smelling123 Posted February 12, 2012 Report Share Posted February 12, 2012 The 'vesty replica' at Telford had a reed valve conversion. Has anyone any experience of the effects of this mod? I'd expect smoother running at low revs because of cleaner low down carburation...anyone ever tried it? Quote Link to comment Share on other sites More sharing options...
feetupfun Posted February 12, 2012 Report Share Posted February 12, 2012 Its a pretty common mod on late model Bultacos where I live. Yes it improves the even-ness of the firing. Quote Link to comment Share on other sites More sharing options...
pschrauber Posted February 12, 2012 Report Share Posted February 12, 2012 I have heard that there where a few Sherpas around, as I remember right, (definitely not sure here), had Paxau once fitted one to an engine? Fitting reeds to the Bultaco engine would be not allowed in general in Germany or at the Inter Nordic Cup, (Scandinavia). Probably if you build a completly replica bike. If you really want to go with reeds I would try to get the Pursang reed intake and maybe also a cylinder (if possible to loan?) just for blueprinting and determine how the reds should fit best. The Pursangs had a reed intake, maybe you can find a reed intake in the US: Quote Link to comment Share on other sites More sharing options...
mattylad Posted February 13, 2012 Report Share Posted February 13, 2012 I have a 250 pursang barrel fitted with a reed. It is just so full of transfer ports you would not believe. Cannot see it being suitable for a trials engine but I may just give it a try!!! The standard sherpa barrel has a bolt on manifold and is just crying out for a reed as produced by Keith Horsman etc. If I understand correctly the Aussies are using Sherco reeds? 1 Quote Link to comment Share on other sites More sharing options...
feetupfun Posted February 13, 2012 Report Share Posted February 13, 2012 I have a 250 pursang barrel fitted with a reed. It is just so full of transfer ports you would not believe. Cannot see it being suitable for a trials engine but I may just give it a try!!! The standard sherpa barrel has a bolt on manifold and is just crying out for a reed as produced by Keith Horsman etc. If I understand correctly the Aussies are using Sherco reeds? Yes Sherco reeds are used here in some late model Sherpa Ts which have been modified relatively recently. There are also conversions using other reed cages, and I learned recently that converting Sherpa Ts to reed induction was being done here during the 1970s. Quote Link to comment Share on other sites More sharing options...
dadof2 Posted February 13, 2012 Report Share Posted February 13, 2012 I had a number of Sherpas, 250 and 325 from 1970 to 1980. All the post 1975 models ran beautifully smoothly right from tick over to full revs. They had plenty of power and ran smoother than ossas, yams, Gas Gas, betas and other reed valve bikes I have owned. I know reeds give more power than piston porting but I would be happy on a non reed bulto today, they would pull from nothing in 3rd on the steepest hill. I also had one of the last non reed 1982 Maico motocrossers. On a dry day the 83 bikes with reed valves (honda particularly) could see it off up the start straight. But when it came to finding grip out of slow corners or grassy cambers in wet conditions it would leave the reed bikes standing. I would be inclined not to fit a reed to a bulto. At least until you had tried one out and compared it to a properly running standard non reed verion. Cheers Quote Link to comment Share on other sites More sharing options...
mattylad Posted February 13, 2012 Report Share Posted February 13, 2012 Dadof2 If you look at the way modern bikes are ridden it is stop, faff around, rev drop clutch and go. Reason is down to tyre and suspension technology. I think the old Bultos in standard trim are pretty wooly compared with other bikes and much prefer the immediate response of a TY twinshock with much of the flywheel weight removed and more importantly it has a smooth light clutch which allows me to ride in a more modern fashion. Not saying your logic is invalid it is just coming from a different direction to mine. I try to make my bike ride like a modern because I think it is more effective for me. Quote Link to comment Share on other sites More sharing options...
bullylover Posted February 13, 2012 Report Share Posted February 13, 2012 Hello all. I have to say that I agree with Dadof2 on this one. The reason that Bultaco`s feel woolly compared with later or Jap bikes is the fact they have twice as much flywheel weight in them. I love modifying bikes but I have never felt the need to add a reed valve to a Bultaco. I once owned a 158 that I had a 32 teeth per inch hacksaw blade cut/1/8 inch high in the intake side of the slide and it would idle at about 4 revolutions a minute and snap to full revs very quickly. I also know a bloke that has ten odd Pursangs and none of them has a reed valve. He has won numerous QLD Classic MX Championships and the only one he has tried a reed valve in was a 117 which is a mk 7 125 running on Methanol and he tried it and pulled it off. It has been sitting on his bench for about five years now. I think the only Pursang that had a reed valve from standard was the mk 15 which there is very few off in the world. Bully Lover. Quote Link to comment Share on other sites More sharing options...
woody Posted February 13, 2012 Report Share Posted February 13, 2012 The 'vesty replica' at Telford had a reed valve conversion. Has anyone any experience of the effects of this mod? I'd expect smoother running at low revs because of cleaner low down carburation...anyone ever tried it? If you really want to 'pep it up' a bit, the cheapest and most effective way is to fit a single crank weight from a 250 in place of the double weight on the 325, or a 250 ignition flywheel which is almost 2lbs lighter. Or both. It will pick up very quickly / very very quickly... Quote Link to comment Share on other sites More sharing options...
pschrauber Posted February 13, 2012 Report Share Posted February 13, 2012 The mentioned weight loss is a good idea and will have a lot of effect. Here a comparison what you will loose in weight between the big flywheel weight of the 350 to the 250cc model: I personal would only change the right crank weight and try with this, it will change the habit of the engine already a lot. When exchanging the rotor too the engine will get really "snappy". The use of the smaller flywheel weight was done very often, some former Bultaco riders in Germany even tried to turn them down which is not easy as the flywheel weight is completly hardened. (Anyway I have been told that a weight reduction on the rotor side too will make the bike/engine less useable for trials, I persoanl haven't tried out this). If you really can't get away from the need of reeds, here some NOS ones from the US E-Bay, (as mentioned there where a lot of Pursangs sold in the US, a complete set up): Bultaco reeds Quote Link to comment Share on other sites More sharing options...
feetupfun Posted February 14, 2012 Report Share Posted February 14, 2012 The intention of fitting reeds to Sherpa Ts, is not to make the motor more snappy or more powerful. It is to make it run more evenly at low load and low throttle opening combined. Dare I suggest those of you who haven't yet directly compared riding a Sherpa T both with and without reeds, you should have a go and see for yourself before you say how silly the idea is. Bultacos are not the only Spanish trials bikes that can benefit from reed valves. Some OSSA MARs have also been converted to reeds. The benefits are such that that some recently posted new rules I saw for trials bike eligibility in Spain, specifically excludes the use of reed valves in pre-72 class. Having said that, my Bultacos do not have reed valves and I have no intention of fitting reeds (or lightening the flywheels) as I love them just the way they are. Quote Link to comment Share on other sites More sharing options...
mattylad Posted February 14, 2012 Report Share Posted February 14, 2012 (edited) I think the only Pursang that had a reed valve from standard was the mk 15 which there is very few off in the world. Bully Lover. Didn't realise I had anything special as it came with a box of Bulto bits. The reed valve area is massive in comparison to a trials intake. I had a 325 Model 159 which I sold a while ago to which I fitted the above mentioned Pursang clutch (duplex chain alloy basket) and primary flywheel which looks like the width of the internal part of the flywheel shown above at the side of the engine but mounted externally if you see what I mean, along with a Femsa ignition (I think) as it was smaller than the original. Ignition was the legendary Reg May recommendation of 2.4mm btdc. Never got on with the bike (didn't like the handling) but it was pretty good at hillclimbs. Edited February 14, 2012 by mattylad Quote Link to comment Share on other sites More sharing options...
smelling123 Posted February 16, 2012 Author Report Share Posted February 16, 2012 Thanks for all the comments. As 'feetupfun' says the reed would be not be to achieve more power (in fact becasue of the port geometry with a reed it could easily make less top end power) but it should make the low down running better. Think I will try it without modifying the barrel and then I can do a direct comparison. Im not expecting the bike to be ready for several months but I will report back with results for anyone interested. Quote Link to comment Share on other sites More sharing options...
dadof2 Posted February 16, 2012 Report Share Posted February 16, 2012 Hi there Mattylad, just with regards to your comments about modern riding techniques. Smalling 123 is located in Yorkshire and the chances are the bulto if used in trials at all will be non stop event. I don't do many trials these days but I have nover come across a trial for classic twinshocks like the bult run under WTC type stop & hop rules. Cheers Quote Link to comment Share on other sites More sharing options...
mattylad Posted February 17, 2012 Report Share Posted February 17, 2012 I ride a fair bit around Europe (belgium, france, germany, switzerland) and most of the expert routes require a degree of modern riding techniques even if they are technically non stop. The "dynamic stop" seems to be acceptable before a big step or drop off to compose yourself. Technically its a five but we seem to be able to get away with it. What I was trying to convey was the fact that the bulto was being used when tyres were rock hard and finding grip was at a premium. Nowadays that is not the case with modern tyres being light years ahead. This means the engine characteristics which were good for the time are not necessarily the best now. I generally ride a Yamaha with a clutch as good as a modern bike on tight turns this is definately a positive atribute as I can crawl round slower than if using a "wooly" engine with the clutch fully engaged. A lot of your riding style depends on your experience prior to going (back in my case) to twinshocks for me I rode modern trials and thats how I feel the most comfortable. I could not ride a bike without having my index finger on the clutch as it would be just as alien as when I started riding with a finger on the clutch 25 years ago. I'm sure I could adapt but that would make it more difficult to ride. Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.