Ran out of petrol..At speed.

[Radlan2]

I have been getting 4 bikes ready for 31st Beezumph 24/25 July at Cadwell Park. My A10 has a short rod conversion, 357 cam 7:5 to 1 Early road rocket head with twin carbs. I was doing maybe 80, gathering speed and going very well when the motor cut. I did not think petrol but opened the left hand tap and the motor soon picked up again.
         However the bike does not quite run the same, hard to start and generally a bit flat. Yes first thought is contamination from the bottom of the tank in the carbs and I have had them apart 3 times, funny thing is it seems to be running more rich with sooty plugs so i have lowered the needle a notch. I have checked the mag points and the gap had closed slightly, now back to 0.012". I have new Brisk plugs on order. Anyone got any other thoughts about what could have changed?
       Also I will mention Beezumph again, I have been to nearly all of them. It is on a Thursday and Friday this year and daytime admission is free so if you fancy a great Classic event checkout the website, track time is on the Friday.

[chaterlea25]

Hi Radlan,
I would check the valve clearances and also do a compression test.
The engine must have ran lean as it was running out of fuel, this happening at high rpm runs the risk of burning a valve or piston crown

John

[Triton Thrasher]

Like Radlan say, compression test might tell you something.

There’s a risk of partial or near-seizure having damaged the bore and stuck the rings.  As well as the hazards already mentioned. 

[Radlan2]

Thanks for the input Guys.
     I have never done a compression check before but my best mate has recently got hold of one. Even with one cylinder plug out and the gauge screwed into the other it was quite a job to kick. No electric start so we bumped it down a slope, in 3rd gear, with WOT, we are both getting a bit old for this lark.
      Anyway the gauge registered a similar reading both sides of 9BAR+ which is just out of the red according to the Gunson tester, of course I don't know what it was before but I am calling it ok.
         Cheers
                Chris



         

[BagONails]

Sorry to hear of your woes Mr R.  The compression test has told you both cylinders are similarly affected in terms of the pressure they can build up being on the low side although I don't know what the limits are.

If you can also do or get done a compression leak down test this will generally give you a better idea of where the compression is being lost and how quickly, if in fact it is being lost...

You can often hear the air escaping into an exhaust or inlet in the case of a bad seat or burned valve or from a head gasket joint or from rings etc.  In your case it may be accelerated wear or scoring in the bores/ damaged rings and it may only be slight due to running weak and overheating temporarily. Thing is it won't get any better by continuing to run the engine.

On the other hand these engines are so simple that it might be less bother just to take the head off and have a good look!
 

[Worty]

Sort of hard to believe that running out of petrol can bugga yer motor.   I tend to ride UNTIL I need to switch to reserve, i.e., run out of petrol, and the bike still runs the same.

Incidentally, and unrelated to the above issue, my GF has always huffed, puffed and run a bit rich - still makes no difference to anything - still keeps going the same as always with good compression.

However, this sounds like a motor with a few tweaks - perhaps a bit more highly strung than my old chuffer.

[BSA500]

a leakdown tester is very useful, mine detected leaky valves and a leak between the barrel head gasket.

[Radlan2]

Hi Guys
      Following your suggestions and trying to get to the bottom of the problem a breakthrough came when clean new Brisk plugs highlighted timing side running rich and drive side weak. I must have done 20 plug chops, one of the benefits of twin carbs is that I have been able to raise the drive side and lower the timing side needle independently. At the moment the bike is a 2 or 3 kick starter and feels good.
      A last call for Beezumph 31 at Cadwell Park which is less than a week away, The NMM is taking Slippery Sam, Works North T150, Works Norton Rotary, Thruxton 500 winning Commando and more. Daytime entry is free come and say hello.
         Best Regs
              Chris

[berger]

you going worty ? i might be able to make it on betsy2 with my mate , i will see.

[Worty]

you going worty ? i might be able to make it on betsy2 with my mate , i will see.

I doubt it mate, jobs stacking up at home (and the missus is about)

[Radlan2]

To bring this up again I now have the reason behind this one, the running out of fuel was perhaps a red herring. As mentioned I took it to Beezumph and the bike become increasingly hard to start to the point where it would not. My other BSA went pop on the track with an ign prob as yet unresolved so the rest of the days fun was on the Trident. When I got around to looking at the short rod A10 there was now no spark and I soon found that the points unit had come loose, cleaned it up and all seems good again. I will report back on the other one, which I had been holding full chat in third when it stopped with a few pops and bangs, once I find out what's happened there.
        Chris

[Triton Thrasher]

A 1950s mechanic would tell you.

Plugs, then points.

[Radlan2]

FFFFact is I had checked and made a small adjustment to the points when the problem first arose but of course the cam is loaded at that point and the central bolt though loosened was not rattling. Hindsight is a wonderful thing.

[Lindsay S]

I had the self same thing happen on my GF. Occasionally mis-firing and holding back. Difficulty in starting…until it didn’t. Only then did I find the central nut on the mag loose and the points flopping about. You do have to keep an eye on that thing but I don’t like to over tighten it!