Running on

Engine Oily Bits, Ignition, Fuelling, Cooling, Exhaust, etc.
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torque2me
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Running on

#1 Post by torque2me » Thu Jan 02, 2020 7:18 am

Hi Groupies,

Just swapped another 2.5s engine into my 's' six months ago. Engine fine in the other vehicle but runs on in it's new home. Engine has a fast road cam - nearer a 150bhp profile than a 125 profile. Carbs swapped from my knackered engine to this unit. Refurbished about 20 years and 30,000 miles ago.

Any easy way to see which carb is leaking fuel into half the cylinders? Plugs are new and I think NG12 equivalent.

Kev

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Re: Running on

#2 Post by johnnydog » Thu Jan 02, 2020 8:49 pm

I thought the 'S' bhp was 106 not 125. 125 was the late PI.
Isn't running on caused by either a weak mixture, incorrect ignition timing, tick over too fast, or the engine temperature (coolant) too high.
If the air collector box is off, you may be able to see if a carb is flooding by looking through the aperature at the bridge (where the bottom of the piston sits above the jet) which would be wet, or you would smell the fuel.
Alternatively after it has been running, switch off, remove the top of the affected carb and piston, and if it is flooding, you may see excess fuel seeping out of the jet.
If it has a different cam than the original engine, I think you need different needles to suit the cam. I would either contact Burlen Fuels, or go on the Minty SU website to see which alternative needles would be suitable for it; alternatively it may be worth contacting CW to see what he recommends.
If you change the needles, check the jet isn't oval which is caused by the bias of the sprung needle. I'd replace the jets with new anyway if replacing the needles.
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Re: Running on

#3 Post by Carboy0 » Fri Jan 03, 2020 8:21 am

In common with many other engines from the same period, the mechanical fuel pump exacerbates running on, by continuing to pump as the engine turns over continuing to fill the float chambers and supply fuel to the dieseling engine.

I have found problems with engines needing a decoke where the carbon build up in the combustion chamber is glowing sufficiently to ignite the fuel/air mix being drawn in through the carbs.
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torque2me
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Re: Running on

#4 Post by torque2me » Wed Jan 15, 2020 10:44 am

johnnydog wrote:
Thu Jan 02, 2020 8:49 pm
I thought the 'S' bhp was 106 not 125. 125 was the late PI.
Aahhh, I was referring to the cam (my knackered engine had been fitted with a 125 pi cam) but the new donor engine is fitted with a non Stanpart cam.

Isn't running on caused by either a weak mixture, incorrect ignition timing, tick over too fast, or the engine temperature (coolant) too high.
Yup, Dale at Moordales has looked it over. Temp checked with a temp gun. Not sure if timing has been checked. Tickover about 700-800rpm. Fuel...Momentum 99 octane from Tesco. Not given me problems with my last engine, nor this one until the transplant. Fuel has been given additional additives from the Millers range plus RedX and this on occasions helps. Only other pointer is that on a short run (around 15 miles) run-on percentage reduces.
If the air collector box is off, you may be able to see if a carb is flooding by looking through the aperature at the bridge (where the bottom of the piston sits above the jet) which would be wet, or you would smell the fuel.
Alternatively after it has been running, switch off, remove the top of the affected carb and piston, and if it is flooding, you may see excess fuel seeping out of the jet.
If it has a different cam than the original engine, I think you need different needles to suit the cam. I would either contact Burlen Fuels, or go on the Minty SU website to see which alternative needles would be suitable for it; alternatively it may be worth contacting CW to see what he recommends.
If you change the needles, check the jet isn't oval which is caused by the bias of the sprung needle. I'd replace the jets with new anyway if replacing the needles.
Yeah, I will probably go back to the un-refurbished SU's that were affixed to the engine before the engine swap as they may have different needles to the re-furb'd carbs. The engine was perfectly useable in the other vehicle 3 months before the swap without this issue. The only visual difference is swapped engine has an electric fan with the crank driven fan removed.

Kev

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Re: Running on

#5 Post by torque2me » Wed Jan 15, 2020 10:57 am

Carboy0 wrote:
Fri Jan 03, 2020 8:21 am
In common with many other engines from the same period, the mechanical fuel pump exacerbates running on, by continuing to pump as the engine turns over continuing to fill the float chambers and supply fuel to the dieseling engine.

I have found problems with engines needing a decoke where the carbon build up in the combustion chamber is glowing sufficiently to ignite the fuel/air mix being drawn in through the carbs.
Certainly carbon build-up was the other main reason for an engine run-on. The glowing carbon residue would be enough to ignite any fuel residue. However, all explosions need fuel, oxygen
(or other such vapour) and an ignition source. Carbon residue would be the catalyst (ignition source) but it would still need additional fuel to move the engine over more than a couple of times. Also with the detergents they use in fuels to-day I have not found it in such evidence as forty years + ago.

I intend to swap the SU's for the set that was on the engine before the swap and this issue arising. Have to see what effect that has before investigating any further. However, will not be able to start on that until I've finished building the Ark and rounding up the animal kingdom for boarding (the band Wet, Wet, Wet) has nothing on this present weather.

Danke for reply,

Kev

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Alec
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Re: Running on

#6 Post by Alec » Wed Jan 15, 2020 9:50 pm

Hello Kev,

when the controlled ignition source is removed, if there is incandescent carbon then fuel will continue to be drawn into the engine as long as it is still turning over. Running on can continue for some time, in severe cases, unless the engine is deliberately stalled using the gearbox and clutch.

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Re: Running on

#7 Post by wild bill » Thu Jan 16, 2020 6:40 pm

Alec,I totally agree with you.This reminds me of when many, many years ago I banger raced.One car was a Series 4 Morris Oxford Estate,with the 1500 "B" series unit.Car was rotten as a peach,but a great engine.When it returned home for the last time for stripping before scrapping,I ran it, without radiator to see if it would seize(please forgive me!) This included holing the throttle wide open for a long time----no difference.So I switched off the ignition at high revs,and the car ran!I could let it tick over,open the thgrottle and it would gradually pick up the revs.I had never seen anything like it before. Unable to seize the unit,I disappointedly sent it to the scrap.One engine I think I should have kept......
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Rod 2500S
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Re: Running on

#8 Post by Rod 2500S » Fri Jan 24, 2020 7:43 am

gday all
later model S`s Like mine, have an anti-run on valve fitted which applies manifold vacuum to the top of the float chambers when the ignition is turned off.
This has the effect of immediately pulling the fuel back from the jets. Hey presto the motor stops.
Very effective. This is all fitted with the late model emissions controls, carbon canister and return line to the tank.
HTH
Rod

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Re: Running on

#9 Post by Rod 2500S » Fri Jan 24, 2020 7:43 am

gday all
later model S`s Like mine, have an anti-run on valve fitted which applies manifold vacuum to the top of the float chambers when the ignition is turned off.
This has the effect of immediately pulling the fuel back from the jets. Hey presto the motor stops.
Very effective. This is all fitted with the late model emissions controls, carbon canister and return line to the tank.
HTH
Rod

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Re: Running on

#10 Post by torque2me » Fri Jan 24, 2020 6:07 pm

Alec wrote:
Wed Jan 15, 2020 9:50 pm
Hello Kev,

when the controlled ignition source is removed, if there is incandescent carbon then fuel will continue to be drawn into the engine as long as it is still turning over. Running on can continue for some time, in severe cases, unless the engine is deliberately stalled using the gearbox and clutch.

Alec
Not a bad idea to apply handbrake, stick it in gear with clutch down, turn ignition off and if it runs-on release clutch!

Kev

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