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There is quite a lot of room inside the Manx head in the plug location. To check clearance position the piston at TDC and measure with a Vernier (depth) at the low side of the spark plug hole, then measure the overall plug length (the bit that goes in the motor). You need 40thou min clearance. If you mark on the plug where the electrode is welded ensure this is at the top (12 o'clock) when tight. Personally I would avoid protruding plugs. Sometimes its worth getting on eBay and search for some Champion N54R or harder, KLG FE295's buy new old stock. B9 or B10EGV are fine, perhaps later iridium plugs around the 9 or 10 range.

The gardener is simple to set up. set the fuel height to approx 1/3 of throttle opening. With the fuel on and the throttle open to about 1/3 the fuel should gush out of the central fuel jet. If not the fuel height is too low. Setting the needle can be more problematic as there are many needles, different lengths and chamfer so you may need to experiment. with what you have, screw the needle all the way in onto the last indexing notch, then turn out 5 turns. Run the bike to till hot and if the bike spits on 2/3rds throttle on load = weak, turn the needle out one full turn and run the bike again and so on.

I dislike the Gardener float they've always flooded or leaked, maybe I have been unlucky. I prefer the matchbox.

Starting your Manx with a Gardener = roll back onto compression, fuel on and open the throttle to 1/3 point and count to 3 if the engine is cold, 1 if hot. This floods the inlet tract. Then bump. Easy. My 92mm Bore engine runs with a 42mm Gardiner and it will idle when hot! Not a good idea really (as the engine knocks the hell out of itself) but it does prove what a great carb they are.

By the way you can run your Gardener without a float chamber if you want, they are happy to run that way too.
 

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Regarding ignition timing. These bikes really are not that sensitive. I have found they can be a few degrees out and it make no difference.

I have lots of old spark plugs with their guts removed and fitted with threaded studs (made from hard nylon) which I can lock up with a locking nut. I find an absolute TDC by inserting the plug / stud with the stud long enough to stop the piston rising to TDC on compression - I rotate the engine toward TDC until I feel resistance then note the engine position on the degree disc. I then back off the plug and rotate the engine over TDC, retighted the plug and rotate the engine back against the plug and note the engine position on the degree disc. TDC is the mid between the two points. Once you have found TDC, remove the plug rotate the engine to the ignition setting you require, slacked the locking but on your TDC tool and back off the stud, insert back into the engine and screw the stud home until it meets the piston. Check that the degree disc is still reading correctly, if so tighten the stud lock nut. Mark the tool with the engine number (all engines are different!) - finding the ignition point takes 30 seconds after by find tdc on compression rotate the engine backwards, insert the plug then slowly rotate forward until resistance is felt. Sorted, its then just a matter of releasing the mag sprocket and rotating the mag till the point just start to open. with a little practice you can time the engine in 5 mins. If you are using a Vernier belt drive to the mag its even easier.


As I said these engines can run a few degrees out without a problem, in my experience these engines are all a little different some like low 30's advance (especially replicas) and originals late 30's. Norton figure is 35deg BTDC.
 

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If you purchase plugs on eBay, you need to be aware that there are knockoffs out there. I bought a bunch of NGK B6 for the road roach from EBay, but as mentioned NOS (New Old Stock) is your best bet. I found a box of NGK's made for Honda, so they came in Honda boxes that looked like they had been around for a while. It is less likely that the counterfeiters would bother with Honda or Yamaha boxes. It also seems with the new plugs it matters where they are made. Folks I know in the U.K. curse NGK and claim they easily foul in filthy old carbureted engines. There is some speculation that the ceramic used by the French factory works well in modern clean fuel injected engines, but fouls easily in richer environments. No idea if it's true, but the plugs we get on this side of the pond seem to be all made in Japan and work well.

As for the knockoffs, info can be found here PLUG STUDIO / NGK
It's older info, so the fakes may look better. I had the opportunity to inspect some knockoff oil filters and they are getting pretty good from a visual point of view, but they barf oil all over the road.
 

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The ceramic in modern plugs is very different to the old. its finer and doesn't burn off like older plugs which operated in a far more hostile environment. I have had a few plug failures in recent years, ranging from the electrode falling off to the threaded cap, the bit that fits into the white ceramic top coming loose. The reason why plugs foul is possibly down to two thing, the fakes tend to be all the same grade and if a soft grade they’ll foul up quite quickly. Another reason is their material and electrode design it quite different today and we tend to expect plugs to last for years today. Putting this in context modern combustion chambers are friendlier and plugs are reliable but I’ve found modern plugs don’t like wet/fuel rich environments of older bikes. My personal experience is that years ago I would have a few spare plugs under the seat of the bike just in case, lost count of the times I’ve changed plugs on the roadside. I still carry spares plugs with me today, I have clients who demand expensive iridium plugs when a b8es costing a few quid will last just as long in their old Honda or Kwacker. As for bike performance differences new verses old style plugs I doubt you’ll notice the difference.

You also need to consider ignition types, today most bikes run electronic high energy systems which deliver an intense spark (quite cold) with a very short duration, older magneto and points systems produce a very different spark, hotter and longer duration. Plugs today are designed for later systems, if I use an iridium plug with a race magneto the spark looks very different to a the spark generated using period Race plug which gives a fatter more orange / blue colour which turns plasma like at Race rpm.

Today I will not use moderns Race ignitions on old bikes, say pre late 80’s, even though modern systems are more accurate. I will use self generating CDI types like Krober and period hitachi, old Boyer systems and similar but not types from companies like ignitech and some PVL programmable types. They just don’t work as well on older bikes in my opinion. That said if you are just pootling about at 4000 rpm I don’t you’ll notice the difference.
 

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Discussion Starter #86
One problem with living in what some people would call in the middle of nowhere is the time to get parts, raw material and tools. Just getting a cycle thread nut usually takes a week. Might explain why the Manx has taken much more time than expected. As per ignition timing, some progress is made. An adaptor on the crankshaft end holding a disc is made. Steve made a good description on how to find Top Dead Centre. I think the less than +/- .5 degrees obtained is as good as I can get.
TDCfinder.jpg
Next problem. The ignition I have has to be set with a strobe. My solution is to set a pointer indicating TDC on the lock screw on the chain wheel. So a modern fancy timing light is needed. They can be set to a specific advance, so I only need a TDC mark. An added feature is that it shows RPM too. It will be interesting to compare with what the old Smiths rev counter says.
A week has passed since I ordered the timing light, I'm still waiting.
TDCpointer.jpg
 

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Discussion Starter #87
Finally got the strobe timing light. Sadly it took weeks to find a helping hand. It is almost impossible to keep engine running at constant rpm and checking advance with the strobe alone. Set ignition timing to 36.5 at 4800rpm. As the vernier can adjust in steps of 3.2 it is as close as I can come to the 35 Steve recommended. Maybe it is possible to come closer by changing timing belt. One tooth change on it is 22.5 degrees. Something to figure out during the winter. Then loaded bike and all other stuff needed and went to last track meet of the season before the winter. Found that recently bought roller starter let me get going alone. Next problem appeared. Carb slide did not close, stayed at 1/4 open. Happy to have installed a kill button. Took the Gardner apart. As expected the grub screw used for idle adjustment had gone inside the carb and blocked throttle slide from closing. Replaced the grub screw with an hex head screw. So now it can't happen again. Then started her up again and steered out on the track (only 23 years and 2 months since her last time on the track). She pulled out strong from the pits a hundred meters, then died a couple of seconds then run well a while and died again. It continued like that, but I managed to get her round the lap and back into the pit.
Did some adjustments and tried again. Same outcome.
My impression so far is that she handles as well as a Norton should, though it is fifty years since last time I had a featherbed Norton. Brakes are good for the period. There is very little engine vibration compared to my other english singles. I really feel at home on her. I'm surpriced that there is so much power in a 350. It is quite interesting to handle a bike that goes on and off all the time. In the bends a bit too interesting.
Now time to figure out where the problem is. I think it might be a fuel problem. Not certain if it is starvation or too much fuel. Will check petrol tap,and fuel lines. Main suspect is problem with the float chamber.
Hopefully will solve it before next time, which will be in April.
 

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See if you can find a big Del'Ortto carb and do a straight swap, see if it runs steady wherever you can get it out with no worries of enjoying flashing non-holiday lights.
 

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Discussion Starter #90
Emptied the fuel tank. According to my calculations, she used 1.5 miles per gallon! My guess today is that the problem is something with the float chamber.
 

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Discussion Starter #92
Might very well be that Steve is right.......AGAIN
Will play a bit with the present float chamber a couple of days before ordering a matchbox.
Still some time before Brexit, until then easy to get parts from UK. After that no one knows.
 

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If the float chamber is good and doesn’t flood - set the fuel height so that a 1/3 throttle opening the fuel gushes out of the fuel jet.

It’s sound as though you bike is running the fuel low in the float then the engine starves and dies. You need a big bore fuel tap too. Make sure the fuel free flows out of the float chamber and that the tank is breathing properly.

You can realease the vernier back plate from the magneto shaft and time traditionally.

What’s the plug colour sooty?
 

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Discussion Starter #94
I'm quite certain that fuel flow to the float chamber is adequate. Will doublecheck it though. Tap is same as it had before, so I believe it will suffice.
Plug a bit sooty.
The difference between the GP and the Gardner is that on the GP there is a short rubber tube between carb and float. On the Gardner the tube is longer as it has to move up and down.
My present guess is that the float chamber now can swing easier to and fro. At higher revs it will vibrate so much that the fuel overflows and goes out of the top vent. I have seen this happen on a Velocette KTT with AMAL Matchbox float chamber.
 

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Does the fuel flood out of the fuel jet a 1/3 opening?

Float chambers flopping about is a problem and the resulting fuel frothing. The only fixed points you have is the anti vibration mount and fuel tap, fit some copper pipe say 8mm bore inside the feed line and bend to shape. Clamp as normal leaving about an inch on tube either end the copper tube will help stop the float moving too much. On tradition gp set up I fit copper tube in the pipe from float to carb banjo.
 

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I should have said - don’t use braided fuel line you must use something that stays flexible from the float to the carb bottom feed. The sort of hose used by Japanese manufactures is perfect. Many fuel lines go hard quite quickly which isn’t much help for the carb feed line but can help holding the float still. Every cloud.........
 

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Discussion Starter #97
As season comes closer, time to do some preparations on the 350. I did some experiments with the Gardner and an AMAL Matchbox float bowls. I believe that the Gardner is more sensitive to vibrations than the Matchbox. To be able to return to the Gardner, I made new mounting parts for the Matchbox. For adjusting fuel height. I used a supershort circuit tank, took it from a scrap vibro plate. Gave much better work space. So a test start next.
Very short circuit tank.jpg
 

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Discussion Starter #99
Test start accomplished. It'a a lovely engine (thanks Molnar), really smooth. Only air in tyres and petrol in tank (not the opposite). It's a very easy starting machine. As an old racer explained it, compression ratio should be where it gives lot of power and is easy to start. In the old days when engine was off when the flag was dropped. Seems the float bowl change worked. Now load everything in the van. Practise on track sunday.
After test run.jpg
 
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