Zel's Fleet Blog - BX, Jag XJ-S, Sinclair C5, Mercedes 208D & 230TE, AC Model 70.

[Zelandeth]

Now..... Mr Iain Tyrrell of classic car fettling fame manages to do an exceptionally good job of balancing carbs with nothing more than a length of something like inch-and-a-half hose and a working ear. He's demonstrated the technique and - providing you've got at least one working ear - a decent job can be done by all most.

I suspect they've got rather more experience in this than I have! Thinking back through my back catalogue I believe this is the first car I've owned which has twin carbs. You kiiiind of had to balance things on the Jag, but that was purely syncing the throttle plates to ensure they started to open at exactly the same point and checking with a CO meter at each tailpipe to make sure the numbers matched. The IAC valve pulled from the left hand intake anyway so you'd always have far more draw on that side (which was evidenced by how much dirtier that air filter got!) than the right, which would preclude using any sort of pressure differential reading usefully.

The whacking great direct drive fan on the Rover wouldn't help doing things by ear either as I think all you'd be able to hear would be wind anyway! Does kind of surprise me they didn't use a viscous coupling on it given how many other lengths they went to to ensure that the car was quiet and refined, yet still sticking with a cooling fan that sounds like a 747 throttling up for takeoff anywhere above about 3000rpm.

[MattBLancs]

Given the long in service life of the Rover V8, could you retrofit a viscous fan? Improvement in noise but also potential efficiency improvement too - those big fans consume a surprisingly large amount of power.

Suppose equally a Kenlowe electric fan instead would give the same benefits (though more load on the alternator (presume not a dynamo?))

[xantia_v6]

I thought that the P6 V8 had a viscous fan coupling. The SD1 certainly did.

[CitroJim]

I misread that! Mind you, cooling fans can be a bit vicious...

[Zelandeth]

Given the long in service life of the Rover V8, could you retrofit a viscous fan? Improvement in noise but also potential efficiency improvement too - those big fans consume a surprisingly large amount of power.

Suppose equally a Kenlowe electric fan instead would give the same benefits (though more load on the alternator (presume not a dynamo?))

Biggest issue I imagine might be space (which may well be why one was never originally fitted).

I'd be wary of swapping to an electric fan simply given that under bonnet temperatures are known to be an issue with these cars at the best of times, so losing that continual airflow whenever the engine is running could exacerbate that problem.

[bobins]

For anyone wondering how you tune a carb with a bit of hose pipe, here's a youtube of Iain Tyrrell tuning up a V12 LamboDiddley using that method. Video starts at the point of him actually using the pipe. The concept behind it is actually quite sensible. Anyone who's ever used an automotive stethoscope on a car will know how well it transmits the noise you're after, and this hose pipe method is much the same.

[CitroJim]

I wonder if you can still get a Gunson 'carbalancer' kit?

When I ran motorcycles I used to have a mercury manometer for this job... Easy to build one and the best way to do the job really. Only problem is the availability of mercury these days. It costs over £1800 a kilo for a start.

If you know any old classic bikers Zel, they may still have this apparatus in their garages...

I can confirm Robin's 'by ear' method is good, used it a few times in the past on bikes before I got my manometer... Slip off your fanbelt for the duration if the fan is a bit too noisy but in practice you'll likely find it won't be a problem.

[bobins]

I've got the modern version of the old stylee mercury manometer kit, the newer ones use a Titanium (?) slug in the tubes. The vacuum pipes on the manometer have slight restrictors in them to even out induction pulses. I think the motorbike ones rely on having a tap into the individual intake pipes so you can take the running readings without having to remove the air filter and associated fittings, whereas I doubt you'd find such a take-off point on a lot of car set-ups.

[Zelandeth]

Manometer. Thank you. That's the word which my vocabulary was absolutely refusing to allow me to find yesterday evening.

Good point actually on finding a good manifold vacuum tap. Probably the closest thing on the Rover would be the ports normally used for the PCV, which is ported in between the metering piston and the throttle plate. Should do the job here though as all we're interested in seeing is the relative figures between the left and right banks. I think!

[bobins]

You're welcome to borrow my Carbtune kit if you think you can make it work, Zel.
On my motorbike I have to set a very specific unbalance to an exact degree of vacuum, but on your car you're just going to be after a balance in line with the correct tickover.... assuming the valves are all good and the carbs aren't worn.... etc, etc

[Gibbo2286]

SU used to do some excellent tuning leaflets for their carbs and the still have a site online here: https://sucarb.co.uk/technical/technica ... ning-multi

[Michel]

I can confirm Robin's 'by ear' method is good, used it a few times in the past on bikes before I got my manometer... Slip off your fanbelt for the duration if the fan is a bit too noisy but in practice you'll likely find it won't be a problem.

Yes, I used the "by ear" method on the 4 carbs on my ZZR-1100 4 or 5 years ago.

I'm sure I'll be able to locate one if needed, I'll ask the IAM guys when I go to the next meeting..

[Zelandeth]

Today on "haven't cars got fat?"



On the carb balancing front I figured I could probably keep it simple here. As best I can tell the actual mixture and such from the carbs is fine. It smells right and performance seems right about where I'd expect. Keep meaning to pull a couple of plugs to read them but I keep forgetting. Idle speed is also in the right ballpark (maybe a touch high, but not massively so).

I know enough to no go twiddling all of the carb settings without good reason, and these carbs have given me no reason to. One got a bit grumpy briefly after sitting upside down in the boot for a week or three when the head gaskets were being done, but behaved itself thereafter once I'd whacked it with a screwdriver a few times.

So today armed with nothing but enthusiasm, a reasonable understanding of how carbs work, a screwdriver, and a bit of pipe I decided to have a shot at balancing them.



Disconnected the throttle linkage between the two carbs, then used the hose as a stethoscope to listen to each intake as I adjusted things until I got both the desires idle RPM and the same amount of air being drawn through both carbs. The linkage was then adjusted to compensate for the rest position now being slightly different (as predicted, the car was really heavily leaning on the offside carb with virtually nothing being done by the nearside one at idle) and reconnected.

Idle speed is sitting at 700-750rpm in neutral, dropping to 550-600ish in gear, which sounds reasonable enough to me.



Idle is definitely smoother. The biggest difference though is that the engine feels far more responsive coming off idle on light throttle openings. Which makes sense really. One of those things that would be really hard to show in video, but is immediately apparent when you're the one whose foot is in control of the throttle and your behind is in the seat judging the level of go being provided.

Definitely sounding a lot better now than when the car arrived here.



The exhaust is generally pretty subtle, but has a hell of a bassy rumble at idle which I'm not sure if the mic will ever really pick up.

While I had the air cleaner off I took the opportunity to finally ask a question about what this unused hose connection on the back of the air cleaner is meant to be used for?



Given the surface rust on it I don't think it's had anything attached for a good number of years. Answers on a postcard?

Evidently I do need to do some more leak searching on the cooling system as there's a bit of coolant which has gathered on the valley cover.



It looks like a lot there but one paper towel was fully able to soak it up, so not actually a massive amount. Those heater hose clips are both secure (the lower one is actually on there fine - the fitting the hose goes on to extends a long way into the hose). I'd be tending to look more suspiciously at the thermostat housing or the connection up front to the lower heater hose as they're really quite awkward to connect up as there isn't much space to play with.

Not trying to do that now though while the engine is hot. Same reason I've kicked looking at fine tuning the kick down cable adjustment down the road - trying to do that now is just a recipe for burned fingers.

Last thing I did today was to provide a bit of protection for the coolant bleed line that runs between the top of the intake manifold and the top of the radiator.



This was chafing on the alternator belt shield - and given the direction the fitting coming off the radiator points I really don't see how it's meant to go anywhere else.

I realised when going to secure this though that I'd somehow actually managed to run out of zip ties...so securing it properly will need to wait until I've had a chance to pick some more up.

[CitroJim]

Looking good Zel

I saw just how fat cars are now when I washed my AX and C3 yesterday... The AX is like washing a matchbox... The C3 is a small car by todays standards but seems to have about three times the surface area!

[Zelandeth]

Looking good Zel :D

I saw just how fat cars are now when I washed my AX and C3 yesterday... The AX is like washing a matchbox... The C3 is a small car by todays standards but seems to have about three times the surface area!

They also seem to have so many...I don't know how other to describe them than "really fiddly bits" which make cleaning the car way harder than it needs to be.

The Audi TTRS that Chris had a couple of years back wasn't very big, but it was incredibly time consuming to wash. Took me nearly as long as both of the cars next to it. Thankfully I don't think we'll ever be seeing another one of those as it was a perpetual problem child and had very few redeeming features.

Granted, the front of the Rover is a right faff too, that grill may be iconic but it's also really fiddly.

I'm pretty sure when I get around to giving it a proper polish I'll realise how small a car it isn't as well. Guess at least I don't need to do the roof!