TR4A Run-on Technicalities

[Allan Westbury]

Having read Roy Deal's problem with run -on my first thought was ' what about the top end'. Surely run on is more likely to be caused by carbon build up on the valves and/or over heating than carburation?

I had a similar problem with my 4A & tried moving to BP7ES plugs to see if cooler plugs would help & ended up with a black sticky mess where the gap should be & the engine still ran on!

While I can still get the odd occurance of running-on the problem seemed to improve dramatically when I de-coked the head and fitted a Phoenix sports exhaust with tubular manifold. Not only did I notice a big improvement in performance and response but the engine definitely seemed to breath better and the run-on all but disappeared.

Could it be that the whole engine just ran cooler as the exhaust gases escaped quicker?

Thoughts please.

[Mikell]

Having read Roy Deal's problem with run -on my first thought was ' what about the top end'. Surely run on is more likely to be caused by carbon build up on the valves and/or over heating than carburation?

I had a similar problem with my 4A & tried moving to BP7ES plugs to see if cooler plugs would help & ended up with a black sticky mess where the gap should be & the engine still ran on!

While I can still get the odd occurance of running-on the problem seemed to improve dramatically when I de-coked the head and fitted a Phoenix sports exhaust with tubular manifold. Not only did I notice a big improvement in performance and response but the engine definitely seemed to breath better and the run-on all but disappeared.

Could it be that the whole engine just ran cooler as the exhaust gases escaped quicker?

Thoughts please.

Hi,

Interesting. I've had run-on problems for some time on my 4A, and wondered if de-coke etc might help. This winter I've 'gone unleaded' in any event - and she still runs on, albeit not so much. Hence I read the TRaction article with great interest. I'm already on optronic ignition, so am guessing that the combination of "new" head and the ignition shouldn't be contributing to the problem. Interestingly, I'd previously found that switching on the (manually operated) extra cooling fan shortly before ignition switch-off helped to reduce the run-on. Hence I'm leaning toward the temparature and cooling notion. I also run with stainless exhaust. One point that I'd really like help with please ....... spark plugs. I'm currently on NGK BP6 HS (as fitted at service by TR specialists of national renown). However the talk seems to centre around using ES not HS. Is that likely to be the issue ? However, from the NGK website the ES plugs seem to be about 6mm deeper than the HS - if I convert to ES are they likely to experience a painful meeting with my pistons, or cause any other grief ???

 

My peer group wisdom will be greatly appreciated please ?

[monty]

Hi All,

I have had run on problems in the past (& still very very occasionally) but have found that by using Shell Formula (used to be Optimax) 98 octane the problem is virtually eliminated. Costs a bit more in fuel but engine seems to run better & I get 30 mpg. Using BP6HS plugs (tried BP7HS as engine was running a little rich at one time but no change in running on).

My TR4A has all the mods (stainless 4 branch, improved cam, electronic ignition etc).

If I have to go down in octane then run on reappears.

Regards,

Monty.

 

 

 

Hi,

Interesting. I've had run-on problems for some time on my 4A, and wondered if de-coke etc might help. This winter I've 'gone unleaded' in any event - and she still runs on, albeit not so much. Hence I read the TRaction article with great interest. I'm already on optronic ignition, so am guessing that the combination of "new" head and the ignition shouldn't be contributing to the problem. Interestingly, I'd previously found that switching on the (manually operated) extra cooling fan shortly before ignition switch-off helped to reduce the run-on. Hence I'm leaning toward the temparature and cooling notion. I also run with stainless exhaust. One point that I'd really like help with please ....... spark plugs. I'm currently on NGK BP6 HS (as fitted at service by TR specialists of national renown). However the talk seems to centre around using ES not HS. Is that likely to be the issue ? However, from the NGK website the ES plugs seem to be about 6mm deeper than the HS - if I convert to ES are they likely to experience a painful meeting with my pistons, or cause any other grief ???

 

My peer group wisdom will be greatly appreciated please ?

[Smokey]

I'm currently restoring a 1962 TR4, and this is my fourth TR4 variant. The 1965 TR4 I used as a daily driver in the 1960s used to run on regularly, and I'm convinced it was simply a coking issue. Coking increases the compression ratio substantially, and presumably the coke also acts as a glow plug. That's why running on is sometimes also called "dieseling".

The cure was a high speed drive from Cleveland to Boston and back - about 1500 miles, if I recall. After that, no more running on. So if the timing and mixture are correct, the running on is caused by coking, and the answer is to decoke or to take a 1500 mile high speed drive. Using the highest octane fuel available will also help.

Set the carb mixture, and then do an "Italian tune up": warm up the car, and then do some standing starts, advancing the ignition each time a little until it just starts to ping SLIGHTLY on full throttle acceleration. Then retard the timing until the pinging stops. As the coke builds up, the ignition needs to be continually retarded slightly. At least that was my experience in driving a TR4 daily for five years through. YRMV

[North London Mike]

Set the carb mixture, and then do an "Italian tune up": warm up the car, and then do some standing starts, advancing the ignition each time a little until it just starts to ping SLIGHTLY on full throttle acceleration. Then retard the timing until the pinging stops. As the coke builds up, the ignition needs to be continually retarded slightly. At least that was my experience in driving a TR4 daily for five years through. YRMV

 

 

Well, they all run on a bit don't they

 

Mine is set up for max power so it's max advance for the engine spec before pinking but runs on. I then back it off on the dizzy at the side of the road until it just does a single hick up and stops. Loses a bit of grunt but doesn't run on. 30mpg

 

You pay your money and take your choice

[ianc]

I have been using BP7HS (not 6HS) plugs and electronic ignition for almost 15 years now. Compression ratio is something beyond 10:1 (prbably 10.5:1). I fitted an anti-run-on valve some years ago and have only an occasional tendency to run-on, but I always put the car into 1st and bring the clutch up as I turn the ignition off, just to help kill any tendency to run-on.

ian Cornish

[AndrewMAshton]

Hi,

 

I run a 4A with an unleaded head, I have an electic fan so don't run hot too often but I used to run on, since I changed to Shell Optimax like Monty I have not had a problem, it is slightly more expensive but as I don't do a high milage it has little effect on my pocket. On the Ordinary Shell/Optimax use, a friend did a trial for 6 months, 3 months on ordinary unleaded and 3 months on Optimax, the result, exactly the same miles per pence,

 

Andrew

[harrytr5]

I fitted an anti run on valve from Moss to a TR6 and it cured the run on.What disturbed me was the high compression (200lbs) and believe that it contributed to the run on.I also put in NGK BP7ES.Time will tell.

Regards Harry TR5 Nutter.

[harrytr5]

Oh' Oh!.,spoke too soon.Engine tuned and anti run on valve now fails to stop run on.I still feel the very high compression is the factor in this.Sh#t give me injection anytime!.

Regards Harry TR5 Nutter(no I am not on carbs)

[mog620]

Oh' Oh!.,spoke too soon.Engine tuned and anti run on valve now fails to stop run on.I still feel the very high compression is the factor in this.Sh#t give me injection anytime!.

Regards Harry TR5 Nutter(no I am not on carbs)

 

I have a high compression engine as well....230 lbs. Elec ignition etc, etc. The highest octane we have in the US at the regular gas stations is 93 octane. I use BP6HS plugs now(just changed from Champion L82YC, can't really tell any difference) Add to the low octane, the hot weather in Texas and I sometimes have running-on problems. I find that running at 800 RPM idle helps this. If not, just put it in 2nd, turn the key off and release the clutch.....HTH Frank

 

1968 Morgan Plus 4(TR)

[RogerH]

Hi Folks,

engines run on because they are spiteful and as Frank says the answer is to give them a good jamming - put it in 2nd and let the clutch out (gently)

However here is a funny thing - if the engine is going through one of its spiteful periods then I turn the ignition key to turn off the ignition

very slowly and hey presto no run on. You think I'm mad - well thats not new, the wife would agree but it does seem to work.

It could also be down to chance and it wasn't going to run on at that point anyway.

Give it a go and give some feedback!!!

 

Roger

[Mikell]

Hi Folks,

engines run on because they are spiteful and as Frank says the answer is to give them a good jamming - put it in 2nd and let the clutch out (gently)

However here is a funny thing - if the engine is going through one of its spiteful periods then I turn the ignition key to turn off the ignition

very slowly and hey presto no run on. You think I'm mad - well thats not new, the wife would agree but it does seem to work.

It could also be down to chance and it wasn't going to run on at that point anyway.

Give it a go and give some feedback!!!

 

Roger

 

Hi all,

thanks for the thoughts - I never thought of a "contrived stall", but I see your points one and all. I'll probably try the highest octane approach first coupled with a slightly lower tickover. Failing that it'll be different rated plugs - and if not it'll be 'stall time'. If those measures fail I guess it'll be anti run-on valve time. I'll post a follow up in a couple weeks time assuming the weather has enabled a good few miles.

 

Mikell.