Hiya all, it appears my heater flap is not working in the neck of the oil bath air filter, tried hair dryer, no movement. Mine is the type with no cable linked to heater flaps of which mine are missing, surprise, surprise. Has anyone out there got the small brass thermostat that operates the flap for sale?, they don't appear to be available but i could be wrong. If i can't fix this should i fix the flap in the 'open' position or leave the 50mm dia warm up pipe off or both?. I've always experienced engine getting hot on long hills ,loaded up etc could this flap not opening when engine is hot be the reason i wonder.
Tricky isn’t it? Hot engine or carb icing? I’d try to get it working if I was you after advice on here. Mine has the thermostat in the top and that part is still available. Surely you can get the part with a good look?? Sent from my iPhone using Tapatalk
I expect that the only place you will find exactly the correct part is on another very old air cleaner. However, wax thermostat capsules can be found in domestic radiator TRV valves. Something may be creatively bodgeable. Otherwise do like they used to on BL air cleaners. Set the flap to hot in the winter and cold in the summer. It might be easier to score a more modern vacuum/ thermoswitch operated air cleaner from the likes of FBI VW or Megabug, or at a swapmeet. [Only 50 years rather than 60 years old...] And flogging your bus up a hill will get it hot. Just make sure you go down the next hill in third gear at 45 mph / 4000 rpm to maximise cooling air and save the engine. Dont turn off at the top of the hill...
I 'm thinking the winter/ summer setting idea is a good one. Another thing i don't get is why does the carb have hot air rammed into it from No2 head when all petrol engines run better on cold air induction, especially as these engine run hotter than water cooled ?. Maybe a winter / summer option too?.
Because they have such long manifold runs the air needs heating to keep the fuel in suspension. The manifold is also heated from the exhaust gas.
If you have the later vacuum operated flap its more clever. At idle with a cold ( less than 30 deg C) air intake, the manifold vacuum sucks the flap to hot air position. This compensates for the temperature drop through the carburettor and helps keep petrol as vapour. As you open the throttle the manifold vacuum drops and the flap moves to the cold air position for efficiency. Once the little thermo valve on top of the air cleaner reaches 30 degrees C, the flap will stay in the cold position. All your older design can do is try to keep the intake air reasonably hot by adjusting the flap, through the wax capsule being in contact with the air cleaner body. Even stock dual carbs have hot air feeds as they cool the air thorough the carb and are improved by the warmer air. If your bus engine is getting really hot, its not really the temperature of intake air that is the issue, its about 20 cubic metres of cooling air for 3 cubic metres of air intake per minute ( 1600 cc@ 4000 rpm is 3.2 cubic metres on a 4 stroke engine) On a T4 its scaled up to 23 cubic metres and 4 cubic metres intake air. Its the heat generated from combustion and the way that heat gets carried away from the engine : how much hot gas hits the heads and pistons versus how much goes out the exhaust: your compression ratio, deck height, timing, mixture will all have a bearing on how hot it gets. And if you reduce cooling air flow by sitting in 4th at 40mph instead of 3rd at 40mph for instance, the engine will run hotter for the same power output as the cooling airflow reduces with lower RPM.
I have 1600TP engine with Solex 34pict3 carb and oil bath air cleaner. When I bought the van, the air cleaner thermostat had been removed. The heat risers are both fine and warm up the manifold very quickly and only in the coldest winter is there some manifold/carb icing but that doesn't last long and soon melts. The choke works perfectly as it should. My engine starts and runs fine and no hesitation or rough running on cold winter days, runs better with all that cold air. The MGB has twin SU carbs with simple stock style paper air filters, no heating or flaps or anything else and the car runs fine in all seasons and in the winter it loves the cold damp air. There are a lot of Bay owners out there who have simple pancake style air cleaners and they run ok.
The SUs on the MGB have short inlet manifolds and fun and games with oil leaking out of the dashpot and dashpot air bleeder blockages on my neighbours TR3 . On my bus, I found severe hesitation when running without the proper air feeds. So I reinstated them. If you jet your engine really rich and drive very gently somewhere you dont have to accelerate hard in the first ten miles you may get away with it. Personally "headbutting the steering wheel" wasnt pleasant.
Do you think the hot air pipe from No2 cylinder to the air cleaner is best left connected even in the summer, loaded up with camping gear etc on long trips?.Mines off at the mo with hole in tinware sealed but can be easily reversed. I've wired the flap open that's supposed to be operated by the wax thermostat. My heat risers were supposed to have been cleared out during my recent engine re -build but the left hand one still doesn't heat up any where near as quick as the right hand one. Thank you for the input folks
Very interesting info, i believe the timing , mixture etc is ok, i wonder if the thermostatically operated flap being stuck shut (in the air filter) was part of the problem of getting hot when labouring up hills especially in hot weather.
VW classics in Germany had them a couple of years or so ago. Try contacting them direct rather than through vwheritage.
I have twin 1.75" S.U.s on my Triumph Vitesse Mk2. I agree about running smoother etc in damp air, proper choke too.
SU and Stromberg carbs are variable venturi carbs a totally different design to fixed jet carbs and suffer less from icing but still can and usually have air cleaner inlets which can be directed to the exhaust manifold in winter.
With a stock exhaust the heat is meant to flow from one side as the heat risers are vented to the tail box one side, and connected to the exhaust pipe near the head on the other. It should be really hot, like so hot that oil smokes off, as the exhaust gas should reach the manifold. And colder the other side as the hot gases have heated the manifold
