4A Running on and on and on...

[JFerg]

When I bought my current 4A it had had the "race motor" rebuild. This made it almost undriveable on the road, and the only way to stop it was to stall it in 4th.

So I pulled the cam and replaced it with a "fast road" grind. While the head was off I had it overhauled and had hard seats fitted for unleaded fuel.

It was now driveable, but still ran on desperately. I only run 98 octane premium, which makes a slight difference over 92 octane.

I had the advance curve in the distributor re-mapped, no difference. I messed with the timing. With zero fixed advance, or even with it retarded, it still ran on.

So I started making SU needles and going to the dyno until (on about the sixth attempt) the mixture is spot on right through the rev range.

It has an aluminium radiator, but was still prone to overheating in traffic, so I fitted the biggest electric fan I could fit. That solved that problem, but it still ran on.

Compression in each pot is 155PSI, which is good and certainly not too high, so that is not the cause of the running on.

Reluctantly I had resigned myself to pulling the head off again, in the vain hope of finding something awry.

 

At the weekend a mate of mine suggested heat shielding the carbs from the extractors. Given that this could be done without removing the head I thought it worth as try, so quickly bodged a temporary shield from a sheet of exhaust manifold gasket.

 

Guess what? The effect is profound. It has not eliminated the running on, but it has reduced it now to very infrequently, and predictable off the temp gauge. The engine now runs cooler in daily driving, temp gauge sitting at about a quarter when moving, rising to about half way in traffic. It used to sit at half and rise from there in traffic. It is Winter here (Melbourne, Oz) and so only 15*C outside, but still the result is a major improvement.

 

Question is, therefore: Does anybody else heat shield their carbs?

 

cheers,

JFerg

Edited August 5, 2010 by JFerg

[graeme]

Hi JFerg,

 

I have suffered this problem on a couple of TRs with various states of tune. I have also fitted heat shields to the carbs with little or no effect.

 

However, fitting webers with no other change solved the problem instantly.

 

I think you are heading in the right direction, ie dealing with the carbs, but I am not sure what the cause is. Some cars do not suffer at all, even with low octane petrol, and serious mods. I can only imagine that there is a hot spot somewhere in the combustion chamber and the SUs allow petrol carry over which keeps the engine running. Incidently, it would appear that my engine runs on backwards, as putting it into forward gear to stall the engine causes the car to move backwards.

 

Cheers

 

Graeme

[TR 2100]

What plugs are you using, and have you tried experimenting

with colder plugs?

 

AlanR

[Badfrog]

Hi,

 

I too have a fast road cam. I wrapped my exhaust in insulating tape (starter motor too) but did not add the steel plate. I never encountered run-on with cold plugs (NGK BP7HS or the iridium equivalent) unless the engine temp was on the hot zone.

What is your comp ratio? TR engines don't like excessive compressions (above 10.6) unless it's a full race modified engine with all the goodies.

 

How about a good Kenlowe fan and a 68°C original AC thermostat?

 

I understand you're making your own needles. What profile are they? what is the closest standard profile and its differences to your home-made stuff?

 

Cheers,

 

JF Savouret

 

PS: I just remembered: when going to Malvern 2010 on the first attempt (wednesday, when the dizzy burned), I got caught in a jam and overheated badly. I had to stop in a gas station on A3 motorway. I cut the power, even removed the key....and the engine went on a steady 2000 rpm. I had to stall it in third against the handbrake. Never had that before. Talk of a hotspot... The car doesn't seem to have suffered from it.

 

PSs: Graeme, a running-on engine always goes backwards to my experience.

Edited August 5, 2010 by Badfrog

[vivdownunder]

Hi Jferg, after a run, try letting the car idle for about 1/2 minute with the electric fan on before switching off. This works in many but not all cases.

 

The heat shield probably helps because it is known that a cooler charge will act to dampen any hot spots in the combustion chamber.

 

A local 3A that diesels on like a pig has just had its fast road engine torn down twice, yet can't find a thing in the combustion chambers. Compression was dropped to 9.5, tried cooler plugs, re- timing, but nothing helped. Complete mystery. He doesn't run a heat shield but I'll suggest one.

 

I've cured running on with new jets and needles where a car was running rich, but a lean engine will run on too, due to hotter combustion chamber temp.

 

Freezing winter isn't it......... still we're laughing when you look at last year's northern hemisphere winter snow pics.

 

Regards,

 

Viv.

[JFerg]

Hi,

 

I too have a fast road cam. I wrapped my exhaust in insulating tape (starter motor too) but did not add the steel plate. I never encountered run-on with cold plugs (NGK BP7HS or the iridium equivalent) unless the engine temp was on the hot zone.

What is your comp ratio? TR engines don't like excessive compressions (above 10.6) unless it's a full race modified engine with all the goodies.

Not sure what the actual ratio is, but with 155psi in each pot, it's not excessive.[/font]

How about a good Kenlowe fan and a 68°C original AC thermostat?

Already have that!

 

I understand you're making your own needles. What profile are they? what is the closest standard profile and its differences to your home-made stuff?

Its a wacko custom. Stations 1 5 are 20 to 25 ten thou leaner (fatter) than CIW, the rest of it is 5 10 ten thou up on CIW, with a 10 ten thou bulge at stations 9 and 10. If that was taken out it would probably remove the top end lean-ness, but as before; I cant be bothered. CIW is the factory lean standard needle.

Cheers,

JFerg

JF Savouret

 

PS: I just remembered: when going to Malvern 2010 on the first attempt (wednesday, when the dizzy burned), I got caught in a jam and overheated badly. I had to stop in a gas station on A3 motorway. I cut the power, even removed the key....and the engine went on a steady 2000 rpm. I had to stall it in third against the handbrake. Never had that before. Talk of a hotspot... The car doesn't seem to have suffered from it.

 

PSs: Graeme, a running-on engine always goes backwards to my experience.

 

Edited August 5, 2010 by JFerg

[JFerg]

What plugs are you using, and have you tried experimenting

with colder plugs?

 

AlanR

 

 

Can't remember precisely what plugs are in there, but I did try one level colder. There was an improvement, in that the running on was less, but the agony of getting there wasn't worth it. It started readily, but would not pull its own weight until the engine thoroughly hot. The car is my only modern car, and whilst not a daily driver, is the car I use when I need one. It needs to be practical, and teh colder plugs just weren't.

 

JFerg

[Alec Pringle]

Wrapping the exhausts has to be worth doing, and a heat shield will help also - the two in combination will significantly reduce the temperature of the carbs themselves, which is the real problem.

 

There is also the option of changing from mechanical to an electric fuel pump, switchable on the dash - you can at least kill the pump before you kill the ignition . . . . yes I know it's a bodge, but if all else fails !

 

Cheers,

 

Alec

[Guest DeBartolomeis]

Wrapping the exhausts has to be worth doing, and a heat shield will help also - the two in combination will significantly reduce the temperature of the carbs themselves, which is the real problem.

 

There is also the option of changing from mechanical to an electric fuel pump, switchable on the dash - you can at least kill the pump before you kill the ignition . . . . yes I know it's a bodge, but if all else fails !

 

Cheers,

 

Alec

 

 

If its a racing motor, then... just put louvers in the hood. Just a thought

 

James

[ianc]

You could add an anti run-on (dump) valve, which lets air into the inlet manifold as soon as the ignition is turned off. I have one attached to a bracket, which itself is attached to the rearmost righthand cylinder head stud (on top of the nut which secures the head, of course). This requires just a very short length of pipe to feed into the inlet manifold, because I have the TR4A manifold, which has the attachment for the rocker cover breather system (which I don't use, of course). This certainly helps to reduce the tendency to run on.

With a bit of luck, you'll be able to spot it in the photo.

Ian Cornish

 

[TR 2100]

Wrapping the exhausts has to be worth doing, and a heat shield will help also -

the two in combination will significantly reduce the temperature of the carbs

themselves, which is the real problem.

 

Hi Alec,

 

I always understood running on to be essentially the plugs

getting so hot that they continued to ignite the mixture.

(Or a hot spot on the head, possibly due to No. 4 cylinder

often suffering from less cooling due to build-up of gunge)

 

For sure, a weak mix can lead to the engine running hotter

than it should, I can believe that petrol getting too hot

could as well (although further explanation of how would be

appreciated).

 

But surely the real cause comes back to plugs (or whatever)

getting too hot?

 

I'm not saying I'm right - just asking where I'm wrong.

 

AlanR

[Alec Pringle]

Hi Alan,

 

yes you're correct of course, there'll be a hot spot causing the diesel effect. However, even a modest increase in temperature of the fuel/air charge can disproportionately exacerbate the tendency to run on. In this instance, given the apparent improvement after temporary shielding, fuel/air intake temperature would appear to be relevant.

 

There has to be a cause for the hotspotting, and I'd agree a coolant circulation problem is the most likely. Flush and backflush, chuck in some kettle descaler, repeat the procedure. Then use oil-fashioned flushing oil to clear the oilways. This could be one instance where an oil cooler might be appropriate, to assist in cooling the block and head. As James suggests, improved airflow through the engine bay might also help.

 

Cheers,

 

Alec

[Badfrog]

Hi again,

 

From the 3 letters code, I understand you have sprung needles or is this a stromberg code?

 

My experience on sprung needles is that they are less efficient than fixed ones in SUs. Have you tried the fixed sort?

TS, KU and RH are contenders for best function with a fast road and HS6 carbs.

 

Cheers,

 

Badfrog

Edited August 7, 2010 by Badfrog

[Dazzer]

Hi

 

Luckily we currently have a TR4 which doesn't suffer at all with running on, even when over hot. However I have had one that did and I tried everything to cure it, heat shields the works.

 

The one thing that minimised it was very simple.

 

Ensure the throttle spindles are well lubricated and the throttles are snapping off against the stops with no resistance. (You might want to first check, with the carbs off the manifold, that the butterflies are completely closing off in sync)

 

Next reduce the tickover down to 500 rpm or as low as you can practically go.

 

This may cure it all together.

 

I also have running on problems with the 2000, I reduce the tickover for everyday use which near as damn it cures the running on, and for rally autotests I speed it back up (to avoid stalling). It runs on beautifully when idling at 800 rpm!

 

Might be a nice simple fix just to reduce your tickover.

 

Cheers

 

Dazzer

[Steve Priest]

I just do as someone suggested on this forum a while back (sorry, can't remember who). Just press the throttle to the floor as you switch off the engine. Stops my TR4 running on.

 

Steve

[tony-qld]

Isnt 68 degrees a bit cool to run your engine at. I was always told that running an engine too cool doesnt allow everything (including the engine oil)to operate as it was designed. I know that when we were running 350 chevs in ski boats the guys running cold raw water straight through the engines without thermostats would be rebuilding the engines sooner than the guys running closed systems with thermostats.

[Badfrog]

Isnt 68 degrees a bit cool to run your engine at. I was always told that running an engine too cool doesnt allow everything (including the engine oil)to operate as it was designed. I know that when we were running 350 chevs in ski boats the guys running cold raw water straight through the engines without thermostats would be rebuilding the engines sooner than the guys running closed systems with thermostats.

 

 

 

You're right about boats. In that case it's a question of having cold water entering the engine and creating thermic shock with brutal metal distortion. It's in microns but still very deleterious. Like when you take earthware from the stove on a cold surface: "clack!!"

 

The original AC sleeved thermostat opens at 68° (celsius). But the flow-by retriction ensure that the engine stays a bit hotter. Now that I've reverted to HS6 SU, the 68° thermostat puts the temp needle dead on the N for normal mark. I'm not sure but I seem to recall that's close to 85°.

If you install a modern thermostat, you'll be around 90° (with a 82°) or more (with a 88°).

 

My experience: if the engine overheats, the thermostat won't do anything. When I was fiddling with the HS8s lately, the car heated exactly the same way with a 68°, 82° or no thermostat.

 

BTW, I did a last test yesterday with KU "all along" richer needles and the max advance (24°) for the TR4 race dizzy. I had a bit of run-on and ping. Changed to TS needles (normal low stations like SM needles, richer upper like KU) and 22° advance: all perfect.

 

Badfrog

Edited August 9, 2010 by Badfrog