Jumbo for sale

Heavy heart and all that, but genuine reason for sale

I’ve been thinking about it for a while and Martin has been running an advert for the bike for a while.

A few calls but I’m now ready to sell it. It went well at the Classic Experts , pulled well low down, got plenty of grip and could handle it in the streams and with rocks. It more down to me and have probably developed a mental block riding.

Its a 350 and pulls like it. It’s not as small as a TY175, but its not a big bike. So if you are interested have a look at the articles that make up the Jumbo story

Looking for around £950-1000 for the bike and there are some spares (including a barrel, piston, front light unit and a spare PHBL28 carb.

If you are interested give me a call on 07720 079845

Jumbo in the Rain

Jumbo: LHS



Jumbo 4

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

Tweaking the Jumbo

Following the first couple of trials, the Wye Valley classic trial and the 1st Sammy Miller round, the Vic Ashford Trial , it was time to look at what was working and what isn’t working with the Jumbo and make some alterations if needed.

Following the Wye Valley trial, there were a couple of problems with the bike;
– it was clear that the kickstart shaft was knackered and I must have put the bottom kickstart knuckle back on the shaft about 10 times; so much so, I gave up turning the bike off and left it runnng for most of the three laps.

With Gavin rebuilding the 320TLNW I had sold him a couple of weeks before, he noticed that his kickstart spline was also screwed, so suggested a modification. The problem is that the kickstart shaft is hollow, with the gear selector shaft running inside. Therefore, you cannot overtighten the kickstart bottom knuckle as it pinches the selector shaft and it tends to slip on worn shafts.

Therefore the solution was to put a line of weld on the outer half of the splines on the shaft, so that they lined up with the gap in the bottom knuckle, giving it something to tighten against. Drilling or trying to attach the knuckle to the shaft in someway is a little tricky. The only downside is that having a 2-3mm line of weld on the shaft makes it a little awkward to remove to the clutch cover…

Other encountered problems on the Vic Ashford trial
– decompressor cable broke, so luckily the modified kickstart shaft held up for 28 of the 30 sections.
– chain tensioner spring also broke
– leaking fuel cap
– lack of low down power, especially in first gear.

My soldering skills (or lack of them) was to blame for the cable and the tensioner was a little tired, so simply replaced the spring. Need to make another fuel cap seal, so will carve another one out of an old inner tube.

The power issue was a little puzzling, as the Jumbo has a fearsome reputation, so some further investigation required. One thing to try first, was to repack the exhaust mid box, as when it was looked at originally I took out the packing. In hindsight, this has changed the back pressue characteristics and probably contributed to the missing spurt of power in bottom. More on this after the next trial to see if it has improved the situation.

SWM Electrics

Though I’d blown a couple of condensers on the 320TL, I’d but this down to problems with the loose connections on the wiring, but the Jumbo seems to have also developed the same habit.

When I’d originally got the Jumbo, one of the main problems was that electrically is was the proverbial dodo. At the time, in order to get a spark I’d swapped the stator plate and loom (probably a generous description for a simple wire and return) from the 1980 320TL. The wiring layout is different on the stators, with three wires on the Jumbo being connected to the condenser, this now being on the 320TL (but they are now swapped round).

SWM 320TL stator plate

The main problem was that Jumbo was now eating condensers, with two failing on the same day. Ok, the condenser is potentially the weak spot on the circuit, so rather than being a problem with the condensor its an indication that all is not well. The purpose (as far as I understand) of the condesor is to store (briefly) a charge and prevents arcing across the contacts, and burning the contact surfaces.

Jumbo stator plate

Ok, so looking at why the electrics were playing up, what are the potential causes ?
– loose connection. I blew a condenser on the 320TL on a Gwent Schoolboys trial and this was (I thought) because the earth lead from the ignition coil had come loose from the mount on the frame after one of the bolts had dropped out.
– problems with condenser(s) failing. The original condensers (that are soldered onto the wiring are much larger that the later condensers, but unlikely that all the condensers I’d had were not good.
– contacts, either the gap is too small or too large, or not properly prepared.
– poor wiring, there is a fault in the wiring, with a short somewhere
– ignition coil failing, could be breaking down as the bike heats up or problems with spark plug.
– bad or poor earth.

So the facts about the ignition system. I’m using NGK B5ES plugs (I’ve not checked the gap), contact breaker gap is 0.40mm and the bike is using the stock, original wiring. So, in a systematic attempt to prevent the world supply of SWM condensers being consumed during 2007, did the following work on the Jumbo:
– condenser: put in a old-style larger condenser (thats all I had in the workshop)
– changed the ignition coil. The one that came with the bike has seen some action (and some silicone sealant)
– checked the continuity, including the earth across the whole wiring loom. I find that doing continuity tests on the contact breaker to be very confusing (it never gives you the reading expect)
– cleaned the contact faces (they weren’t scorched) and reset the gap
– new B5ES plugs (from ebay for £1.20 each)

Also, then did the ignition timing with a strobe and set it to close to TDC (for now) and will adjust later. More reports on the electrical system to come, no doubt.

The Completed Bike

…well its just about complete and its “ready to trial”. Thought I’d add some pictures to show the finished article.

Been running the bike for a week and I’ve been able to get it road registered as well. The engine has been settling down and sounds a bit smoother. Also managed to put a stud into the striped thread for the exhaust manifold, so have got that tightened up.

SWM Jumbo 350TL

Did briefly consider taking the bike down to Robinson’s Quarry for the AL King trial series run by East South Wales Centre to give it its first trials outing, but had visitors etc, so it can wait a week or so [1]. Currently content to give it a run round the field and local roads (though do need to getting a number plate made up for it\). There is a bit of smoke, but all the gears are there and it pulls well. There also seems to be a slight ‘lurch’ with a noise when pulling away quickly under load and there is a noise from the rear wheel, but have a set of bearings to put in if needs be.

SWM Jumbo 350TL

When recovering the seat, noticed that the base was broken, so hence the swoop up on the front of the seat, something that could be a bit nasty.

I need to work on the specification sheets for the Jumbo and add in some of the facts and figures I’ve picked up during the project. The site / blog has been getting some visits and hopefully will be a useful resouce for people working on SWMs and other trials bikes.

SWM Jumbo 350TL

The Jumbo runs…

Starting at the end of August, its taken 4 months to get the Jumbo up and running. A spin round a rather wet and muddy garden and things sounded good.

After getting the new piston installed and the initial start up some further fettling was done prior to giving the bike a longer run:
– added the 50mm springs that were originally in the front forks; they aren’t stiff enough without them. The cap on the damaged fork doesn’t has much thread holding it in place so will need some further work, but being 35mm rather than 38mm forks means I can change them with the TL280 forks I already have.
– changed the rear shocks to a longer set (14″ instead on 13.4″), with a 50 rather than a 40lb spring rate. Need to look at getting the right shock set up now the bike is running.
– put in the lever adjuster for the clutch cable in place; the adjuster on the second cable seems to be threaded
– one of the threads for the exhaust manifold bolts is knackered, so will need some remedial engineering
– swapped the kickstart level over; the replacement I’d had from Martin Matthews seems to pretty badly worn, so have used the one from the recently acquired TL280.

Jumbo running...

After getting the bike running and the carb cleaned out the previous day, it was good that the bike fired up with the choke on the third kick. The engine seems to take a little while to warm up, but does sound ok and pull well after a couple of minutes.

The ignition timing is currently set to the middle of the adjustment, though I’ll look at advancing and retarding it later to see what will give the best trials performance.

Getting the bike on the road

Road registering the Jumbo. A How-to for all twinshock owners

I’d road registered a couple of bikes before (a Yamaha DT250 and a Honda TL125), so had an idea of what to do

What you need:
– Registration of vehicle form (V55/4) from the DVLA. Contact the DVLA help line and they can post you one. More information on the DVLA website .
– a dating letter (for the bike, not a lonely 40-something)
– an MOT
– insurance
– personal identification
– the first registration fee and the annual license fee.

Dating Letter
If you want an age-related plate, rather than a “Q” plate you will need a dating letter. This needs to come from a club, association or organisation that is recognised by the DVLA as able to provide an official dating letter.
There is a list of vehicle owner’s clubs on the DVLA site who can provide a letter authenticating the date of manufacture of the bike. I’ve used Roy Bacon a couple of times and he charges a £25 fee to provide the required letter. For the Jumbo, I provided him with some photos (including one of the VIN plate, which includes Anno Fab. 1983), a quote from Peter Knight / Rotax which showed the date the engine left Austria to go to the SWM factory in Milan and the engine and chassis numbers. Also worth including the engine capacity on the dating letter. As from the 1st January 2008, agencies that produce dating letters are required by the DVLA to have a photograph of the engine and frame numbers.

You will need to MOT the bike, usually for daylight use only. The detailed requirements are provided on the MOTUK web site. For me the key items to bear in mind are:
– finding an MOT tester (or testing station) that understands what testing a trials bike is about, ie testing for a daylight MOT
– if you don’t have working front and rear lights, you don’t need indicators, break lights or reflectors
– you do need an electric horn (not a bulb one) for a bike after 1.1.1973 and it has to be audible
– registration plate; the MOT tester’s manual talks about layout, but not size (?). For the first MOT before getting a registration, the MOT is done on the chassis/VIN number, not the registation.
– making sure the bike is put together correctly and bolts are tightened etc

I’ve used Ray Griffiths at Eric Rees Motorcycles in Hereford for my trials bikes and this is where the Jumbo was MOT’d. I took it on the van, but if you want to ride the bike to MOT testing station, you need to phone in advance and make an appointment (to cover yourself with the cops). The current bike MOT cost is £27.50, which is around half of the car cost (which is fair enough given it has half the number of wheels).

I’ve a road bike and a couple of trials bikes on my insurance policy with Carole Nash all part of the same policy, but the Jumbo presented a couple of challenges. Carole Nash’s classic policy only covers bikes up to 1982, and not the SWM, and my insurers (Admiral) required more information on the bike. I spoke to their Customer Services dept, because I had an existing policy, but getting a new quote might be a challenge.
Therefore, sent an email to CN, attached a couple of photo’s and a link to Martin’s web site SWM history page. About 30 minutes later, they confirmed they could insure the Jumbo also rating it the same as a Honda CR400 (?) and for £26.00 per annum fully comp.
The insure on the chassis number for 14 days only, so you need to have all the other documents in place and a trip to the DVLA office already planned.

Trip to the DVLA office
You will need to visit your local DVLA office
to submit the forms. I’ve used a couple of DVLA offices, Worcester and Cardiff and they don’t do things the same way.
At Worcester, they always have in the past always insisted on a vehicle inspection, despite having an MOT, and this can only be booked once you have submitted the application. Therefore you need to make two visits.
For the Jumbo, I went to the Cardiff DVLA office at Ty-Glas, taking the bike in the van. Submitted the form, with the supporting documentation and my personal ID (driving license) and that was it; they don’t require a vehicle inspection and the bike stayed in the van unlooked at. The Cardiff office was revamped in December and although parking is a bit of a problem, took 15 minutes to queue and complete the process.

The first registration fee is currently £38 and the license fee for a 150-400cc motorcycle is currently £31.00.

You now have a road-registered twinshock you can use for ‘proper trials’. The Jumbo is ready to go; it cost me £116.50 to get it on the road, not cheap, but does mean you can use it for Sammy Miller and ACU classic trials.

SWM TL350 Jumbo: Replacing the Piston

After getting the right piston, a simple (sort of) job of installing the new piston and getting the bike running

After identifying that the barrel was worn and that piston I had was too small (see article), I bit the bullet and ordered a new 84.25mm 2nd overbore piston from Peter Knight. It took a couple of weeks to come over from Austria and when it arrived, it turned out to be the same size, 84.17mm, as the piston that was already in the bike. The sizing must therefore be for the barrel, rather than for the piston, so sent it back and promptly got the 3rd overbore, 84.50mm piston back.

However, by then it was Christmas Eve, so no real opportunity to get the barrel bored out to the New Year. After a quick chat to a couple of people at the Herefordshire Classic trial on News Year Eve, took the piston and barrel to Hereford Rebore

Quick service, got the bored barrel back the following day. The barrel hadn’t work evenly, so there was an area low down on the barrel that didn’t get machined. Re-assembly took a couple of hours, mainly due to time taken to get the new gudgeon pin and circlips in the piston. The Rotax pistons have an arrow marked “Aus” (which I assumed was something like Ausgang or exit, ie the exhaust port), so after some deliberation decided that the this pointed to the front of the bike. When I stripped the engine, the piston had the arrow pointing to the rear, inlet port.

Jumbo in the workshop

Initially the bike didn’t want to fire up and the kickstart lever kept running off the shaft after a few kicks. You can’t overtighten the shaft as this then pinches in the internal gear change shaft, so as a shortcut, while I look at the lever later, took the kickstart off of the SWM TL280 I’d just acquired.

Changed the plugs a couple of times, though they were “wet” and had a good spark, but then the bike fired up. No rattle or slap from the barrel, but the bike would only run with the choke on and only then for a couple of minutes.

Seemed like possible fuel starvation, so took the carb back off the bike. It took a couple of go’s but where I’d changed the float needle before (see), the housing had become clogged with the stale petrol being washed through, so petrol was only seeping through into the bowl.


Changed the fuel pipe from the tank to the carb, as it had split and put the carb and tank back on the bike. Again a few kicks required and she fired up, again no rattle. Time for test spin round the garden, though by now it was 20h00, very dark and raining. Managed to negiotiate my way up a pitch black and very muddy lawn to ride round in lights on the drive, all sounded good. Had to adjust the clutch in further and also moved the bars further forwarded, as well as apply some cable ties to the main cables so that the routing under the tank was ok.

Well, its a running bike, with a few small items to finish off, this includes:
– the seat needs recovering
– front brake mounting bolt sheared and was fixed with araldite; a more permanent solution is needed
– cleaning the plastics, mainly the tank and side panels
– replace some of the old original cables and put the adjusters into the cable system

Hopefully can get an MOT done fairly soon, work commitments allowing.

SWM TL350 Jumbo: Wheels and Brakes

The wheels on the bike were a little scruffy, as where the hubs. The brake pads themselves useless, so should a case of just cleaning them up.

The wheels on the bike have stainless Akront rims, with steel spokes. The spokes all seem tight and didn’t really need much in the way of work, though they are a little rusty in places. Swapping them for some stainless ones at somepoint in the future may be desirable. The rims, the front especially, were well marked, so looked to clean them up and get out the Autosol for an hour or so of cleaning to see how they came up.

I ordered new break pads from MotoSWM and cleaned out the hubs. Removed the glaze using some wire wool and just general tidied up the wheels. I also replaced the front and rear wheel bearings and as the front in particular seemed a bit worn. The bearings are standard sizes, but got those from Martin Matthews.

I also replaced the front and rear tyre clamps, as the original one in the rear (the front didn’t have one) had little rubber on it. They are WM-2 1.85 sized clamps and I got them from LG Racing in Pontrilas, who are a local Motorcross / Enduro supplier who travel out to lots of events and run a mail order business.

I also got the tyres from LG Racing and went for a Pirelli MT-42 front and a Michelin Trials Competition rear. This is a cheap combination (£30 and £49 each) and I like the Pirelli fronts. They are a stiffer tyre and having used them on the Honda in the past know that the rears are not as good as some modern tyres. Michelin X11 Trials Comp’s or IRC’s are probably better on the rear, but are an extra £20 and may not make a real difference except in the long run.