Runs fine, but stalls at idle speed...

[AngryInca]

Hi Folks,

I bought a '91 Bandit 400, I beleive its an american model.  Its not the VVC one around April for £500  I will post some pictures this weekend after I have given it a good cliean :)

I have loved riding the bike, but it has one problem that I can't seem to get sorted.  The bike runs fine once rev'ing, but once it drops to the 1.3~5k rpm speed it seems to struggle and the note of the engine goes up and down a bit, and will then stall.  I have to keep giving it a bit of rev's every 15 seconds or so to stop it from stalling.  This is when its cold and hot.

I have had the carbs cleaned, balanced and have had an in-line fuel filter fitted, but the problem still persists.

Can anyone help me work out what it is?

Thanks!

[mosquito]

Could anything in this thread be applicable to you? http://forums.banditalley.net/index.php?topic=2186.0

[gixxer]

I know some people bypasses the idlesystem of the carbs as a quickfix, and adjust the the throttlecables so that they function as a sort if idle.  This will cause the problems you mention.  Weak and unstable idle that sometimes causes the engine to stall.  So I would recommend you check if the throttlecable have som slack when the throttle is at idle.

[AngryInca]

After reading the thread, it looks like testing the battery is going to be a nice easy check for me.

I have no tools (I just bought my first spanner set this week!) so I am buying new, will this allow me to check the battery on my bike? (and others and cars too!):

http://cgi.ebay.co.uk/Draper-Car-Battery-Load-Drop-Tester-100-AMP-6v-12v_W0QQitemZ280322594803QQcmdZViewItemQQptZUK_Diagnostic_Tools_Equipment?hash=item41448757f3&_trksid=p3286.c0.m14

Also, when I bought the bike the guy showed me the idle speed "dial" thingy.  If I totally disconnect the throttle, should the bike idle and the idle speed be adjusted by the idle dial thing? I could do this to test the idle if so.

[gixxer]

Yes, at idle the idle dial thing should be king.  The throttlecable should not interfere at idle. 

[mosquito]

Yea for spanners!

I'm going to point you to a lot of info, but don't worry:  take it slowly, read, learn, and just do the things that you understand and you'll be fine.  And here's a basic summary of what I'm going to say:

- With the idle wheel you should set it to 1400 RPM (US and German models) or 1300 (others).
- Get a multimeter instead of the load tester.
- Check the battery's charge / DC voltage with the multimeter; if it's lower than about 12.5 Volts, you'll need to charge it. 
- You may need to get a motorcycle battery charger.
- Download a PDF and check the voltage at the battery at 2500 RPM (then maybe also at 5000 RPM).

--

The idle wheel and the throttle work together.  Twist the throttle and it opens up valves in the carburettors and it goes vroom.  When you let go, the valves close and the engine slows down.  The idle speed wheel sets just how closed the valves are when you let go.  They're supposed to be held open a smidge and turning the idle wheel sets how big  your smidge is.  Sometimes when I'm having trouble getting mine to idle, I'll wind up turning it up and down so I can just get home. 

I bet you're going to have the same problem even if you increase the idle speed.  (If it's a fuel delivery or electrical problem idle speed won't affect them much.)  When Friend / shop cleaned and balanced the carbs, did they also set the float heights?

That load tester looks like a nice thing to have, but it's the sort of thing less than 0.2% of home mechanics would have.  You should get an inexpensive digital multimeter, something like this: http://www.radioshack.com/product/index.jsp?productId=2103174 .  That will allow you to do most of your electical checking on the bike.



and also if you find your battery is undercharged look into finding a motorcycle battery charger.  There are a few reviews and lots of info about batteries here: http://www.webbikeworld.com/motorcycle-battery/ .  (FWIW it's easy to ruin a moto battery with a car charger.)

The PDF available here: http://www.electrosport.com/electrosport_fault_finding.html is a great tool for looking at electrical issues, *but* there's a lot there.  Go ahead a grab the PDF but don't go past the line "Count the # of DIFFERENT wire COLORS..." on page 1 (unless, of course, you 'get it' and are having fun). 

--

OK, lest *I* overload you, I'll stop here.  Basically, yeah, you can easily check the battery yourself with a multimeter but once you have a multimeter you can just as easily do some more electrical checking on your own. GL and ask when you have questions. :)

[AngryInca]

Excellent, thanks :)

I have a new multimeter already from when I took A-level electronics 10 years ago.  I never used it as I changed courses!

I will try the battery tonight and see where I get up to.  Thanks.

[AngryInca]

I haven't been on my bike for 13 days as I have been on holiday, but tonight when I tried to start it it took quite a while to coax the B4 to start, the starter motor was turning the engine and it seemed to want to start but it was a good 3 or 4 minute of trying before it eventually sprung into life.  This isn't normal for my bike, it normally starts first time.

I left it running for a few minutes, turned the choke off... and it idled without stalling! It was a tiny bit lumpy, but it wasn't stalling at all! I don't know whats changed.

Anyway, the multimeter tests were:13.34 before I tried to start it, and 13.90 with the rev's at 3K RPM from having the choke on, so I don't think its the battery.

I think the next thing I should try is taking it out for a run and getting it hot to see if it stalls.

[PitterB4]

Where are your air/fuel screws set?  Did you sync the carbs after pulling them to clean?  Just a couple thoughts....