'97 M900 dirt in carbs..?

Hi,
All my own fault, I suspect.
By accident, I had to run my M900 down to the dregs in the bottom of the tank. The engine was misfiring as I pulled into the filling station, and I hoped that it was merely fuel starvation. Having refilled the tank, the bike fired up ok, but the tickover was uneven. Having taken the bike out a few times now, starting is fine, but pulling away is hesitant and one cylinder is clearly misfiring. Beyond about 1/3 throttle the bike is fine; but slow running around town or (worse) around a roundabout is a bad experience.

I haven't done anything in the way of investigation or diagnostics yet, beyond browsing the relevant chapter in my Haynes manual. I suspect that some muck has been ingested into at least one of the carbs and is blocking the jets of (possibly) one of the carbs.

Before I invest in carb service kits and the like, does anyone have any words of wisdom?
Can I remove the carb jets for cleaning without having to re-balance the carbs after the event; or will rebalancing be a necessity? I accept that a rebalance may be beneficial anyway, but that is the one bit of kit that I lack.

Thoughts? Anything beyond "how dumb to run the fuel so low" would be appreciated.

Graham

[Darren69]

My guess is that water from the bottom of the tank is getting through. I'd drop the float bowls and empty them and drain the tank. If you drain the tank into something clear and allow it to settle for an hour or 2 you might see if there is water and where it is. Quite a few having similar problems it seems and I'm guessing it's through the bike standing for long periods that water in the fuel is separating out. Any ethanol in the fuel will naturally attract any moisture in the air as well which will only add to the problem.

Hi Darren,
thanks for the input. Wouldn't water in the fuel/float chamber impact the bike across the rev range?
Anyhow, your suggestion sounds a lot less major than the work I had anticipated, so I will try that first and report back in the fullness of time.

Graham

[Mr Gazza]

Draining the float bowls via the drain bungs is way the easiest thing to do first.
As Darren suggests, try to catch the contents in a clean container to check for detritus.

Water in the carb would more likely be sucked onto the main jet when it was pulling harder and drop away when the suction dropped.. ie when it was revving lower.
So you would get normal tickover and slow running but misfire and hesitation at higher revs

As your symptoms are opposite, it suggests a blocked pilot jet, which will cause poor idle and slow running but if the main jet is clear it will run fine with the throttle open.

If draining down the bowls doesn't cure it then the carbs will have to come off for a clean.

[Darren69]

It probably is a blocked jet but before you take the carbs off, its a complete pita to do. You could try spraying carb cleaner in the airways but also some Redex in the fuel and run a tankful of that mix through.

Modern fuel doesn't keep well and leaves varnish if the bikes stood, Redex might clear it, i use their Inj cleaner in mine. I still think its worth draining the old fuel from the carbs and tank as it can go off quickly

[Dukedesmo]

Originally Posted by Darren69

I still think its worth draining the old fuel from the carbs and tank as it can go off quickly

My Monster has an electric fuel shut-off valve, if I'm putting it away for a long time (over winter) I'll switch the valve off and run the carbs dry in the hope that no fuel sitting in the carbs means no crap developing.

[Darren69]

That's probably a good idea for the carb bikes, my thinking is that for the inj bikes it's best to keep them wet (pump, fuel rail, injectors etc) and prime them, bung in some inj. cleaner and start up every so often, get them fully warmed up. I've never bothered draining the tanks on mine completely during winter lay ups but try to keep the amount of fuel low. That may not help the water absorption issue as there are some theories that a full tank is better. Still it works for me, but I may pull the tank and drain it sometime, just to see if there is some water.

I did have a some cause for concern a few years back when a colleague of mine had the tank on his '01 748 which had been stood some time, start pissing fuel everywhere. When we looked it was only the paint keeping the fuel in, some places had rusted right through. At that point I panicked and pulled my 748 tank and drained it out but it was clean inside and no rust whatsoever but there was a bit of water but no damage. I've seen an S4 tank completely rusted too to the point that it was unusable, but last time I looked mine was fine. I think the protective treatment they put in some tanks is hit and miss or maybe none at all in some cases. Some have problems, most others don't.

I think it's standing that's the main problem when the water separates out and settles at the bottom of the tank or float bowls.

[Dirty]

Originally Posted by Darren69

That's probably a good idea for the carb bikes, my thinking is that for the inj bikes it's best to keep them wet (pump, fuel rail, injectors etc) and prime them, bung in some inj. cleaner and start up every so often, get them fully warmed up.

I'll add that to my 'reasons I prefer carbs' list