Mysterious Engine Problem – '92 Bandit 400N

[morrisonaj]

Hi all, I’ll start my first post with a brief introduction.  I have a red ’92 Bandit 400N and love the bike to death.  I bought it in ’97 while at University and have been babying it ever since.  It has 41k km on it and was totally overhauled last winter (including getting the tank interior coated, detailed carb cleaning, valve check and a painfully long sanding and new paint job - tank and all) with hopes that the problem I’m about to describe would be solved when it all went back together (looking almost better than new I might add…).  I've used the forum search tool, but must not be using the right keywords because I haven't found what I'm looking for (and I'm at awe with how much you guys know about these bikes...).  Hopefully someone can help me get my bike back on the road!

So here’s my problem…

The bike won’t idle below 3,000rpm and while it will wind through the complete rpm cycle while stationary, it is lacking power under load.  Basically the bike won’t go over 120km/hr right now and even that’s feathering the throttle.  It sounds like one or two of the cylinders is cutting out.  I’ve taken the carbs apart and cleaned them out (both myself and at a shop), synched the carbs, replaced the plugs and didn’t have any luck.  I then took the bike into my local bike shop to see if they could help me out…  $1,000 later, it still has the same problem…  I have the Suzuki Service Manual and the shop tested everything they could by the manual.  They said that all of the resistance specifications are within specs (coils, regulator, etc).  The tech narrowed what he thought the problem was down to the CDI unit (he said the voltage out of the CDI to the #1-4 coil was consistent, but the voltage to the #2-3 coil was fluctuating, leading him to believe the fault was the CDI), so I bought a new aftermarket CDI unit.  However, even with the new CDI unit, I have the same problem…  I’ve brought the bike home and am really at a loss with respect to what to do next.  I’m not bad around bikes (I have a couple dirt bikes that I work on), but am at a loss when it comes to electrical stuff.  I have a multimeter that I’m about to break out to try testing stuff myself, but need some advice.  Can anyone here help me out?

Thanks for reading.

Andrew

[turbofb]

Check the connections at the coils,both the high tension leads and the little wires.
Just happend recently.The same symptoms, the same problem..... was just a loose coil power wire.Usually when cylinders act up in pairs its the coils, since its less likely that two carbs,sparkplugs,valves or other totally seperate items,would have the same problem at the same time.

When idling,you can spray a little water on the exhaust headers to isolate which two cylinder are acting up.That makes diagnosing a lot easier when searching for a running problem on a multi carb,multi coil engine.

[gsxr400 racer]

do you have a in line fuel filter?
again re crimp the plug positive and negative wires so they are tight
check the pick up coil wire at the cover if this is frayed you would probably lose all spark
check that the kick stand detente that pushes the kick stand safety switch completely activates the safety switch.

[PitterB4]

$1000 later???  Jesus!  

Check to see which cylinders are firing.  Start it up let it warm up a little and spray water on each header.  If you're down a cylinder or two, you'll be able to tell.  If it's the two in the middle or the two on the outside, you're probably headed down the right path (my guess pick-up or the stupid connectors going into the coil or a bad coil).  If is only one or some other combination, it might be motor related and you should probably check compression.  

Been there.  This ain't fun.  Good luck and  

[morrisonaj]

Hi all, thanks for the suggestions, but I’m still having the same problems.  Here’s what I’ve done (as suggested):
1. Started the bike and sprayed water on each header.  They are all hot, with #1 and #4 appearing to be hotter than #2 and #3.
2.   Taken out the trusty multimeter and tested all of the resistances of the coils and associated wires (including the wires from the signal generator all the way through the igniter box to the coils themselves.
3.   Taken the spark plug cap off of the high tension wire and inspected for damage, cutting back to create a new connection where necessary.
4.  Re-crimped the leads for the wires going into the coils.
5. Insulated the wires going into the coils (Orange-White tracer and Black-Yellow tracer to #2 and #3 coil and Orange-White tracer and White to #1 and #4 coil) with many, many wraps of electrical tape.
6.   Checked the kick stand detent safety switch continuity (it’s working correctly).
7.  Traced the wiring from the signal generator (from where it exits the engine on the clutch cover side) and confirmed that it is not frayed or broken.

It doesn’t want to start after sitting for a while and when I do get it going it’s really tough to keep it idling until warm, and even then it won’t idle below 3,000rpm.  I took it for another ride today (after completing the work mentioned above) and it ran smooth until I tried to really drive it, and then it just gives out.  When I try to give it gas it’s almost like it’s bogging down/cutting out.

GSX400 Racer, I do not have an in line fuel filter (I don’t believe that’s standard on the bike, and my bike is completely stock – less the rear signal lights – I put short ones on to allow me to use saddle bags).

Anymore suggestions?  I’m going to try and get my hands on a heat measuring gun (not sure the correct terminology) to see if I can’t do a better job of narrowing down which cyclinder(s) is/are the problems.  Does this sound like an electrical problem or maybe a carb/engine problem?

By the way, I’ve got a new aftermarket CDI for sale if anyone’s interested… (at least I know that’s not the problem…).

Thanks again for reading.

Andrew

[interfuse]

I just touch the pipes with my fingers... a real quick touch so not to burn yourself, but you can tell which pipes are getting hotter.

Have to tried switching the coils? Move the coil from #2,3 to 1,4. If the problem follows the coil then you know that's at fault.

Also what's the compression like on those cylinders?

[Banditmax]

Clean the carbs again making sure the pilot jets are clean.

[magicGoose]

Hey Andrew,
All the likely stuff has already been covered, but I will throw in a couple of unlikely things.
First, it isn't clear to me when you say you re-crimped the leads for the wires going to the coils, the typical problem is not with the connection between the wire and spade connector, where you would 'crimp' it to connect it, but the female part of the spade connector itself does not fit snugly on the male part of the spade connector sticking out of the coil. Sorry if this is obvious, but sometimes people run in circles over simple misunderstandings like this.
Second, check the output of your reg/rect (at your battery terminals) at the ENTIRE RANGE of RPMs. I had poor idling and engine losing power as RPM climbed, and my problem was a snarfed reg/rect which would cut out at higher RPMs. The voltage should steadily climb as RPMs increase.
Good luck,
Steve

[morrisonaj]

Hi all, thanks for the suggestions/help, but I’m still having the same problem.  Here’s some answers to some of the Q’s posted previously.
1.   When I said ‘re-crimped the leads for the wires going into the coils’ I tightened the female connector to ensure a tight fit onto the male connector.
2.   The regulator/rectifier is within the specs outlined in the service manual.
3.   The carbs have been taken apart and cleaned 3 times in the last 4 months, the last two times specific attention has been paid to ensure the pilot jets were/are clean.
4.  I’ve done the ‘touch test’ and water test again on the headers and although #1 and #4 cylinders appear a tad hotter than #2 and #3 cylinders, I really don’t think the coils are the problem (they are both within specs outlined in the service manual).
5. I have NOT done a compression test on the cylinders though.

So here’s where I think I’m at:
1.   Not a wiring problem (traced the wiring from the signal generator to the coils and it is all good to go).
2.   Not a CDI problem (I’ve replaced the CDI and the bike runs the same).
3. Not a Regulator/Rectifier problem (it is within specs outlined in the service manual).
4. Not a Coil problem (they are within specs outlined in the service manual).
5. Not a Carb problem (they have been taken apart and cleaned thoroughly several times since the bike has been running poorly).

I’m really at a loss.  One thing which I’ve tested the resistance of (and it’s within specs outlined in the service manual) is the signal generator/stator itself.  Does anyone have any voltage values/graph for this throughout the rpm range?  Has anyone ever had a problem with their stator going?

Anyways, once again I’m in all of your debt for any further suggestions.

P.S. I’m heading away on vacation for 3 weeks so REALLY won’t be able to look at the bike (not that I’m the quickest at getting to this stuff…) for a bit.

Thanks.

Andrew

[turbofb]

Sounds like a compression test should be next.
If the engine overheated or was run hot for an extended time,the center cylinders would take the most abuse since they are in the core of the engine,flanked by hot parts on both sides.Possible the rings have lost their tension.....

And, coils can be bad even if they are in spec when you test them.Getting hot when running can change the resistance values greatly, and can even make damaged windings seperate altogether.Its not hard, while you have the tank off swap the coils and see if the outer cylinders start acting up.

[gsxr400 racer]

Sounds like a compression test should be next.
If the engine overheated or was run hot for an extended time,the center cylinders would take the most abuse since they are in the core of the engine,flanked by hot parts on both sides.Possible the rings have lost their tension.....

And, coils can be bad even if they are in spec when you test them.Getting hot when running can change the resistance values greatly, and can even make damaged windings separate altogether.Its not hard, while you have the tank off swap the coils and see if the outer cylinders start acting up.

  good suggestions

[morrisonaj]

Hi Guys, it's been a long time... but I thought I'd let you know where I'm at with my bike (it's still in the shop though... but close).

1.  I finally did the compression test and had low compression in all cylinders, but especially low in #2 and #3.  I would have been fine with a piston and ring replacement, but #2 was too far gone and I had to get the engine bored out... Ouch.
2.  Replaced the voltage regulator/rectifier (the bike was still running like @#ap after the engine job and the unit was acting funny (giving weird/unexpected voltage values throughout the RPM range).
3.  Replaced one of my coils (this after the bike STILL wasn't running right - was diagnosed by swapping coils and inspecting plug colours).
4.  Rejetted the bike with an aftermarket jet kit (needles and jets - as the needles were slightly corroded and not a consistent taper anymore (likely due to the rusting in my gas tank I mentioned last year).

So... the bike's still not running right.  It looks like I'm going to have to replace the 2nd coil as it appears that it is now the problem...  the darn bike is going to practically be new once I'm through with all this.

One final question if you don't mind...  Do I have to replace my old coil with an OEM Bandit 400 coil or is there another OEM coil with the same specs (gsxr400?)?  The OEM Bandit coil is on backorder and it'd be really nice to ride the bike this summer...  Arrgh.

Thanks again for reading.

Andrew

[andrewsw]

I'm scared to learn what really simple problem this turns out to actually be...

meanwhile, this thread discusses alternate coils briefly near the end: http://forums.banditalley.net/index.php?topic=11086.msg89928#msg89928

[gsxr400 racer]

First off how did you get yor bike bored when there is no stock pistons bigger available...? NO where...

[morrisonaj]

The shop did the job, so I don't have all the intimate details (except what's on the invoice).  Just know that it cost $250 to have the engine sent out to a machine shop and I was billed for new pistons and rings....  Part No of the new pistons is 12100-32C00-040.

Andrew