[willsleddon]

Hi Tom. I have had brain freeze on a few occasions when starting my bike after a rebuild and thought that the problem was X when it was Y. To my unlearned eye it was also hard to know which timing mark works for which lead and whether pushing the timing lever away from the bike was full advance or not. They seem simple things now but as a modern bike person it was new to me.

I set my timing to 5/16 BTDC and usually there is a mark on the flywheel there from previous owners. The mag should be on full advance when you set the timing, if the points end of the mag is on the left side of the bike, and full advance is when the mag is the furthest point clockwise. On my bike I pull the lever towards me and the mag arm is on the left to set it.

I have taken the transfer ports off before and poured quite a bit of oil into the crankcase. As far as I understand this provides the seal to get the suction from the crankcase to pull the fuel in.

Air leaks are from where the carb bolts on to the engine as the ears tend to bend if done up too tight (I had to grind mine flat), the transfer port doors and the crankcase doors which I remove, put a smidge of fine grinding paste on and fit them that way with a rag stuffed inside to capture any rogue paste. And a final gasket. If you undo the bolt and remove the crankcase door strap and the door falls off on its own accord it is not sealing. It should take a kick or two to blow the doors off.

Fuel height, don’t know for your bike but if your plug is wet then I would say that there is enough fuel for starting and that I am inclined towards saying that fuel height affects running more than starting as long as you actually have fuel. You could set you float bowl in its highest position by rotating it backwards to ensure there is indeed enough fuel if you like, but as a last resort. What about sticking the plugs in the flame of the gas cooker and then trying it then. Does pouring a capful of petrol down the plughole do anything? Do you have a sodding great hill nearby?

Air screw 1 turn out and see how it runs once started and make sure that the slide in the carb is fully down to the screw as a stuck open slide will mean there is too much air for it to start.  I had this on my Yam at the weekend on one side and the cable had come out of its locating sleeve because it needed lubricating.

Saying all that, it is likely to be none of those. If you remove the plugs and earth them on the frame does it spark?

Apologies if all that sounds like I am insulting your intelligence and knowledge Tom and I hope that what I have written is right in the first place! These are the things that have flummoxed me before. Sounds like you have good compression anyway.

[willsleddon]

Thanks Richard and I will visit Barnet when I have been through a few more things. As for the different spring length Dave, well that might explain it. My steering races on the frame measure 8 inches ball to ball and the suspension part on the forks measures 10 1/2 inches button to button. The fat part of the suspension is 6 1/4 inches and I have a loose main spring that measures just over 6 1/2 inches which is quite bouncy. If you stick that spring into the fat part of the shock absorber I can’t imagine there would be much room for any springing of any sort and my own bike is pretty solid an affair.

How do these dimensions compare with yours Dave or others folk’s please?

How long are the mainsprings and is there a choice. Mine should be around 6 inches me thinks to offer any degree of bounce.

Thanks. Will.

[willsleddon]

Thanks Gents. I gather from the replies that there is no mysterious and usually encountered gremlim I should be looking out for then.

The next thing then is to check what I have against what I should have. Since I am not running out of thread on the spindle it must be the fitment of the ball in the cups. The steering turns without being notchy at all so I will have a look at the balls themselves. I know the bike was stripped completely before I had it and I would say that the cups would be a less likely /easy thing to renew than the balls during any renovation.

You can see a lot of ball when the arrangement is supposedly tight, to the point where I suspect that they might fall out. OK thanks for the feedback. the picture is becoming clearer.

 

[willsleddon]

Gents. I have always thought that the Isle of Man Classic Event would be a great, although partially impractical, place for the AGM. The Scott marque is always seen as something of a rare and exclusive thing, owned by folks that only ever occasionally use them. Having them turning up all over the island would be a great thing. But not for the environment.

[willsleddon]

Hi Martin. Thanks very much for that kind offer which I might take you up but Eddie Shermer is sending me a pair over which might be suitable. I see yours has got a spring at the end in the photo. I was thinking of a making a direct drive to the actuator arm but the spring thing might end up as an option depending on how much force is needed. Interesting and thanks again.

[willsleddon]

Hi Lewis. I might have a close to not leaking radiator for the bike and a ready to go engine for a 1926 if that is any use. Graham has just collected a load of 2 speeder exhaust bits which might fill a gap too. Also have one of those tool boxes with the diagonal side.

Will.

[willsleddon]

Hi Martin. Very useful thank you. I had read that it also operates as a cut out and I thought this was a necessary function of the decompressors somehow but I have a separate cut out button on the bars so I am assuming I just need a normal lever then. I read about the peg and was wondering if this was used to hold the pressured decompression lever owing to the number of arms I possess.  Some of the literature that Lewis put me onto has you holding your hand over the carb intake and somehow doing other things whilst holding the bike because you shouldn’t start it on the stand.

The picture is building and basically, a word oft used mistakenly, both valves are sprung so that they are always closed and operating the lever presses the valves in against the springs and decompresses the engine. Once I get the bits it will make sense. Still looking for the springs and ends of the decompressor valves if they are around though as mine were full of sh=== and I don’t want to mess with them if I have to.

[willsleddon]

Hi Lewis. I had a look at that document and I have got part nos 66 and 67 on the bike and the two plates nos 69 and 70 so with your bit it seems that it is nearly complete. I see on parts 66 and 67 that it looks like there is a nut and spring on the end which I do not have, assumingly these return the pistons back home. I think I might actually have them unused and unneeded on my other bike so Bob is possibly your Uncle.

So with your part added and me having a look at the decompressor lever parts in the catalogue, my brain still can’t visualise how the bowden cable connects to your part and operates it and possibly holds it. That looks like a special lever which I can overcome I am sure and I can get a lever and a cable and I am pretty sure I have the frame mounted recess for the engine end of the cable. Is there a picture you can point me towards that shows the arrangement at all please. By the way Lewis I don’t have your number any more as my phone lost most of its contacts. I am on 07531781196.  It’s probably more simple than I imagine or is it just a hole the cable goes through. Thanks again.

[willsleddon]

Err, yes please. That sounds like divine intervention there Lewis. My postal address is Holly Bank, Heath Lane, Boughton, Chester CH35ST.

That is much appreciated and thanks for confirming my fears Martin so I will park the bike to one side (Yam cylinder studs to sort) until I get the decompressor fettled because the starter does now seem to have much more load on it and they must have been leaking somewhat for a bit.

I will have a look at the parts catalogue in the document archive too. Not sure of the arrangement.

Progress comes in fits and starts.

[willsleddon]

Thanks Peter. That gives me hope then. I have fitted a number 3 slide with 6 needle and a larger than usual but unstamped 106 nozzle on clip 3 with 3/4 turns out of the air screw with a 170 main. I did have a number 4 slide and a 190 main and a genuine 106 nozzle so I have made the whole thing have less air and more petrol at the crucial point hopefully. Getting rid of the gauzes is my aim but maybe this should be accompanied by work on the brakes too.

I have been busy stripping the threads on the cylinder head bolts on my YR5 Yamaha so test ride number 76 on the Scott has had to wait. Incidentally I have had a drive chain break and a mag chain roll off the sprocket and plugs go all wierd on me during my sojourns and this has prepared me well because my spares and tools have taken on a new exacting life and I have yet to be unable to get home. That will doubtless change though. In fact I was able to catch up accidentally with friends who I was unable to see whilst at the roadside only for them to reassure me that they thought it was going to be me anyway.

Will.

 

[willsleddon]

Thanks for all those comments and thanks Glyn but I head already read and actioned your advice about the exhaust divider as this was one of the things you wrote about in one of your Potty mods I believe.

So I took Chitty Chitty Bang Bang out for another 30 mile ride around Cheshire and caused a lot of consternation to riderless horses and small children.  before I set out i moved the needle to clip 2 with the air screw just over 1 turn out and she ran well to be honest but when it got hot things started to go wrong which I think is a lean thing, especially in that just on the needle bit. Once onto main jet, it’s fine.

So I stopped after 10 miles and turned the air screw in to half a turn out and moved the clip to 3 and this probably did not do anything except when going down hill and you back the throttle off whilst at the same time going fast, produced the most noise yet. Nothing I did would stop it and it can’t be good for the engine. The difference was though that it was coming out of the exhaust and not the carb so that’s backfiring which is rich. Next time I will turn the air screw to 1 again and if I would have had my wits about me I would have done it there and then but the noise deterred me. Having re read this posting, it seems obvious that I should choose to have the air screw out 3/4 of a turn.

Interesting to hear Leif on about the slide. I think it is a air/ fuel mismatch that affects some engines differently. I am inclined to agree with Richard that each bike has become slightly unique over time and likely also in manufacture.

I was going to stick the gauzes back and be done with it but I have a number 6 carb that is bigger than the 276 I have fitted so I am interested to see if what this does. As the internals are the same and hence the petrol flow, the increased bigness of the bore should mean more air and more spitting which I am growing to appreciate.

Going back to my Yamaha carb fiddling, either a less wide needle is to be tried, or a throttle cut out with less of a cut out. Or gauzes.

The Yamaha needles are all shapes, some with very skinny bottom bits and fat top bits and clearly Yamaha were imparting all their knowledge to get the mixture dead right to go to the trouble of having such widely differing profiles. You wonder if the bottom part of the needle on the Scott were skinny that it would help fuel flow in the very first parts of when the needle comes into being…………… Or gauzes.

[willsleddon]

Hi Richard. Interesting comments. I did have gauzes top and bottom on both sides and this worked well but restricted power so I took the bottom ones off and it has started again but I also moved the needle one notch down too.  I have a 276 carb, which might be too small and all standard size carb components that are new ish and this was clip 4 from the top, so set rich. When the bike is running down the road it does not spit at near main jet  speeds and it only seems to occur on the overrun or at lower revs. This suggests to me that it is not a timing thing, nor is it a porting thing but, as you suggest, a fuel air thing. I messed about with the timing lever to see if this made any difference but it doesn’t and just as I was getting home it seemed to like being choked at lower revs.

The snail shell on mine has a big bolt going through the middle and is not restrained from the frame as I have seen on others, so the gases have to negotiate the curved tube and this bolt too which is hardly a smooth path but there again we are only talking a few horsepower. Thank God mine doesn’t go as fast as others seem to because I have yet to master the art of braking in any situation resembling an emergency stop in 100 yards. My seat covering is already the right colour brown as it is.

As far as my brain goes with the spitting, this is either a case of it being too lean or too rich at either the air screw or the needle so I will mess about until I end up back where I started and with no sensible conclusion realised.

Before that I will try the left hand gauze thing too because that makes sense. There is a lot of swirl going on which Yamaha, my second favourite bike company, researched enormously. I wonder if reed valves would do anything?

Fitted a Weldonia fork brace incidentally and this has made the front end a much more confident thing. A work of art to be honest because that was designed by hand and if you fit a big brace along the back, it also works as a steering stop too. It would have definitely needed to be designed by CAD such is the way is passes around everything and it still works really well.

[willsleddon]

I got one from Roger after all that. Thanks.

[willsleddon]

Hi Tom. If you use Pistoneze through the pump you CANNOT then use a two stroke in the petrol. I have just saved you an engine rebuild as they mixed and jammed up my rings beautifully. Yes Silkolene Comp 2 throughout for me. Bottom end and in the petrol.

[willsleddon]

Hi Richard. I spent far too long on my kickstarter mechanism before realising the simplicity of it. I had it all too long and the thing kept on jamming when it fully returned. I use a split link to connect the chain to the rod. Forgive me if you already understand this is.

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