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Bike Profile - Posted 10th October 2011

2010 Jawa 350 Classic
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David Mace experiments with de-restricting his 350 two-stroke twin, and unleashes its inner beast...

In RC88, I wrote about my first impressions of my Jawa 350 Classic, purchased new from F2 Motorcycles in early 2010. For those that missed it or couldn't stay awake until the end, the bottom line was that I was very pleased indeed with my purchase. Build quality is good, and handling, roadholding and comfort were all very impressive indeed, and the performance was better than I had expected, having been aware that some people used to refer to the older models as 'tractors'.

That being said, I had the distinct impression that the bike was somewhat 'strangled' having had to be restricted in order to pass the current noise and emissions regulations as imposed by the Brussels fun police. I speculated that it would be interesting to see what would happen if these restrictions were removed - not tuning the bike per-se, merely letting it breathe and run as its designers had intended.

2010 Jawa 350 Classic, before derestriction... 2010 Jawa 350 Classic

Luckily for me, the ever-resourceful David Angel (proprietor of F2 Motorcycles, the UK Jawa importer) had the same idea, and had spent a great deal of time experimenting with different modifications, until he felt confident to offer a tune-up kit, which I duly purchased. The kit addresses the restrictions on both the inlet and exhaust side of the engine.

New gasket goes in here...

Starting with the inlet side, the standard inlet manifold gasket is restrictive, having a hole notably smaller than the bore of the carb and the inlet manifold into the barrels. A replacement gasket with a much larger hole is provided, and is a piece of cake to fit. At the same time David provides instructions for modifying the standard carb settings, and also for letting more air enter the airbox, which as standard is almost hermetically sealed.

Next comes addressing the exhaust part of the equation. The bike as standard is remarkably quiet, the long shiny silencers on the Jawa containing long, very restrictive baffles. The tune-up kit contains shorter 'sports' baffles, and in addition David's instructions tell how to modify these further for optimal performance. It's nothing difficult, needing just a hacksaw and a pair of stout pliers, but makes an important difference.

Take up the strain, and... Heave!...

The final part of the job is to make some simple modifications to the exhaust downpipes using the aforementioned hacksaw (and I'd recommend a brand new, sharp hacksaw blade, the pipes are made of sturdy stuff!). Again it's a very simple procedure, the biggest difficulty I had was in separating the exhaust pipes from the silencers. That was a surprise as they are just a simple push fit, with the exhaust going through a neoprene seal in the silencer. However this seal is a pretty snug fit and will grip the smooth chromed exhaust fairly tightly at the best of times. Add a bit of carbon residue to the inner part of the exhaust (as you will have done whilst running-in the bike) and you find that the silencer seal has a pretty tenacious grip on the exhaust pipe.

Hacksaw attacks this bit...
Jawas on Right Now......

It's at times like this that a helper would be very welcome, ideally a helper with the sort of build as those chaps who typically anchor a tug-of-war team at a village fete. Whilst I don't have any direct experience to justify the comparison, I couldn't help thinking that pulling a fully-laden pack mule out of a quicksand pit would have required less effort than it took to separate the Jawa silencers from the exhaust pipes.

In any event, it was eventually done, and all was soon back together again. Was it worth it? Oh yes!

You can almost *see* the extra power...

The transformation of the bike was quite remarkable. The changes have made it much more lively, particularly in the mid range. It wasn't at all bad before, well able to keep up with general traffic flow, but where previously if one opened the throttle from a moderate cruise it would pick up speed in an acceptable manner, now there is a noticeable 'kick' of hard acceleration.

At first, when riding the bike around my usual test route that I use whenever I want to try out the effects of a modification or to test the results of a repair job, I thought that maybe the tune up kit had drastically reduced engine braking, as I kept arriving at corners much faster than I was used to or had intended. It took a while to realise that two-strokes don't have much engine braking anyway, and that what was happening was that the bike was arriving at the corner at a much higher speed, due to having accelerated away from the previous corner in a much livelier fashion.

It's also good to note that the modifications have not in any way made the bike anti-social. The sports baffles are supposed to increase the noise output by a few decibels, but in all honestly it doesn't seem noticeably louder to me, though I would agree that there is the hint of a harder edge to the exhaust note.

2010 Jawa 350 Classic, after derestriction... 2010 Jawa 350 Classic

For the modest sum of 75 the Jawa tune-up kit must surely represent the best value for money performance upgrade available anywhere, and I can thoroughly recommend it to any owner of a Jawa Classic, I can guarantee you won't be disappointed.

I'm now awaiting delivery of the latest F2 modification, a new gearbox sprocket to raise the gearing somewhat. The derestricted bike will easily be able to pull a higher gear, and this should make main-road cruising even more relaxed, whilst extending the range of third gear, ideal for hustling round country lanes.

These changes really have taken an already good bike to another level. It's no Fireblade of course, but if you like classic-type bikes, perhaps you go on ride-outs with a classic bike club or like to attend classic rallies, or just like riding country lanes, then the modified Jawa Classic will be more than up for the job.


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