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After 20 years it’s time for the RS and the original fitment Dunlops to part ways…it’s an Italian bike, so Italian tyres will be going on this time…in the words of Juha Kankunnen, I have opted for black, round Pirellis. Diablo Rosso III’s to be precise, which are my favoured road tyre of the moment.

The original Dunlops still rode well, however the history showed the rear one had been plugged, and so it was, on removal the plug was still there!

Of course, while the wheels are off it would be rude not to inspect the front calipers and pads and also deep clean the swingarm area.

There’s not much wrong with the calipers. I have bought a replacement Brembo caliper seal kit but this will have to wait a bit longer, along with the new front brake master cylinder as I’m itching to get this on the road now. For today it’s just a clean up of the pads/gubbins and clean and regrease the pistons.

The rear comes up nice and shiny…

The gearbox oil was last changed about 400 miles ago, and about 20 years!! So despite looking reasonably clean I drain it out for replacement. I drain out over 800ml.

The oil plug is also relatively clean.

Cleaned off and ready to reinsert!

On the advice of the tuning works, I go for Silkolene light gear oil, and fill it to the correct 700ml measure.

However after consulting the manual, it looks like Medium gear oil would be the correct choice! As a result I shall probably drain this out and replace with medium soon!!

From reading the Silkolene data sheets, Gear oil ‘medium’ is the equivalent weight to engine oil SAE 20W/50 as called out in the manual. Gear oil ‘light’ is a 10W/40.

The original crush washer was clearly reused previously and crushed to nothing! I fit a new washer to the correct torque setting.

Edit:

Gear oil light I feel is too thin, so it has been replaced with medium, a mere 40 miles later!!

While everything is apart I decide to do a compression test. These can vary widely depending on gauge used etc. My gauge set is designed for car engines and therefore the hose itself is about 10mm diameter. This means that a motorcycle specific meter (Kawasaki gauges have a 3mm diameter hose) would likely yield a higher figure. The more important metric is to check that both cylinders are reading a similar amount rather than the outright figure. With this in mind, the reading looks a little on the low side for the lower cylinder.

However on checking the upper cylinder, the result is much the same, in fact, it’s identical 🙂

The above test was taking with a cold engine. On a hot engine and some more vivid application of the kick starter, both yield 105psi.

The spark plugs are also looking a nice healthy shade after a run.

Although I’ve purchased some Iridium plugs, I haven’t fitted them yet, preferring to make sure it is all running perfectly first as is, then hopefully I can measure (albeit subjectively) any perceived improvements when I swap to iridium.

It’s time to bleed the front brakes, the fluid smells vinegary and there is some dirt around the cap to clean up. I flush the system through and put fresh fluid in.

While bleeding the front brakes I have another WTF moment, as I spot another problem!

This time, it isn’t something menial that has the potential to ruin the engine like the previous carb issues or potential oil feed blockage, no, this time, it’s the brake hose banjo bolts! I’m bleeding the brakes and I see leakage from the banjo.

I barely touch the hose end and the fitting spins. The same on the other side. Both hoses are barely finger tight!!!

Once again a reminder of why I do my own maintenance, it’s frightening to think in the last 200 miles this bike has had a service, a sales preparation and an MOT by a reputable bike specialist that even sponsors a race series! Between the nick in the rear brake hose covered by tape and the loose front hoses, coupled with the failed rear master cylinder, any one of these could have been very dangerous but all at the same time wouldn’t bear thinking about! I ordered some new copper washers for the banjo’s and fitted them.

I’m getting to the end of the preparation now and I’m itching to go out for a ride. All of the Blogs for this bike up until now have involved thoroughly checking the bike over to preempt as many problems as possible by ensuring that this is running as it should be following it’s lengthy lay up and it’s increasingly apparent sub standard recommissioning.

Back to the invoice of the last works that were carried out, when the carbs were done, there was mention of a new plug for the ignition. I looked around at the coils and plugs and could find no evidence of any plugs having been replaced. However while working on the oil reservoir, I came across the ‘Wurth 3 pin connector’ that was shown on the invoice. I noticed it purely because it looked out of place to all the other connectors and looked uncharacteristically large. On closer inspection, the bad workmanship that I’d come to expect from the dealer revealed a wire that was ready to fall out. With no effort it does.

I re-crimp this wire with a new terminal (fortunately I find one of the same size that fits) but then notice the white wire is also similarly badly crimped.

So with this re-crimped and the brown wire checked, this block connector is good to go…or is it?

It turns out that this plug is the ignition signal feedback circuit. One of the checks I was going to do is plug in a Zeeltronic ignition controller (bought specifically for this job) to set up the power valves. Ideally the exhausts need to come off for this check so the valves can be seen in their respective positions. I have bought all the exhaust gaskets to do this work however for now I’m going to get a couple of runs in first! The power valves appear to be operating fine and even the markings line up where they should. However a quick test run with the zeeltronic unit is thwarted because this Wurth connector, happens to be the same plug that the zeeltronic connects to…

This means that the Wurth connector will need to be replaced for an OE block connector which I have now bought.

Happily, this will put the bike completely back to stock and is the last of the hashed items for me to remedy!!

More to follow once the connector is replaced!!

Yes, here we are again, this time, having topped off the 2T oil tank, I discover a leak from the level sensor. This will explain the out of place looking jubilee clip!

I take the opportunity to start fresh. Fully strip, remove, clean and refill with my chosen 2T oil, Silkolene Comp 2 Plus.

The oil filter is in a bit of a mess, and in cleaning the tank, I find the remnants of the seal tab of a previous 2T oil container.

This could have easily of blocked up the oil supply so once again, it has paid dividends to go the thorough approach and strip it all down. Also in evidence was silicone sealant that had been gummed around the level sensor, remnants of which had also made it into the tank…

I put some diesel in the tank and slosh it around to capture the final bits of debris…

New filter fitted…the old one cleaned up ok so I’ve kept it as a spare.

To cure the leaking oil level sensor, I place 2Nr 16mm x 1.5mm O ring seals on the level sensor to seal it correctly. This works perfectly.

I test this by topping the tank up to the brim and tilting the bike forward on the Abba stand into the stoppie position. Oil leaks out of the overflow/breather hole, but not the level sensor!

That’s one more thing ticked off the list. No more oil leaking down over the rear of the bike.

The final check, is to open up the purge screw to bleed the oil pump and ensure there is no air in the system…

No, we’re not talking about too much sugar!! Rather, bad carburettors to be precise!

So the Carburettors were rebuilt 8 miles ago when the previous owner had the bike recommissioned in 2018 at a non Aprilia motorcycle dealership. The invoice shows 6 hours labour and a carb overhaul kit. I was hoping that they had just been cleaned out and new seals fitted. It turns out I was wrong and my worst fears were confirmed.

One of the carbs (the l/h) had been removed from the fuel delivery hose as this was now secured by a cable tie rather than the proprietary Aprilia click clamp. The fuel filter sits at the entrance to the carb, this one had come away from itself and would allow unfiltered fuel through.

The other looked to have never been removed.

The fuel filter shows some residue/sediment.

Unfortunately both carbs had been opened up, evidenced by some rounded off screw heads at the base of the carbs and further by some of the original (and very expensive) Mikuni parts having been junked in favour of Chinesium, one of the many Chinese full overhaul kits available on ebay, which include everything for both carbs for £32. I was dreading this! My view was the least done the better, unfortunately that wasn’t the case.

So it was time to identify what was original and what had been done. It’s not a great sight as I open the first carb, the fuel filter is split (this could have happened during the removal process) and the float looks eaten away on one side. This would be from the bike leaning on it’s side stand and probably came from being eaten away by ethanol which is corrosive.

The fuel had lots of black specs in it which had come from the corroded float, of course this is after the fuel filter so the muck could have found its way into the engine regardless. As with the air filter, I’m very glad that I’ve taken the bike apart first before being tempted to thrash it down the road. It seems like this approach is paying dividends in disaster avoidance. Curiously, this float does not ‘seem’ to have any oem markings on it, however the markings would have been on the corroded area so perhaps it is original after all! It would seem like a lot of damage for 2 years otherwise! The float furthest from the side stand is not marked despite being in the same float bowl suggesting it was not sitting in fuel.

Of even more concern is the power jet circuit which performance 2 strokes are equipped with. According to Mikuni, this can provide extra fuel at high rpm full throttle. On removing the float bowl, the elbow to the hose connecting the power jet to the carb body snaps.

There was no force applied, it just came away with no effort. The hose was completely gummed up, I had to use a drill bit to clear the hose, clearly ethanol fuel had been sat here and had corroded the metal weakening it. Thankfully this is the left hand bowl which is still available, the r/h one is no longer available. The power jet circuit on this carb would have been totally ineffective potentially leaning out the mix at high revs/full power applications which is when you need it most, again I’m thankful I hadn’t been down the road with it. Sadly I’ll never know how bad it was suffering or not as I never rode it but better this way I think.

On to the r/h carb.

This would appear to have oem markings on the float, and was also rusty, suggesting it wasn’t sitting in fuel when the bike was standing. I guess if the fuel tap was shut off and the bike allowed to run until it stalled while on its side stand, it would have run out in the r/h carb first. This would have stalled the engine leaving some fuel in the left carb bowl with only one float dipped in the remnants of fuel, which is also where the power jet pick up was, explaining the corroded elbow.

The needle has some congealed fuel on it and the throttle valves could use a clean.

I strip the carbs down, on further examination, some of the jets are not original. Both pilot jets, one air jet, both needle jets as well as both float valves and needle valves are non oem.

I lay out the parts which need replacing for oem, as well as the float bowl itself which will need renewing on the l/h carb. This little lot in the picture below represents £438 as a replacement value. Junking the Mikuni parts for Chinesium was an expensive exercise and probably an unnecessary one, I find it hard to believe they couldn’t have been restored with a little TLC. That figure includes obtaining parts from Suzuki where required as they are the same Mikuni carbs as used on the RGV and cheaper than sourcing them from Aprilia. I’m replacing the vacuum lines as they contain a jet, I have no way of knowing if they have the correct jet so decide to replace them as a matter of course. The unknown unbranded Chinesium items have no markings on them so I cannot even verify if they are the correct size.

In the meantime, after stripping the carbs, they go in the ultrasound tank for cleaning.

They clean up as new/

I pack them up respectively while awaiting for new parts!

The new parts duly arrive. There is a marked difference between them and the non original items. Not least they all have the official Mikuni markings and sizings on them. The float valve and needle valve in particular are very much more robust and precise.

The carb rebuild process begins. New parts and cleaned up originals now installed.

The Main jets, needles, power jets, spacers and float pin are the only originally retained parts, everything else is new. Pictured below is the new float valve and needle valve.

The float height needs to be set. As they are installed out of the box, the measurement is 10.6mm from the measuring point to the gasket surface. According to the manual this figure needs to be 8.1 +or- 1mm.

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I adjust the float to the recommended height. There is a further test which is to measure the fuel level through a clear tube. The manual also provides this information, this is actually the more test and is the one I will be targeting for accuracy.

For this test, the tube should show a dimension of 7.1 + or – 1mm from the indicated points. To achieve this, I find the left carb requires a float setting of 8.65mm.

The right hand carb required a setting of 9.02mm.

The carb needs to be carefully setup at the right angle and centricity for this test. My fuel level is within the tolerance of 7.1mm + or – 1mm.

With both carb float levels correctly setup and checked, it’s time to finally fit them and reconnect the chokes, fuel lines and throttle cables.

The throttle slides need setting up next to ensure that they are in sync with eachother. The throttle cable is adjusted so both are on the same mid marking together at half throttle.

The idle position is also adjusted to a 0.7mm gap, this was pre adjusted off the bike using a cable tie that was conveniently 0.7mm thick!! This must be done off the bike as the measuring cable tie meeds to be inserted in the back of the mouth of the carb (engine side).

The new air filter is inserted, air box cover back on and all ready to go!!!

Edited to add, I have since been back and renewed all the fuel lines with new as well as replaced the carb drain hoses.