520 carburation

With a new plug fitted i would try dropping the needle a couple of notches for a short run. If better try raising one notch.I am presuming the plug comes out dirty. If its clean we need to do something else.

Mk 1 Amal: No 4 slide and 270 main jet, mine is a 530cc ES2.

106 needle is sound.

What bore size is the carb? What colour is the plug? It should be possible to tune the carb for the mega. Has it been like this since Mike built the engine? Are these his recommended settings for that carb?

Hi Geoff,

I should have said that I use a 28mm Mk1 , though my poor man's Manx on std bore uses a 30mm.

My 530cc ES2 uses a standardexhaust / silencer but it has taken two thousand miles of running in to get it something near right. Best advice is to make a single small change at a time and try it, but most important is to get lots of miles on the clock and things should improve with the bedding in process further on. Good Luck.

It is a mighty big carb, Geoff, as big as the largest fitted to a 500 Manx in their final years, according to Amal. A 30mm, which were fitted to Velo Venoms, would be about right, I should have thought. If you coaxed it to go as well as a Venom that would be a result! Too much carb for the bike, imo.

Cheers. Ian

Previously geoff_mcnulty wrote:

Hi Ian thanks for the reply I think your right and will get a 30 bore.

i would like a second opinion from mike pen but don't seem to be able to make contact .maybe on holiday

cheers anyway

Geoff. It would be good to hear Mike's thoughts. It rather got by me that you have only done 150 miles since a full engine rebuild. Given that, to tune a carburettor you need to set the main jet up first, which involves running the engine flat out in top under load, that is not a good idea at that mileage! Or caning it through the gears for that matter! I would be inclined to dig out a 28 - 30mm Mk1 or an 1 1/8"to 1 3/16" Monobloc, for which fairly close settings should be readily available, and run it in and enjoy it for a few 100 miles. When it is nicely loosened up, you could go back to your big bore carb, at which point it may be easier to find settings which work.

Cheers. Ian

Have to agree with Ian, Geoff.

A 28-30mm Mk1 will help you run in for the several hundreds of miles you will need before you can put the engine to the test.

Also, check the oil regularly, not just for use as we all know a running in engine uses more oil but also for the condition of the oil. The SAE 40 oil in my 530 ES2 was quite dirty and needed changing every couple of hundred miles until the motor loosened up and the carburration improved.

Good luck.

2000 miles running in, why?.When I was racing some years ago with a short stroke ES2 if it couldn't take full bore after about about 50/60 miles over an afternoon at Mallory Park without problems It was no good to me. An engine needs a little bedding in rings usualy about 50 miles ish, raising the revs each outing. That many miles just glazes the bore. However the carb settings do need to be about right but unless you give it some stick your never on the main jet anyway.

A race engine would be set up to racing tolerances; slack as a vicars handshake. Not ideal for a road bike, though, Tony. We don't know what the brief was for this engine rebuild. As you point out, and has been already said, the carburation has to be about right in a new engine, and you can't give it the beans until it has loosened up. That is why it is suggested that a carb with available settings is used for the bedding in period, so as not to cause any damage. I have run in 2 bikes recently, my 650ss and a 350 Matchless single, with newly rebuilt engines, and have felt them loosen up, and be happier to rev, as the mileage goes up. I bet I am not the only one on here who in the past has paid the price for thrashing a new engine too early, and felt it nip up! Erring on the side of caution seems to be sensible advice.

Tony, the points Ian makes are much the same as my own. Many times I have seen Speedway riders take out a new engine after a meeting and run it in over a few laps, ready for the next meeting. Not the same as a road bike, especially one built with a tight interference at the bore.

In reality it probably took about 1,000 miles to free up the engine but other issues such as oil discharging through the timing case breather, asmoking exhaust, dirty oil and oily plug took another 1,000 miles to resolve. The smoking exhaustwas improved by using a rare hot plug, a Champion N 8 I think. (they used them in Vincent's)

Nipping up was an issue during the first few hundred miles and you really did need the decompressorto have any chance of starting.

The 520 in question and my own 530 are not quite stock and the book is barely a starting point for settings. Bit at a time and patients the only way, I got there and so will this 520, just that it might be a while yet and we haven't even discussed what fuel is being used!

To be fair the bore on my race ES2 bike was ceramic plated as the barrel was my own alloy casting. I supplied Mike P with these for a number of years before Mike purchased the pattens off me a couple of years ago. I also ran with a modern low expansion piston running .0015" (yes a thu and half) clearance never showed any sign of tightening. The rest of the motor was also new with big end and new mains. Not quite as slack as you may think.

My 650 Norton which I won the VMCC unlimited championship 3 times was run in the same. This only had an extra thou in the bore. If you start building motors to slack you will lose to much power. This motors bottem end was not stripped until it had done several years racing with only the Valve springs being changed during the winter.

It was run to 7250rpm max but spent most of it's live in the high rev range. I ran it on cheap 20/50 and changed the oil twice a season and pump 4 star on about 10.5:1 cr.

Maybe I was lucky but over 25 years racing on all types of bikes and engines there was never any time to do big miles running in.

Modern motors never need any miles before they can be run flat out.

I was in the NW200 a few years back helping a mate and we went with a new GSXR Suzuki with 3 miles on the clock before the first track session which he went through the speed trap at over 180mph. I know modern engines are different but guys dont do these sort of miles to bed motors in, it's not 1948 any more.

Sorry to highjack the post, just another look at the running in thing.

A very good year, 1948!

Hi if you are worried i would be tempted to put some type of oil temp gauge on it just for piece of mind. that will be a good indicator of over heating due to incorrect mixture, timing ect. a simple 30 quid gauge would save thousands.

Previously geoff_mcnulty wrote:

Hi guys

Interesting the different comments but as the engine as cost me the best part of 3 k the last thing I want is failure so I will take it easy.i am sure the jets are about right as the plug is clean.I can confirm the mk2 has 34bore where the jury's out on too big,the pilot 30 main 300 needle 106 and the needle is set 1 down from centre.i have put a reverse cone mega on it and it runs reasonable I can at least ride it but if I put the Manx mega on its terrible. As regards to the build it has an alloy barrel with mikes road race cams lightened rockers and full bottom end rebuild.i don't know what piston is in it but it's 87 bore.

its also got a twin plug head which I only use 1 but I have 2 coils and thought about trying the twin system.

any more info would be appreciated and tony you rode this bike when I had vibration problems about 3 years ago but was taken off the road for a total rebuild .if your interested I could nip it round to you if you have time to give a few pointers I only live in Sapcote.

regards

geoff

Hi Geoff

I have been to bed since then. I am away for a few days but email me on nortones41000@gmail .com and you would be most welcome to come over and we can have a coffee and put the world to right as your only 5 miles away.