wrong cylinders
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I've never had it running.
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Ah, in which case i'd go for
Fresh plugs,
Check the spark on each one,
Check leads are on the correct cylinders,
Check valve clearances
Check top end timing, eg are cams on the chain in the correct position, unlikely but you never know
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PLugs are fresh. Each of them have spark.
Correct leads on correct cylinders.
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Clearances and top end i would suggest
Also when it's back firing is it ignited mixture and flame coming back through the carbs or wet unburnt mixture and is it on all 4 carb intakes?
I presume that you're running it with the air box off for now?
Edit to add: Also check for vacuum leaks round the carb rubbers and also on the vacuum take off stubs
Cheers
Chris
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I wonder if the problem isn't related to the Ignitor Box.
The Denso ignitor box on these Bandits is very delicate. Over the lifespan of this motorcycle people were ruining them all the time by accidentally inducing an over-voltage in the bike's electrical system (it usually happened when somebody was trying to start a bike that had a dead battery by jumping it off of a running car). The ignitor box apparently doesn't have any over-voltage protection built into it so the capacitors blow up/burn up.
When one of these not very mechanically skilled owners realizes that the ignitor box isn't working any more they go out an purchase the first "Bandit" ignitor box they can find or even a GSX-R400 ignitor box without a thought to the fact that there were several different ignition system configurations during the Bandit and GSX-R.
Correct me if I'm wrong here: Your Bandit has never run since you got it, right? You have been working to get its carbs and ignition system working and you've made some progress but it has always backfired through the carbs. That's the closest to running you've gotten, right?
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Correct. It has no run since I've bought it and the back fire out the carbs is the closest.
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you should to do a bit of research on your Bandit to determine which CDI box you need.
Here's a datasheet that forum member T6nis showed me:
(http://i679.photobucket.com/albums/vv158/EWflyer/82b54c8a-3c45-477f-9beb-0c6d8c22126b_zps5224bb69.png)
As you can see this datasheet indicates there are at least 2 different CDI boxes out there for the Bandit 400. The datasheet shows that during the production lifespan of the Bandit the ignition system sub-contractor, Denso Corporation of Japan, changed the configuration of the signal generator wheel (the arrangement of the "teeth" on the wheel are different). Also, if you look at the wiring pin-out on the plugs you'll see that at some point in Bandit production Suzuki reversed the inputs from the signal generator (pins #7 and #8).
To further complicate things I've discovered that my 1993 U.S. import model Bandit 400 has 7 wires leading to the CDI from the wiring harness instead of 6 wires. Every wiring diagram in both the Bandit 400 Service Manual and the Bandit 400 Service Manual Supplement only shows 6 wires going to the CDI. My CDI has 2 plugs from the wiring harness, one plug has 4 wires in it and the other plug has 3 wires in it.
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About a month ago I sent my CDI box to T6nis.
Because I'm modifying my Bandit with a fuel injection system that will also control ignition, I won't be needing the OEM CDI. So I gave it to T6nis.
When he got the CDI in hand and tried it in his Bandit he was initially disappointed because it didn't work. Then he checked the wiring at the connector plugs from the bike's wiring harness and discovered that pin #7 and #8 were reversed (he had a black wire in the plug going into a brown wire on the CDI and a brown wire in the plug going into a black wire on the CDI). As soon as he sorted this mis-wired situation out the engine ran just fine.
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To further complicate things I've discovered that my 1993 U.S. import model Bandit 400 has 7 wires leading to the CDI from the wiring harness instead of 6 wires.
There is some speculation that the 7th wire controls a limiter that is engaged in 5th and 6th gear. Some machines apparently have a variable resistance that comes from the gear selection and controls this. My 7th wire on my '93 was just open when I got it. I've grounded it through a resistor based on various anecdotal bits of data floating around with the idea that the proper resistance will force it to be unlimited at all times. :shrug:
I've never seen any definitive information on whether that is true...
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To further complicate things I've discovered that my 1993 U.S. import model Bandit 400 has 7 wires leading to the CDI from the wiring harness instead of 6 wires.
There is some speculation that the 7th wire controls a limiter that is engaged in 5th and 6th gear. Some machines apparently have a variable resistance that comes from the gear selection and controls this. My 7th wire on my '93 was just open when I got it. I've grounded it through a resistor based on various anecdotal bits of data floating around with the idea that the proper resistance will force it to be unlimited at all times. :shrug:
I've never seen any definitive information on whether that is true...
I was also speculating/wondering about this 7th wire, but my guess at its purpose is different:
I searched around and found wiring diagrams for other Suzuki models that were being produced at the same time as the Bandit 400 and whenever I found a wiring diagram that showed a CDI with 7 wires coming out of it the 7th wire was just an input feed to the Tachometer.
For some reason the Bandit 400 uses a spliced-in tap-line on the #2 coil to feed the tachometer so it didn't need to have that 7th wire connected to its tachometer. My guess is that this little difference didn't stop Suzuki from using the same 7-wire Denso CDI box on several models. This CDI box was just a "parts bin" item, probably purchased in huge lots of several thousands at a time, so it was just economical to use it on a bunch of bikes.
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To further complicate things I've discovered that my 1993 U.S. import model Bandit 400 has 7 wires leading to the CDI from the wiring harness instead of 6 wires.
There is some speculation that the 7th wire controls a limiter that is engaged in 5th and 6th gear.
I was also speculating/wondering about this 7th wire, but my guess at its purpose is different:
I searched around and found wiring diagrams for other Suzuki models that were being produced at the same time as the Bandit 400 and whenever I found a wiring diagram that showed a CDI with 7 wires coming out of it the 7th wire was just an input feed to the Tachometer.
For some reason the Bandit 400 uses a spliced-in tap-line on the #2 coil to feed the tachometer so it didn't need to have that 7th wire connected to its tachometer. My guess is that this little difference didn't stop Suzuki from using the same 7-wire Denso CDI box on several models. This CDI box was just a "parts bin" item, probably purchased in huge lots of several thousands at a time, so it was just economical to use it on a bunch of bikes.
That's an interesting idea. I was never able to demonstrate any difference between leaving the wire open and grounding it. Further, there is no sensor (on *my* bike anyway) to actually inform the CDI what gear it's in. If I had a scope I could hook it up to that thing and see if it's producing a signal. Ah well. I like your idea :)
A
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Cyl 1 had 55PSI of compression.
Cyl 2 had 30PSI.
Time for a motor.
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If its been stood for a while, the rings may be gummed up, you may get away with taking the barrels off un sticking/replacing the rings and honing the barrels
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To further complicate things I've discovered that my 1993 U.S. import model Bandit 400 has 7 wires leading to the CDI from the wiring harness instead of 6 wires.
There is some speculation that the 7th wire controls a limiter that is engaged in 5th and 6th gear. Some machines apparently have a variable resistance that comes from the gear selection and controls this. My 7th wire on my '93 was just open when I got it. I've grounded it through a resistor based on various anecdotal bits of data floating around with the idea that the proper resistance will force it to be unlimited at all times. :shrug:
I've never seen any definitive information on whether that is true...
That may be true. AFAIK japanese regulations after 1993 forced bikes under 400cc to be limited to 170 km/h or maybe even 150km/h (in addition to have lower power output, which is why post-92 bandits have different power rating than older bandits). I've also read that german post-93 (in fact unified post-regulation change model) model had rev limiter on 10500 rpm because of reliability, but that is bullshit. But it is possible that in 6th gear rev limiter is on 10500 to limit speed to 170 km/h (or 150 km/h whichever is apropriate). Other gears limiter is higher. Older CDIs have no 7th wire, the only wire coming out of engine is neutral switch for sidestand interlock.
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To further complicate things I've discovered that my 1993 U.S. import model Bandit 400 has 7 wires leading to the CDI from the wiring harness instead of 6 wires.
There is some speculation that the 7th wire controls a limiter that is engaged in 5th and 6th gear. Some machines apparently have a variable resistance that comes from the gear selection and controls this. My 7th wire on my '93 was just open when I got it. I've grounded it through a resistor based on various anecdotal bits of data floating around with the idea that the proper resistance will force it to be unlimited at all times. :shrug:
I've never seen any definitive information on whether that is true...
That may be true. AFAIK japanese regulations after 1993 forced bikes under 400cc to be limited to 170 km/h or maybe even 150km/h (in addition to have lower power output, which is why post-92 bandits have different power rating than older bandits). I've also read that german post-93 (in fact unified post-regulation change model) model had rev limiter on 10500 rpm because of reliability, but that is bullshit. But it is possible that in 6th gear rev limiter is on 10500 to limit speed to 170 km/h (or 150 km/h whichever is apropriate). Other gears limiter is higher. Older CDIs have no 7th wire, the only wire coming out of engine is neutral switch for sidestand interlock.
No german gsf400's are limited to 50 bhp by not allowing the carb needle to go up fully. The cap on the carbs have a stopper.
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I know. but i'm not talking about german model, but about japanese model (with engine probably identical to UK, FR, IT, ESP specification of pre-1993 models). Even plain japanese "unrestricted" model is in fact restricted by Japanese manufacturer's "voluntary code" which all four big japanese manufacturers follow for years or maybe tens of years (the same code which limits every production street motorcycle not to exceed speec 300km/h). IIRC, japanese specification of B400 made pre-1992 was "restricted" this way to 59HP. Same as GSX-R 400. In 1992 (affecting 1993 models) limit was pushed down to 53 HP. Change in code in 1992 pushed limits for up-to-400cc and up-to-600cc classes down but introduced over 600cc cycles to japanese market as native article (again, IIRC). Due to this change palette of different per-country specifications of Bandits were unified into one with 53HP. Code change in 1993 introduced (again voluntary, but still followed) limitation of top speed for up-to-400cc class to 180km/h (again for all models). This limitation was not present in former "revision" of code. That's why some B400 CDIs have one more wire than other. It depends mainly on year of production and on number of motorcycles which the parts for that one particular come from.
For some reference: http://www.gaijinriders.com/showthread.php?8528-Japanese-Bike-Domestic-Restrictions&s=2f9e95e4539c9a8d4a1377f541a9d377&p=96275#post96275