CRM wrote:good post.
some of those prices are eye watering.
surely better to make a good set from a couple of sets of carbs.

Well, yes and no. Ultimately that will depend on how much another spare set of carbs is going for when you need the bits. I was lucky with this set, I lost out on a set a few weeks/months before and they went for about a ton. No-one else bid on these and I seem to recall they cost me about £25. As I mentioned in a previous post, there are a couple of sets floating about on eBay for many times that cost, and you never truly know what's lurking inside them until they've arrived. If I needed a set of diaphragms at £400/500 a set, I'd gamble on another set of carbs secondhand or go to a breaker before taking the plunge. If I needed a few cheaper bits, to be honest I'd buy them new. I don't personally see the point in faffing about scrimping a few quid here and there on potentially iffy quality mechanical parts that could ultimately come back to bite you later on. I'm one of these sad people who almost always follows the instructions to 'always use a new o-ring/seal/gasket/washer' etc when doing stuff, yet I know that in a lot of cases you'd happily get away with reusing them. In the case of these carbs, they've stood for years and years. The rubbers have turned into concrete, the float bowl gaskets are like bits of last year's liquorice catherine wheel you found under the sofa, and the o-rings on the fuel pipes are probably not all that healthy either. At the very least, the gasket sets are needed, and I'm also changing the main jets. So that's over a ton for starters. Suddenly another £25 or so for some o-rings seems like false economy to ignore, and then the carb rubbers on the bike now may not be all that brilliant either. Then I've decided that as ther carbs will be off, the valve clearances might as well be done, so there goes another £30-odd on the cam cover gaskets and timing cover o-ring. There'll be no change from £200, but if I can get the carbs and valves done myself, even at mate's rate from my old mechanic friend I'l lbe saving several hundred quid in labour. If not, at least I can put the thing back together and give it to someone who knows what they are doing!

Drunkn Munky wrote:Great detailed post, when you doing one on the engine

When someone gives me an engine, an engine stand, some torque wrenches, a plethora of special tools and a load of gaskets....

i agree totally i am another stickler for genuine every time even down to pads and esp fastners, mainly because they work well and are not that expensive compared with pattern.
but for carbs, i have been lucky every set i have bought has been salvagable i have 2 sets of RVF carbs here (and 2 NC too) which are all ready for either stripping or selling, and the years have been good to most i have bought over the years. had one set of each which were fit for parts only. always good to keep a set for spares

You can use ordinary viton (petrol resistant) o-rings instead of genuine items, they're very cheap.

If I only had a couple of o-rings I wanted to change, then I'd probably source them on their own. Petrol o-rings are petrol o-rings. However gaskets are a different kettle of fish, and for bike ones I'd rather go with the genuine thing. A previous bike shop I used bought a set of pattern gaskets from a well known source at the time (I forget now, but it wasn't a one man in his shed operation, this was a very popular name) and the thing piddled oil all over their floor before they even started it up. They said tongue-in-cheek you'd be better off not bothering with gaskets than use these things, and ordered genuine ones to replace them with at about five times the cost. Glad it wasn't my bike! I may have to do the head on my missus' car, and that won't get a genuine gasket as it's a popular engine and is prone to HGF (did anyone NOT guess it's a Rover K series lump? lol), so lots of OEM exceeding spec gaskets out there. I do use genuine bits on most of the rest of it where I feel they might be better than aftermarket.

CRM wrote:i agree totally i am another stickler for genuine every time even down to pads and esp fastners, mainly because they work well and are not that expensive compared with pattern.

Brake pads? Have to confess I always use EBC HH ones. I'm not massively hard on brakes, so I find they last years and years. In fact, I got the bike in 2003, and it had new pads when it was serviced the next year, then it had the only replacement due to them wearing out about four years later. Cost a bomb! About a year after that, it was apparent that the front discs were shot, so I bought a pair of EBC ones. Pads were fine, but I binned them as supposedly old pads on new discs can make them wear funny. I'd got a full set of front pads on eBay for £12, so I wasn't bothered about throwing new ones on. However, these discs were rubbish. If they got wet, they went orange and the pads welded themselves on. The mounting buttons corroded to hell, and after the first winter they looked like they'd been at the bottom of the sea. This winter just gone, I was unlucky enough to be out in -12C, and the next time I rode the bike it was apparent that they had warped quite dramatically. For the last six months they'd had a little bit of warp, but it was bearable. Enough was enough, and about a month ago they were junked in favour of some wavy-ish ones I got on eBay for £100 (the seller usually has them BIN for £185, but only ever sells them when they start at £100, wonder why...?). I junked those pads too, again loads of meat. They might possibly have been the second set on those discs. Whatever, they cost about £12 a pair too, and believe it or not, I have two full sets of fronts and a pair of rears in stock as whenever they are cheap on eBay I snatch them up. I don't think I've paid more than £16 a pair, and it's common to see them advertised at low to mid £20 range....

Right, took the plunge and orderd a shed-load of bits. Exchange rate is favourable at present and supposedly the rate my card company is going to use was within about three decimal places of the real one, and they don't charge a fee. We shall see! Also, DSS were O/S on several bits I wanted and reckoned a week or so to get them, and allegedly CMS have them on the shelf. Well see about that, too.

Four carb gasket sets, 1 o-ring set, 4 carb rubbers, 4 112s, 8 screws for the airbox base (I figure at half a Euro each versus the usual shoddy Honda cheese-like screw heads is a no-brainer!), 2 cam cover gaskets, timing cover o-ring, thermostat housing o-ring and caps for the front brake caliper pins (mine are shabby). Can you tell what other jobs are coming up?

Fraction under 269 Euros delivered. Time will tell how close to the alleged £210 the card company comes thorugh at...

Well, after the order which I placed on the date of the post above has spent the last forever saying it's estimated that it'll be sent this Monday coming, it's now changed to today and it's apparently being picked. I wonder if being £200 worth of stuff it'll go with someone like UPS and maybe, just maybe I'll get it for the weekend? For the record, the cost worked out almost exactly what the exchange rate was at the time, so my card company was pretty good. I have to confess that I'm not impressed that CMS don't differentiate between the stock being in THEIR stock on being in stock with another supplier or the vehicle manufacturer. I have a suspicion that some of the parts came from Honda in Japan seeing as DS list them as special order with three weeks wait. Anyway, DSS would have had to do the same, and I saved about £15. Not much, but it paid for a few of the parts if you look at it another way.

Pilot screw adjustment by ear.
This may be a pointless exercise if the pilot circuit plays a much greater role over the rev range than just idle, as it has been reported for various carburettors. However for interest's sake if nothing else.

On all of the Mikuni and Keihin carbs, that I know of, the screw is an air screw. As you screw it out you allow more air in, therefore leaner. On Dell'Ortos and Bings it is a fuel screw, the opposite. Adjusting a fuel screw by ear is very easy. Well it is for me. For many others it seems to be difficult. I do not know why. You adjust the screw to achieve the highest idle. Then lower the idle and move to the next cylinder and repeat. The more cylinders, the more difficult it becomes. With an air screw it is exactly the same process but more subtle. It takes more turning of the screw to achieve the same dramatic effect. It helps if you can hear the intake at the same time as the exhaust. I have seen it mentioned that you can adjust the fuel screws altogether. For example, if they are all at 1 1/2 turns out then take them all to 2 turns out. In other words do not set them individually but use the highest idle technique by moving them in unison. This might be the best way for a novice to start with, but I am going to describe the individual method because that is what I do. The unison technique means to find the best average, but it seems a bit rough to me.


"You adjust the screw to achieve the highest idle." Ok this needs a lot more detail.
1/ Set the idle at the lowest speed where the engine is idling smoothly, not labouring.
2/ Imagine your screw is at 1-1/2 turns out. Wind it in, slowly, until you hear the idle lose speed, a very slight drop. Now lets say that occurred after you had turned the screw 1/4 turn, so now it is at at 1 1/4 turns out.
3/ Okay wind the screw back 1/4 turn and you are at your start point again.
4/ Now repeat the process but this time winding out, again slowly. Lets imagine the idle faltered at 2-1/4 turns out.
5/ So you move the screw to the midpoint of the two points which will be 1-3/4 turns out.
6/ If the idle has risen then lower it and move to the next cylinder.
7/ As you repeat this process the number of turns between too lean and too rich becomes smaller and smaller.

If the compression is low or the carbs have vacuum or seal leaks then the carbs will not be responsive. In fact the more responsive the carbs are the better condition the engine is in and vice versa. For example, the pilot screw will do nothing if you have leaking valves.

The intake makes a gasping, moist sound when it is too rich. You will never distinguish it without practice and being able to hear the intake easily. Too lean does not seem to make much intake sound, just dies. Of course all bikes make a different sound too. Okay I better stop now. Sounds a bit like fairies in the garden doesn't it?

By the way if you cannot see the tip of your screwdriver then you could put a mark on the handle to make it easier to count the turns.

Given that most people do not seem to be able to do this with a fuel screw, which is the easiest, then it may be an impossibility for many with an air screw. I think some people just have an ear for it. Give it a try and focus on the sounds not the screw.

Good luck
Blair

So, to clarify, I basically go to each cylinder in turn, wind the screw in counting turns until the engine starts showing signs of being unhappy, then wind it back to where it started, then out using the same method, and then back in to halfway between the two unhappy points? They look a right bugger to get to when the carbs are on the bike, but I took the plunge and bought the expensive screwdriver from Carbtune when I got the vac gauges, so hopefully that will help. Am I correct to assume that your wording in point 7 means that I revisit each cylinder until the difference becomes next to nothing?

My only other question at present would be what order to do things? Do I balance the carbs first, or set the pilot screws first? I can't help thinking that one would affect the other...