Oil and Petrol!

[Duccout]

I went out for a long run on the 250 this morning and the engine seemed to be more rattly than normal, even for this engine! Came home, and this afternoon went out to the garage to lock up, and while there did a couple of small jobs including draining the carb float bowl. After that I thought that I would check the engine oil level as I had not looked at it for a while...... Undid the filler dipstick and oil flooded out!

After grabbing a drip tray and putting it under the sump, I let the oil flow and it was obvious that it had turned to SAE 5! Drained the sump and I reckon that about 4L of very thin oil came out, stinking of petrol, no wonder the engine was noisy.

Now, how has this happened? I do not leave the fuel taps on and they do not leak, and there is no sign of the carb flooding and the spark plug is not sooty to indicate flooding, so how has the fuel got into the sump? God knows what damage this has done to the engine; I thought it odd this morning when the clutch would not free off on the kick start. I am puzzled why no oil was blown out of the breather with the level so high? I am letting the sump drain, but how do I prevent it happening again?


Cheers,


Colin

[blethermaskite]

Colin, i had exactly the same thig happen to my 250 desmo......but I didn't start it, I went into the workshop and it was stinking of petrol, there was a large puddle under the baby desmo both petrol taps were off! I took out the spark plug and turned the engine over by hand my reward was a face full of petrol. Oil level in the sump was up 1/2" on the dip stick. So the inlet valve had been open the carb had flooded and petrol had filled the cylinder and leaked down into the sump.
This had all happened while I had been away from home for 2 weeks........why did this happen? I can only assume a bit of grit or something got stuck in a petrol tap making it leak? when I investigated the taps there were no leaks Thankfully I didn't start it
Cheers,
George

[George]

Sorry to hear your troubles Colin. I had the same on my Elite. Tap was new and not leaking! I cleaned the carb replaced and the problem stopped. No real answer why this happened, was float letting by slightly? did petrol in pipe drain into engine when parked? did I leave tap on at sometime?

I remember that you had trouble with rust in tank and it does not take much to hold float open just enough to keep engine running but slightly overflowing and this is the only thing I could think of in my case.
Unfortunately I was using the bike for some time before I realised and I believe this was the beginning of the end of my big-end. hopefully you have caught yours in time.

[Duccout]

Hi George(s)

I reckon that rust particles are the culprit, as there is always a red residue in the float bowl and the in-line filters, but surely it could have only happened if I left the petrol tap on? Maybe I did forget to turn it off sometime.......I just hope that my engine has not suffered.

George (Essex) how did you find out that your big-end had gone? Was it a knocking noise that couldn't be ignored? Any news on the repair?



Cheers,


Colin

[George]

Hi George(s)


George (Essex) how did you find out that your big-end had gone? Was it a knocking noise that couldn't be ignored? Any news on the repair?



Cheers,


Colin

After I found petrol in oil, cleaned carb ( some fine rust in bowl) and changed oil, engine a little loud and got progressively worse, could not be ignored.
Crankshaft with Gard Engineering waiting for Conrod to be fitted. Have spent some time making sure every thing is clean. Changed crankshaft bearings, although they felt OK for what they cost worth changing.
My guess was that a fine particle of rust was embedded in float needle rubber allowing a very slight leak. Only a theory, one of life's mysteries

[themoudie]

Aye Colin,

Whilst they might not stop your taps leaking, or something holding your float needle off its seat, I fit very non-standard paper fuel filters to both of the fuel feeds after the tank taps, so as to prevent any crap getting near the carb on all our machines.

Having sat astride an SRX600, at temporary traffic lights on the A9, slowing from 60-65mph to 0mph, a cloud of white petrol vapour enveloped me and the bike! Fuel was flooding from the carburettor onto a hot running engine and the underslung exhaust. Needless to say a quick dismount and turning the ignition 'OFF' killed the engine and because the SRX has a vacuum petrol tap, stopped the flow of fuel. Luckily, there were no stray sparks and once the vapours had dispersed, I was able to move the machine onto the verge.

Stripping an SRX Mikuni slide/CV carb is not a roadside job. So once recovered home and stripped, a small piece of rust flake was found embedded in the float needle 'Viton' point. Ever since the A9 incident, I have used quality filters between the tank taps and the carburettor float bowl feed. Toasted nuts, or SAE5 oil/fuel, with E10 are not good for your or your engine.

Hope that you get it sorted and that you have minimal or nil mechanical mayhem to deal with.

Good health, Bill

[Duccout]

Hi Bill,

Thanks. I do recall smelling petrol when I went into the garage a couple of weeks ago, so that must have been it. It is annoying as this coincided with me gradually trusting the 250 more, and venturing further afield and thrashing it more, which is not compatible with petrol as a lubricant. It is not just the big-end, but I wonder what effect the petrol has had on cam and rocker faces and oil seals?

I would think that this problem is exacerbated by using Amal carbs which are bolted on at the downdraught angle, unlike the original Dell'Ortos on Italian bikes that are vertical and therefore the fuel may not run down into the cylinder.


Cheers,

Colin

[blethermaskite]

I know its a bit after the event now.....but to insure it can't happen again always turn the engine over on the kickstart until its up against compression that way the inlet valve is closed and petrol can't get into the cylinder.....if you are lucky you might get away with the petrol oil mix, don't forget this is what 2 strokes run on with no ill effects.
Cheers,
George

[Duccout]

Having left the engine to drain overnight, I have refilled with fresh oil and given the engine a good spin via the back wheel while in top gear; it is down to luck now.

I have also just ordered a new 27mm Amal from Burlen! I had been running on the original Amal, but it gives a jerk when opening the throttle and the tick-over races all the time, which must be due to wear in the slide letting air through past the body, so....... This is the second new carb that I have bought for it - I foolishly thought that when buying a Mikuni it would be a straight bolt-on, but that is not the case, they need R&D, and in the end I got fed-up with trying to sort it out. My guess is that Mikunis will not run at a down-draught, they need a curved manifold to work properly, and mine exhibited weakness and richness. The good thing about Amals is that although crude and poorly made compared to the beautiful Mikuni, we have proper settings available from the Mototrans bikes, on which they were standard fittings.

Cheers,

Colin

[Duccout]

Got to find a way of getting rid of the rust from inside of the tank! I have tried everything, including electroysis, but fine rust powder remains, fine enough to pass through the fuel line filters.

One idea that I have definitely works, and that is to capture the rust with a magnet. If I drag my magnet wand along the bottom of the tank, it collects a load of rust on the head, so if I could find a way of sticking a magnet onto the bottom of the inside it would collect the rust and then I could periodically clean it off. The problem is - how to get the magnet out again? Any ideas? I thought about twisting a look of wire around a horseshoe type magnet and then using it to hook it out, but if it does not work then the magnet is stuck in there!


Cheers,

Colin