Carb leaks

I am pretty sure that my petroil leak is coming from the seals that are behind the carbs. There are 2 O'rings that go between the carbs body and a plastic spacer and then the rotary disk cover. There is a small slot in the rotary valve cover which accepts the O'ring, and there is (on the carb body) another slot for the o'ring.
I think the slot in the rotary covers is a bit deep, and my impression is that it swallows the o'ring up, not leaving enough protruding rubber to make a seal, with the plastic spacer. I had ordered some slightly different size o'rings for the carbs to try and rectify this situation. Simply Bearings in the UK offer a huge range of products, and I purchased two slightly different types of NITRILE O'rings. I ordered 2mm section ones which are slightly bigger than standard, and one that are 1.78mm section which are standard size.

Unfortunately the larger ones would not stick in the slot in the valve covers, so I used the larger ones next to the carb body, and the standard ones in the valve cover slots. Don't know if it will make any difference - we'll see.

Video from the weekend at Nogaro

Noagro Race Report

Arrived at the Nogaro circuit in the South West of France at around midday on Friday. The weather forecast was for hot on Friday, even hotter on Saturday, and then stormy rainy weather on Sunday. In principle this meant we should have sunny practise and qualification, and then 2 rainy races, as the races were programmed on Sunday morning (8:30) and then Sunday afternoon (16:30).

I was a bit pissed off because, I was expecting the weekend to be dry, and due to wheel problems, I hadn't brought my wet tyres. Although everyone tells you Suzuki GSXR wheels are mostly compatible it would seem that they are definately not!

I had up jetted considerabley on both bikes because I have the bad habit of siezing the engine as Nogaro has a long straight, and it's always hot! So this weekend I was determined not to damage my engines.

Olly (my son) had suggested we go halves on an onboard camera, so I had a play with that during practise - the results are excellent in HD, but are less so when you watch them on youtube. The thing manages to get everything in focus even through the screen of the bike! It doesn't really come across after scrunching by Youtube, but it's certainly impressive on the PC. The only problem was that I didn't have the lense around the right way so the initial images were 90 degress off! Won't make that mistake again! Thank goodness for editing software! I filmed during free practise, the first (warm up) couple of laps.


The bike ran well, although very hot, I started to slow on the straights when the temp hit 88 degrees centigrade, just to allow it to cool somewhat. Still had a great time getting used to the track again! My tyres were so sticky at the end of the session, and used to the very edge and back! Just for information I had also reprogrammed my valves to close at 7300 and open at 7200 instead of 7800 and 7500 respectively, but honestly didn't feel any difference at all :-( I had been hoping this would lessen the hole around 7500 rpm.

For Saturday's timed practise, I decided to go for higher gearing (replaced the 39 with a 41 tooth sprocket at the rear), and also I thought I would ease off on the advance of the ignition in an effort to bring the temperature down. The bike felt a lot better, and ran cooler, but I am still in the middle of 2 gears in a couple of places on the circuit, and still only getting into 6th about 200 metres from the end of the braking point for the straight, so I should try even higher gearing next time. My best time was worse than Friday's practise, but still good enough to get me on 19th spot on the grid (1:51.783).

Sunday morning, I awoke to rain falling on the roof of the van, which continued to piss down throughout the race, I got a crap start, and really with no appropriate tyres I was destined for a crap position. I managed a lowly 2:31 second best time, and 23rd spot! At least I was in front of the fallers! The best time of the session was someone with full wets and he managed a best lap of 2:03 (well done Georges!). The bike had run well, and cool given that the ambient temperature was a full 10 degrees lower.

Sunday at 16:35 for race 2, We had just had an enormous downpour at around 15:00, so everyone was on wet/road tyres (Michelin Pilot Road 3's seem to be the popular tyre) as we sat on the pre-grid, but out on the track everything had dried up nicely, and although wet in a couple of corners, I had full confidence in the my choice of tyres (my only ones!). My start was pretty bad - I really must invest in a different clutch! I managed to get past a good few guys in the first couple of bends and then gradually work my way forward, picking off 3 riders in the later stages of the race to finish 13th! My first 3 points in the championship yipee. My best ime in the race was 1:52.144.

The bike had run well all weekend, and no oil/petrol leaks, although at the end of the second race I noticed there was some petroil mix coming out of the left side, but this really confirms that when I seal the carb o'rings with gasket mastic, it really stops the leaking, at least for some time, so it  does definately seems to leak from behind the o'rings, I must try to get some thicker ones so they don't get as squashed during tightening.

Next race from Croix-en-Ternois (again) at the end of the month.

Technical Preparation for Nogaro

RG 500 Setup
Main jets are 240s at the front and 250s at the back.
Starting gearing is 15/39.
Ignition Zeel 2
Exhaust valve Closes at 7300 (from 7800)
Exhaust valve Opens at 7200 (from 7500)

Piston Replacement

The new piston arrived, and before installing it I wanted to note the relative weights and dimensions :-

The old TKR piston  weighed in at 205 gms and the new Mikata Piston came in at 195 gms.

The dimensions were pretty similar, I hope the 10 gms difference doesn't induce any vibration. Having remvoed the carbs I put in 390 main jets, I mistakenly removed the float bowl on one carb as that is what I am used to doing and promptly found myself with 2 floats in my hands. They run on sliders, connected to the float bowl, and are released as you remove the floatbowl, in fact on the new carbs (VM34), you have a big nut covering the main jet so changing them is real easy. I also put some gasket silicon around the carb balance pipe as it may have been leaking air there. I won't start it again until it gets fine enough to take it outside..

I also have found a vendor for the rubber o'rings behind the RG 500 carbs. Simply Bearings in the UK seam to do two different o'rings that are about the right size, I have gone and ordered up 10 of each to see which is the best size. From what I can measure (difficult to measure a rubber band!), the Outside Diameter is 36mm, the ID is 32 and the approximate thickness of the ring is 1.75.

I ordered these and these.

Nogaro in a few weeks, and I still need to upjet the 500, change my wets onto different wheels, and change the Exhaust opening revs.

Cracked Piston

After Croix, I wanted to be 100% sure of the state of the 350 so I decided to remove the head and get a good look at top of the pistons. You may remember that the left sparkplug was a bit light, and the left was a nice chocolat brown (caramel). Well, the short of it is that the left piston had cracked quite severly but thankfully no bits had cracked off. The bore is not touched, but I will need a new piston.

The cause is obviously some heavy detonation, which could be (probably is) either a very lean carburation or some airleak. No reason to suspect an airleak, although when I put it back together, I will ensure that the reed rubbers are well sealed, as the new rubbers are not that great a fit around the pipe joining the two sets together, I don't know if this would cause just one side to go, but it's a plan.

The base gasket looked a bit tired aswell, (could it be leaking!) so this will get changed aswell.

Nogaro is my favourite circuit for seizing at the end of the straight, so I will be upping jets on the 350, and also the 500, just to make sure of know disasters. For info. Nogaro is about 100 meters lower that Croix, so normally I should running bigger jets as the air pressure should be higher.