Archive for the ‘air’ Tag

XS650: VM34SC Mikuni   Leave a comment

Yamaha’s Racing Tips Manual, 1974, suggested using VM34SC Mikunis. Round slide. Magnesium bodied. No Power Jet/Accelerator Pump/Beschleunigungspumpe.

Today, TM’s are supposed to provide significant performance improvements. Flat slides and the jet blocks help create a smooth bore effect. Air flows faster and smoother through the TM Series venturi. Higher air flow velocity gives a stronger vacuum at the needle jet needle. Provides more precise metering and better throttle response.

For known geographic and climatic conditions.

However, I do a fair bit of touring. Low to High altitude. For this I actually prefer the original BS series carbs. They automatically adjust themselves for air pressure. Easier to keep tuned.

… VM34SC carb … XS750(650) Racing … adjustments … jet needle 6F9 (#2 clip position)

 

… carb adjustments

 

… carb .. VM34SC … adjustment

 

… VM34SC carb … 3/4-full throttle adj … main jet

 

 

… VM34SC carb … 1/4-3/4 throttle adj … needle jet

 

… VM34SC carb … 1/8 – 1/2 throttle adj … slide adj and cutaway

 

 

… VM34SC carb … 0-1/8 throttle adj … air mixture screw – pilot jet

 

 

… VM34SC carb … idle speed screw

Posted December 21, 2011 by xscafe in Carb - VM

Tagged with , , , , , , , , , , , , , ,

XS650: Engine Temp. RHS   Leave a comment

A week or so ago CM wrote asking about operating temp differences left and right. Why does the rhs run hotter?

 

 

1 .. xsjohns, rip, engine temp recording ... with cooler ... left and right can run up to 30° or so difference

xsjohns, rip, engine temp recording … with cooler … left and right can run up to 30° or so difference

 

 

I’ve been out of town. Away from my computer. Exiled. Disconnected. But not deleted. Basically this is the answer I sent him.

Over the years I’ve heard many postulate. From aerodynamics to exhaust placement.

When you look at the engine design you see all the mechanical parts are focused to the right. As is oil flow.

Hot oil is sucked up through the pump. Slowed at the filter.

Mechanical action from the tacho, oil pump, primary and clutch all add frictional heat.

Aluminium is a good conductor. Heat gravitating upwards meets that from the combustion chamber and exhaust ports.

To the left we have the generator. In an air cell. Dry. Different thermal properties.

Allows the left to act more efficiently and effectively as a heat sink.

When Yamaha built the carbs they did so symmetrically. Jetting specs both the same. Each operating in different thermal environments. Built in imbalance. With appropriate feedback loops.

If you have adjustable needles it is possible to richen the right hand carb by raising the needle.

 

 

2 .. lowering the clip raises the needle ... enrichening the mix

lowering the clip raises the needle … enrichening the mix

 

 

XSJohn, rip, ground needles with different tapers as a set. Left and Right. The canadian needles apparently are similar. Replace needle jets and jet needles together as a pair.

 

 

3 .. xsjohn, rip ... on his needles ... no grooves here, his production needles were grooved

xsjohn, rip … on his needles … no grooves here, his production needles were grooved

 

John also built wings or foils to deflect airflow over the cylinders.

 

 

4 .. xsjohn's wings ... notice the deflector under the lower clamp

xsjohn’s wings … notice the deflector under the lower clamp

 

 

Others install oil coolers.

 

 

5 .. remote filter and cooler ... so positioned the cooler will reduce air flow over the head

remote filter and cooler … so positioned the cooler will reduce air flow over the head

 

 

6 .. heidens side filter-cooler

heidens side filter-cooler

 

 

Today there are many diagnostic techniques. Years ago I had an interesting conversation over too many beers with an Australian Naval NCO. Have never been fond of military types. Too rigid. Thinking actively suppressed. Later I was to learn the corporate world is, in theory, no different. In practise, a lot worse. Establishment meeting punk – the shock was mutual. He was a vibration analyst. Spent his time listening to machines sing. No different really to listening to your motor through a long solid screwdriver. He had a lot to say about the internal workings of Australia’s navy.

I would like to see a series of  Infra Red pictures of an XS650 motor running. Done in a resolution capable of  differentiating temp gradients within the 80-300° range. You would see some definite nodes on the right and fronts associated with temp assymmetry.

I come from the southern hemisphere. Live in the north. Apart from north and south there are other differences too. Here they drive on the wrong side. When you pull the bath plug, flush the toilet, water runs anticlockwise-the coriolis effect. I wonder what this does to other physical gradients Winking smile.