Cutting out and behaving badly in traffic

Hey,

My 68mgb roadster is behaving badly in traffic. Starts to missfire, the revs drop at idle and eventually when I stopped in to a petrol station i couldn't get it started again until it had cooled down a bit. After which off it went again until the next bout of slow traffic (crawling). I recently set up the carbs with new AAM needles recommended for a standard engine with K and N's and a freeflow exhaust with a 3-2-1 manifold. I am thinking that it has something to do with the amount of heat coming off the manifold affecting the carbs somehow but not sure. Would welcome any ideas. When I set up the carbs I checked the mixture with a colour tune, leveled the jets and also balanced the carbs. I should also note that it is running really well when out on the open road, this only serves to make the traffic problem more annoying.

Regards and thanks'
Nick.

NIck,
You may have already answered your own question. The heat disapation of a tubular exhaust manifold is greater than with the stock cast iron unit creating more heat under the SU's. The heat may be 'boiling' the fuel in the tube from the float to the body of the HS4's leading to fuel starvation and the stublling cutting out behaviour you are experiencing. What state is your heat shield in? I has a similar problem with much the same setup as you and things improved with a cleaned up and painted heat shield and some new heat shield material on the back. If the problem persists after this, some header wrap or gettign the header jet-coated can inprove things further.
tc

Tom's response makes a lot of sense, but its worth noting that a condenser going bad will produce many of the same symptoms. There have been many bad condensers in circulation recently and if you have replaced yours recently, it may be at least part of the problem.

I have no clue but I do love galway, went there once with my best friend half his family lives near by and we had a hell of a time.

thanks for that guys, I have an electronic ignition in her so the condenser possibility is out, but Toms suggestion makes a lot of sense. I had an idea that that was the problem but was unsure what the reason was (thought it might be something to do with the heat affecting and closing the jet.....) fuel boiling makes a lot of sense. The heat shield which i have only seems to have heat resistant backing behind the fuel bowls and none behind the jets or anywhere else. It is easy to feel that there is a huge amount of heat coming off the manifold. Think I might look at wrapping the manifold and hopefully that will sort it out.

Nick.