Engine chokes up when warm

[antiblent@yahoo.co.nz]

Hi again, looking for some ideas... my car starts and runs fine from cold but when I stop for a while and then start and drive off again, it chokes up and conks out a few times before getting going again. Any ideas what might be causing that?

Cheers Tony.

[davidr]

Hi Tony - it would be a great help to fellow members and give you a better chance of getting some helpful responses if you give us more details of your car. Which engine, year, transmission etc.

[antiblent@yahoo.co.nz]

Sorry, it’s a 1978 Daimler coupe with the 4.2 engine and auto. It had the engine rebuilt, the carbs rebuilt, new tanks and fuel pumps all in the last year, but it’s hardly been driven. I drove it for an hour this morning, then stopped for an hour and a half, then when I went to drive back I had the problem. I stopped on the way back and same thing. I’ve noticed a few times before today as well.

[mike020150]

"it chokes up and conks out a few times before getting going again" Is this a literal description? Does the car emit black smoke (as if the choke's in operation even though it's hot)? Or does the car come to life slowly, perhaps with a spit or two? If it's the former, I'd start by checking carb float valves and levels. If it's more like the latter, it may only be a slight carb adjustment issue requiring a tweak in the richer direction. Mike.

[antiblent@yahoo.co.nz]

Thanks Mike, I should have said in the last post I have a manual choke fitted. It sparks to life on the button when warm but after a few minutes starts to cut out like its struggling to get enough fuel, so I have to pull out the manual choke to keep it running and then there is a bit of black smoke.

[RichardSEL]

Is this just a tickover? Or will the lumpy firing stop if you take it up to say 1500rpm without adding choke?

[antiblent@yahoo.co.nz]

It’s still rough, ie half power no matter what the revs.

[mike020150]

You have to be lucky to spot a solution to problems like this without working logically through both the ignition and carburation systems. If the car still has points and a condenser, they should be gapped and replaced respectively before checking the ignition timing. Also, whilst inside the distributor, ensure the braided earth wire between the base plates is intact and the cap has no signs of tracking/carbon brush damage. The rotor arm needs checking too. Modern versions often fail prematurely due to loose rivets. If the car has electronic ignition, still check the rotor arm and look for a strong spark at each plug. If in doubt, substitute components. Don't forget to check the oft-neglected coil with both ignition versions. It should be clean, crackfree and free from tracking/arcing marks. The resistance of the low tension side of the coil should be compared with the coil spec. The high tension leads too should be part of the checking process. Only once the ignition system/timing has passed all checks is it time to suspect carburation. A manual choke (properly set up) should make it easier to check carburation because it does away with the infamous AED (auto enrichment device). Apart from leaks, check float valves and levels before attempting to balance and tune the carbs. That would be my recommended checklist for a standard car. If the car has been altered and things like heat shields for the fuel piping have been lost, other issues like heat soak, may be at play here. Mike.