Just got back from a short (25 mile) run and had some hesitation when pulling away on the way home. I immediately suspected that the engine was too cool as it ran fine on the way out and after sunset the air was noticeably cooler. It's fitted with electronic ignition which is all strobed up correctly. I overhauled the PICT34 carb in the summer with a new gasket set and I think the accelerator pump is giving a sufficient squirt at the right time, so I don't think it's anything like that. However, I noticed when running it around this summer (I've only just got this on the road and must have done less than 200 miles) that I had hesitation until the motor had been running for ten or fifteen minutes. I noticed that the pre-heater tubes didn't get as hot as I expected (no leaks or anything like that) but didn't worry about it too much. Can any of you experienced air-cooled people confirm my suspicion that the likely culprit is the pre-heaters? When I got home I popped the engine bay lid and the inlet manifold was stone cold and so were the pre-heater tubes at the manifold end. I think the hesitation was worse after a 55 mph run along about five miles of dual carriage way (during which it ran exceptionally well). My theory is that when running around at low speeds the engine compartment gets warm enough for it not to be a problem but a higher speeds all the heat is drawn from the manifold. Words of wisdom appreciated
It could be, particularly if the manifold is cold enough to have condensation/ice on it. Is your fan housing set up properly with the flaps, linkages,thermostat?
The thermostat and flaps were removed by the PO. He also left off most of the important engine tin, but I've put all that back except for the thermostat etc. I'm assuming that the pre-heater tubes should get as hot or almost as hot as the exhaust headers, but they don't even get warm at the manifold end.
I don't know much about 1600 engines, but I remember seing a post on here about some preheater pipes that were completely blocked and furred up. Could this be why the heat is not getting through? I have had a quick look for the thread, but it was a while back.
As silver said, might be worth checking the riser pipes aren't blocked, but i'd say it's more important to put the thermostat and flaps back in because it'll make the whole engine run cooler not having them in this weather. This used to happen to mine years ago before i learnt more about them, in mid winter it would idle,people reccomended electric manifold warmers are all sorts. Then i found out it had no thermostat of flaps and when i put them in it worked fine.
Are the preheat pipes actually connected to the exhaust? They should at least get hot by conduction, even if they're blocked. More important is the warm air feed to the air filter - is this working? Don't worry about the thermo & flaps - this only has an effect when the engine's cold. Once the thermo's open, it's open for good. May be manifold icing, but I'd say also may be the carb. If anything, the engine should run noticeably better in cool air.
Just spent the afternoon unblocking the pre-heater tube - it was completely blocked. Used the bowden cable and drill method which was time consuming but worked really well - getting full flow from the airline now. Will get everything back together tomorrow and let you all know if it worked. My bus was f**ked about with by the PO and currently has an aftermarket pancake air filter so no warm air intake - I'll be putting a standard one on ASAP (it also has a K&N type crankase breather filter which makes the engine bay and hence the heating smell oily). It had a Marmitee exhaust system on it which I've returned to standard - the ends of the pipe were connected but of course there's a gasket which is a surprisingly good insulator. Not planning on using the bus during the depths of winter so don't imagine the thermostat will be an issue - however I'd much rather have everything back to standard. I do wish people wouldn't attempt to "improve" things they don't really understand.
Where do your fuel breather pipes go if you have a pancake filter? If you get a stock filter you can reinstate those as well as the crankcase breather should get rid of a few more smells. The heat riser does get hot enough to burn your fingers, I've done it You might not need the air filter preheat, parts might be difficult to find anyway.
Problem solved . Went out for a spin this afternoon and the pre-heater and manifold now gets hot. I notice that the direction of travel of the exhaust gas through the pre-heater tube is from left to right. The left hand end gets too hot to touch (over boiling point) and the right end is hot but most of the heat given up to the manifold. Next job: replace the air filter - anyone got one?
Get an air filter that matches the bracket in your engine compartment. Round = oil bath, straight-sticky-out = paper air box. I'd prefer the latter.
