Author Topic: Trawling for Insight  (Read 19641 times)

Offline L.A.B.

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Re: Trawling for Insight
« Reply #15 on: September 08, 2007, 02:20:15 AM »
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My Type 632 outfit towing a Velorex 700 has a top speed of 89 MPH, though riding outfits at this speed is akin to flying a twin engined bomber on one engine.

I hope you are not quoting that from the speedo reading? As the speedo on the one I  rode showed at least 20% fast.

Quote
The original JAWA 350 Type 634 had a small airbox and filter from the 1960's Californian model. This put out 22 BHP. Later ones churned out 28 BHP


Yes 28 BHP @ 5,250 RPM as stated in the owner's handbook and workshop manual.

Yet the handbook/manual quoted torque figure of 3.4 kgf/m @ 4,750 RPM for the 28 BHP model doesn't convert to anywhere near your quoted figure of "massive 38 pounds per foot torque" that you mentioned?

(3.4 kgf/m x 7.233 = 24.5922 lbf/ft .)

Or: http://www.gordonengland.co.uk/conversion/torque.htm
L.A.B.

Offline Panzergranate

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Re: Trawling for Insight
« Reply #16 on: September 08, 2007, 03:21:17 AM »
The speedoes normally read 2 to 3 MPH slower than actual.

I received a ticket for 38 MPH from a following motorcycle cop (I'd seen him) when my speedo reckoned I was doing exactly 30 MPH in the 30 MPH limit.

It's probally because some are sprocketed down for sidecars. Changing the 18 tooth front sprocket fo a 15 or 16 tooth for a sidecar, on a gearbox driven speedo, will have a huge effect on the speedo. I've always had the ones with under reading clocks. I've had mates ride alongside on various Japanese bikes over the years and comment on the speedo underreading. The trip meter also always measures distances less than mates bikes on long trips, etc.

Which manual are you reading?? I've have two of the various workshop manuals they produced including the early version.

The Type 638 has a 29 - 30 Pounds per Foot torque reading, but this is a higher revving engine. The unrestricted 1986 version made 34 BHP and had a reline at 7,000 RPM. I've had two of these. A friend still has two in his garage. Later post 1988 version had restrictors fitted in the carb manifold, exhaust baffles (a large choker collar) and in the airbox, to comply with Dutch and Austrian 350cc motorcycle power limit rules.

These only make 23 - 25 BHP and do just 80 MPH grudgingly. I know someone who imported a Austrian RD 350 YPVS that was restricted in a similar was to 27 BHP. It took a lot of money to unrestrict it. We are so lucky here at the moment!!

The CZ 250 was rated at 28.5 Pounds per Foot, exactly the same as the GT380M, another bike I've had here.

As (Torque x RPM) / 5,252 = BHP (I've operated a proper torque measuring dynomometer!!), generally high revving engines will have lower torque rating than a lower revving engine of the same cubic capacity. It's a fact of engine physics.

The Japanese went for low torque high BHP engines and JAWA, CZ and a few others went for high torque low BHP engines. MZ and a few others went for the middle ground.

The old RD250 put out less than 20 Pounds per Foot torque.

As BHP, like Wattage, is a calculated resultant number from two measured figures, it can be totally meaningless when quoted out of context.

25 BHP on a 125 will feel totally different to 25 BHP on a 250, the 125 having less obviously less torque than the 250 in order to make 20 BHP.

Basically BHP is a calculated measure of crank innertia, which is what does the work. HP is calculated from Wattage created from a generator and works out at a higher figure than BHP. This is Watt's Horsepower.

Then there is Power Starken (PS) which works out to be about 1 PS = 0.86 BHP. So a bike quote at 100 PS is actually 0.86 BHP and 1 HP is about 0.94 BHP.

The Dynos that folks can go and have their bike tested on measure HP and not BHP, uless they can give a torque reading as well. If it is calculating through current produced  only, then it will be measuring Wat's Horsepower only (HP).

It is the torque that accellerates a bike and it is this that the rider feels. High torque engines will always out accellerate high horsepower bikes of the same cubic capacity.

Having tuned strokers for drag racing and road for so long, I generally just ignore horsepower quotes and focus on how much torque I have to work with.

My old Suzuki GT 550 B drag bike used to shatter the cluctch basket on runs. I warunning Nitro Toluene diluted with petrol, but the torque still destroyed the transmission from time to time. That had frightening amounts of torque and delivery.

The world's current fastest accellerating production bike, the Feuling W3C, 2.5 Litre has 216 Pound per Foot torque and puts out 217 BHP at the rear wheel. Best top
speed, down an airstrip with the rider strapped on, was 228 MPH and still going.

The bike is a naked super cruiser, like a V-Rod done properly. Needless to say, being a fan of high torque for their size engines, I want one!!

Go type in Feuling W3C and see for yourself.... its fantastic.
I'm no Power Ranger!! I'm a genuine spanner welding, engine fxing, bike restoring proper Biker!!

Offline Panzergranate

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Re: Trawling for Insight
« Reply #17 on: September 08, 2007, 03:52:46 AM »
The point of the original posting has been missed here, anyway.

On the advice of friends who've owned and suffered these and myself also, usually having to try and mend them, avoid any of the following.:-

Voskhod 175.... No body has ever seen one running!! I know a friend who has one and it has never run in 15 years despite his and mine efforts. He see it as a challenge.

HONDA CB250N Superdream.... this was the slowest 250cc learner bike in the late 1970's and early 1980's.

Every magazine slagged them off. Bike magazine speed tested one and stated that it was 3 MPH slower than the CZ 250 and MZ 250,at 83 MPH, making it the slowest 250 on UK roads.

Chinese 125s will out accelerate it!!

It is so unbelievely heavy for a 250.

"They don't accelerate actually, they sort of gain momentum", is what a friend reckoned about it when he rode one.

Basically they're overweight slugs and have put many youngsters off motorcyling for life in their heyday.

Bike refered to them as the "Side Street Sleeper", everyone else called them "Wet Dreams"

Exhaust note is like a sick BMW.

Just don't even consider buying one.

Yamaha XS 250/400.... carb diaphrams, similar performance to a Superdream, mechanical auto advance rusts and seizes up. However they do sound good when they run.

Any Kawasaki with KH in front of it, unlessyou enjoy constant maintainance and fettling. These are for serious fanatics only. They were just as bad when new!!

A GT 380 makes a reasonable choice of classic bike.

It sounds good, spares support is good, easy to work on.

It isn't that fast, even when new they do only 101 MPH.

OK they handle poorly but aren't the worst 3 cylnder bike with handling hastles.

The engines are pretty easy to rebuild and the only bug with them is the wiring rotting with Verdegris, a problem with all old Suzukis.

They go and sound good.

They were generally stronger buit than the finnicky and fragile Yamaha and Kawasaki 2 strokes.

The Japs did manage to make the occasional reliable 2 stroke bike and the GT380 is one of them.

I'm no Power Ranger!! I'm a genuine spanner welding, engine fxing, bike restoring proper Biker!!

Offline L.A.B.

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Re: Trawling for Insight
« Reply #18 on: September 08, 2007, 03:53:18 AM »
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Which manual are you reading?? I've have two of the various workshop manuals they produced including the early version.

= First edition (A).
L.A.B.

Offline Panzergranate

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Re: Trawling for Insight
« Reply #19 on: September 08, 2007, 09:51:40 AM »
I've that one for the 1974 models in the garage somewhere.

I've also the late 1970's (B) and (C) Manuals. Also the Type 638 TS 350 (NOt KS 350 versions) dealer service manual (the glossy one), which I bought in Prague.

Over here it cost £38, over there it cost me £6.

A friend has the joe public service manual. It is the usual red covered recycled paper type one, just like the old Type 634 manuals.

My brother had the GT380M at the same time that I had the 1977 JAWA on the road in 1988 and he used to hate the fact that the JAWA peed all over the GT except on top speed. I'd hit f;at out at 96 MPH and see him gradually closing in the mirrors, then stagger past flat on the tank in a cloud of smoke.

Then I made the mistake of porting out and gas flowing the GT, fitting K&N filters, changing the needles and guid in the carbs for GT550M ones and fitting All Speed Formula 3 racing pipes (not the joe slow road ones).

He could now out accelerate the JAWA and also make 65 MPG instead of the stock 45 MPG. Another improvement was that the GT could cruise in top gear, something stock GT380s struggle to do as top is usually the downhill gear.

Top speed was about 115 MPH and the bike had 44,000 miles on the clock by then. He raced a Honda NS400 once and out paced it.

It was immaculate and still in the original black finish with perfect chrome. He sold it too a dick head who triked it. His new wife had made him promise to give up riding motorcycles.

A good GT380 can be had for under £500 with cosmetically pretty ones going for £1,000 or more.

They are a good all rounder, are surprisingly reliable and tough, for a Jap 2 stroke and are comfortable to ride on long distant rides. They also look just so different.

Avoid the Suzuki GT550 (I own one) as they have worst fuel consumption than an SUV (mine does 18 MPG cruising but it is tuned), handle like a drunk carthorse on roller blades and handle 10 times worst than a TL1000!!

No seriously, these bike put riders in hospital and you need to be extremely focused when riding one, because, just like a Welsh woman, they can go from nice to nasty for no apparent reason. I lost the front whilst lightly braking a GT550 on a hot summer's evening on a bone dry road at 30 MPH in a straight line.

I ended up in hospital.

The violent power delivery does make them eat a lot of internal parts and also contributes to the terrible handling problems.

Like all evil handling bikes,  GT550s steer on the throttle. Any bike that steers on the throttle has handling issues. The GT550 totally steers on the throttle.

I let people ride mine and had them come back white as a sheet. A mate still jokes today about the YPVS owner who has so shaken up that he couldn't stop shaking or let go of the bars when he came back.

I've crashed mine at 20 MPH even when the bike sat up and decided that it wanted to go up a bank rather than around a corner after I shut the throttle off mid bend.

Oddly enough, the GT380 has none of these evils, apart from the flexy frame.

I recomend either the JAWA 350 or the Suzuki GT380 as they are both tough as nails, easy to maintain, easy to source parts and have dedicated owners club followings.

Both look so bizzare today too.
I'm no Power Ranger!! I'm a genuine spanner welding, engine fxing, bike restoring proper Biker!!

Offline L.A.B.

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Re: Trawling for Insight
« Reply #20 on: September 08, 2007, 07:05:04 PM »
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I've that one for the 1974 models in the garage somewhere.

The 'A' handbook = 1976 (well that's what it says!) - same info.


Quote
Another improvement was that the GT could cruise in top gear, something stock GT380s struggle to do as top is usually the downhill gear.

As I own a standard GT380 I would have to disagree, my GT happily pulls sixth gear under normal conditions.



L.A.B.

Offline Panzergranate

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Re: Trawling for Insight
« Reply #21 on: September 09, 2007, 10:21:29 AM »
The coments, in the used bike magazines of the 1980's and 1990's were usually on the lines of the GT380 could only pull 6th level. On owner joked that the bike would do 85 MPH in 5th and 65 MPH in 6th if there was the slightest headwind.

My yonuger brother's GT380M could still manage to put 106 MPH on the clock (about 101 MPH in reality) when prone on the tank. He passed his bike test on the thing with a Sidewinder attached. It was faster without it obviously.

On long bike rally journeys, it was confortable and he even rode with his mate "Heady Skid", so named as he fell off of the back of another friend's GPX 600 and discovered that unlike on TV and in the movies, he needed to do his helmet strap up. Yep, he had gravel rash on the back of his thick head which took months to heal up. However the nickname "Heady Skid" is with him for life.

The split middle exhaust is what slows he bike up. A friend's wife's brother fitted another right hand pipe to his, ala the KHs, and this improved performance.

We junked the centre stand and saved about 3 stone on weight!!

The only serious problem he had wth it was when a piston ring broken and scored the left hand cylinder. It was 1 day before a rally and so I had to arrange for a mate's bike shop to rebore the cylinder that morning, fit the new piston and rebore cylinder, then have my younger brother ride up and down the local bypass, that evening, until he'd put 100 miles on the clock to run it partially in.

At 4 AM, the following morning, we met up with the rest of the gang and set off on a 300 mile run to a rally. We travel fast, hence the running in of the new piston and rings.

On JAWA and CZ speesdo errors....

On my cousin's XS250, 70 MPH on his clock was 62 MPH on a CZ 250 clock riding alongside. That was actually the first time I was aware of the error being negative and not positive.

Every JAWA or CZ I've owned reckons that cars and trucks in the slow lane on motorways are doing 44 MPH when it is obvious that they are doing 47ish MPH (50 MPH on a car speedo allowing for the up to -10% error).

My outfit doing 89 MPH.... the following Kwack GT550 had me at 93 MPH!! I could only stick at this speed for about 3 miles as the drag form the sidecar is extremely heavy on the bars. The bike wants to veer left and I have to use muscle power to keep it straight. This becomes very tiring.

About 60 to 65 MPH cruising is the fastest the thing will go without arm ache for the rider. Speeding on outfits is for masochists only.

Having been called in to fix numerous 2 stroke triples over the years, I reckon that the GT380 was the only practical one of that era. I've ridden and fixed KHs, which were luckily someone else's problem, all of which were horrid.

The last KH I fixed was 3 years ago whilst up at a mate's place in Oxford. Someone he knew had bought animmaculate Y -Reg KH 250 B5 but none of the bike dealers in the area knew how to set points (true)!!

So I was roped in and spent an afternoon servicing the thing.

I was even nice enought to struggle to remove the biscuit tin airbox, dismantle it, remove the engine power intake restrictor pipe in the airbox and reset the carbs again.

It now went better and did more than the stock 88 MPH that the B4 and B5 versions were restricted to. I'd converted it to B3 spec.  

The general rule with KHs is, unless totally insane, steer well clear of the things. They require constant fettling, even during rides, to keep going properly.

Given the choice between a GT380 and a KH400, I'd pick the GT380 ever time. They're just so nice to cruise around on.

Catenaccio, you can buy a sorted GT380 for under £500 at the moment. A GT380 will cruise at 70 MPH for hours on end, as my younger brother used to be able to match the cruising pace set by my 1977 JAWA 350 back in the 1980's.

We once rode from the M25 junctionof the M3 to the M27 non-stop at between 75 and 85 MPH coming home from one Essex bike rally in 1989. I was riding one of the 6 only 1980 rare unrestricted faired CZ350 Custom Sport Mk.III. bikes, which was the only stock CZ sold in the UK that could go faster than 100 MPH. Only six were built and I own one of them!! It is soooooo different than the stock CZ350 to ride.

You should look around for a sorted nice GT380 and you will find that it will fill your requirements just right.
I'm no Power Ranger!! I'm a genuine spanner welding, engine fxing, bike restoring proper Biker!!

Offline catenaccio

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Re: Trawling for Insight
« Reply #22 on: May 14, 2008, 06:09:20 AM »
Thanks for all the help and advice guys!

I've PM'd a couple of you before reading the 2nd page of replies. D'uh.

So please disregard those ..