Practically Classics Forum

I have a couple of air cooled NSUs which increasingly have become prone to stalling when hot and being difficult/ impossible to restart unless left for 10 minutes or so. I suspect fuel evaporation, and seem to remember a few months ago some reference in Practical Classics to some type of insulating wrapper ( excuse the non technical term) which you fit over the fuel lines to help this problem. Does anyone remember anything about this or know of any such products?
Thanks
Paul

Fuel line insulation wrapper isn't something that's very common to be honest, in my experience anyway. However, you could start by routing the fuel lines as far away from heat sources as possible.

Vapourisation is more likely to happen in the tiny channels of the carburettor itself rather than the larger fuel lines, so first step I'd take on that sort of engine is to buy or make up some kind of thick insulating gasket for the carb., to thermally insulate it from the intake manifold. You may be able to buy such material, or find something suitable - even wood might work! I've often seen this on old British motorcycle engines (e.g. Triumph, Norton etc.) which are air-cooled and could suffer from this problem - you might even get a bike carb "thermal break" gasket thingy to fit if you search around enough - I don't know what the carb attachment arrangement is on the NSU engines but it's a thought.

Secondly, you might want to take steps to cool down the engine compartment as a whole. Insulating exhaust wrap (available from Frost and others) helps a lot, wrap it around the exhaust manifold and pipes that are inside the engine bay. Also, explore possibly finding a way to duct more cool air into the engine compartment.

Hope that helps?

Cheers

Aother possibility might be to fit an electric fuel pump to force liquid fuel into the carb

We had a similar issue on a Triumph Stag recently. It turned out to be two things, firstly the coil was getting overheated and breaking down internally and the engine earth lead was not making a good contact with the engine, the car would start and run and then die after about 10 mins. Once the lead was relocated the issue disappeared. I knew pretty much what the fault was because I had had an identical issue on my Scimitar GTE

I think that the fact that both your cars have developed the problem, the culprit is the increasing amount of ethanol being added to fuel. Ethanol is more volatile than petrol. Something you might try is to use super unleaded. Ethanol is added to the fuel at the distribution terminal and the majority (though I wouldn't like to say all) don't add it to super. It may cost more, but you'll get a few more mpg which will offset the increase.

suffolkpete wrote:It may cost more, but you'll get a few more mpg which will offset the increase.

Assuming you adjust the timing to make the most of the increased octane rating.

I had a similar problem while waiting at traffic lights in the mog but it was fine once it had been moving for a minute or two. It was solved by putting a heat shield between the carb's float bowl and the exhaust manifold. It has not been a problem since.

My 6 pot Princess has always suffered from vapour lock when hot and I have taken all of the steps already mentioned which have improved the situation considerably
A comment from a Princess forum member recently was, that according to his research, BP and Esso are the only oil companies NOT adding ethanol to their super brands at present:thumbs:
If the proposal to go to 10% ethanol ever gets EU approval, then us classic owners are in for real problems on the evap front. I have also read that even modern classics with first generation fuel injection, such as Bosh jetronic, will become almost un drivable under certain conditions and re- building fuel systems with ethanol proof components is certainly going to cost a bomb

As I said in my previous post, ethanol is added at the terminal, not by the oil company. The last time I checked a few months ago, 26 of the 40 - odd terminals did not add ethanol to super. Under proposed regulations, 10% ethanol must be marked as such, as it is on the continent, and there will be fuel available with no more than 5% available for the foreseeable future.

Firstly....don't ignore the rotor arm. I've had this problem, was convinced for ages that it was fuel evaporation. Turned out to be the old rotor arm heating up once the engine was off for a short while after a run, or stuck in traffic. It keeps cool enough ( just ) untill residual block heat warms it up when there's no passage of air through the engine bay. THEN...at start up it satarts arcing and runs like a box of nails for the rest of the day! New rotor arm..problem went away.
Secondly, other contributors are quite right, if it is evaporation, it's unlikely to be pipes, more lilely in the carb itself and a thermal gasket between the carb and manifold will help. Even better, a gasket and a home made heat sheld between carb and manifold.

Trampintransit you are right about the insulation blocks for carbs and home made heatshields, I have done both but have only improved the situation not cured it. The dashpots of the twin SU's are still too hot to handle after a run and shutdown so the carb body must be similarly affected. Old style petrol didn't mind this, in fact it probably aided atomisation.