Talk Morgan Forums Morgan Sports Cars Maintenance & Servicing 1983 4/4 rough running after 10 miles

my 1983 4/4 stars ok when cold, after approx. 10 miles it starts to misfire in town, it's Ok on motorway, it gets very hot under the bonnet, I have changed the ignition amplifier, the car has magnicor leads and the plugs are iridian both approx 6yrs old. I would appreciate any suggestions as it is almost undrivable.

Do you have a rotor arm? Try a swop.

Are we talking carb/s and distributor?

Heat related misfires can be hard to trace. Fuel vapourisation is always on the list but it can also be rotor arm or cap. Try replacing both and bear in mind that new rotors can be faulty. Clean the leads. Can you replicate the misfire in the garage? Look in the dark to see if there is any visible tracking.
How old is the fuel? Full tank? Check filter? Check carb float chamber.
The list goes on and often it's a matter of persistence that solves it.
Good luck.

1983 will be either late x-flow or early CVH, on carb, assuming an unmodified car...

Start with ignition - if points replace and correctly gap. Change condenser at same time.
Next try plug leads then plugs. Followed by rotor arm then distributor cap.

If all the electrical bits are OK, try fuel filter, then clean out carb.

Hope I haven't missed anything...

Good luck!

I would go for leads on first guess, if the core has a fault, it may get worse with movement not nessecarily heat. Start the car and while idling, move the leads around (use a wooden hammer handle)then give it some revs and do the same thing, as they may only fail under load.

Basicallly I agree with Graham. Hot engine, or rather, hot engine bay could be the result of to lean mixture. Could be dirt in the jets or badly adjusted mixture screw (if appropriate here...). Exhaust manifold can get red hot. It fits with your experience that cold start is ok.
Check spark plugs for coloring; very little or no brown or black deposits, sometimes slightly glazed is typical for lean burn. Plugs can get overheated and stop working properly.

Only thing I'd add to Grahams list is the coil. Assuming its a 'standard' coil, these can be ok when stone cold but fail completely when hot. If it runs ok until it gets hot , i.e. in 10 miles its off enrichment its more likely to be electrical than fuel. A blocked fuel filter will be blocked when its cold and if anything the demand for fuel is higher then anyway.

How bad is the misfire? is it just dropping a cylinder or is it more than that? If its more its unlikely to be a single lead or plug, probably condenser or coil... either way I'd go for electrics first.
Steve

Often the coil is mounted horizontally and I have read that they should be vertical but as to why I cannot say without research. I too would look at the coil it does sound an electrical issue.

Possibly because the coil is oil filled to keep it cooler.

Yes, on my TR6 I moved it from the hot engine block location to the cooler inner wing, it's a common 'mod' and no problems since.
Steve