Reed Valve: or not ?

The later Jumbo’s were shipped with a modification, where the reed valve block was removed and replaced with a blanking plate. Unlike the reed block on a Yamaha TY or on the later Beta TR240’s, which is directly between the carb and the inlet manifold on the barrel, the TL350 engine has its reed block between the inlet manifold and the lower crankcase chamber.

On the operating table

Not sure what the reason for the modification was, probably to soften the power, but having seen Woody’s (now Paul Cooks) and Chris Dark’s in action they have significant go from a standing start. My Jumbo has always struggled to pull away strongly and smoothly and hance gained a reputation has being a bit controlled when the power kicks in.

Blanking plate and Reed Valve Block

It took a relatively swift 1.5 hours to fit the reed block, as there’s enough room to fit the block without removing the engine from the frame. The main thing is to place a rag over the crankcase mouths as you don’t want to loose the screws from the block into the cases.

First impressions is that the pick-up and response is better and the transition from idle to main jet is much smoother. That said, I’ll need to change the jetting as the replacement carb I obtained has the ones for the plate, not the block.

Both bikes have a PHBL 28 carb (with you can new at a reasonable price from Eurocarb ) and have a range of needles, jets and tubes.

|Carburettor Part |Later Non-Reed Valve|Reed Valve Model|
|Pilot Jet|50|60|
|Needle|X2 1st stop|SX200 2nd stop|
|Valvo Gas|60|70|
|Emulsion Tube|AS272|AS268|

So that’s the next part of project and also to potentially fit it out ready for a trial; there’s a Wye Valley one in a couple of weeks. Here’s to a better performing Jumbo

Twinshock Team Trial 2008

To Derbyshire and the first Twinshock Team trial. The Wye Valley club has got a team together and with the best three from four riders scoring, the plan was for me to have an enjoyable day out, whilst the other Needless to say, things didn’t go quite to plan.


Fairly prompt start on a nice sunny Sunday morning for the 2.5 hours up to Winster, Derbyshire, with the two grey VW Transporters taking the team north. Four riders in the team, Dan Sanders, Gavin Spencer, Andy Pitt and myself, Malcolm Herbert [[There is of course the older version of me, but he tends to ride a lot better]]. John Sanders and Brian Watkins (Team Captain) also came along for moral and physical support. Makes a change to do a road trial with a support crew, but it hopefully won’t encourage a break down.

Start was at the Miner’s Standard in Winster, not too far from Matlock. Plenty of riders, of modern bikes, twinshocks (for the team event) and also modern sidecars. They were competing in the Doncaster Cup, part of the British sidecar championships.

Another Beta Twinshock

Quick mooch around the start to look at what machinery was out for the event. A lo of the usual Honda TLRs, a large number of Fantics (Bernie’s 2nd La: The further north you go, the more Fantic’s you’ll find, all the Bultaco’s are in Surrey). Some pictures attached to the article, including (surprisingly) another Beta TR twinshock. A recent find from a greenhouse in Cornwall, and fitted with a 125 tank-seat unit, but very much a 212cc bike. The value of the bike had just been doubled with the additional of a pair of Rockshocks, complete with price tags attached.

Off with Gavin for a bacon butty and cup of tea, then back to the van for the team photo before the start.

Team Wye Valley

There were 9 centre teams and 7 club teams entered, some of them looking pretty formidable, with some well-known riders. Apart from the South Birmingham club teams, the rest were to some degree unknowns. No illusions for us though, me in particular. Finishing was the aim.


About a 4 mile run down to the first group of the day, including plenty of tracks; missed a marker to add to the fun, but spotted by Andy. Lost the support crew on the way over. After spending the week tinkering the Beta TR240 was still not running right, with more smoke than usual and also a little lumpy.

First sub, fairly straightforward, but the misfiring Beta meant I needed second and therefore dropped a dab. Dropped one on the tight slippery turn in the second sub, but so did plenty of others. Down into the stream at Ible and some slippery banks and roots. The third sub was tricky, with a sharp bank to start and then over some logs in the stream. We all dropped a mark in this sub.

Dan Sanders at Ible

The backup crew made it to watch the final section, which all of us managed to clean exiting with a climb over roots. A good start for me and confidence was up.

Carsington Pasture

Back on the road and over to the open moors and limestone outcrops. However, after walking the first sub, Dan’s Fantic refused to fire; no spark. Change of plug, and a check of the coil (by putting your finger up the HT lead) indicated that it was fried. Team Wye Valley helped with problem solving, but the bike had to go back in the van. That was it for Dan and it therefore meant that the rides of the remaining three (including me) were to count. Oh Dear.

John McNulty at Carsington Pasture

Couple of straight-forward climbs over grass past the limestone pavement and outcrops. However, after watching Andy and Gavin nail a climb, I didn’t get enough drive and recorded my first 5. Cleaned the next 2 subs before heading off to the next group of subs. Dan was now confined to the van which was really disappointing for all of us. There was a spare coil kicking around, but some reluctance from the vendor to pass it our way during the trial. Also, the Midlands Centre team was having problems, with a puncture to a Fantic.

Nick Dyble's Montesa

Longclifff Tops

Short section of road work took us to the next group, Longcliff Tops; more grass banks with limestone outcrops. First section was typical, sharp climb through the rocks and over some karst to the end cards.

Longcliff Tops

Second sub had an awkward drop, which I decided to ride down after Gavin’s leap nearly took outside the markers. The next sub, was a long double and was where Andy got distracted and missed a marker for a 5, something which had a big impact on his score on the day. The Wye Valley team were in attendance with lots of comments on the reason; I managed a clean and a dab, on the exit drop, though thats probably because I was concentrating on Paul Cook’s Jumbo parked nearby.

Observers: no trial could run without them

Next sub I dropped a bit of a clanger and got the wrong line at the bottom of the climb, stupid 5. Cleaned the next sub, which was a fairly straightforward traverse round the limestone; if it had been raining it would have been a completely different proposition. Next sub had sharp climb entry, with a turn over more limestone and then a nice jump to exit; good fun and my best ride of the morning. Nearly missed the last sub here, but need not have bothered as the throttle didn’t shut off over the first rock and then just get going, so missed a marker, right pain.

Longcliff Tops, climbs and limestone

By this time, Andy and Gavin had settled into a good rhythm, with only the one 5 as a blemish between them. Road work back to the start at the Miner’s Standard and change the card for the afternoon groups. Quick turnaround as we’d spent 3.5 hours on the first 22 of 40 sections.

Dudwood Farm

Speculation at the stop that things would toughen up for the afternoon and indeed they did. Andy’s cleans through the Dudwood sections were spot on, as both Gavin and I recorded consecutive 5’s on the big boulders in the woods. The large rock step had lots of slime carried up it, but Andy used his usual “its about to stall” tactic with the Majesty to clean it with style.

Andy at Dudwood Farm

This step had claimed plenty of 5’s during the day and it then resulted in a trip to casualty for Paul Cook as his bike landed back on top of him. Its not called a Jumbo for nothing [[ Not heard how Paul is, but speaking to Woody and Chris later it sounded painful]]. Only 1 clean in 6 subs here for me, as well as 2 5’s. Not good, but you could see that the Clerk of the Course was looking to extract some marks from the top riders.

Dudwood Farm: Malcolm on the last section

We also had the disadvantage of riding round behind the Peterborough lads, who were riding a blinder, one of whom had ‘borrowed’ a TY175 which was going back in the shop the following day. An excellent buy for 850 quid as it seemed to have plenty of go in it. They were making it look easy.

Last section here was enjoyable and it took some smooth fluid riding to get round a rock wall. The Beta was still not running that smoothly or pulling sharply from tick-over, and although not a major impedence to performance, it was on my mind when riding. Time for tune-up and a think through of what’s going on (and usual what change that I’d made that may have caused it).

Rockhurst Farm

Another road section, with an off-road section to follow (which the Wye Valley supporters drove my van along as well) which brought us to the next group. Most of the sections were laid out along a wooded bank with more limestone and grass banks.

All 3 of us contrived different methods of cleaning the first sub, but the next couple included some steps which caused me some problems. Both Gavin and Andy had hit some good form and cleaned all the sections here, which involved some tight turns and rock steps. Some great sections, and this group, like the others would be an excellent spot for some practice or infact a multi-lap club trial. Excellent location and will be back to Derbyshire for more trails hopefully.

Grange Mill

Last group of the day in some woodland with old quarries and steep climbs and drop-offs. Andy continued to clean some difficult subs, the second in the group included a big descent and then a climb out over a rock. Filling myself with confidence managed to get through but without too much style.

Grange Mill

Gavin tacked one of the steps in a subsequent sub on his TLR250, removing a nice big rock in the process. I won’t say this is the reason I failed the sub, but it must have been a deciding factor 🙂

The Rock

Just to sum up this last group, managed to 5 the last sub; I need to work on my turns and climbs as sure its a matter of confidence. Lining it up and getting the power on correctly would help too. Andy cleaned and Gavin dropped a single dab, and we checked our time, 23 minutes from 6.5 hours to spare. Last bit of roadwork brought us back to the start, after some great sections and good weather, time to reflect and think about how I screwed all those sections up.
Last section of the day


Quick drink before we left and the results; Andy 8, Gavin 19, Malcolm 73, giving us a total of 100. my second half ride not being too clever. The Wye Valley team were 5th from 7 teams, with the 4th placed team, South Birmingham I, loosing 34 marks. So made me feel slightly happier as we were no where near them. Dan would have had to drop less than 7 for us to get 4th. The Peterborough team won, dropping around 4, with one of their riders going clean.

Not an easy trial for the clubmen, but though people went clean and the likes of Colin Leese, Dave Thorpe, Nigel Birkett and others dropped < 5, it shouldn't be made too much harder, especially if you want to encourage the club teams and a strong entry. But, hey, I would say that. Great trial, good fun and though (as normal) I could have ridden better towards the end, had a really good day.

The TY lives again!

The mystery electrical problem goes on its summer hols

Weeks of head scratching have taken place while the TY gathers dust. Consultation with an expert in the field of jun- er, classic bikes and a bit of
diagnostic work revealed a distinct lack of spark.

A vote of the TY owners’ syndicate resulted in a resolution to get hold of a flywheel puller. JK Hirst supplied a new condenser, coil and HT lead (on the basis that they were cheap), which finally arrived after a couple weeks’ delay – neatly timed to coincide with Nick’s return from sunny Bloomfontein.

First on the list were the TY’s forks, never its strong point, which had developed a very distinct leak on the right-hand side after the first sessions of abuse around the farm. Draining the left hand fork produced a mucky black mixture. This seemed fairly unpleasant until the right fork was tapped, producing a copious rust-brown effluent.

After much struggle, the forks were disassembled, degreased, cleaned and covered (intentionally and unintentionally) in oils of many weights. We even managed to get them back together again, and in the right order. 15w fork oil and some new fork seals got some additional protection from tasteful black fork gaiters. At the very least, the oil should stay inside the gaiters and not run down into the front brake! We also made the saluotry discovery that our mudguard was not bent, but rather whichever previous owner put the front wheel back on last had put the spacers on incorrectly. So now the TY has a front wheel in line with the rest of the bike, putting an end to its budding career as a Daytona 1200 impersonator.

With the easy bit done, we settled down with our flywheel puller and an assortment of old TY workshop manuals to diagnose the mystery electrical problem. Which is to say, Nick sat down, while I stood and kicked. Initial analysis suggested that the condenser was toast, making the replacement an inspired purchase. After struggles with solder and knives, however, no improvement was evident at the plug. The coil and lead were changed, again producing no improvement. In desperation, the magneto’s coils were removed, cleaned, inspected and replaced. A desultory kick was attempted, eliciting (to our surprise) as healthy a spark as 6v electrics were ever likely to produce. After the usual ceremonial dousing of the crankcase with premix and swearing, the TY fired first kick and was soon thrumming away happily to itself.

A short test ride and some mild leaping from highish things showed substantially improved damping from the forks. Whatever magic had been worked by Nick on the electrics produced substantially improved tickover and bottom-end response, and turns became tighter and wheelies easier than ever. We’re both looking forward to actually getting the TY in a trial!

Arthur Bates Trial 8th June 2008

Warm and sunny like the previous year and 72 entries for the 2008 version of the Arthur Bates trial.

The trial takes a circular route around Rhayader and this year it was run in an anti-clockwise direction and uses a couple of sections from the Classic Experts.

The start at Smithfields saw a healthy number of Honda TLR’s (as usual) and Fantic’s in the twinshock class, with 2 Ossa’s, 1 Beta and 1 TL125. (the gallery of bikes is attached to the end of the article).

Mark looking the part

A fairly confusing start, which involved getting people away as quickly as possible though never was clearly stated that it was 1 minute intervals. Always like the start from Smithfield as you get to ride off from the middle of town. The Rhayader trials, this and the Classic Experts, are based on double subs; long sections but really on 15 sections to walk.

First double sub at Aberceithon and I’d noticed on the run down that the bike wasn’t running smoothly. Could be timing though I’ve changed two-stroke oil from Castrol TTS to Motorex. We’ll see. Straight forward first part, then a turn and exit over a rock step, where a dropped a wasteful dab getting the bike lined up.

First section

The Beta’s not picking up well, but spluttered round on the road to Ashley’s. First section had an awkward off-camber slope after a tight turn. Gavin, first up, in sunglasses picked up a surprising 5, whilst I managed a not very slick 3. The second half of the section was straightforward. The next double sub was interesting with some awkward gullies and then a murky pool with some loose boulders in the bottom. Choice. Picked up my first 5 of the day, but avoided flooding the bike in the pool, just. Gav picked up a good 2 on the first half and like myself managed to clean the second half.

Round to Cross Keys and three double subs. First things first, changed the plug as no doubt when the old one was taken out it was oiled up. First section was a familiar one. Managed to get over the crux rock step by taking a line to the left, but then screwed it up on the top set of rocks; as always on the bit you weren’t originally looking at. The other two double subs were tricky and with both second halves having some nice muddy sections.

Back on the road and round to Cefnllyn, a nice stream section thats usually included. . The first half was in the stream but involved a loop round a tree with a step off back into the stream. The second half came out of the stream and across a the boggy section; more a case of finding a suitable line and giving it a blast. Got another 5 here, but only I ended trying to exit on the right, when the left hand line was the better option.

Cefnllyn: lots of mud

Really long road section then, including along the A44 and A483 round to the Bryn double sub. Don’t mind road work on lanes and a short section of main road, but this was fairly painful and had to get my numb bum and fingers into life. Also check to see if any bits haven’t vibrated off the bike. Nice collection of E-Type Jags coming the other way, though the actual number was heavily debated with estimates ranging from 5 to 40…..

The section at Bryn again had an easy half and a hard half; the latter being the exit round a muddy corner then up a steep slope. No grip here for me, though with a solid attempt in 3rd.

Alan at Skeleton Alley

A shorter run then down to Skeleton Alley, three double subs up the road from the lane. The first on the side of the hill was as hard as last year, though managed to clean the first half. Made a mistake on the last section and selected 1st gear and didn’t carry enough speed through the cow muck into the slope. Whoops. Bike smelt nice though.

Nice run over to the hill to the last two groups, including going past 5 (or so) E-type Jags outside a hotel.

Brynscolfa was a double sub in the stream and remember launching the Jumbo up here at speed in the past. Some good riders here and its a good feeling to get it right.


The second section at Bwlch had a nice muddy exit slot; excellent. I dropped 3 on the exit, but this is where Phil Wiffen dropped one of his two marks.

The last section was the scene of Kev’s famous first section drowning on the Beamish (and Andy Pitts in the last Classic Experts). The left hand marker was far enough left to avoid the main step in the stream. Gav took this line for a clean; I went for the purist route and took at 5; at least I felt happy about the ethical decision 🙂

Finish: another team photo

Short run back into Rhayader and the start and made it back for an astonishing 14h45, probably our earliest finish and not at the back,.