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Engine overrun
- Thread starter Mikestr4
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Timing advanced a bit, carb throttle plates (butterflies) not closing completely on shutdown are a couple possibilities.
Hi Mikestr4
What year and model? Later TR6's had anti-run on valves that helped correct dieseling. The wiki has a set of articles under Triumph/Buckeye Triumph Org. that has a technical article on rebuilding carbs that also has theory.
here is an extract:
The last part of the breathing apparatus is the electrically operated anti run-on valve introduced on the
’73 TR6. Power from the ignition switch in the OFF position is feed through the ON position of the oil
pressure switch to the valve, #6 in the sketch; the valve operates when the ignition is turned off and
there is still oil pressure. The operated valve closes the external air input to the bottom of the canister via
tube #6 and instead connects tube #6 to the intake manifold via tube #7. The depression in the intake
manifold sucks air out of the canister and via tube #2 to the float chamber creating a depression in the
float chamber. This depression in the float chamber prevents fuel entering the carb via the jet thus
preventing run-on or dieseling. The valve releases a few second after the ignition is turned off when the
oil pressure drops.
FWIW
What year and model? Later TR6's had anti-run on valves that helped correct dieseling. The wiki has a set of articles under Triumph/Buckeye Triumph Org. that has a technical article on rebuilding carbs that also has theory.
here is an extract:
The last part of the breathing apparatus is the electrically operated anti run-on valve introduced on the
’73 TR6. Power from the ignition switch in the OFF position is feed through the ON position of the oil
pressure switch to the valve, #6 in the sketch; the valve operates when the ignition is turned off and
there is still oil pressure. The operated valve closes the external air input to the bottom of the canister via
tube #6 and instead connects tube #6 to the intake manifold via tube #7. The depression in the intake
manifold sucks air out of the canister and via tube #2 to the float chamber creating a depression in the
float chamber. This depression in the float chamber prevents fuel entering the carb via the jet thus
preventing run-on or dieseling. The valve releases a few second after the ignition is turned off when the
oil pressure drops.
FWIW
TR3driver
Great Pumpkin - R.I.P
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How's your idle rpm ?
I always had sporadic run-on problems with my TR3A; though it did get less after I rebushed the throttle shafts so the throttles would close reliably.
So I got in the habit of killing the engine with the clutch, just after turning the key off.
Hot spots (glowing deposits) in the combustion chamber are another cause.
I always had sporadic run-on problems with my TR3A; though it did get less after I rebushed the throttle shafts so the throttles would close reliably.
So I got in the habit of killing the engine with the clutch, just after turning the key off.
Hot spots (glowing deposits) in the combustion chamber are another cause.
NickMorgan
Jedi Knight
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Don't really know the technicalities, but I think it is something to do with hot spots and fuel combusting without the ignition being on.
Two observations from myown car. Firstly, the engine ran backwards when it ran-on.
Secondly, I cured it by always making sure that the engine was idling at around 800 revs before I switched off. At anything above that, when the engine was hot, it would run-on.
I don't think modern fuel helps either.
Two observations from myown car. Firstly, the engine ran backwards when it ran-on.
Secondly, I cured it by always making sure that the engine was idling at around 800 revs before I switched off. At anything above that, when the engine was hot, it would run-on.
I don't think modern fuel helps either.
Don Elliott
Obi Wan
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Since I started using lead-free in 1990, I have never had run-on in my 1958 TR3A during 99,000 miles of driving. The engine temperature was often hot wen I shut off the engine and it never did it.
I removed the head in 2000 after 43,000 miles on the new engine (at 80,350 miles) to have exhaust valve seats installed for lead-free gas and the head was clean. There was nothing there to "de-coke". Again last spring when I rebuilt the engine, there were no deposits to create "hot spots" with the lead-free gas. This was 51,000 miles after the earlier time I removed the head.
If the head on your TR still has leaded gas residues in the combustion chamber, then these hot-spots might be the cause.
I removed the head in 2000 after 43,000 miles on the new engine (at 80,350 miles) to have exhaust valve seats installed for lead-free gas and the head was clean. There was nothing there to "de-coke". Again last spring when I rebuilt the engine, there were no deposits to create "hot spots" with the lead-free gas. This was 51,000 miles after the earlier time I removed the head.
If the head on your TR still has leaded gas residues in the combustion chamber, then these hot-spots might be the cause.
AltaKnight
Jedi Knight
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The ignition timing is likely too far advanced.
Has any work ever been done to the engine? higher compression from milled head or a wilder than stock cam can cause this also. Incorrectly set valve timing (because the timing chain not set right) also causes this.
Has any work ever been done to the engine? higher compression from milled head or a wilder than stock cam can cause this also. Incorrectly set valve timing (because the timing chain not set right) also causes this.
The funny thing about run on with my two cars:
The TR3 has a TR2 head. The head was rebuilt with valves and seats for lead free about 14000 miles ago and that engine never runs on.
The TR4 has a complete TR3 engine with TR4 carbs and manifolds, both the head and bottom end have been rebuilt about 3000 miles ago and that engine runs on about 25% of the time.
So from this I conclude..... absolutely nothing! But at least this is some data for you.
Adrio
The TR3 has a TR2 head. The head was rebuilt with valves and seats for lead free about 14000 miles ago and that engine never runs on.
The TR4 has a complete TR3 engine with TR4 carbs and manifolds, both the head and bottom end have been rebuilt about 3000 miles ago and that engine runs on about 25% of the time.
So from this I conclude..... absolutely nothing! But at least this is some data for you.
Adrio