The xbr project continues

[JOOLZ]

I have just fitted a new carb to my XBR500 cafe racer. The old carb was a 42mm Keihen which I was not happy about for various reasons. The new one was purchased from Ebay, it is a 40mm Amal mk2 that came off a racing goldie and has been highly modified, its a beautiful piece of work ultra snappy throttle response (plus lots of bangs when shutting the throttle, smiles but cringes) and im sure it will flow far better than the old larger diameter carb that I had. Its a bit hidden at the moment but I plan to mount it on a length of 45' angle tube so the bellmouth comes out from underneath the tank.

The next stage is to improve the useless ignition timing by changing the cdi box to one from another rfvc motor, although which one I dont know I have seen a list of cdi units for these motors on another site but cant make head nor tail of which fits what, Any ideas or help would be appreciated.

[guest7]

Blimey, all I ever did was change the main jet in mine and slap on a Goldie pipe. Although in retrospect, that is about as much as I can be trusted to play with.

What prompted this choice of carb? are you looking for those hidden ponies in the motor? (the eight or so ponies that Honda says are there but no dyno can find   )

As for ignition timing, the RFVC race motor in my Ikuzawa has been converted to points (yes seriously) so that the timing can be easily played with (this was done in the 80s before such things were easy to do with remappable gadgets and goodies). It looks bloody ugly though.

GC

[JOOLZ]

Hi I have a lot of experiance with Amal carbs and have used them on most of my bikes, they are easy to tune and not overly complicated. Im not really looking to squeeze every ounce of power out of the engine but I am interested in quick throttle response and as much torque as possable but dont want to go over 500cc or have high domed (high compression pistons) as this affects flame front burning speeds, you can actually get less power from a high domed piston

[guest564]

I ran a 40mm Amal MK2 on my XBR, many racers did in the mid-80s. What type of slide do you have? the normal ally slide has a tendancy to stick open in the wet if you don't run an air filter.
My ignition pick up was modified to run about 5 degrees of additional advance with a 10.25:1 piston on superunleaded. I also ran a big diameter motorcross throttle because its a lot of cable to wind in before you get to full throttle.
What was wrong with the 42mm Keihin?

[JOOLZ]

Hi I have chrome plated brass slides. I was thinking about altering the ignition trigger but was unsure untill now. How did you modify the pickup

[JOOLZ]

Hi sorry didnt have time the other night to answer all the posts.
How did you drive the points and where did you put them?
The keihen was a knackered one bought from ebay and someone has driled the slide wrongly I repaired it but ints not perfect

[guest564]

Sorry, I've been away on business. The trigger was built up with weld and then the opposite side ground down to maintain the correct width. On my race engine I have a Piranha system which fits in place of the alternator but I'm going to build a new system which will interface to the stock pick up.

[guest564]

Thinking some more about this, I think there are two types of XBR ignition. Early types had a CDI ignition with a high voltage coil in the alternator, these models didn't need a battery. Later types were inductive discharge and were powered from the battery.

[blew]

I have a late model xbr-reg 88.The ignition works without the battery.