Ménage à trois : who came out on top ?

So picked up Alan and Mark early Sunday morning and arrived at the track at 08h15; nice and early. Kevin had had electronic ignition fitted to his CZ and the rare Beta motocrosser had also made the trip down, with a ‘For Sale’ notice attached to. Some interest in the bikes, but with the usual follow up question ‘how easy is it to find spares ?’.

Walk of the track and the breakfast bacon roll all provided the warm up before practice, which was delayed until enough marshalls had been located. By then the sun was out and the day was going to be fine and warm.

Relaxed days racing

Mark, known for his thrift (see previous reports for his 30 year old opaque goggles), had a new pair of Alpinestars boots, bought from Llanfoist car boot for a fiver. It was mentioned that he had trimmed his toes to ensure a good fit for the bargin boots.

My Yamaha MX250, with its recently acquired replacement engine performed well and survived practice. Kevin’s CZ didn’t and on his second lap the bike stalled and whilst trying to start it the engine locked solid. A tow back to the paddock, and some quick work with the spanners showed that the flywheel was still in position and with speculation on the exact cause continuing, the bike was put back in the van.

The MX250 was starting first kick and pulling from the line in second so all good. The track however wasn’t perfect, with a lot of rocks and it was pretty rough. The 4 jumps were still there, though practice had helped me sort out the best lines for each of them. The only problem was that the high-and-wide Steve McQueen bars I’d fitted moved around in the clamps, especially after landing after the jumps. Also, I’d manage to crack the mid-placed exhaust mounting bracket again on the Saturday, but manage to rig up a flange to hold it in place. Looks like I need to move it to another frame, without cracks.

Only 3 over 250cc pre74 bikes on the line for the first race, but it was a close affair, but surely with a number of the main contenders not there, they could have moved things around a bit. In the end, they went from 8 race block of classic racing (there was also a novice, well not so novice and a quad race ) down to 5 races in the 2nd block.

My first race went okay, until the bars came loose on the second (and largest) jump on the second lap. Confidence was somewhat diminished, though the riding position with the bar was much improved. The track was also pretty dusty (something that wasn’t going to improve during the day) so spotting the jumps was difficult.

Kevin’s day didn’t get any better as he managed to ditch the Beta on the first bend. By the time he got it started he was half a lap down. A good ride from there on saw him make up a lot of ground, nearly catching Mark. Alan, choosing the inside line from the start, got into 4th round the first corner and had the pleasure (and the dust) of the field going past him.

The second race finished off my handlebar clamps, with a bolt threading. The bars were very adjustable by the end. Managed to raid Mark’s bolt supply to find a couple 50mm bolts and locknuts to go right through the top yoke. A modification I should have done earlier and much more stable in the third race.

The track was now pretty rutted and I managed to hit the couple of big holes in parts of the track. Did work out the wider line on the last jump and was beginning to keep the throttle open wider on the approach. The bike was performing well but with the 4-lap races taking only 5 minutes or so, it was all a bit short and could have raced a couple more.

Kevin’s day got better and after a good start to race 2 managed to finish around 6 or 7th. The last twinshock race, for which he borrowed my helmet and camera, started poorly but contained an excellent passing move on both Alan and Mark, over the first jump. The Beta was going well and the comparison of the two camera runs shows the difference that long-travel suspension makes [[It also shows how much suspension effect the body has, as the head / helmet tends to remain pretty still]].


There was a group decision to go for the Grand Slam at the end, though the start line was dominated by the new bikes of the ‘not so’ rusty and novice riders. The guy on the KTM who’d won a couple of the modern [ amended following [ MXtrax thread ]] races (despite a half lap handicap in the last) was next to me. He briefly offered to swap bikes and off the line he was quick but then lost it directly in front of me going into the first turn. Managed to avoid him, but was then down the field and into the pile of dust. Good fun and despite being passed by lots of new bikes, managed to avoid being passed by any classic bikes, though not many on the line.

The end of the race proved to be dramatic, with Kevin trying to pass Mark on the line. Mark heard the screams as Kevin hit his back wheel and continued in the air over the line without the bike, right in front of the commentator and the waiting clutches of the St John’s Ambulance. The latter had had pretty quiet day and their initial enthusiasm for a bit of mouth-to-mouth was dampened by the the prostate site that greeted them. A bit sore, and with the number of stars being viewed diminished, he managed to get up and we pushed the bike back over to the paddock.

Plenty of good racing, but the track, with its large number of stone and fairly short length, wasn’t the best in the end. Good fun and the Yamaha with its new engine had started easily and was running well. Given the dust, the hope was I’d resolved the air filter issues.

SWM 320 TL For Sale

Time to sell one of the bike collection, my underused 1980 SWM. It’s got the best Rotax engine I’ve had in a SWM and apart from one flywheel issue and a propensity to blow condensors (both solved) its been very reliable. The bike was originally sold by Peter Jerred to a competitor in the 1980 SSDT and is road registered. Its not the tidiest bike, but is complete. It has replacement Betor rear shocks and some tyres with a good amount of tread. I used it to compete in the 2006 Sammy Miller Series and it was by Gavin my neighbour for a couple of the 2007 rounds.

You can see (and hear) it at the 2006 Classic Experts . Its hardly been used since then.

At it is currently the last SWM I have (having owned 8-10 over the last 5 years) I also have a collection of spares (pictures below) . The list of spares needs amending as some items have been sold.

Looking for £1250 for everything, but could sell spares and bike individually. There are also some frames which I’d include.

Give me a call on 07720 079845












De-tuning the MX250

The experimentation with a clip on filter at Narberth hadn’t proved to be too success and whilst the engine was better and there was some better starts, it wouldn’t idle and required a bit of tuning between races.

I decided to revisit the carb tuning, going back to stock and then working forward. Armed with two stripped carbs, a carb kit and a 1974 MX250B, MX360B and SC500 Service Supplement manual , time to get the bike into racing trim.

I experimented with the following settings. This is with the airbox fitted and Uni filter in place (more on this later)

|Component|Standard Settings| Setting 1|Setting 2|Setting 3|
|Main Jet|270|270|270|250|
|Needle slot|2|3|4|2|
|Pilot Jet|50|50|50|50|

* from Keystar carb kit

Some comments on the different settings; basically they were all a bit crap. Some go in 1st, but no pull in 2nd at all. Tolerable and no worse than at some of the meetings earlier in the season.

Tuning the MX250

After a while, and a few laps of the field to annoy the neighbours, I failed to start it and the process of trying to restart, managed to flood it. Used the opportunity to take the head and barrel off. Not good, with loads of fuel in the crankcase and in the exhaust. Further inspection and a second opinion later it was clear that:
– the piston ring was knackered. Massive end gap and at least 1mm off the thickness on the exhaust side
– main bearings; very noisy and shot
– big end; lots of play and shot

Revealing the horrors

The reason for the damage, well there are a number of possible reasons
– dirt intake; all of the meetings (with the exception of Teifiside) had been really dusty and the air filter hadn’t been perfect
– the rebore; the tolerances provided by Yamaha are on the slack side
– the cylinder bolts coming loose, may have hasten the demise of piston rings
– the big end may not have been perfect from the outset
– oil premix may have been on the low side, with not enough oil getting to bearings. Time to re-visit the 2 stroke oil and ratio of the mix

All up, not good and with less than 20 races. Classic scrambles is a bit tougher on engines and bikes than trials, without an engine strip on the Beta in 2 years. It may however, be an indication that its a completely different ball game (or bike event). Things like the air filter and oil mix are much more critical, as is engine performance.

In the subsequent few days, I managed to pick up a spare bike, an engine and also a crank / big end kit from Keith Alderman at Motolink .

Engine #4, attempting to remove the front sprocket

The spare engine needs some work and although it seems to run, the exhaust manifold bolts are non-functional and it needs a new gasket. The cases are ‘nicely’ polished and need returning to normal. The engine from what now must been seen as bike 2 seems good though bit of a risk running it as is.

Swapping it into the running bike and yea, the power is back. Bit of a top end rattle, but will see how it runs for now (and see what else I can break)

Overall ‘Bike 2’ is mainly complete (well until I took the engine out), with only the rear shocks and cables really requiring replacement.

More info and (hopefully) race reports to come.