Bandit 250 dies under load

[imdying]

A friend roped me into making a new throttle cable for a bandit 250 for a friend of his. No worries there, works good. So I went along with him for something to do, as he had to go visit this guy because the bandit still has some troubles. Big mistake... never show an interest

I get there and they're convinced the fuel system is dirty, so they take the tank off, empty the fuel out, and proceed to remove the ball bearings that are for some reason rattling around inside it.

Tank strainer looks fine, fuel filter has a small amount of little black gunk bits in it... looks like a fuel line breaking down to me. So I take a float bowl off, to see if any crap has made it further down the line. Doesn't appear so, but cleaned the bowls and checked the pilot and main jets for cleanliness... all good so far.

So finally they get it back together, and I get to hear it run, which is good cause by this stage I've yet to be able to get a straight answer as to why it had to be taken to bits in the first place (I'm lazy, would rather leave things be if I can avoid it).

Won't start on the starter, battery is healthy enough at 13.1v and winds over good, but doesn't make an effort... so they push start it. That doesn't help. Eventually gets back in the garage, I give it full choke, thumb the starter for a little, and eventually it chugs into life.

I get the distinct feeling that it's running on three.

Any touch on the throttle makes it stall, so I let it warm up.

Eventually I figure out I can get the revs up if I open the throttle incredibly slowly, still doesn't rev above 8000 though, definitely sounding on three.

Now that it has warmed up a little, it lets me use a little throttle, and I can get it to idle (a little roughly) without the choke.

So I start giving it some grief, and it starts to rev albeit slowly. A few backfires and a pretty flame out the exhaust and it appears to clear whatever cylinder is giving it grief, and it starts to respond well, reving cleanly and quickly. But pretty much straight away it starts to bog down (presumably a cylinder is dropping off) and becoming hard to rev again. Continued abuse on the throttle sees it repeat that cycle, cleans out, runs on four, then drops back to three.

I haven't had the plugs out, it was late and I wanted to go to bed and also have an opportunity to consult other KBers. I'm thinking that they're probably as neglected as the rest of the bike, and worth a look. I think pointing a infrared heat reading gun at the headers might help figure out which is the crook one.

Normally I'm a grumpy shite and whilst generally happy to help with the things I specialise in (brakes, cables, drinking), I've only got so much time to give away. However, this fella is young (I'd pick about 17), at Polytech, so therefore not really flush enough to take it to a professional.

So I'd like to have another crack at this bike... can't be much wrong, has spark, fuel and presumably compression. What should I check next? Cleanliness of the plugs? I've not got a compression tester, but it seems to healthy to be that... although such a tiny wee 16v motor at such high revs, perhaps it has bashed an inlet valve?

Or is their an obvious solution that someone experienced can point out?

[skelstar]

I'm no mechanic but you could pull sparky leads out until it makes no difference to the idle? Time consuming though.

Any probs I have with vehicles always seems to come down to electrical for some reason.

On ya for helping him out though.

[marioc]

check plugs for sure,similar problem for me,whipped out plugs and gas torched them[filthy as fucxk] been mint ever since.

[Katman]

When you first start the bike up, lightly touch each header pipe. The one that doesn't burn your fingers is the crook one.

[Paul in NZ]

By all means change the plugs but before you get sucked into it too deep - get a leakdown test done.

I'll bet a sack full of farty weasel poop that the rings are half shot and the valves are not sealing well or have not had a clearance check for a decade or so. The 250 and 400 4s seem very sensitive to a little loss of compression that you would never notice on a big twin.

Cheers

[White trash]

Sounds like low compression to my untrained ear. Also could be a really weak spark. Suzuki coils are fairly shit on those imports.

[imdying]

So I blew of TCWNR to go have another look... I get there, and they've got those damn carbs off again (well, nearly back on), which they recleaned and fitted a nice big filter. Fair enough, whatever. The owner and Andy went inside for pizza, so whilst they're doing that I'm sitting in the shade, baking cause I'm in leathers. Bored of that, so took the plugs out. They all look sweet, so I evened up the gap. They come back, bike starts, runs on two. Find a plug not firing. Hmmmm. Had a jiggle on the low tension wires on that coil, one breaks off the spade lug. Excellent. Fix that, starts and runs on four sweet as. Eureka I'm thinking!

Owner goes for a ride, comes back running on less than four. Says that he got about the same distance as he did earlier in the day when they got it running sweet.

So I don't think there's actually anything wrong with either the fuel or the spark, it simply runs too well when it's going fine.

My theory: I suspect that 16 tiny little valves have receded over the years, and now the valve clearance has closed up beyond the spec. When it gets enough heat into it (<2km of riding), everything naturally expands, valves get held open every so slightly on the suspect cylinder(s), and that's your lot. Andy will give it another go tomorrow... if it runs fine, then after a short distance does the same thing, it might be the right track.

Of course, there are plenty of other things that can break down due to heat. I do not have the time nor patience to sit in someone elses garage checking valve clearances on such a tiny motor, I think Andy will take it home and do it there. Good on him, I hope he solves it, tag, I'm out.

[imdying]

When you first start the bike up, lightly touch each header pipe. The one that doesn't burn your fingers is the crook one.

Yep, Andy was doing that, seemed to work out ok for him

I'll bet a sack full of farty weasel poop that the rings are half shot and the valves are not sealing well or have not had a clearance check for a decade or so. The 250 and 400 4s seem very sensitive to a little loss of compression that you would never notice on a big twin.

I agree

Sounds like low compression to my untrained ear. Also could be a really weak spark. Suzuki coils are fairly shit on those imports.

Yep, ran perfectly till it got warm, then I'm guessing valve open, thus no compression, runs like shit...

I simply haven't got the time to devote to looking after it though, I was doing pretty well to invest to nights thus far

[Pussy]

We had to replace a faulty coil on Gassit Girl's GSF250VXV when it was only 5 months old. Could be a coil.....

[imdying]

Sure could be... I wonder if Andy would let us steal the coils from his ZXR750 to test with?

[VF AAR]

Won't start on the starter, battery is healthy enough at 13.1v and winds over good, but doesn't make an effort... so they push start it. That doesn't help. Eventually gets back in the garage, I give it full choke, thumb the starter for a little, and eventually it chugs into life.

Hey mate, I know exactly what you mean, on my cbr600 it had a 2nd hand battery in it when i got it,
it wouldnt start on starter
but roll starting it would get it going
then after awhile the battery got less and less powerfull

to a point where when i would roll start, it would only have enough power in it to make enough spark to idle, and push itself along a wee bit on choke.

I could help but wonder why my bike would idle but under throttle it would die,
and when i let it run on idle then turn the lights on it would die.
i.e; battery doesnt have enough power to run bike and lights.

This made me think that the battery had done its time and that it wasn't outputing enough to create a good spark.

Replaced the battery, everything went back to normal.

Also just replaced the battery in my vfr as its up for sale now and is running mint.
was $70 at red baron

Hope this helped cheers

[imdying]

I admit that although I checked the voltage at rest, I did not check it at idle. It's definitely worth the 30 seconds to check though

I guess with between that and swapping in some known good coils, we aren't done for yet

[jrandom]

Normally I'm a grumpy shite...

You like to pretend, but we all know that deep down on the inside, you're just a big softy.



Do the gentlemen working on the bike have a set of feeler gauges handy for the next obvious diagnostic step, or have they moved on to sacrificing chickens under the full moon?

[paturoa]

Also ask them if they have been playing with the air screws or pilot jets / pilot needles (assuming slide carb). The bit about choke to get it started in the first post, and opening throttle at idle causes it to stall.

And have the float levels been checked?

[imdying]

Do the gentlemen working on the bike have a set of feeler gauges handy for the next obvious diagnostic step,

Yes, I have all the tools, just insufficient spare time.

And have the float levels been checked?

I would dearly love to know the spec, a workshop manual would be great.