Try Colin Heath, he built the ” Waye replica” that I raced with some sucess in the 90’s before putting it on the road with nitrous oxide injection. It steered really well after I fitted front fork dampers. Colin bought it back from me a few year’s back. if you call me on 01243 830094 I’ll give you his number.
I have fitted these to various Scotts starting in 1968!
It took me several months before I became good at setting them up, but I found them to be better than the standard carb although there was a slightdifference between a full and empty tank of petrol. I fitted a constant head device to one bike by sealing the cap and allowing air in via a small bore tube which passed through the sealed cap ending about 25mm from the bottom of the tank. This worked well, but I’m not sure it was worth the effort.The biggest problem with the device was the rubbish quality of most of the components. It really needs re-engineering with decent qulaity moving “bits”. The standard version wears out quickly and in the worse case the butterfly flips over leaving you on virtually full throttle…very interesting when you are using a magneto for the sparks. Having said all that when running well they are as good as a TT Amal.
My advice for what it’s worth is to try it and if you like it ,rebuild it!
By the way Scotts need a much larger “main jet” than the four strokes.You will need to buy some small drills from about 35thou of an inch inch . I’d start at 35 and go uo graduaaly. I ended up with about 48thou if I recall. On my modified Scott i used a 35mm bored out version with a much larger central spindle so that the larger jet would shut.This came from an alcohol version used on the speedway bikes.Anyway I definitely got better mpg(5plus) and mph(5 plus) but I never did a back to back with a decent unworn carb.
One of the more obscure reasons for poor starting when hot ,is the position of the carb and the length of the bellmouth. In my experience you must not use a bellmouth of any appreciable length. As an example a std Amal TT bellmouth is too long and gives rise to a rich mixture flatspot just off idle(it cannot be cured by changing the slide). I believe that the extra inlet length on the atmospheric side of the carb means that the inlet pulse wave is reflected across the primary “jet” (for want of a better word) several times , picking up extra fuel each time. This makes the mixture too rich for hot starting. If you have a std amal carb , at the std distance from the crankcase then this is not applicable.
When I corrected the bellmouth length, I was rewarded by much better hot starting.
The other point that has been mentioned is fuel height in the float chamber. This is very critical, and if the bike is leaning the wrong way when parked . fuel will bleed into the motor(even with the tap off) sufficient to give poor hot starting. As alredy ststed by others, in order to check this , it’s worth draining the carb, preferably by running it dry, before trying a hot start.
Stan’s point about the mag is well made, but I believe the comments about “modern” petrol are more to do with the fact that a poor ignition system will not ignite petrol that has lost some of its “volatiles”.
I have used modern petrol that is 18 months old in my old bikes (with good mags) that has been a nightmare with modern machines. Where I have been able to drain the float chambers on the trouble bikes, they start fine – I think that some of the volatiles “boil” off in the float chambers due to engine heat/natural evaporation, leaving a fuel which gives the ignition system a tough job.
Incidently I have a lawn mower which starts promptly with petrol that has been left in it rom the previos summer – it has a cheap and powerful CDI system which produces a mammoth spark!
Most Scott radiators that have 3 bolt fixings have a marked restriction to water flow around the single lower bolt fixing. The position of this bolt in the core is important.Many are very low which just exasperates the problem.The potential problem can clearly be seen when you look inside the matrix via the bottom outlet.It is also possible that this area is blocked with debris etc. It may be worth unsoldering this bit of the rad and sorting it out.
I have always had radiators built with only 2 top mounts. I also leave at least a quarter inchspace under the bottom row of tubes (a sort of collection area). These radiators have about twice theflow when compared with a std one and I have never had a boiling problem, either on the race track or road. Having said that, std radiators normally only give a boiling problem either under prolonged slow running or continuous high speeds (65mph plus).
Both honeycomb and later rads seem to perform equally badly if the bottom mount is restricting the flow. Ian Pearce fits an expansion tank to his Brum road bike, allowing the excess water produced from boiling to be sucked back into the rad upon cooling. His racing bikes have special one off rads.
Give me a call if you wish to discuss 01628 891507(home evenings)01494 887569 (work)
Try Ian Pearce at Sam Pearce and Sons
Regarding resleeveing, it can be done Colin Heath and I successfully raced resleeved barrels. This allowed us to use scrap barrels and change the porting .
By breaking the skirts off you save some time!
If you want to chat about it give me a call on 01628 891507 evenings. I’m sure Colin will have the drawings of the liners he had made.
However, It is a lot of work and it’d be a lot easier to find a sound block.
Don’t bin the broken one just yet!
I use TTs on both of my Scotts.
The correct float height is found when petrol starts to weep(difficult to see- be patient) out of the “hole” underneath the pilot screw when the tickler is pushed down for an instant, ie a jab , not a push and hold down. The petrol should then continue to weep out of the hole, slowly forming a drip.This will only stop on switching the petrol off. If you have raised the float too high you must drain some petrol off before starting again. Under static level conditions there should be no petrol coming out of this hole.
I use a torch to help my aged eyes( you may be more fortunate) , then you can see the film of petrol leaving the hole before a drip forms.
All tests should be done with the bike level .
Take your time, and you should be rewarded with easy starting and good low and high speed performance. I think TTs are magic!
I have used petroil on my racing and road Scotts for many years. I use the cross over system with one way valves. This ensures that the mains are lubed. I use 25 to 1 mix with Silkolene Comp 2 or decent equivalent. The semi-sythetics seem OK for most uses, but I do like R40.
I have run std oils at 20:1 but they seem to be marginal and this ratio is very smokey. Running a good oil at 32:1 is probably OK for the road, but oil is cheap compared to engine rebuilds!
I fill in the crankcase oil resevoirs , not to increase the primary compression ratio(which I prefer to lower from standard) but to reduce smoking on start up or after long periods in traffic.This works well.
Fantastic Roger, Well Done!
Regarding the cylinder head shape, I have always felt that the std plug position/head shape is too much of a compromise: just look at the insensitivity to ignition advance.
The later “car” engine head shape/plug position seems so much more sensible.
Colin Heath and I stopped using full squish heads, even though we had no mechanical problems at over 15:1 compression ratios(22cc head volumes). We ended up with full squish on the exhaust with a large volume on the transfer side with an “encouragement ” space for the flame path where the deflector edge bisects the combustion chamber at TDC.This drops the compression to about 12.5:1 but the bike is at least as quick. This was an attempt to get to the “car engine head shape with the std plug position; I’d love to try a different plug postion.
Anyway congratulations once again ; I can only stand back and marvel at your continuing and amazing enthusiasm for these flawed, yet fascinating motorcycles.
Over the last 36 years running 14mm without inserts detachable head motors with various compression ratios up to 15 to 1(Full squish head).
I have found that NGK B6HES(lohg reach) with spacers, or B6HS(short reach) with the combustion chamber modified so that the electrodes slightly enter the combustion chamber work very well. I have used these for racing,sprinting and with nitrous oxide injection. I do however run less advance on all my engines, around 25deg.
Ian Pearce used the same grade of plug(eg a NGK 6) when racing and uses an “adjusted” B5HES for the road with excellent results. I’ve never bothered to run a 5 as I’ve had no trouble on a 6(I use a mag, Ian is on points with his road bike). Ian also uses less advance than std.
There does seem to be a power penalty if a short reach plug is used .
I have only run one engine with inserts, but only for a short time. I suppose you might get a hotter running plug and perhaps in that case you’d need to run a B7HES.
I wish you luck!
Have you tried Mike Field(sources of supply)?