Tri carb - overheating issue ????

[Norman]

Hi all - I'm slowly going mad with this problem, so any help will be gladly received. I'm in the UK and this problem mainly occurs during hot (for the UK ) weather.
Symptom - Towards the end of a long run (50 miles), if I stop at traffic lights or roadworks lasting for more than a couple of minutes the engine starts to miss when I pull away. This lasts for about 2 miles and then corrects itself. Sometimes the missing is so bad that the car finally dies - 1 hour wait and all is good again. The car is not overheating - the water temp is stable, I believe the problem to be fuel related. The temp of the rear float chamber (checked with a laser heat gun) is about 10 degrees higher than the front and middle float chambers. You would expect it to be higher as it is pretty close to the bulkhead with limited air movement when the car is stationary.
All electrics have been changed except the actual dizzy - plugs, leads, coil, points, rotor arm, dizzy cap.
The car has suffered with this problem for about 5 years - when the ambient temp is low it does not suffer at all.
The car has a new rad, new hoses, Kenlowe fan, oil cooler, ceramic coated headers and ceramic coated float chambers. The carbs have been rebuilt. The net result of everything has been - No Change.
Has anyone tried re-routing the fuel supply to supply the rear carb first ( colder fuel - not been around the engine bay for long ) or even adding a return to tank system supplying the carbs from a "fuel ring" - might need to change the fuel pump for this one.
Help - any thoughts greatly appreciated

 

[RAC68]

Hi Norman,

Your description of the issue would lead me to believe it is fuel overheating as well. I would suggest improving engine compartment cooling by increasing the efficiency of the fan with the installation of simple shroud. Take a look at this article with particular focus on the installation of simple vertical (fan shroud) panels. These panels, installed on each side of the radiator via the radiator bolts, would reduce the air leakage off the end of the blades and more effectively direct air movement in the engine compartment and around the carburetors (https://www.healey6.com/Technical/I%20always%20wanted%20a%20COOL%20Car.pdf). Although a fully encompassing fan shroud would be more effective, these simple vertical panels would allow you to test the concept without getting too involved.

Also, am I correct that your fuel pump is mounted over the exhaust? If so, I would suggest searching the archives as a number of threads have addressed this setup as a potential vapor lock cause and describe resolutions.

Hope it helps,
Ray (64BJ8P1)

 

[HealeyPassion]

Norman,
I'm no expert, as some on this forum, but I'd try a heat shield between the exhaust and the fuel pump (as Ray suggests) first. It's easy enough to build one and install to test the theory. I had to do this on one of my cars (not an LBC) for exactly the problem you describe. I made mine with aluminum and insulation.

Cheers,
Steve
https://stevesaustinhealey.com

 

[drambuie]

I used to have the same problem with my bj8, If you are running a modern type thermostat....GET RID OF IT! Install the original sleeved type thermostat as those modern thermostats block of a portion of the coolent flow. Next check you timing, Very important as well! when i corrected these two things, My bj8 ran cool as a ice cube.And get rid of that 4 blade fan if that is what you are running. Try a Texas cooler or kenlow fan to improve air flow when the car is sitting still at a traffic light. That stock 4 blade fan is useless. But first try checking the thermostat and timing first. Sometimes we overlook the simple things and get to extreme. Hope this helps, Michael. IL.

 

[Norman]

Hi all - thanks for your replies.

I already have a sleeved thermostat fitted.
I have a Kenlow fan and a 6 bladed fan (original went some years ago).
The timing is spot on

I am going to try deflector plates on the radiator sides and will look at a heat shield for the fuel pump.

The car does not overheat, the temp gauge remains rock steady whilst driving

Keep the ideas coming please - I have to crack this.

 

[andrea]

Hi Norman
a Heat shield as this can be a successful solution of your problem
https://picasaweb.google.com/lh/photo/lndbmMbovXprK18K02GREigbN-vM-p5md2wTDjyvWzM?feat=directlink
and/or
https://picasaweb.google.com/11277081986...feat=directlink
Cheers
Andrea

 

[Johnny]

Hi Norman, if I'm not mistaken your're using 3 HS 4 carbs, correct? I had a similar problem recently with my 63 BJ7 with two HS 6 carbs. My problem was the back carb jet needle had dropped down allowing more fuel than necessary into the intake. An easy check of this problem is with the engine warmed up raise the throttle on each carb separately they should increase the engine speed. In my case when I did that the back carb would stumble and cause the engine to die, just as you wrote. Try it and let us know.

 

[FrankH]

A new coil solved a similar issue with my car.

Frank

 

[chickentender]

A new coil solved a similar problem for me also.

 

[Ed_K]

Hi Norman,

I agree with Andrea because I had the exact same symptoms as you described on my BJ8 until I built a new heat shield out of hardiplank to replace the worn out, too thin, piece of asbestos attached to the metal plate of the heat shield under the carbs. The problem was immediately corrected with this one action.
...
Before I did this, I tried a lot of other things which did help the overall cooling but never fixed the exact symptoms that you just described.

Ed

 

[EV2239]

Mine does the same thing in heavy traffic on a hot day. It clears once you're on the move again.

Originally the cars were fitted with 72 degree thermostats, but customers complained that their heaters were useless in cold north American winters, so BMC switched to 82 degrees C or 170F.

I intend to use a 72 for the summer as we used to way back. Lots of Silver Cloud owners have had the same problem because the later models used hotter thermostats and modern fuels can be naughty in open fuel systems when under bonnet heat is very high.