Hitchcocks Forum

Thoughts on cam timing.
Hi Guys, I’m back on my bike after back surgery and using the festive weeks for some useful work on my so-called tuned 1996 Classic 500cc.

I have tried many settings for my performance cams and adjustable pinion, advice received and read from many of the bulletin board scribes over the past few years (Cjay, Steve Eads, Paul Henshaw, LesH, Tom Lyons/AceCafe, Lone Rider and many others). These vary from exhaust and inlet retarded or advanced 1-2 teeth compared to “on the dots” using the pinion in advanced and retarded positions. That’s a lot of tests amd had a LOT of use out of my dial gauge the past few weeks and can now change cams and get restarted in an hour.

So far, I’ve found that it goes best when the overlap is closest to the old Redditch cams, i.e. ~65°. Mr H’s Performance cams have an overlap of ~100°, so I had to advance the exhaust cam one tooth (18°), the inlet cam retarded one tooth (-18°) and the pinion set to advance (+6°).

Now it goes well with a raucous throaty snarl, easily reaching 100kph on half throttle even though it still won’t exceed ~4500rpm or ~110kph in 4th (GPS speeds not speedometer). I must admit I have windshield and panniers so that slow top speed could be a function of drag, so I did the same testing in 2nd and 3rd gears with the same results!

Yes ignition is correctly set, with my 8.3:1 compresssion I need to have max advance at 30° BTDC which I have set by modifying the A/R mechanism to an actual 10° advance with liquid steel (it had been worn to 12-13° giving me some 35° at full advance) – checked with a strobe (I superglued a degree circle onto the rotor).

Remember my bike has free flowing header pipe and shorty silencer (p/n91007), high capacity oil pumps, metal-metal head joint (head skimmed ~2mm), gas flowed head (by a local classic bike tuner), radiused valve grinds, slightly roughened but smooth inlet tract, polished exhaust port, H’s performance cams and adjustable pinion, competition valve springs, Samrat rockers, larger nitrided exhaust, larger inlet, twin plugs (with decompressor on top of cylinder header operating through a 2mm hole), uses Mr H’s EMGO twin coil and iridium plugs. Oh and an alloy barrel with viton sealing rings recessed around the pushrod tubes a JP 7:1 piston, and a K&N filter crammed into the Indian air box. Compression is 8.3:1 (~125psi cold) and I can stand on the kickstart (95kg +clothes) for 3-4 seconds before it starts to leak-off, so I guess the decomp and valves are sealing OK. Mikcarb 28mm has P2 needle jet, needle clip in base slot (but no richening washer), pilot=30, slide=2.5, main best at 125. These settings give perfect light tan plug chops at ½ , ¾ and full throttle.

So whatever is the cause of the slow maximum speed, I doubt a better cam setting will do the trick.

I don’t want to go fast, I just want to have enough power to cruise at 90-100kph with a 19T gearbox sprocket and still beat the incessant wind and frequent hills and I am sort of there at ½ -3/4 throttle but that’s a lot of throttle to have to use to cruise at barely 60mph.

Next change is to put on the 32mm Amal concentric with Ace Cafe air box, but I’d rather exhaust all other tweaks before that step. I don’t think I’ve missed anything, but can anyone suggest something else to try before the Amal.
Cheers, ChrisD from Cape Town.

Chris, you have done a huge amount of work on it but you have done something wrong I constantly read here of 350's capable of 80 mph so maybe you need a 350 Sorry not much help, bit late now but you should have longstroked it then you have a real Enfield not one of these woosy 80 kph ones

Wow! A lot of work and a lot of mods. My 2004 500cc classic goes much faster than that with just a free flowing exhaust and amal mark 1 concentric - and it has fuelling problems at 70mph that are about to be sorted. I would be expecting to take mine up to 75mph with ease once the fuelling is fixed.

Hi Chris, two things jump out at me in your list of specs for your bike - 28mm Mikcarb and 19t gearbox sprocket - I bet it has a job to pull full revs in 3rd gear, never mind top! I would go no greater than 18t on the gearbox sprocket and then only with a 30 or 32 mm carb fitted at the very least, also make sure the twistgrip is opening the throttle completely - many don't. I made a 500 go very well with a 28mm Mikuni fitted after some tuning work,with 9:1 C.R. and standard cams and timing, I also lightened the crank by a few pounds, but I left the 17t gearbox sprocket on and this was with an 18" rear wheel [trials]. That machine could just about hit 90 mph flat out and was happy to hold a steady 70 - 75 mph, whilst returning around 65 mpg. I sold it to a friend a few years back [after much pestering by him] and it is still doing the buisiness to this day, with only basic routine maintainence, as required. Regards, Paul.

A lot of money spent, a lot of work done & the bike is not as quick as our fully freighted near standard 1992 500...
I too spotted the same clue as Bullet Whisperer - it is over geared so it is simply running out of puff....Fitting sprocket will be an improvement.....Just my 2 drachma

Fitting 18 tooth sprocket was what I intended to write