Intermittent Electrical Fault?

[Andrew Smith]

Following-on from Vincent's post about ignition coils:

 

TRK has a Lucas Sports coil fitted; it was fitted in 1988 until TRK was taken off the road in 1992 and laid-up until the engine was rebuilt in 2003.

 

I have not changed the coil, but suspect it may be responsible for an intermittent fault, and it is this:-

 

Whilst accelerating under load e.g. up long hills (not in overdrive) or sustained high(ish) speeds (in overdrive) the engine stutters and revs begin to fall (usually from about 4,000 rpm) until I slow then all appears fine - until the next time. Other than this scenario, all is fine when I’m just trundling along.

 

I realize this could be a whole number of things electrical or even fuel starvation and I could peeing into the wind, but does it sound familiar to anyone?

 

If so, what was it and what was the cure?

 

Your thoughts are welcomed.

 

Thanks

Andrew

[unclepete]

andrew

try the condenser? cheap to change.

coils normally completely pack up if they overheat and will work when cooled down so your problem doesn't sound like the coil.

the vacuum advance pipe might have a little air leak - that would let you potter around but play up under load?

had a TR6 parked up next to me at duxford that refused to start.

luckily, being a good little boy scout, or paranoid, i had the boot full of tools and electrical test kit and briefly became a TR6 rally support vehicle.

the guys from east saxons descended on this chaps engine and had it in bits before you could say 'bosch fuel injector'.

turns out it was loose connection on the coils spade terminal!! let him get all that way then packed up.

good luck

pete ::

[jean]

Chris this sounds like a fuel flow or air flow problem.

When the engine is reving high it needs more fuel and more air.

So in your case it's lacking one or the other.

One thing I would do is to clean the whole fuel system, you could have a look inside the tank and see if no flakes are floating around that could block the outlet as soon as the fuel outflow is increased. Unfortunately with a mechanical pump it's more difficult to check the fuel flow as you have to run the engine at high rpm.

In general airfilters are so simple that they should give no problems, but it's always worse checking if no one has mounted a wrong gasket on the filters or put one across the inlet.

Maybe your engine is running too lean, this will without doubt limit the topend power output, to try out open the adjusting nut on each carb by one flat and check for result.

Jean

[Andrew Smith]

Pete, Jean

 

Checked the vacuum pipe and air filter gaskets and all is well, the condenser is new too.

 

Also checked the plugs and they are very black a sooty, therefore TRK is running rich so I'll have to get a Colour Tune and see where the air/fuel mix is at. Maybe this is the problem?

 

Thanks

Andrew

 

 

PS, Jean, I'm only Chris(tine) at the weekends, and then only at night!  

[jean]

Sorry Andrew, at my age I have to reduce the amount of Pastis before lunch

 

In case of overfuelling it should pickup when you throttle back, you could have the ignition curve checked to see if the springs are correctly fitted    ???

Jean

[marvmul]

I also think that fuel starvation is the cause. When you are just trundling along, the fuel chambers of the carbs are slowly filled, when you have a long acceleration, or sustained high speed, the fuel consumption is higher than the supply, and the fuel level in the carbs is falling.

Cleaning the fuel pump and checking the fuel line between tank and pump will probably resolve the problem.

[Andrew Smith]

Jean, Marvmul

 

Thanks for these tips; I'll try these after I've sorted a rusted-in/seized piston in my n/s brake caliper.

 

Andrew

[Andrew Smith]

........checking the fuel line between tank and pump will probably resolve the problem.

Well, fixed the seized brake piston and so checked the fuel line from tank to pump.

 

Yep, there was a split in the braided plastic pipe where it connects to the tank (thanks Marvmul); and on investigation I made it worse!

 

So, I've just drained the 10 glns of fuel in the tank (wife's chuffed, it's in her Clio now!) and stripped out the line.

 

I'm considering changing to the original copper tube with the fuel tap, or I might just replace the braided plastic tube (cheapest option!).

 

Any opinions from those with experience of both?

 

Suggestions welcomed.

 

Thanks

Andrew

 

PS, thanks for the other tips; I’ll work through them if this isn’t the solution.

[jean]

Andrew, Cunifer, I think it's called, use it as much as possible.

Flexible hoses are good for connections. Braided hoses are nice, but the rubber pipe inside is often rubbish

I bought some braided hoses, but used only the outside for extra protection against chafing. I removed the rubber part and put a canvas reinforced quality fuel pipe inside.

Jean

[unclepete]

[Yep, there was a split in the braided plastic pipe where it connects to the tank]

what was happening then andrew.

you didn't mention a fuel leak - was the braided pipe sucking in air?

pete

[Andrew Smith]

Jean, thanks for that info.

 

[what was happening then andrew. you didn't mention a fuel leak - was the braided pipe sucking in air? pete]

 

Pete

 

I noticed the fuel leak following Marvmul's advice - being the easiest to diagnose - it wasn't on my list of suspects.

 

I can only assume the split was sucking in air at speed or possibly interrupting the fuel flow; there was also a nasty kink (80 deg) in the pipe where it exited the fuel tank union, this caused the initial split.

 

Once I've replaced the fuel pipe I'll be better placed to tell if that was the problem.

 

The battle for supremacy continues!!

 

Andrew