Help.............

[Jim Haines]

I wonder, please, if any forum member can help me, please?

My car is a 1971 MGB Roadster, which I had professionally rebuilt 23 years ago. It has served me reliably, but in the last 3 years I have decided to upgrade/modernise parts of it until meeting a problem I have never experienced before.
If I take it out now I get about 5 miles down the road, and suddenly without warning it seems to drop down to 3/3.1/2 cylinders firing, and I just have to limp home. Leave it for 2/3 days and it will start again perfectly, but repeat the same process of only running properly for a few miles. This has happened to me 3 times now, over a fortnight or so,
Earlier this year I ad the car properly serviced, the tappets were set, and I fitted new pancake air filters. 3 years ago I fitted a 'Lucas' Type 45DE4 electronic distributor with new (black) leads, all of which have now probably only covered 700 miles. I also fitted NGK equivalent spark plugs set at 35 thou., and this combination had noticeably improved cold starting. I had intended to change the rotor arm but the one I was sent is defective (see my previous post) so I still have the original in place. The carburettors are set well, and the engine runs and ticks over well before the problem sets in, after which it runs 'lumpy'. If I remove a spark pug lead in this condition it seems to make little or no difference,
I have checked all the electrical connections on the LT and HT ignition circuit, and can find no apparent fault.
I just wonder - as anybody else had any similar experience, please? Any advice/ideas would be welcome.
Thanks for reading this.

[Geoff Edwards]

Hi Jim,

A few thoughts:-
I would certainly change the rotor arm for a new "red" one
Presumably the distributor cap was replaced - thinking of cracks etc
Was the engine tuned after the pancake filters were fitted?
Have you a fuel filter on the car - if so has it been changed recently?
Have you tried taking off and replacing the fuel cap to check for any blockage?
Are the fuel lines OK - I had a problem a while ago with a perforated fuel pipe
between the carbs which only caused problems initially when the engine was hot.
Have you tried another set of plugs/ht leads (not necessarily new; use the old ones
if you still have them and they were OK at the time)
Check if the coil becomes excessively hot.

I expect that you have already tried most of the above - but you never know!!

Regards,

Geoff

[Jim Haines]

Thanks for your reply.
Yes - a new cap has just been fitted.
Yes - the engine has been tuned after fitting the new filters.
Yes - I took the rubber fuel lines off both the pump and the carb. to see if there was any 'fouling', but they were perfectly clear.
Yes - I have a fuel filter and this is perfectly clean (I fitted a new tank when the car was rebuilt so it should be o.k.).
The plugs and the HT leads are about 2/3 years old and have covered only 700 miles in that time, but I have ordered new ones now, although I am not sure this will cure it.
I am thinking there may be a fault inside the electronics of the new distributor, but I have no immediate means of testing this on the car As it is 3 years old I can't really go back to the supplier, so the only thing I can do is buy a new one - again - but I was hoping that somebody out there might just have had a similar problem and could shed some light for me.
Cheers..........

[Peter Cresswell]

Hi Jim
I've had a couple of misfires on a Mini engine, one turned out to be the rotor arm loose on the spindle. Check it is seated and tight, as if it is loose it will miss one of the contacts in the cap. When the misfire occurs is it always the same cylinder? Check by spitting on the exhaust manifold near the head. Bit difficult to determine with cylinders 2 and 3 but it might give you some idea.
The other wasn't electrical at all, but a carb problem. The damper in the dashpot was sticking and so giving the wrong mixture. Take the dashpots off and give them a good clean out. Rub a finger around the inside to see if there is anything that would stop the damper dropping freely.

Have you changed to wire wool type aircleaners? If so check there are no stray bits of wire stuck around the butterfly area of the carbs.

Are the fluid levels normal, particularly the coolant?

[Jim Haines]

Thanks for your reply.
At the time that I posted my request for help I also sent an e-mail to the original supplier of my - aftermarket - distributor, describing the symptoms and asking if they recognised them. After a few days I got a response to state that I am apparently describing the symptoms of heat failure, and that renewal of the electronic parts were required.
I actually have a replacement, and as 'belt and braces' I had also bought a new set of plugs and leads and a coil, all of which will be fitted in the next few days.
I am optimistic that I may now have an answer but - once - again - is this simply typical of the quality of modern components? My 'old' distributor is less than 3 years old and has covered less than 700 miles - should this happen?
Fortunately I can afford to 'indulge' new parts when I want them but if this is what we face in the future with our old cars I can see some people having real problems.

[Dave Linkson]

Does sound like ignition fault, a lot usually are. What about the coil itself? Treat yourself to a new blue Bosch coil, the best you can get which give the best high volts of any coil for your electronic distributor and 35 thou plug gap.
Were only about £18 on eBay, but may be more now. They are also sold on Simonbbc.com as are other ignition parts. What make of coil are you using? I'm using a Lucas gold sports coil over the last 6 months, and GT goes well, but have now read that there are known to be problems with these and failures have been noted, can't win can you! lol.

[Graham Barker]

There is another reason for dropping a cylinder when it has warmed up, that is a crack in the combustion chamber allowing water in and you would loose that cylinder.

Just a thought.

Graham

[Jim Haines]

Thanks - I am pleased to say that having now fitted all the new electrical equipment the car is running at it's best.