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nzpeterb

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About nzpeterb

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    Christchurch, New Zealand
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  1. Section Swept. Thanks for the additional reply. I was able to try another Dellorto PBHL25BS carburettor today and this resolved the current issues and confirms the need for a replacement carburettor. As it seems no-one has experimented with different carb sizes, and I don't want to pay for a carb that doesn't work well, I have decided to purchase the original size. I like your suggestion of trying different diameter collars though so will look at how to achieve this. You are right that the Fantic offers no scope for extending the inlet tract unless a custom air box is used. Your mention of the IT range reminds me of the boost bottle I made before these were in vogue. A 75 mm irrigation tube the size of a baked bean tin connected via a hose between the carb and reeds. Not sure it increased response but the bike idled much better and would idle as long as you kept fuel in the tank. I think its best use was psyching out other competitors on the start line rather than any increase in performance. Thanks again for taking the time to reply. Dellorto (Eurocarb) have also been good, so I have learnt a bit by asking these questions. Regards, Peter. PS All my riding is low altitude so this one variable I can ignore.
  2. In case anyone is following this I am adding a note to complete my reply above. I have been talking to Dellorto and they confirm the venturi pressure is related to slide diameter not carburettor bore diameter. The 22, 24, and 25 Dellortos all use the same slide diameter so I now understand Section Swept's original comment that they will all have the same venturi pressure. I guess this also explains why gains can be achieved using a flat slide carburettor, though I was only looking at the different Dellorto body sizes.
  3. Section Swept. Thank you for taking the time to put together a lengthy and informative reply. My comment that the bike is not used for trail riding or road use is really describing that I only do classic trials with the bike. When new the bike had to be set up as the purchaser could use it for trail riding or commuting requiring higher engine speeds for longer periods. I am only using the bike for easy classic trials with short loops and all sections ridden in first or second gear. I have experimented with 2 stroke exhaust design in the past which is a fascinating subject, but I am not proposing a change to the standard exhaust. Re air volumes between the carb and cylinder there is also no scope to vary this if the existing air box is retained. I haven't followed your logic that different carburettor sizes pass more air but somehow the velocity over the venturi remains the same. Velocity is proportional to velocity pressure so both must surely rise together? I realise the smaller carburettor bore will reduce top end, but I never use that anyway. So the question is whether gains can be made to bottom end and mid range by fitting a smaller carb as these are the rev ranges I use. At this stage it appears no-one has tried it. I may try the 22 Mikuni off my TY175 however I will need to make adapters and it will only be luck if the TY jetting suits the Fantic. Has anyone tried a Mikuni on a Fantic? The beauty of using a Dellorto is all the sizes 22, 24, and 25 have the same body dimensions and spigot sizes, as well as being compatable with the standard jets as a starting point. Regards, Peter.
  4. Has anyone experimented with carburettor size on a rear kick Fantic 200? The bike is standard with no modifications. It is used in classic trials but not on the hard line, so doesn't need more top end power. I have calculated carburettor velocity for a number of air cooled trials bikes including Bultaco, TY175 and 250, TY Mono, and Gas Gas Aire, and all have the same velocity through the carburettor. The Fantic 200 carb would need to be reduced to 22 mm to match the velocity in all of the bikes listed above. 25mm is standard but the bike is not used for trail riding or road use. Has anyone tried a smaller carb to increase throttle response? Regards, Peter
  5. Thanks for the replies and especially to Paul who provided a brilliant reply. I also sent an enquiry to America and got a very helpful reply there too. Spent this evening using the information provided and was able to start the engine. What I did is summarised below. I am advised the original coil was a single wire red Motoplat, and the Denso CDI coil I have fitted is a compatible replacement. It was also confirmed that the wiring diagram I posted is also correct. All measurements I recorded for the coil and stator were within 1 or 2 ohms of the values Paul provided with the exception of one. When measuring blue to blue Paul got 281 ohms. One mine each time I connected the meter I got around 100 ohms briefly then it went to no circuit. I had read on my trawling through the web that some Motoplat coils had this characteristic, so unsure whether my stator was good or bad I tried kicking the bike over with no plug. With each kick an AC volt meter connected across the two blue wires briefly showed a voltage between 10 and 17 volts. Next cleaned all the connection plug contact surfaces, then plugged the control box back in but left it hanging so no part of the case was touching the bike, connected the earth wire from the control box direct to the coil, sat the coil on top of the head, and disconnected the kill switch. Kicked the bike over and there was a good spark! Then bolted the coil into place in the frame and retried but no spark. Scraped paint off the coil mounts to get bare metal, put the coil in place (still with the control box hanging) and the bike started, so this problem is solved. Found the 1991 parts book on the web and this gives the plug as an NGK BP5ES. Is this still the recommendation? Also what is the standard idle mixture screw setting? Mine was 3 1/2 turns out but seems happier at 2.5 turns. So thanks to the help from this forum the bike is running and motor seems good, though bike needs the following new parts: tyres, chain and sprockets, rear suspension bushes/bearings, and a rear guard, plus sticking rear brake, and a number of small parts, but feels like it will be nice to ride. Thanks again, Peter.
  6. Thanks for the reply. I have found names for people in UK, America, and Australia who can repair the units. Rather than send the whole system, (stator, control box, and coil) I was hoping to be able to identify which component is faulty, then replace or have repaired. At present I believe the coil fitted may not be compatible with the Motoplat control box so would first like to resolve if that is right. Regards, Peter.
  7. I have just purchased a 1989 Gas Gas 327 Air Cooled Mono. It is fitted with Motoplat Electrics and has no spark. I have been unable to find a wiring diagram that looks like mine. The stator has a black, grey and 2 blue wires plus the yellow which is not connected. I understand the yellow is for lights but the bike has none fitted. The resistance of the spark plug coil tests OK but, from reading what I can find, should the bike have a different coil with both the green and white wires connected? Does anyone have an original wiring diagram and measurements for testing the components. Regards, Peter (in New Zealand) Motoplat System.pdf
  8. You note your bike is on standard gearing of 10/41. In New Zealand our Gas Gas was supplied with 11/42. The taller gearing may smooth the response. Also make sure you have a slow throttle fitted. If a Domino throttle is fitted this would be a black tube under the grip. A slow throttle has full travel over around one third of a turn, while the fast throttle movement is the same throttle opening over a quarter of a turn. Hope this helps. Regards, Peter.
  9. In the States go to Speed and Sport. These bars are unbraced and listed for TY175 and others. I am using them on my Greeves. https://www.speedandsport.com/index.php/parts/controls/handlebars-sammy-miller-classic-trials/ Regards, Peter.
  10. Hi Tony, I have no experience with repairing fibreglass but am getting advice from someone who works with it every day. What I have learnt so far is that there are a number of different epoxies and polyesters. On my tank the wrong filler has been used which means it hasn't cured properly, resulting in the tank leaking. The previous owner fixed this by adding more filler until the tank no longer fitted over the frame tube. Luckily the incompatible filler softens (and the original fibreglass doesn't) by using a heat gun so first task is cutting and peeling the repairs off. regards, Peter
  11. Mark, Thanks for the reply. Your bike is looking good. Unfortunately mine needs to be restored before it can be used, as it has suffered too many modifications in the hands of previous owners. I now have most parts I can identify are needed before I start, but I am sure there will be more once I start dismantling. Focus at the moment is repairing the tank which had part of the tunnel removed, plus a couple of extra holes cut in the bottom. These were then patched with aluminium and a resin that is not compatible with the original. At present I am cutting and peeling the repair layers off to get back to the original tank. Regards, Peter
  12. Mark, Thanks for the reply. Not sure if there was a change but we can only go on what we find. I have searched the web and some unrestored M27's appear to have the aluminium badges and others just have the decals. My tank has the metal badges and these were obviously still on the tank when it was repainted to look the same as an M49. Is your M27 running? Regards, Peter.
  13. Graham, Thanks for the reply. Looks like the aluminium badges were only on the early Bultacos. My M27 has them fitted but an M49 uses the resin ones. I now have identified two sources for the aluminium badges. If others are looking for them these are: www.recambiousado.com www.motosdelabuelo.com There may be other sellers. Regards, Peter.
  14. My Model 27 Sherpa has metal tank badges fitted. I have just removed them to repair and paint the tank, and would like to fit new metal badges. I am sure I previously found someone selling new metal badges on the web, but have been unable to find them again. All the sites I checked just have the vinyl adhesive badges. Is anyone able to point me in the right direction to someone who sells the metal badges? Mine are pictured below. Regards, Peter.
  15. Gary, Apologies for not replying to you earlier. I just had a look back on Trials Central and only just saw your post now. Thank you for the excellent photos which clearly show me what I need to fabricate to put the frame back to original. I did manage to get a Bultaco brake pedal, but had to buy an assorted box of 10 Bultaco pedals from America to get it. Current issue is the fuel tank. Part of the tunnel has been cut away, then patched with aluminium covered with enough epoxy that the tank no longer fits over the frame tube. Currently I am grinding and peeling the layers back to the original tank to see if what is left can be repaired. Having never worked with Fibreglass before, I am still deciding whether to have a go myself, as so far have not found anyone willing to take on. Given it is a year since your post, I hope you have made more progress with your bike. Regards, Peter,
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