Hitchcocks Forum

Hi all, it’s my first post here.
I’ve had the bike for a year now, I bought the bike with the 535 kit fitted by what I can only describe as a plonker (my fault for buying it tinkered)
Shortly after it died, and when I stripped the engine it had detonated and melted the piston crown.

Fast forward to now, I have new piston and barrel from Hitchcocks.
It’s fitted, run in gently for 200 miles. Now in higher throttle position I’m still getting some knock. I’m convinced it is and was a very lean fuel mixture causing the problem.
My set up is;
Amal mk1 concentric
220 main jet
Needle on highest setting
Performance pipe with baffles removed
Mesh filter (this was an open trumpet when I bought the bike)
B8ES plug
Fully retarded ignition

I have set the idle and pilot air screw as per the sequence in the technical pages on the website and I’m just managing to get some slight black on the plug in the low range. But still the high end knock under load. And the exhaust is blueing for 10 inches after the barrel.

Do you think I need a larger main jet still or different throttle slider or is there something I’ve missed or potentially cocked up.

It runs, starts, idles and rides really well apart from this but I really really don’t want to be buying another 535 kit again.

Any advice is very gratefully received as I’m no expert

I would fit a main jet of around 240 - 250, 107 needle jet - possibly even 108, make sure the needle isn't set too low [weak] and advance the ignition timing to full advance at 8.5 - 9 mm BTDC [approx 35 degrees]. I would also take a look at the cams to see what's in there and their timing and possibly retard the inlet cam by 1 tooth if the timing marks are currently all lined up, especilly if it has standard cams fitted.

Excellent thanks for that!
Now I’ve got more options to try
I’ll call the shop on Monday and order more parts. I’ll let you know when fitted and tested the results.

If it did have an aftermarket cam how would that be identified

Thanks again
Edd

Indian factory cams usually have steel bushes in them, while most aftermarket cams - and Redditch cams have bronze bushes in them.

The only thing I would add is check the cams first before anything else. Then when you're trying it out/ride testing, carry the spare jets with you and change at the roadside, if you're happy to do so, for comparison, and see how it behaves climbing.

When you say "knock" is it a knock, or pre ignition pinking ?

It is a distinct knock, very noticeable.
I have a vintage tractor which pinks when hot and under heavy load, retarding the ignition usually clears that in the tractor hence I retarded the bike to hopefully help.

I am going to check the piston with the borescope tomorrow and hope no damage has occurred to the new piston

If it has aftermarket cams, make sure the inlet tappet is staying in touch with the cam. I recently found the knocking/clattering noise on my 612 bullet was due to the tappet bottoming out and coming off the cam. I had to burr away some of the alloy to allow it to function properly.

Make sure there are no air leaks round the inlet manifold.

Ordered 240 and 250 jets today.

Jobs for the weekend, take the head off check piston crown for damage.
Re jet to the max size and richest needle setting.
Spend some time to get the ignition timing spot on.
Check valve timing.

I’ll keep you updated whatever the results.

I’m very grateful for everyone’s advice!
Thanks again
Edd

Don't forget those needle jets!

Update… it’s much improved but I don’t think it’s perfect.
250 main jet
Standard needle still (sorry bullet whisper!)
Timing set to 8mm btdc

What can I do next?

It now doesn’t knock unless it’s under a heavy load, full throttle is fine on the flat if I let it climb steadily, but if I pull it hard in a high gear I still get some slight knock. But it is 80% better than when I previously posted.
Thanks again for all the advice!