sluggish starting after 2 weeks

Discussion in 'Mech Tech' started by Youngdub, Nov 3, 2019.

  1. Okay, my 1641 TP (1971/2) is not a daily driver, so I only run it every 2-3 weeks...

    After this time period between use, when starting I find it takes a good 10 secs of the engine turning over (turns over well as starter and battery good) before it fires. Sometimes it fires after this time and then dies a second or two later. Next turn over it starts and runs perfectly. Left even a few days it starts on the button...If engine is restarted (say any time in next few days) it starts straight away no problem.

    The carb settings and timing are set correctly.

    My hypothesis is a fuel supply lag / carb emptying after being sat without starting - is this usual after a couple of weeks??

    Advice gratefully received :)
  2. My guess would be stale fuel, modern fuel when exposed to air goes off very quickly. The stuff in your carb's float bowls is going off, cranking the engine is using up the stale fuel until relatively fresh stuff is getting pumped thru'.
    JT1, mgbman and Youngdub like this.
  3. ^^^ This, mine is the same if left for a few weeks between starts. The fuel evaporates from the float bowl. I can hear the electric pump running for a while refilling the carbs after it’s been stood for some time.
    If you’re running a mechanical pump your going to have to churn the engine over for a while to refill the carb.
    Let it spin over for a bit then give the pedal 2-3 pumps to let the accelerator jet squirt some fuel in.
    Bhubesi, Youngdub, Day and 1 other person like this.
  4. As the others have said, sounds like a combination of evaporation and the fuel system draining down. The stock mechanical pump doesn’t shift much fuel - it doesn’t need to - so may take a bit of a churn to fill the system up. Normal stuff.

    My twin carb setup has lengthy pipework, and if I leave it for a couple of weeks, it needs lengthy churning on the starter before it fills up. Once there’s fuel in the system, it fires straight up.
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  5. I have a mechanical fuel pump so of course needs the engine turning to do anything.
    Thanks all - mind at peace now!
  6. I have the same on my MG with twin SUs, it helps if I squirt some 'easy start' in the air filters, then it fires straight away. In my case I think its fuel flowing back into tank so I am going to fit a one way valve before the pump. On my bus its fuel injection (electric pump) and starts after a few turns. NB Didn't start the MG last year for 3 months and would just not fire after many turns, so drained the old petrol out of the carbs, replaced with fresh and he presto started instantly! Assume the petrol had gone off. I now start them both cars every month and keep putting a little amount of fresh petrol in the tanks every two months over winter.
    JT1 likes this.
  7. On your MG, the fuel from the tank gravity feeds down to the SU electromechanical pump, which then pumps fuel uphill to the SU carb float bowls. I wouldn't fit a one way valve. My MGB has the same issues due to evaporation of fuel from the float bowls. Long non start standing is not good and I run mine up at least once a week and charge the 12v battery to maximum afterwards. I top up with fresh fuel often and now no issues at all.

    If your MG has the old twin 6v batteries, I would replace them with a single 12v which gives much more punch for starting.
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  8. Its interesting. Mine did exactly what you describe, but even after leaving overnight. It would often fire immediately, die then take 10 seconds of cranking to start.

    Eventually, separately, the electronic ignition module started to play up with really chaotic misfiring, the dwell angle was basically all over the place causing rough idle and loss of top end power. Ok cruising at 50, but sometimes flooring it , it would backfire, stumble then pick up like nothing was wrong.

    I put an osciloscope on the coil and saw the timing mess.

    So I changed the electronic ignition module and now it runs OK as soon as it starts.

    I will be getting a 'high output" coil as I persuaded myself in a conversation with un ancien TLber that this would reduce voltage stress on the ignition module.

    Last edited: Nov 4, 2019
    Youngdub likes this.
  9. Mines the same. If I’m on holiday and using it everyday it starts at the touch of a button. Parked in the garage for a couple of weeks and it cranks over a gd few seconds before it catches.
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  10. JT1


    As above except I use only Esso Super Unleaded Supreme Plus as it is the only petrol which doesn't contain ethanol. As MGBman has said starting it regularly and running up to temperature is a good idea or even better using it.
    IZZYBAY and mgbman like this.
  11. Except if you buy it in Devon, Cornwall, the Teesside area or Scotland.
    JT1 and F_Pantos like this.
  12. Yep, all fuel from Grangemouth has Ethanol in it :(
    77 Westy likes this.
  13. Correct. :) Do you work there?
  14. JT1


    That's right - reply from Esso 5th August 2019

    Dear Sir,

    Thank you for your question.

    As it was stated in our first reply in 2016, Esso super unleaded petrol (Synergy Supreme+ Unleaded 97) is ethanol free (except in Devon, Cornwall, the Teesside area and Scotland).

    The situation since then is unchanged. In other areas of the UK, we do not currently have any plans to introduce ethanol into the Supreme+ fuel brand.

    Kind regards,

    Ms Reka Toro

    End Consumer and Customer Care Specialist

    Customer Service, Fuels & Lubricants, EAME Budapest BSC
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  15. Nope, don't live too far away, it seems quite a well known fact among the locals, well, leastwise among the ones that care.
    77 Westy likes this.
  16. The rate I get through E5 petrol om my bus it does not stay in the tank for more than a few weeks. Plus I use nitrile fuel lines which can cope with pure ethanol or even methanol..

    For my little outboard motor, I keep E5 for months in a sealed tank and it still works.

    Even tried E10 as it was cheaper in France, no real difference.

    I think a lot of the horror stories about ethanol come from the states.. where the biomass used is more likely to be corn, strange that USA petrol/ethanol issues you see on YouTube always seem to feature yellow sticky goop...
    matty likes this.
  17. I have the 1500 engine (spitfire) with a mechanical fuel pump which is higher then the fuel tank which makes me assume if the tank is low the petrol just flows back into tank making a long turn over to restart after a week plus of not running! Hence the thinking of fitting a one way valve before the pump. NB has a single 12v battery in the engine bay.
  18. All carburettors have a float chamber where petrol runs down from a metering valve across an air gap into a small reservoir. This is usually big enough for the engine to start and the fuel pump to catch up refilling it before it runs out.

    If there is no petrol in the float chamber , either it dripped or evaporated away...

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