Mikuni missfire - white deposits

[leaky]

Anyone seen this before please  ?

History - As a general refurb following starter clutch replacement and long lay up, carbs were cleaned (new needles/jets and o-rings, float heights checked etc) and valve clearances done (increased) about 7K miles (~2 years) ago.  Also replaced ignition pickup and HT leads for good measure. Intake rubbers and air filter also replaced. Filters in tank and carb inlets replaced by inline filter. Bike runs fine follwoing inital problems (misfire - sometimes from cold, nearly always hot - at ~2K revs tracked to blocked pilot circuits). All jets factory size - pilot screws 2 turns out.

After 7K miles, similar misfire back again plus now reluctant starting from cold (seems to flood with normal full choke but will start with small choke or when hot).  Misfire kicks in either straight from cold or after a couple of minutes wamr up. Pops from RH exhaust. Fuel flows freely on run or reserve. Tank cap is clear. Pilot screws Drained off fuel looks clear of water and crud.  No change with replacement coils. (Ignitor box is only ignition bit not replaced !).  Choke plungers closing OK however petrol smell possibly more than usual ? makes me suspect float needles /seat (not previously replaced).

Finally got round to taking off carbs today suspecting possible blocked pilots as symptoms similar to before ( bike seems ro run rich when running 'normally' - slightly sooty echaust). Found some crud in float bowls and unexpectedy fuelly (?) streaks running from throats back towards airbox.  Airbox drain dry. Odd.

HOWEVER really novel bit (from my experience) was build up of white deposit around all 3 needles (estimate 0.5mm thick and ~2mm tall). slight variation between needles but not much.  Never seen this on carbs before..... Combustion products due to loss of intake valve clearance ? why just round the needles ? No obvious sign of discolouration/melting anywhere -  plastic slides, intake rubber stubs, no deposits on inlet tracts in head and valve uppers but I'm not sure I've evr seen what happens when the inlet valve clearance goes....possibly very slight trace of white deposit on head side of butterfly ?  

One other thing that may be relavant (!!?) - I'd put in pilot screws washer, spring, o-ring last - should be oring, washer, spring last - I was sure I'd put them in right...........
 
I'm assuming that deposit actually is blowpast due to the inlet valve clearance disappearing and this also explains poor starting........although it seems unlikely that clearances in all 3 cylinders have closed ?

Any other thoughts much appreciated please before I attack the rocker cover and check the clearances (especially those which mean I don't have to struggle with rocker cover seal or pay for any more shims !)

thanks

[rybes]

cant see nuffin in pic 1 pic 2 is normal so nuffin wrong there. pic 3 however.....my guess would be water in the fuel some where ?

[leaky]

1st and 2nd pics were intended to show rest of carb was pretty well clean

Ever seen carbs where water's gone through ? Deposits dislodged easily and crush up to 'nothing' between fingers . From appearance was expecting to find gritty/persistent like combustion on plugs. No deposits like this around pilot jet discharge holes but haven't looked at state of emulsion tubes yet....

Think it's worth cleaning and reassembling carbs, flushing out tank and retry before chekcking valves ? (BTW previosuly checked tank cap drain line was clear - no sign of water).

If this is water 'damage' ..... petrol's expensive enough without getting it watered down...

[Mustang]

if your valves are not at zero clearance you will have no problems that will cause anything in the carbs .


If your valves are at zero clearance on some intakes it will be damn near impossible to start when cold . it will also pop back thru the airbox hard enough that you can almost feel the side covers move  :shock:

After 7K miles, similar misfire back again plus now reluctant starting from cold (seems to flood with normal full choke but will start with small choke or when hot).  Misfire kicks in either straight from cold or after a couple of minutes wamr up. Pops from RH exhaust. Fuel flows freely on run or reserve. Tank cap is clear. Pilot screws Drained off fuel looks clear of water and crud.  No change with replacement coils. (Ignitor box is only ignition bit not replaced !).  Choke plungers closing OK however petrol smell possibly more than usual ? makes me suspect float needles /seat (not previously replaced).

this would make me look hard at valve clearances , intakes especially

could you make your pics any bigger    {sarcasm}

[leaky]

Apologies for the pictures !! Next time  I'll preview first !!

Starting problems have not been accompanied by any pops and/or bangs - let alone apolcalyptic ones - so perhaps not clearances ? I wouldn't expect things to close completely with 7K miles - I always aim for the wide end.

Starting - recently motor just spins over without much in way of firing going on till eventually catches.  Battery is quite new so turns over at fair rate. Once started it'll either be OK, a bit suspect or, recenlty, not OK - to the extent that you can't pull off to even give a good thrashing to see if it clears out.

Deposits look like they've bulit up over more than just the last run perhaps -  may correspond to starting getting worse ? Unfortunatley can't really rememeber exactly when less than perfect starting began - but not many runs ago.

Similarly can't remember where/when I last filled up (wicked combination of age and stupidity and dealing with offspring)  but I run either this or another bike to work everyday and don't use the same stations all the time - no problems with other one at all but I guess it just takes one bad fill ?.....

If water I'd expect burning problems but not blocking ?

Perhaps this is what dehydrated water looks like ? :lol:

[BruKen]

That white stuff is either Magnesium sulfate or Aluminium oxide. Both indicate that there is water in the fuel causing oxidation of the carb body metal alloys and almost certainly your jets etc will be blocked now. You can try cleaning up with a soak in white vinegar (especially if the port have become blocked) but most likely it will need a ultrasonic bath if the problem has become severe.

[Bixxer Bob]

:shock: Jezus, what did you take those pics with?  The Hubble??

[leaky]

Cheapo 8Mp camera !! - aren't macro settings brilliant....if you look hard you can see the individual atoms and a couple of higgs bosons.

Thanks for the previous suggestion of corrosion but I'm reasonably sure it isn't since mainly a) the rest of the carb is dead clean - this deposit appears to has been left as fuel evapourated in the airflow. b) it's got no real strength and is not bonded to surface, surface is unmarked underneath c) it covers the needles, brass jets and even some of the surrounding plastic

Luckily I've managed to pick the brains of some fuel men through a work contact.  The most plausible explanation seems to be that 'something' has been dissolved into the ethanol in the fuel and then deposited out as the fuel vapourises.  

Triumph claim the fuel system is ethanol proof so none of the 'normal' components should dissolve. The only non-standard bits in mine are the in-line fuel filter I've fitted (unbranded from local garage) plus the replacement fuel tubing.  So, since I'd cleaned all the lacquer etc off the carbs before this happened, it looks like either the filter or tubing is the source.  (I had also flushed the tank out several times before). This might fit with why perhaps no one else seems to have seen this.

I sawed up the filter tonight just in case there was any obvious damage - nothing stuck out apart from that the glue around the paper element perhaps didn't look too good - what do you expect for £1 each I guess ?

I don't think there's an easy way to prove this story for sure from exam of the deposits (if there's any analytical chemists out there, I can send a sample......) but it seems perfectly plausible to me.

I'm going to clean everything up and replace the Triumph carb inlet gauze and see what happens.

If anything interesting comes up, I'll post it.

thanks again for the suggestions - any further thoughts much appreciated