Winter Layup - 1995 Ducati 900 Supersport

[Kickaha]

You have a rubber bandy one?

It belongs to my brother, needs revinning

[OddDuck]

Just back last night from a 900 mile, 3-day trip. No issues with the bike aside from a front tyre nearing the end of its life and going a bit triangular.

It's time to do a few courses and also a couple more track days. Skills are going rusty and in some areas are slipping backwards. I caught myself projecting over the centerline on right hand turns quite a bit, also failing to lean more if a corner tightened up.

That last one - failing to lean more - is a nasty legacy from my first bike, a POS Honda Wet Dream with ancient rock hard tyres. They'd walk sideways even in the dry and in the wet the bike would skid like hell. The tread was just above the legal minimum for the WOF but always made it... and never seemed to wear down. I thought this was normal and never changed the rubber. Oops. Absolute first thing I should have done, along with going to a track and seeing just how far the bike can lean and what it's like to ride banked over.

The trip's been great. I went up with a mate, we went looking for back roads and twisties, and generally stayed off the arterial routes. It worked. Very low levels of idiot driving seen, very high levels of everyone getting along instead. One feature of the back roads, and out of the way places to pull up and have a bite to eat or a coffee / pint, has been how approachable people are. Directions, information, or just having a laugh - there's been quite a bit of that.

It was a big quadrangle across the lower North Island - Lower Hutt, Pahiatua, Ohakune, Whanganui, back through Pahiatua again and not too many bits repeated. I'll stay away from a detailed route description, it wasn't that kind of trip anyway. We'd get the maps out when we'd stopped and just go looking for the next bit of something we hadn't ridden yet. If it was off a main road, not gravel, and going roughly the right way then that was what we'd do. This turned into a fast way to find a lot of really good roads to ride, with the occasional patch of gravel or single lane country road to deal with.

There was a change of plans. Originally we were going to take two days and split up in Whanganui. I'd either go further north or just head home. We got to Whanganui about 6 and we were both getting pretty tired. I listened to his advice and dumped the schedule, adding an extra night to the trip and carrying on in the morning. Good call, both for fun and safety.

Full thermal kit got used on the first day and it was needed. It got bloody cold around Waiouru, especially after dark. No rain though.

Near misses: I had a small group of sheep run out in front of me once and some idiot failed to give way properly at a roundabout in Whanganui, no contact on either occasion. That was it. Fantastic trip all round, home very tired but safe and happy, today is going to be about recovering instead of riding more. Time to go wash the bike and read the paper.

[ruaphu]

Yep love those kind of trips, no real plan, just a general direction and an occasional consult of the map to see 'where else' can be ridden out of the usual routes. Makes for interesting days at times. Good to hear the bike is running well and the comments on skills. Take care eh. Btw, great thread, enjoyed every entry.


Sent from my iPhone using Tapatalk

[AllanB]

The tread was just above the legal minimum for the WOF but always made it... and never seemed to wear down. I thought this was normal and never changed the rubber. Oops.

Hear ya. I had a Kawasaki for years - had done minimum kms on it at one stage for a year or so and had parked it up over winter. I got it out for the summer, handled odd - not as I remembered.

I went through everything - new wheel bearings, checked, greased and reset steering head bearings, changed fork oil. Checked wheel alignment. Pissed around with tyre pressures. Told the shop about it as they new the bike well - I purchased it off them new. The owner asked about tyres - heaps of tread, good shape, great brand. How old? Hmmm checked my log book - can't recall how old - maybe 4 years. We did the old fingernail check - hard. Very hard. New rubber and it was back to normal. He reckons they went 'off' due to low use, age and sitting over the winter period.

[OddDuck]

Interesting that it went from OK to off just over winter. I know they die from old age but that seems like a very short time of not using it for the rubber to go hard.

This current tyre wasn't used for nearly six months but it was still OK when returned to service. It did wear out though. Old rubber rooted, replace with new... S20 Evo gives way to new S21.

The photos are shot from the front. I tried to show a hollow on the right flank of the worn-out tyre; when cornering right, it felt like there was a very abrupt weight transfer toward the edge of the tyre. The bike would change what it was doing quite dramatically with just a few degrees more lean angle. It got downright scary in a few corners toward the end of the day.

One thing about the Evo's was that once they started wearing, they'd go fast... this tyre went from tread and wear bars to as-pictured in just three days of high mileage riding. That said, I didn't think it owed me anything more. I'd got 7,500 miles out of it, not bad for such a high performance tyre.

Doing a spot of light maintenance while changing the wheel, cleaning and re-oiling the fork tubes... one thing about USD forks is that brake dust will collect on the slider legs. The dust seems to lift oil but retain water, or do something similarly corrosive. I'd found the beginnings of rust spots forming through the chrome about two years ago. This is bad news because if the fork is bottomed out, the sharp-edged rust can cut the fork seal lips and cause an oil leak.

The rough fix was to very carefully blend the rust spot's sharp edges with the finest wet'n'dry I could find, 2000-grit I think. Obviously the mirror chrome finish in that area is ruined, but it works for now. The only real fix is to have the legs ground and re-chromed. It's not worth that sort of expense for these forks, they're the cheap non-adjustables of the Ducati range. In the meantime, keeping it clean and protected with a layer of rag-applied fork oil is working to keep the rust spots stable.

The last thing I did was have a go with a different technique of chain cleaning. I wanted a method that was reasonably quick, cheap and easy, since (according to the box for the DID chain) it's supposed to be cleaned and lubed every 500 km's if I want to get the maximum life out of it. 500 k's isn't going to happen, but every thou or so would be nice.

How to clean your chain... cue massive debate. Everyone's got their own method. I used to use a very involved procedure with water based degreaser, low pressure hosing and the like, but it's a marathon. Time to go simple, fast and effective.

Kerosene in an old tin (the DID box specified this as the preferred cleaning agent), paintbrush, rag, nitrile gloves, and the left muffler removed for access, and I had a clean chain in about twenty minutes. Rags can be had out of the better auto tool shops (like Twigg's) for about $45 / 10 kgs or so. Engine was left off of course, rear wheel or chain turned strictly by hand.

Leave the engine off. Really. The world's got quite a few bikers and ex-bikers in it who've lost bits off fingers and thumbs - or worse - while taking the easy route of running the engine in order to pull the chain through the rag. That rear sprocket loves to suck things in. It's only bloody obvious after it happens... don't let it take your hand.

That done, I re-lubed the chain (without a quick fang to the shops and back to shake the kero off first, which should be done next time), then geared up and took the new tyre out for a proving ride.

Awesome. I'd rated the S20 Evo the best tyre I'd ever ridden (admittedly limited experience), the S21 is just as good or even better. The bike is utterly planted and in control, it does exactly what it's told to do.

[SVboy]

I use a similar chain cleaning method, except I finish off by washing the chain using a hose, then ride the bike to dry the chain and get some heat in it. Then I use chain wax and let it penetrate and dry over night. I love the S21s. Bridgestones best tyre so far?

[OddDuck]

I can't speak for the rest of Bridgestone's offerings but the S21's are fantastic alright. Unfortunately I think I've got a slow leak in the front tyre or valve. I'd found it at around half inflation the other day and will have to be checking pressure every couple of days for a while. I've no idea if there's a fix for this yet, or if the problem will settle down.

I've been tuning the carburettors again. Just a couple of practical notes, for anyone else doing this... very often the carbs are positioned so that it's difficult or impossible to get standard tools in. Sometimes even jeweller's screwdrivers won't fit. The safe option is to pull the carbs off the bike completely so that you've got control and can see what you're doing. Petrol everywhere of course.

Then it has to be done again, and again... Bit of a hassle, then I remembered something and got the mountain bike multi-tool out. I took the tool to bits on the bench and got the flat-blade screwdriver out on its own. This was nearly perfect for working on jets, screws etc in situ, because it was the right size and shape, and the P-end gives enough of a handle to work with as well as good position control. A while ago I'd bought some hex-ended drivers for this type of work, the kind of bits intended for a drill driver, and they work for the fuel mixture screw but aren't long enough to get at the slow fuel jet.

The paintbrush is useful for getting accumulated dirt and grit off, before taking inlet trumpets or float bowls off. Gotta stop dirt falling into jets, wedging seam lines open, or similar. I've found that synthetic bristles will be the right combination of stiff / flexible for the job, they'll go into corners and so on, but they'll loosen dirt up nicely. Stuff rags into carb throats first of course, it's amazing how dirt can move around during this job.

The sensor for the AFR gauge had been mounted on the header pipe off the horizontal cylinder. That means that it's under the engine and in the firing line for gravel off the front tyre. Dents on the sensor housing are visible in the photo. The manual warns that the sensor is vulnerable to shock and shouldn't be dropped or subjected to vibration, so this is obviously not good for it.

It's obvious in hindsight, of course... the underside of the fairing has been ripped to shreds. I just hadn't expected to see this so soon.

Now this is pure speculation... I don't think the front wheel spits bits of gravel out at high speed. I think that what happens is that it pulls gravel upwards as the wheel passes over, either by the rubber sticking, or suction. The gravel then goes straight up relative to the ground and encounters the bike, at whatever speed the bike was doing. If that's (ahem) 100 k's, well, that's probably going to chip the paint.

Anyway, I'd found out what I needed to know: there is a difference in mixtures between the two cylinders, but it's slight. The horizontal cylinder runs about 1 point leaner than the vertical cylinder. Given how much the mixture ratio can vary, it's not usually that big a deal except near closed throttle. I'll check the horizontal cylinder readings again once I've got more tuning done, in the meantime the sensor is going to the vertical cylinder header again, safely tucked behind the engine.

[OddDuck]

And here's notes about the carburettor tuning itself... the slow jet kit arrived earlier in the week. It's not Keihin genuine, this was a pattern part set made by A-Bax Engineering and distributed by EBC Brakes, via Amazon. I've been wanting these for a very long time. An ongoing problem has been an over-rich condition in the vertical cylinder, leading to carbon fouling of the plug, piston crown, head, ports... I've done everything possible with the mixture adjustment screw and slow air jet screw, but there's no getting around the jet size.

So, I changed these slow jets from 60 to 52 (horizontal) and 50 (vertical), used the AFR gauge to get the bike running with a ratio of around 13 in each cylinder, went out on a ride and promptly had problems with lean running at 1/4 and mid throttle. I didn't manage to get to full throttle but it became very clear that there was a lean problem. I also encountered serious problems with starting the engine, both first thing in the morning and after the bike had been sitting outside for a few hours.

This led to a session with this excellent guide (shame the charts don't seem to come up):

http://www.factorypro.com/tech/tech_...Burns,Pat.html

My method for learning this stuff has been:

Read a bit
Do a little work
See how it goes
Find the problems
Read a bit more and repeat

It's iterative and hard work sometimes but there's just no learning it all in one go. This time I've finally appreciated how important the slow air jet screw really is. This single screw covers a jet range of 45 to 155. As Pat Burns points out (and as I think I've just found out for myself) this also affects mixture quite markedly at high revs and moderate throttle openings, as encountered cruising the highways and back roads. I'd been running with the screw 1.5 turns out, equivalent to a jet size of 125.

The bike's also, quite persistently, been running rich at low throttle but increasingly lean as the throttle opens up. I'd been thinking for some time that I had the wrong needle taper, but changing the slow fuel jets really highlighted this behaviour. If the slow air screw is the main reason that it's been rich down low but lean up high, it's a lot easier and cheaper to have a play with this before getting into changing needles around.

Further reading also showed that it's quite naive to tune for a constant AFR reading. I'd been aiming for 13 to 14 throughout the throttle range... it's not that simple. The engine will have a sweet spot for mixture tuning at each throttle setting. Near closed throttle, this sweet spot is best found by ear, not by AFR reading. The technique is to idle the engine (once warmed up), blip the throttle, and see how it settles to idle again. If it hangs at high revs before settling, it's running lean. If it drops below idle speed and then comes up, it's running rich. So far it looks like the engine quite likes to run at 11-12 AFR near idle.

Anyway, I left the 50 / 52 jets in place and tried some work with the slow air jet screw and idle mixture adjustment screws. Interim carburettor settings are now:

Slow Fuel Jet: 50 (vertical), 52 (horizontal)
Idle Mixture adjustment screw: 2 turns out, both
Slow Air Jet Screw: 1 turn out, equivalent to 100 jet
Needle position: 6th from top (I still don't know what needle I'm using; there are a whole family of these, with 3 letters stamped on the needle somewhere)
Main Jet: 220 (both)

and of course I'm using the pod filters, which dramatically change how the engine breathes, and which is why I got into all of this in the first place.

[OddDuck]

In the previous post I'd mentioned issues when starting. THe Keihin FCR41's don't have a choke. Voltaire has mentioned starting difficulties with his FCR39's.

A memory that stays with me is being on the road with a mate and trying to get going, first thing in the morning. It had been a cold night, the bike was stone cold, and I had to crank the hell out of it to get it to catch. Then it was gutless for at least five minutes, until it warmed up. In the meantime he zoomed off, while I was desperately trying to not lose him in a strange town, with no arranged meeting point, and the bike stalling every time I tried to open the throttle up... Very frustrating.

There have been times in the middle of winter when it wouldn't fire at all. Crank the hell out of the motor, listen to it fail to catch, get really pissed off with it, keep on trying but the motor just won't fire up. It was certainly a pig to start when I'd been trying to get AFR ratios of 13-14 at idle, I really struggled first thing in the morning when trying to get to work.

Following last night's efforts with the slow air jet screws, that problem has gone away. It's catching, from cold, at the first stab of the starter button. I haven't yet checked the plugs for fouling (AFR tells me I'm running 11-12 near idle, lower than 11 closed throttle), but the motor seems to be happy enough. It might be a very different story when I can get out on the road properly, but there's definitely something to this business of tuning the motor by ear in the lowest 8th of the throttle range.

It got me interested, though. Why would a petrol engine have trouble starting, and what fixes can be applied?

I did my reading, or tried to. There's very little public information about the technicalities of a cold engine start (sometimes I like to nerd out with thermodynamic theory and calculation; no luck this time). About the most that I found was of course 'the choke', deliberately restricting inlet air flow to force a richer mixture so that the engine would start.

It's a pretty old-school solution. It guzzles fuel, it pollutes like hell, and I'm pretty sure it helps to coke up engines or wash piston rings down. But it's cheap, it's easy to put in place, and it works. That's about as far as that's got, with petrol engines anyway.

Then I stumbled across what happens with diesels. Apologies to those of you already in the know, this was quite something to me since I'm from a petrol background.

It turns out that cold starts are a massive problem for diesels, particularly those engines intended for winter / mountain / arctic conditions. Diesels depend entirely on heat of compression for their ignition. If you take a cylinder of air and squash it, hard and fast so it doesn't lose heat, it'll cause oil squirted into it to spontaneously catch fire. No spark needed. This falls down if the engine's cold enough and the intake air is cold too. The heat of compression is lost to the engine and fuel injected into the cylinder won't do anything, since it doesn't ignite.

The engine would heat up in a hurry if it could catch... but until it's compressed enough air enough times that the cylinder has warmed up, it won't fire at all. You could be cranking that starter for a half an hour, and if it's losing heat at a fast enough rate (like in a blizzard, for example) you might never get there at all.

I'm fairly sure that similar happens in petrol engines. When the spark fires, there's a tiny bubble of burning vapour. It's got an internal volume and a surface area. The internal volume carries its heat, the surface area radiates that heat outward. Spheres have tiny internal volumes relative to surface area when they're small. If the surroundings are cold enough, they'll quench that bubble of combustion before it has a chance to expand.

We're all familiar with that burp-burp-burp sound of an engine being turned over, sparking, but not quite catching.. this might be what's going on in that situation. People talk about three things being needed to make an engine fire: fuel, air, spark. I think that during starting we need to include heat as well, the old fire triangle coming into play here.

Among other solutions, diesels use air pre-warmers. They deliberately heat up the incoming air. These tend to be very robustly made heater elements mounted inside a flange, for fitting somewhere in the intake system. The heater elements are made for good thermal connection to the airflow, while not impeding it. A figure I remember for power was a 2.7 kW heater (!) for use with an 8 litre engine, so it looks like they take this stuff quite seriously.

This got me curious, so I had a look at power requirements for air pre-warming for my engine, assuming normal (unassisted) starting would work down to about 10 C, and starter motor cranking speed for my engine was around half idle, say 450 RPM.

There's a useful power source for heater elements already fitted to the bike: Oxford Hot Grips. I checked output voltage and it's 12V, pulse width modulated (25%, 50%, 75%, 100%) depending on setting. The grips are around 7 ohms each.

That means there are two heaters, of 20 watts capability, already on the bike. It's obviously not going to work to try to use the grips to pre-heat incoming air, I'd have to fabricate a custom heater element around the intakes and switch power to it... but what does 2 x 20 watts do, in terms of pre-heating air while cold cranking?

Without going into detail in the calculations, it works out at something like 6 degrees C of warming inlet air up. There's enough power while cranking to do this without affecting the starter motor or ignition, just turn the lights off.

Experience with the bike (OK, with original carburettor tuning) was that it was fine to cold start down to about 12 degrees. Below that, quite abruptly, it became a real mission to get the motor to catch. 6 degrees pre-warm doesn't sound like much, but it might be just enough to make the difference on a winter morning.

I gave this idea a go with a hot air gun and indicated inlet surroundings temperature of 40 C. It seemed to work, but conditions were cool, not cold, and at this time I can't remember if this was with the carburettors tuned lean idle or not. It's a crappy proof of concept, the real test is one of those mornings when breath can be seen on the air, but we haven't had a morning cold enough lately.

In a pinch, on the road, this could be done on tour. Hot air gun, extension cord, power socket from the motel room. I'm not sure I'd want people seeing me do this, though.

[swbarnett]

Interesting. It explains something that I really hadn't thought much about for the past few decades. My wife and I used to have problems with our CB250s on cold mornings back in the '80s (when there were cold mornings). They just wouldn't start until we threw a bucket of hot water on the engine block. After that they would start first crank.

[Ocean1]

My 525 has been hard to start forever, especially on semi-stale fuel. And yet once warm it's fine.

Sticking a 2Kw fan heater under it for 5 minutes works very well.

[OddDuck]

The past couple of weeks has been:

- first attempt to fabricate an induction pre-heater, for starting
- more carbie tuning.

I'd re-read Pat Burns excellent FCR tuning guide and finally noticed this paragraph (important bit in bold):

Main air jet:

If you find that the engine runs perfectly at WOT near the torque peak, but becomes lean toward redline, select smaller main air jets. Conversely, if the engine runs perfectly near the torque peak but richens toward redline, select larger main air jets. Changes in air jets may require changing the main fuel jet. Say you have good performance at engine speeds leading to the torque peak under wide open throttle with a 150 main fuel jet and 200 main air jet. Should you need to richen the mixture at full revs and full throttle and select a 180 main air jet, you may need to go down to a 145 or 140 main fuel jet to keep the lower rpm mixture the same as with the 150/200 combination. Generally (there are always exceptions), once the main air jets are properly selected for the intended application, they need not be changed again unless you change the intake restriction (modify the airbox or use different filter) or change engine or exhaust specification. Varying atmospheric conditions can usually be dealt with by fuel jet, fuel screw, and needle changes.

Now why didn't I notice that the first dozen times I read this guide. I have definitely modified the airbox: it's been changed for K&N RU1750 pod filters.

I've been battling rich down low, lean up high pretty well forever. Maybe this was what was going on, instead of it being the needle taper I'd been obsessing over. I went and found an NZ supplier for the main air jet (thank you Motozone) and promptly ordered a few sizes down from the 200's fitted to the FCRs as supplied. Tuning runs followed. Listen to motor first, check AFR gauge second.

Conditional success. I now have a bike running OK through the useful riding range. Although I'm sure there's room for further improvement, here's current tuning, for anyone else podding a 900SS with FCR's:

Needle: EMT
Clip Position: 6th from top
Pilot Jets: 52 (horizontal), 50 (vertical)
Idle Fuel Screw: 1 turn out (both)
Slow Air Screw Jet: 1 turn out (both)
Main Air Jet: 148 (down from 200)
Main Fuel Jet: 220 (although this is wide open to review)

There's one very important factor in this tuning: adding to the insulation I'd placed on the intake stub pipes.

These dinky little intake manifolds have a huge effect on mixture strength, how the engine runs, exhaust noise etc due to what temperature they happen to be at. In their as supplied state, they basically aren't insulated from the cylinder heads. They get hot. They get stinking hot, in fact... touch them to check how hot they are and you're courting burns.

As they get hot, they heat up incoming air. This reduces air density. A fuel-air mixture will need less fuel to have the same AFR ratio. However when you're starting that motor, everything's cold. You'll need a richer mixture to get the same AFR ratio, let alone something rich enough to start a cold motor. A carburettor obviously doesn't compensate for this temperature variation, so tuning the carbies for closed throttle operation has always been a tradeoff between running ridiculously rich while tootling around town, or the bike not starting at all on a cold morning.

Right... what if they didn't get that hot while running? Wouldn't this reduce that tradeoff in carb tuning?

I'd been to some trouble to insulate the stud bolts, the major conduction path. It reduced the problem greatly but didn't quite eliminate it. With this in mind, I did something I've been meaning to do for a while: making the paper gasket between head and pipe a bit thicker. The OEM Ducati gasket is all of 0.4mm thick. I bought a 500 x 500 piece of 0.5mm gasket paper - good stuff, PTFE-coated, German made, rated to 200 C - and cut an extra couple of gaskets for each inlet, effectively doubling or tripling the heat resistance.

The gasket paper itself deserves a mention. Repco, Super Cheap Auto etc are the obvious places... all they've got is Flexovit. It's not coated and (as I'd found out for myself) it crushes over time, petrol exposure, and under heat. It's simply not up to the job. The paper I'd bought was three times the price I'd paid for the Flexovit and about ten times the quality... go to an industrial seals supplier (I used Seal Imports) and have a chat with the bloke about what you're doing, go in cashed up and try not to wince when you hear the price.

The OEM head studs also weren't long enough. Replacement involved purchasing what I could find and cutting the cylinder head threads a bit deeper into the plain portion of the stud.

Threadcutting: die nut. Holding the stud, without munting the threads in the vise, involved taking a pair of perfectly good plain M8 nuts and putting a hacksaw through one flank, turning them into threaded 'C's. This meant they'd crush in the vise, clamping stud threads with a mating threaded surface, and thus gripping the stud without damaging it. It turned out to work brilliantly for filing / hacksawing, threadcutting turned the stud in the nuts until it stopped and then it'd cut... but it still worked.

Anyway... the insulating bushes on the mounting studs were a good start, the thicker gasket paper has got me the rest of the way. The inlets are now only just a bit warmer than ambient, even if the bike has been running for a while. I might have to thin them down again for winter but for now they're working just fine.

As to pre-heating, to aid cold starting... no pictures for this as yet. I'd had the idea of constructing a wire heater element, mounted immediately around the outside of the pod filters, and had gone shopping. The design was a fibreglass plate top and bottom of the pods, with Nichrome heater wire strung back and forth between them. There'd be many passes, to cover as much pod surface area as possible, and several elements in parallel, to balance electrical loads vs wire resistance.

Then I realised, before building it, that it's just not a good design. It's fragile, it's clunky, and the wire is a very real fire hazard. Aside from anything else, the wire is going to be shaken mercilessly by engine vibration and turbulence from intake air. It'll break by fatigue early and often. Nope. I need something that'll last. Then I realised, I already know that inlet air is heated by hot inlet manifolds. The heater element doesn't have to be in intimate contact with inlet air; it just has to warm up something else that already is.

The current plan is to go shopping for a pair of band-clamp heater elements, designed to fit onto piping, and fit these to the outside of the inlet stub pipes. I have no idea yet if anything's available in 12V / 38 mm. In theory it's got a lot of advantages: I can use the thermal mass of the inlet pipes to store energy, the heater itself can be robust and MIMS (Mineral Insulated, Metal Sheathed), and it's ultimately just a bolt-on modification, not something fabricated. I can also use safeties like bimetallic switches against overheating. Right, further browsing / shopping / building to do.

[pete376403]

For inlet air heaters - how about looking at diesel engine glow plugs : 12volt, robust, probably screw into something so easy enough to mount. Find some up at pick-a-part. For your application they only need to operate under cold start conditions, right?

[AllanB]

Is there a special set of screw drivers or something Ducati mechanics use for carb tuning? Bet they don't remove them in the shop.

[OddDuck]

For inlet air heaters - how about looking at diesel engine glow plugs : 12volt, robust, probably screw into something so easy enough to mount. Find some up at pick-a-part. For your application they only need to operate under cold start conditions, right?

Apologies for the delay in replying, been doing a lot of study and thinking... I had a look at this and the glow plugs are only a good idea if they're heating the inlet stub pipe from the outside. They really do glow, we're talking 800 C plus. I'd have to fabricate a clamp-on, blind bracket of some kind and rely on bulk heat conduction through metal, with fuel-air mix kept away from direct contact.

The glow plug relays that go with them are seriously interesting, though. These are exactly what I need. Timeable from 2 to 30 seconds, able to handle high current, and cheap as chips (out of pick-a-part anyway).

Alternatives. I'd looked at band (nozzle) heaters, there's a page of them here: http://nz.rs-online.com/web/c/automa...heaters/?sra=p

Unfortunately the inlet stub pipes have a flange at one end, then a curve and a rubber boot on the other. The only bands able to get over the boot and around the curve are too long to fit on the straight length available on the pipe. This is the thing about this kind of work - one detail that doesn't match up and that's it, no can do. Then I remembered something from work and realised that these things could work:

http://nz.rs-online.com/web/p/silico...-mats/0245528/

These should go on reasonably easy, I can wrap around with some thin stainless on top and hose clamps to secure the assembly. No fabrication needed. They're only 5 watts but since the inlet pipes can store a reasonable amount of heat, it's worth a go.