Hitchcocks Forum

Hi All

Now that winter is almost upon us Im considering going for the 8.5:1 forged piston option as an upgrade for my old 500..

My mate will be doing the rebore of my barrell and fitting competition valves and gas flowing the head for me.

I am running an Amal concentric.

Can you advise a good starting point for jet and slide sizes.

Regards

Tom

Start with a #220 main, all other settings the same. Most times I find a #200 is large enough, but each bike (head) is different.


The old style tea caddy air filter, (designed for the 350...) and Clamp-on tiny airfilters both do nothing for higher rpm performance; ie main-jet sizing...

Thanks TimNZ ill add a 220 to my order from MrH

My bike is a 500 Clubman S with a Golidie silencer so its breathing very well as it is.. Thought Id give the old girl a Christmas present..

Hi Guys---Yes I'd agree re}--- the Tea Caddy filter...I had one fitted on my last Bullet 500 and it didn't perform very successfully...Having eventually gone for the Amal conversion I opted for the large pancake filter with the paper element and chrome outer clamp...( Page 279 in the 2016/17 catalogue )...

Although I kept to 500cc I fitted the forged 8.5 : 1 piston and went "Up 2 teeth" on the output sprocket...This, along with the disc front brake, raised-straight handlebars and the usual silencer mods. made for a very sporty performance--- especially climbing hills etc......ATF in the forks and fitting Hagon rear shocks made for a comfortable ride...

Tomshayes. I have a 1996 535cc. I fitted our hosts performance cams (PN 200180) and a 32mm Mk2 concentric with a large separate air box from Ace Cafe (I agree the tea-caddy is too small). I too use a #220 main jet but the biggest surprise was that I needed a 105 needle jet not the standard 106.

If you do upgrade the cams, make sure the pushrods are completely straight and that there can be no contact with the pushrod tube, even at full chat. The OEM ones do flex a lot.

Cheers, ChrisD

The jet size will be governed by the carb size, the bigger the bore of the carb the bigger the jet required, don't be tempted by too big a carb unless you are prepared to loose useful bottom end and mid range in favour of outright top speed.

How many miles has the engine done? Are you doing any bottom-end work? More power means more stress, so the bottom end needs to be in good fettle.

Hi Guys------- As this is an older long-stroke push-rod engine then there is another approach that you might like to consider and that is to tune for TORQUE rather than higher RPM.....You can then obtain your improved road performance by changing the overall gear ratio....As "Another Allan" has correctly indicated the bottom end needs to be in good fettle, more so if you are looking to increase the overall engine rpm...........

Try this}--- stay at the standard 6:1 compression ratio but fit our hosts forged piston.....gas-flow the head, fit the larger valves, explore larger valve overlap cam types but at standard lift, consider using a SMALLER choke carb ( the original Mikcarb at 28mm for instance )....keep the de-restricted exhaust system, and finally change your riding style to suit the new arrangement...I used to run a pair of Honda CB750-4 bikes a few years ago....One was a standard set-up K6 whilst the other was a CB750-A Hondamatic.....and it was the auto. that had this type of tuning done by Honda to get the TORQUE that the auto. transmission needed to operate efficiently.... Finally, with all this improved road speed you'll need to uprate the tyres--- brakes,----suspension...Which ever way you decide to go can we have some photos when it's done, please ??

PS}--- That should read "Explore LONGER valve overlap..."!

With another Allan's comment in mind, it could be steel con-rod time. Replacement 500 crankcases aren't getting easier to find, though our hosts have a used set for sale at the moment.



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