Tech. 1

Clutch slip cure

Wayne Kennedy was having some clutch slip problems on his staggered crank XS650 and this is what he did to cure it:- I put new genuine clutch plates in the 650 but when I was doing so I measured some other steel plates I had and was surprised that there was two different thicknesses between them. One set was about 1.35mm and the other 1.6mm. (no they weren't worn) The early 6 plate had thicker steels, as I had put in a later 7 plate to try and stop slipping with the torque. I put the thicker steels in which saved me shimming up the springs, and also left out the rubber rings between the plates. Low and behold, no clutch slip and it is easier to get neutral when the motor is hot. A quick solution to anyone that has a hotter motor and having clutch slip.

Dave Bath also suggests it's a good idea to bevel the edges of the clutch friction plate fingers with a file (just enough to take the sharp edge off ) to reduce to possibility of these catching on irregularities in the slots of the clutch basket which is one of the causes of clutch drag. I've just done it to my new clutch and it seems to work. (Terry Gliddon)

Tony Warner also informs me that the XS650 has two different length clutch actuating arms situated inside the left engine cover, where the clutch cable attaches, so if you have a heavy clutch you may benefit from using the longer arm from an XS1 if you can find one.

While you are in there it is advisable to check the back of the clutch basket to see if you have any broken springs.

Clutch Shock Absorber Spring Refit 

Mikuni VM36 Jetting

I am in the process of adding a few extra ponies to my XS 650C, kit, carbs, head, cam and pipe.  Getting info on "correct" VM36 jetting for a kitted engine took a little time....but here is what I managed to get from Halco (UK) and the States (Bob Bertaut).  It might limit the amount of trial and error....though some members may well have all this baseline info at their fingertips. The HALCO pre-jetting is on the richer side and the Bertaut is leaner.  Both specifications fitted with free-flowing filters (K&N or Unifilters).   I'll  will keep you posted on the final jetting for my bike.

Carb: VM36
Main jet:    220
Pilot jet:     25
Spray tube(needle jet)    159-Q-2
Needle type:    6DH3
Slide:    2.5
Air jet:    2.00

Carb: VM36
Main jet:    190
Pilot jet:   22.5
Spray tube(needle jet)    159-P6
Needle type:    6DP1
Slide:    2.5
Air jet:    None, removed.

Peter Miller

Methanol in Four-Strokes
Tuning for Speed - Phil Irving
Four-Stroke Performance Tuning - A. Graham
Bell .

First things first, methanol is extremely poisonous and can cause blindness and insanity. It is absorbed through the skin or its vapours inhaled, and once it is in your body, it stays there.

Using methanol will have an 8% to 17% power increase over petrol.

It burns slower than petrol so ignition can be advanced 6-15 degrees to allow for this.

The running temperature is much cooler than petrol. This means that the air inducted for combustion is cooler and so it is denser and so supplies more oxygen. Because of the greater oxygen, the jet size is 2.2 times larger than those used for petrol. The slides are cut away to allow greater air intake.

Methanol needs less oxygen to burn :-
Optimum fuel /air mix for petrol is 1:12.5
Optimum fuel /air mix for methanol is 1:5.5

It is anhydrous in that it absorbs water from the atmosphere. If fuel is left in the system, the water it absorbs will corrode up the works.

Compression ratios can be ran at 14:1 as detonation is virtually non-existent with methanol.

It doesn’t mix too easily with petrol because of its tendency to absorb water, but 3-4% acetone can be used to help it blend.

A mix of 60% methanol, 20% benzole, 20% avgas, is a good substitute to 100% methanol as it uses less fuel and so requires a jet size midway between petrol and alcohol. It still retains the anti-detonation and cooling properties of methanol.

There is a danger of a washing effect of the bore wall with a rich methanol mix. The addition of caster based oil will alleviate this problem. Valve guide oil seals can be removed on the exhaust valves to also help with this problem.

If you are looking at a pure methanol fuel, try 97.5% methanol, 2% acetone, .5% Castrol “R”.

The fuel is expensive and is not as easy as petrol to obtain, but, if you choose this path, it would appear that you gain extra horsepower and the motor becomes more forgiving with regard to detonation and overheating. I expect that this could be a fair trade off for the risks involved in running an high compression ratio.

Tony Powell.


I recommend EBC pads and a 13mm master cylinder for the early 2 piston calipers. The late ones benefit from Ferodo Platinum and a 11mm master. Ferodo replacement shoes( FSB 735) are a good upgrade for rear shoes. Check the disc brake tips at my website.
XS1 front brakes have too light a link rod. Replace with Norton Manx ($50), or add a LH jam nut($1). Arm indexing also an issue here, as some off the arms are made wrong, apparently a carry over from the TD1. With the link rod disconnected, the centers between the actuating cam shafts and the link pin centers should be the same. Relining with the 2520V street compound is a big improvement, usually dropping racers lap times 6-8 seconds a lap.
And thanks.
Michael "Mercury" Morse
Vintage Brake
15069 Lupine Lane
Sonora, CA 95370
ph/fax (209) 533-4346

34mm Round slide Mikuni Jetting.

Some of the members have asked recently where to start with Mikuni jetting and I contacted the vertical twin discussion group for some input on this subject. Here are some of the responses:-

Mains: 180 to 190 is most probable. 
Pilots: 20 to 25. 
Needle jets: P5 or P6  both work well. 
Needles: 6F9; start tuning
in the middle notch. 
Slides: the generic 2.5 works fine. 
Air jets: remove.

Main: 180
Pilot: 25
Needle Jet: P6
Jet Needle: 6F9
2.5 slide 
That is at 1000 ft elev. depending on your exhaust should be very close. 

2.5 slides, 27.5 to 32.5
pilots, P-5 or P-6 needle jets, 6F9 needles, 180 mains, air correction jets
removed (standards are 2.0).  Usual disclaimers "Works great on mine, but no
guarantees for OZ" - doesn't the air spin counter clockwise in the carb
throats down under?  Finally got the high ratio primary gears completed, but
have not got the engine back together and in the project bike yet.
Bob Hart

Alternative location for Vacuum Barbs For Tuning

I have attached some pictures of how I installed the Vacuum Barbs for the Balancing of the VM Mikunis when there is no vacuum barbs on the Manifolds.
Instead of drilling the Carburettors, I drilled holes in the flat area on the Cylinder Head that was used for the Balance Tube on the early models and threaded with M6 (The last portion of the hole is only drilled with a 3.0 mm drill).
During Carburettor Tuning, I install M6 Vacuum Barbs from 650 Central.
When not used, they are plugged with M6 Cap Screws and Copper Washers.
I think this would be possible to do with the Cylinder Head installed by using a small Right Angle Drill Machine.
You are welcome to use the pictures for the website or newsletter but only if you write the text as my English is not good enough.
Best Regards
Göran Persson
New Zealand

Who told you that Göran, I couldn't have written it any better myself.

Monday, 24 September 2012