Back firing and breaking down once hot (20mins)

[mikelight]

Hi everyone
I’ve inherited my dads series 2 fhc it was running fine until a few weeks ago,then it started to back fire and break down then it will start 15 minutes later once cooled down but do it again once it warmed up things I have changed to try and sort the problem.
Electronic ignition.
12v coil (got rid of the ballast resister)
New rotor arm from the distributor doctor
Tester the fuel pump seems to be working ok I’m really running out of things to try just wondering if anybody else has come across this problem.
Thanks Mike

[DWW]

Sounds to me like a fueling issue, possibly the mixture overheating? Check manifold cooling or thermostat.

[Jack the lad]

Hi Mike,
You need to replace the ballast resistor and see what happens. If the coil is made to run with one fitted, then instead of 9 Volts at the coil you are giving it 14 volts which will overheat it and cause a miss-fire for now but a total burn out of the coil in the future. I guess your temp. gauge it showing normal, so not a fuel problem as if it was weak the combustion temp would rise. One last thing, check that all the plug leads are in the correct order on the dizzy cap, 153624 and on the correct cylinder's plug.

[Gfhug]

Depending on the electronic ignition, but if it’s a 123 SNG Barratt say a ballast resistor needs to be fitted.
If you’ve got the original Lucas distributor refit it and the ballast resistor and buy a good new coil, some of the so-called DLB5 coils are not what they claim to be. Then you’ll be back as the car was designed to run. Once you’ve set up timing, etc, then adjust the carbs as per the manual. You should get a good running car. Once you’ve done that you can put the electronics back in.

Geoff

[mgcjag]

Hi Geoff....some of the info on SNG website is incorrect.....you do not need a ballast resistor with the 123.....late S2 cars had ballasts... earlier cars didnt......the 123 will work with either setup.......
Mike......welcom to the forum......your issue does sound like a typical coil problem. .....it gets hot then causes problems.....i note that youve changed it but brand new ones can be faulty.....when you car is mis fireing etc put you hand on the coil....if its hot its breaking down.......however youve changed quite a few things already and i assume none of them are known working parts so any could be faulty. ....so start from basics.....fresh fuel, pump working....fuel up to the carbs......timming set correctly......ignition.....spark........Steve

[malcolm]

I had a similar problem when I had plug and king leads breaking down when hot. Have you changed all leads?

[DWW]

Obviously if it turns out to be a coil issue as many seem to suggest then my theory in the previous post doesn't stand.....good luck.

[mgcjag]

Hi Danny.....all suggestions are welcome......no one knows what the problem is yet......so the more ideas for Mike to look at the better.....Steve

[mikelight]

Hi everybody
Thanks for all your quick responses,I’m going to change the leads and plugs like Malcom suggested as I haven’t changed them and don’t know when they were last done.
How would I check the cooling to the manifold so I can tick this off the list ???
Thanks again for all the help.
Thanks Mike

[MarekH]

I had a similar problem when I had plug and king leads breaking down when hot. Have you changed all leads?

Before you spend money, you can check by put a timing light pickup onto each of the leads and see whether it causes the strobe to light each time. Or you can pull a plug and rest it on the manifold and watch the spark.
The other "gotcha" is that you have fitted electronic ignition and should confirm the timing is correct as part of the installation. You can also check the coil very quickly by simply plugging in a (stone cold) spare once it misfires. None of these checks will cost you any money, whereas buying new components first will.

Sounds to me like a fueling issue, possibly the mixture overheating? Check manifold cooling or thermostat.

Backfiring is caused by unburnt petrol in the exhaust igniting, so it is either not being sparked or it is being sparked too late. The latter is unlikely as John pointed out heavily retarded ignition tends to up the coolant temperature and you haven't reported that. It also doesn't explain why you can run for 20 mins, from cold, when you needed more fuel (and it was harder to ignite), not less, once warmed up. Cars still run all the way to boiling out the coolant and beyond, so I'm not sure how backfiring is caused by overheating.

kind regards
Marek

[malcolm]

Understand about testing the leads, but when the car was at test they were fine. When it was underway and thus under load is when they started to miss. The cost of swapping them for new was only small and fixed the problem. I also had issues with copper-cored leads interfering with electronic ignition so bought silicone ones.

[mikelight]

Hi everyone
I seem to have fixed it was the dizzy cap done about 40 miles I’ll keep you posted
Also has anybody ever changed the door rubbers ??
Thanks Mike

[mgcjag]

Hi Mike...search or start a new thread if your haveing problems with door seals. ....plenty of info already here on the forum. ....Steve

[mikelight]

Will do Steve cheers