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Amateur Manx 40M preparation

This is a discussion on Amateur Manx 40M preparation within the Vintage Motorcycle Racing forums, part of the Caferacer.net Forums category; Originally Posted by Mike 40M Test start accomplished. It'a a lovely engine (thanks Molnar), really smooth. Only air in tyres and petrol in tank (not ...

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  1. #101
    Senior Member Cyorg's Avatar
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    Quote Originally Posted by Mike 40M View Post
    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
    Looks very nice. It inspires me to head out to the garage and do something with the shrapnel laying under the bench.
    I’m assuming there are modern bits lurking inside that mag. Wonder if they help with the starting, although nothing wrong with a old one in proper working condition (other than price). Good luck at the track. Perhaps a smidgin of R40 just to add to the religious experience.
    "Non urinat in ventum"

  2. #102
    Senior Member Mike 40M's Avatar
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    Track test done. On the positive side it's nice handling and fairly comfortable to ride. I am a bit more used to the TTI gearbox but still don't like it. On the negative side it still was ok when warming it up but still power for a couple of seconds and died a couple of seconds. So my guess that it was a float bowl problem was wrong. Luckily a Velocette racing friend appeared. He had time to help me trying to figure out what reason it has to behave as it does. After a while, we found that when I put a finger close to the intake, it got soaked with petrol. Much. Explained the 5 MPG fuel consumption. Our guess is that in the fight between intake sucking in and exhaust blowing out, the silencer won and made the carb work the opposite way.
    Some of you probably has a better explanation to it. As carb, engine and exhaust pipe is a proven combination by other racers, the most likely culprit is the silencer.
    Next to do will be either to buy or build a new silencer. I think the way to go is a less tapered cone, followed by a revese cone and after that a large diameter stinger. Lots of calculations though to get it right.

  3. #103
    Senior Member jalsteve's Avatar
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    Quote Originally Posted by Mike 40M View Post
    Track test done. On the positive side it's nice handling and fairly comfortable to ride. I am a bit more used to the TTI gearbox but still don't like it. On the negative side it still was ok when warming it up but still power for a couple of seconds and died a couple of seconds. So my guess that it was a float bowl problem was wrong. Luckily a Velocette racing friend appeared. He had time to help me trying to figure out what reason it has to behave as it does. After a while, we found that when I put a finger close to the intake, it got soaked with petrol. Much. Explained the 5 MPG fuel consumption. Our guess is that in the fight between intake sucking in and exhaust blowing out, the silencer won and made the carb work the opposite way.
    Some of you probably has a better explanation to it. As carb, engine and exhaust pipe is a proven combination by other racers, the most likely culprit is the silencer.
    Next to do will be either to buy or build a new silencer. I think the way to go is a less tapered cone, followed by a revese cone and after that a large diameter stinger. Lots of calculations though to get it right.
    Assuming ignition timing and spark is good, you have the float height set up so that fuel floods out of the needle valve at about 1/3 opening (carb vertical) and you have experimented or took advice on the gardener needle to fit - I would take a look at your valve timing and running clearances.
    Lite the blue touch paper and stand well back!

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  5. #104
    Senior Member Mike 40M's Avatar
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    Most problems solved this weekend. Met a nice Manxrider from Finland on a race in Norway. He promised me that if I took it to the Anderstorp TT race, he'd like to help me sort it out. As he is the fastest Manx-rider in Scandinavia, racing a 500 Petty Manx, a 570 Petty Manx in the 750 class and an ultra shortstroke 350 which he has built himself, I thankfully brought it there. I took him 5 minutes to get it running quite well. Then he said that it had to be tested on track to fine tune it. He kindly obliged to do the testing for me. Great to have an experienced Manx rider do the testing. It suffered from fuel starvation towards the end of the 800m (halfmile) straight. The brand new Matchbox float chamber had same problem as old gentlemen urinating. Damned AMAL. Replaced it with a Gardner one. Improved but still a bit of fuel starvation. Raised level 3mm. Better but not perfect. No more tracktime so we will try to sort it out next race. Also sorted out the classical problem with primary chain tension. When the bike is warm everything expands and tightens the chain. Now I know how much, so it has a nice slack when warm. Good things are that it handles well, what else could be expected from a featherbed framed Norton. Maybe a bit heavier fork oil. No oil leaks, thanks to Molnar. Only remaining problem so far seems to the lack of power in the end of long straights.

  6. #105
    Senior Member jalsteve's Avatar
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    Quote Originally Posted by Mike 40M View Post
    Most problems solved this weekend. Met a nice Manxrider from Finland on a race in Norway. He promised me that if I took it to the Anderstorp TT race, he'd like to help me sort it out. As he is the fastest Manx-rider in Scandinavia, racing a 500 Petty Manx, a 570 Petty Manx in the 750 class and an ultra shortstroke 350 which he has built himself, I thankfully brought it there. I took him 5 minutes to get it running quite well. Then he said that it had to be tested on track to fine tune it. He kindly obliged to do the testing for me. Great to have an experienced Manx rider do the testing. It suffered from fuel starvation towards the end of the 800m (halfmile) straight. The brand new Matchbox float chamber had same problem as old gentlemen urinating. Damned AMAL. Replaced it with a Gardner one. Improved but still a bit of fuel starvation. Raised level 3mm. Better but not perfect. No more tracktime so we will try to sort it out next race. Also sorted out the classical problem with primary chain tension. When the bike is warm everything expands and tightens the chain. Now I know how much, so it has a nice slack when warm. Good things are that it handles well, what else could be expected from a featherbed framed Norton. Maybe a bit heavier fork oil. No oil leaks, thanks to Molnar. Only remaining problem so far seems to the lack of power in the end of long straights.
    That'll be Jarkko...…

    Matchbox floats work well and the least problematic of their products.

    if the engine is getting too hot at the end of the straight you'll loose power, turn the Gardiner needle up a turn or two. If the engine is a new build it'll loose a few degrees of advance when it settles so worth checking it against Andy's figure. Hopefully you're running a mag not electronic for the longer duration spark they give.

    If your forks are old its worth fitting new damper rods and damper tube caps, more that 2 or 3 thou clearance and they don't work well. Also replace the piston for an "A" spec item with is a tighter fit in the tube. Failing that 30 grade oil 180cc to 195cc per leg.
    Last edited by jalsteve; 06-30-2019 at 02:59 PM.
    Lite the blue touch paper and stand well back!

  7. #106
    Senior Member Mike 40M's Avatar
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    Nope, Ari Tiainen.
    Not this Matchbox, Flow is about one pint in five minutes. A friend tested one of his yesterday at approx. 6 seconds per decilitre.
    Thanks for your suggestions on the forks.

  8. #107
    Senior Member jalsteve's Avatar
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    Quote Originally Posted by Mike 40M View Post
    Nope, Ari Tiainen.
    Not this Matchbox, Flow is about one pint in five minutes. A friend tested one of his yesterday at approx. 6 seconds per decilitre.
    Thanks for your suggestions on the forks.
    Seriously the matchbox should flow as much as the Gardiner float, you need to check the fuel level in the chamber as the valve maybe shutting too soon keep the fuel level too low. Given all your fueling problems there must be something else going on. If the valve timing is good, ignition too, setting the carb up, especially a Gardiner is 5mins and 2 or 3 x 5mins track visits. My Petty 92bore uses a Gardiner 42mm (bored) took a couple of mins to setup with a matchbox float. Usually you need a big bore fuel tap will a Gardner, also check the needle number (taper) and length sometimes owners take a file to them.

    My Petty below, about 110kgs dry and 59/60hp at the back

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    Last edited by jalsteve; 07-01-2019 at 04:14 AM.
    Lite the blue touch paper and stand well back!

  9. #108
    Senior Member Mike 40M's Avatar
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    My Velocette friend (7 Velos including KTT Mk III and Thruxton) examined the Matchbox, after some drilling and level adjustment got it better. Obviously Burlen who makes AMAL carbs and parts is keeping the British tradition of sometimes producing crap. So I'll continue to use the Gardner float chamber.
    Off topic. How do you manage to keep focus on a track day when temperature is more than 86F (30C)? And then get the leathers off?

  10. #109
    Senior Member jalsteve's Avatar
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    Don’t do that producing crap thing - or perhaps your mate should sell his velocettes and you your manx. All British produced and still around 60 years on!

    With respect I work with this stuff all the time and never have a problem with reproduction stuff.

    But then.......
    Lite the blue touch paper and stand well back!

  11. #110
    Senior Member Mike 40M's Avatar
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    On an extremely hot day, maybe it's too easy to use a not adequate word like "crap". But on a decent morning with temperature around 20C, maybe saying that it was foolish of me to expect that fitting a brand new matchbox without checking flow rate and level was optimistic. Yes, most reproduction parts made in the UK are good, if bought from renowned suppliers, but not all. I have a number of nonfitting parts in the shelves. And a number of parts that needed milling, turning or bending to fit. No, I have no intent to get rid of my six British bikes simply because I enjoy riding them.

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