luddite Posted January 5, 2011 Report Share Posted January 5, 2011 (edited) I have recently dragged my last remaining Bultaco from the back of the shed where it has spent the last couple of years in disgrace. A few years back I decided to try sidecar trials, so got hold of a chair which was once fitted to a '74 model 125. I purchased a matching bike which was running absolutely perfectly, but had trashed lower frame rails and other frame damage so was ideal for the project. Mods duly done, the bike was reassembled, but wouldn't start. Crank seals I thought, so I whipped a new set in. Still no joy. To cut a long story short I stripped and reassembled the bike (I didn't split the cases though, or lift the barrel) till I was sick of the sight of it, and the best I could get it to do was to start, rev massively, die, rev massively, die, and repeat for a few cycles. New year, new start so out comes the 'Taco. Timing's perfect, big fat blue spark (one of the best I've seen in fact!) so that side's OK. The carb, an Amal 627, is clean and set to book; it's a bit worn but I've run with worse. The fuel flow is a tiny bit slow but is flowing to fill the chamber. If I prime directly into the head or the crankcase, the bike will catch but not run which tells me the top end is OK. Now bearing in mind I didn't split the cases at all, and I have changed the seals, could anyone please offer any suggestions as to what I might check next before I start taking the engine down? Thank you. Edited January 6, 2011 by Luddite Quote Link to comment Share on other sites More sharing options...
big john Posted January 5, 2011 Report Share Posted January 5, 2011 Firstly you say it would rev massively, is that by itself or by you winding open the throttle? Assuming its not a stuck throttle or knackered crank seals... That particular model/type of Bultaco was a bit difficult to start even when brand new. From memory the proceedure was a couple of kicks with the throttle wide with petrol off. Like priming kicks without fuel Then: Petrol switched on, with twist grip wound fully open, tickle carb antil flooding out of the tickler overflow hole. Close throttle. One kick throttle closed, and another and another if it doesn't fire on first kick. She then should then burble into life, maybe even feathering the tickler to give a wee bit more fuel, while she settles down. They were quite prone to flooding-out those bikes with 627 Amals. Hope this helps. Big John Quote Link to comment Share on other sites More sharing options...
luddite Posted January 5, 2011 Author Report Share Posted January 5, 2011 Thanks for the reply, Big John. Rev and die cycle was without me touching the throttle, which now I'm sitting here thinking about it must indicate air getting into the system from somewhere other than the carb inlet, or it wouldn't have the volume of air available to enable combustion to such a degree. Looks like I'll be pulling the engine out for a better look I think. But before that I'll give The Procedure a go. Thanks again. Quote Link to comment Share on other sites More sharing options...
big john Posted January 5, 2011 Report Share Posted January 5, 2011 Thanks for the reply, Big John. Rev and die cycle was without me touching the throttle, which now I'm sitting here thinking about it must indicate air getting into the system from somewhere other than the carb inlet, or it wouldn't have the volume of air available to enable combustion to such a degree. Looks like I'll be pulling the engine out for a better look I think. But before that I'll give The Procedure a go. Thanks again. Sounds to me decidely like you have maybe inserted the seals in their carriers incorrectly or maybe left out the o rings, its drawing air from somewhere, assuming your throttle slide is not stuck wide open! Big John Quote Link to comment Share on other sites More sharing options...
luddite Posted January 5, 2011 Author Report Share Posted January 5, 2011 or maybe left out the o rings, Big John I have a horrible feeling you may have just hit the nail on the head - I can't actually remember putting new ones in, but I'm pretty sure I can remember picking old ones out. Thanks due again! Quote Link to comment Share on other sites More sharing options...
luddite Posted January 6, 2011 Author Report Share Posted January 6, 2011 Couple of pics before it comes to pieces again. Not smart I know. A few 'wrong' bits I know. But once it's up and running it'll do the job I'm sure and I can improve it as I go (and it was very, very cheap ). Quote Link to comment Share on other sites More sharing options...
luddite Posted January 6, 2011 Author Report Share Posted January 6, 2011 Seal holders out - and the diagnosis is looking good. It would appear by their squished profile that I didn't actually change the big O rings and on the mag. side in particular they're not doing a lot of sealing. But in addition, I can find no trace of the RH crank O ring. Not one of my better jobs, must have been one of those early morning garage sessions when my son was a squalling baby and I'd had less than my usual twelve hours :-) Quote Link to comment Share on other sites More sharing options...
big john Posted January 10, 2011 Report Share Posted January 10, 2011 Seal holders out - and the diagnosis is looking good. It would appear by their squished profile that I didn't actually change the big O rings and on the mag. side in particular they're not doing a lot of sealing. But in addition, I can find no trace of the RH crank O ring. Not one of my better jobs, must have been one of those early morning garage sessions when my son was a squalling baby and I'd had less than my usual twelve hours :-) Did you notice if there were gaskets fitted behind the oils seal carriers? There should be! Big John Quote Link to comment Share on other sites More sharing options...
luddite Posted January 11, 2011 Author Report Share Posted January 11, 2011 Did you notice if there were gaskets fitted behind the oils seal carriers? There should be! Hmmm. There weren't, I thought there should be, but chatting to the guys at Bultaco UK convinced me otherwise. I'm sure there were on my model 10 and I think so on my model 80. The witness marks on the seal holders would indicate that none have been there though. The O-ring issue wasn't as bad as I thought. The smaller crank one was there after all, just a lot thinner than it should have been. I changed the crank seals whilst I was in there - the ones I had in seemed very flimsy compared to the Bultaco UK items (they were autojumble specials). Anyway, back together and it still won't go! It does start on wide-open throttle and a hefty prime, holds high revs for a couple of seconds and dies. I'm happy that primary and secondary compression is OK, that the spark is healthy and at the right point, and that the carb pilot drillings are spotlessly clean, and that it is jetted correctly. So I gave Amal a call to chat about acceptable wear on the Mk1 concentric, and they are of the opinion that the wide throttle is necessary to balance an overfuel issue, which is entirely logical. The most likely cause of this is wear in the throttle slide bore causing the needle to wear the needle jet to the point where massive overfuelling is preventing the engine from running. So, to prove the theory I've bought new jets etc. and if that works I'll splash out on a new Amal. I'm waiting for the postman now :-) Still doesn't explain how it could work so well before I took the engine out, though, unless moving the engine around dislodged a blockage in the jet which was compensating. Quote Link to comment Share on other sites More sharing options...
woody Posted January 11, 2011 Report Share Posted January 11, 2011 The early bikes used gaskets on the seal holders, up to around 1973/4, from then on they had O rings, no gaskets. The gasket set usually has the gaskets and O rings to cover either as I doubt there was a definitive change over date/model from gasket to O ring, but it's easy enough to tell, the seal holder will have the groove machined for the O ring or it won't. Can't understand the overfuelling theory to be honest, it would still run, just rich. However, if your bike ran ok before you put it away the needle and jet aren't going to have worn when not in use, so it's difficult to see how that could be the cause. I'd be thinking along the lines that whilst laid up some stale petrol has solidified somewhere in the pilot circuit and is preventing it from starting and running once the initial carb flooding with the tickler has subsided. A blocked or partially blocked pilot circuit can virtually stop a bike from running altogether (don't ask me how, this is just from personal experience) May be worth getting the carb cleaned anyway in a good sonic cleaner for peace of mind which should break up and remove any blockage. For what it's worth I had a clapped out carb on a model 92 I rebuilt last year and I fitted an OKO as it was a lot cheaper than an Amal (just needed the inlet manifold of a later 250 as the OKO is push on not bolt on) With just a slight pilot and main jet change it ran very well. Can't remember the actual jets unfortunately but it ran quite well straight from the box. Quote Link to comment Share on other sites More sharing options...
sherpa325 Posted January 12, 2011 Report Share Posted January 12, 2011 (edited) Hi ,I tend to back up what woody is saying, a worn out needle and needle jet wont stop the bike starting and idling, it will just run rich in the mid to top rev range. I assume you have checked the woodruff key that locates the ignition flywheel as a sheared one will still give a healthy spark but not when you want it. Also it may be worth replacing the condensor as these give all sorts of problems, and will give a spark at the plug when kicking the bike over ,but muck up under real loads. However I think your carbie could be the real problem, check the rubber mounting flange for leaks, then I would go through the carbie again, check that the floats actually float,remove all the jets and soak the carb in fuel and then blow all the holes out with a compressor, make sure all the jets are not blocked particularly the pilot jet, also check the needle valve that is attached to the floats is in good condition,make sure the gasket is not covering the pilot jet or blocking it. These bikes and carburetor are very simple and I am pretty sure there is not that much wrong with it Cheers Greg Edited January 12, 2011 by sherpa325 Quote Link to comment Share on other sites More sharing options...
luddite Posted January 12, 2011 Author Report Share Posted January 12, 2011 (edited) Thanks Woody and Greg. I have to agree with both of you, I'd have thought that with the slide down, the needle jet has little or no influence so the bike should start on the pilot circuit alone. But it doesn't so I'm clutching at straws now! If I change it and it does nothing, I've eliminated it,if it does something, however slight, it may be a pointer and shows me that it's most likely a carb issue. I know about the pilot circuit on Amals; this one is very clean indeed, no blockages of any kind. The float floats at the design height, all jets are clear and unobstructed. The flanges have been trued on glass, including the rubber one. The points open at 3mm BTDC precisely. Good point about the condenser though, I've had issues with these before but they tend to give intermittent firing problems in my experience. Quick and cheap to change so I may as well eliminate any doubt by changing points and condenser. Mentioning the OKO (where did you get it, by the way) has reminded me I have a little-used Mk2 Amal from a later 250 somewhere in the shed. As far as I remember the bore is still 27mm on the later 250s (is this correct?) but I should change the jets to stay the same size as the Mk1 currently fitted to my 350. To start with at least. As has been said, it's a simple bike with a simple carb, but that's what's so damn frustrating! Grrr! Edited January 12, 2011 by Luddite Quote Link to comment Share on other sites More sharing options...
mrb505 Posted January 12, 2011 Report Share Posted January 12, 2011 (edited) With the slide down a worn needle will make a difference as fuel come up through the jet when it is supposed to be shut, with these Amals the needle + jet should be replaced regularly and more so on the 325's it seems. On the 250's these amals seem to work okay and seem to tolerate a bit of wear, maybe the 325 is too big a sucker for these carbys even more so when they have good compression and seal, could be why Bultaco went to a Bing for the 325's and stayed Amal for the 250's later on. My m125 usually starts 1st or 2nd kick from cold I use a similar starting technique to Big John as in tickle while throttle is wide open and get a good flow going, so it lets a bit of fuel+vapours into the venturi a quick determined jab on the kickstarter and away she goes. Sometimes in winter when its really cold ( it gets down to -10c here) once has started I need to press the tickler down occasionally till warms up a bit, my carby has the original 20 pilot jet and 3.5 slide. Its good to see you trued the mounting flange but have you done the float bowl as well,my carby had bent tangs on the bowl when I got it from over tightening over the years. I straighten my tangs in a vice by putting a small round headed screw backwards in each tang to protect the bowl sealing face and a bit of cardboard to protect the bottom of the bowl and gently tighten the vice till the tangs bend back in line with the face and then do as you did with glass just make sure not too much is taken off as the float may stick and put a new bowl gasket on as it doesn't take much of a air leak to upset these carbys might be worth also checking the air screw o'ring as these get hard and crack and even new ones can get nipped when screwing in or out. Ross Edited January 12, 2011 by mrb505 Quote Link to comment Share on other sites More sharing options...
luddite Posted January 12, 2011 Author Report Share Posted January 12, 2011 With the slide down a worn needle will make a difference as fuel come up through the jet when it is supposed to be shut, with these Amals the needle + jet should be replaced regularly and more so on the 325's it seems. Its good to see you trued the mounting flange but have you done the float bowl as well,my carby had bent tangs on the bowl when I got it from over tightening over the years. Ross, thanks for the reply. As you were typing the words, I was realising my floatbowl tangs were bent, and slight burrs around the screw holes were lifting the bowl away from the flange in places. Not sure if it was bent enough to lift the pilot fuel jet above the fuel level but it's damn flat now! It could be that when I cleaned the carb after the engine was in storage, I introduced a leak or air gap. The needle jet was very worn. I'd estimate around 75% increase in area. I did photos, but they're not yet available. Using a simple suck test to compare old needle/jet against new revealed I could hardly suck any air through the new parts, but with or without needle made little difference to the resistance using the old. Now that just has to make some difference! I should get a chance to build it back up tomorrow evening. It will not beat me! Quote Link to comment Share on other sites More sharing options...
mrb505 Posted January 12, 2011 Report Share Posted January 12, 2011 The most important job of the bowl gasket in the Amal is to create a seal for the pilot jet as it draws its fuel nearer the bottom of the bowl from its own secret passage where as the main jet is just dangling there in the main bath, which also of course supplies the needle jet as well. Could be that your bowl gasket has dried out after the bike had been stored for a while, sometimes the gasket will swell a bit again if it is soaked in oil (2 stoke should do) overnight making it useable again till a new one is sourced. Ross Quote Link to comment Share on other sites More sharing options...
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