Moderator Airhead Posted September 1, 2008 Moderator Share Posted September 1, 2008 Hey oldgit, I appreciate all your help but I think there is some miscommunication here. The valve needle (or needle valve as I called it) and float needle are two different items, but when you call them by the same name I just get confused. I understand how the float needle having grooves would leak, but it did not leak when I tested it. When it leaks gas should come out the overflow pipe, and it does. How does this cause the carb to flood the engine? I understand from others on this site that bikes still run with leaky float needles. Second issue: The valve needle has some scratches down the taper. The scratches are insignificant compared to the space between the needle and the nozzle. I don't know how much trouble this causes. There seems to be some difference of opinion as to how these things work. Some people say that when the slider is closed that the needle shuts the gas flow off. I wonder how, because after much internet searching I have found diagrams that show that the needle is not supposed to stop the nozzle up completely, indeed it cannot, ever, because even a new needle is not nearly thick enough to fill the nozzle completley. If it did, say goodbye to the air from the air jet. The air jet supplies air through the nozzle even at idle, yes? Scratches might let some minute extra fuel flow by, but this cannot be very significant to the overall flow. The needle is not supposed to even touch the nozzle according to the diagram I found. This fits with the fact that the needle is free to move laterally when removed from the slider and dropped into the nozzle. The kid who sold me this bike swears that he rode it until breaking the cases, meaning the carb should work as is. He may be lying, I'll never know. There is simply no way for the valve needle to have worn down while NOT operating the carb, so it must have been working. Yes a new valve needle and float needle would be great, I don't know what the parts market is like in Europe, but around here there is NOTHING available. Only one local Yamaha dealer would even respond to my parts request, only to tell me good luck, they cannot supply any new parts for old bikes. E-bay is the only source. I cannot purchase from E-bay, as they require a credit card just to be a member. The local wreckers are my only source, hence the question about the MX175 carb as replacement. If anyone can contribute knowledge about how the slider valve needle works in carbs in general, and specifically how it shuts off the fuel flow into the venturi that would be great. I just had an idea. I could remove the valve needle and stop up the nozzle and replace the slider sans needle. If the needle is causing the flooding this should prevent it and allow the engine to start and run on the pilot jet. Wait, that will prevent air from the air jet to enter the venturi, yes? There is a hole in the carb barrel nearest the manifold side, just past the pilot jet hole. What is this for? Is it a bypass outlet for the air jet? Should air flow from there at idle? If so I think that it might be blocked. I am still learning the basics of the wonderful mystery that is the carburetor. I agree with you on that, carburettors are indeed a fascinating invention. I see what you mean about some confusion creeping in with the two needle's youve mentioned Regarding your float needle, Its important that you set your float height correctly using a vernier caliper is the best way. Having done that you should never see any overflow, If you do you will need to replace the float needle valve and possibly the seat too. If fuel level in the bowl is too high it richens the mixture causing excessive fuel consumption and poor running. On the other hand, a low level will lean the mixture and could cause flat spots when accelerating out of turns, or in extreme cases cause overhating and possible seizure Regarding the hole in the carb barrel nearest the manifold side...Many carbs have a two hole idle system which gives better low speed and mid range throttle response than the simpler one hole type. At very small throttle openings, the bypass hole and not the pilot hole actually provides the engine with fuel. Instead the pilot hole acts as a supplementary air bleed to further atomise the fuel airafter it passes through the idle jet. As the throttle opens wider, the pilot hole too begins to spray fuel. This serves to supply the engine with additional fuel until the air speed throgh the carb increases enough to start the main jet and needle valve flowing fuel into the engine This is a good book if you really want to unravel those mysteries, .... Performance Tuning in theory and practice Two Strokes A. Graham Bell ISBN 0 85429 329 9 Oh and another thing, Look what I found Here And its in Canada too Link to comment Share on other sites More sharing options...
roadking67 Posted September 11, 2008 Author Share Posted September 11, 2008 I just might check that e-bay store out. Did you notice the name of the store? Siriusconinc. Talk about dubious names. Link to comment Share on other sites More sharing options...
Moderator Airhead Posted September 12, 2008 Moderator Share Posted September 12, 2008 I just might check that e-bay store out. Did you notice the name of the store? Siriusconinc. Talk about dubious names. I'm sure the store is just fine and it will sort out all your carb needle problems once and for all, Not a bad price too IMO, Wish we could get them here but I know one thing, They would cost a lot more if we could. Link to comment Share on other sites More sharing options...
Moderator Cynic Posted September 15, 2008 Moderator Share Posted September 15, 2008 I have a 'rough' DT125MX that was a field bike and that has the stator plate and flywheel from a different bike and it goes first kick using points ig that it was never meant to have. I'll have a look and see how they did it. If it counts for anything me and a mate used to play with a maico 490 (mans bike) till it broke waynes ankle when he started it without the decompresser, ha lobbed him right over the bars, started to. Anyway that animal reached the point where we carried spare woodruf keys with us cos it was forever eating them. Ps massive re write cos i'm thick, and blind. Link to comment Share on other sites More sharing options...
roadking67 Posted September 29, 2008 Author Share Posted September 29, 2008 I got the Keyster carb kit from Sirius Consolidated today. Thanks for the link Oldgit. Now if anyone asks how I got it running I'll just say "I Keyster'ed it." Ouch. There are a few kits left, if anyone needs one, get it now. Oldgit did you paint that thing again? You change paint schemes like I change underwear. 1 Link to comment Share on other sites More sharing options...
Moderator Airhead Posted September 30, 2008 Moderator Share Posted September 30, 2008 Oldgit did you paint that thing again? You change paint schemes like I change underwear. Hey, I'm in England...Each picture on a sunny day...Doesnt add up does it? Link to comment Share on other sites More sharing options...
roadking67 Posted September 30, 2008 Author Share Posted September 30, 2008 I thought England was all smiles and sunshine... On another note, in the past, you folks were British, flying the Union Jack, now it's back to English and the standard of St. George. Why the change? New rules under the E.U.? P.S. The old girl's not running yet, but it can't be long now. Link to comment Share on other sites More sharing options...
JimR Posted September 30, 2008 Share Posted September 30, 2008 I thought England was all smiles and sunshine... On another note, in the past, you folks were British, flying the Union Jack, now it's back to English and the standard of St. George. Why the change? New rules under the E.U.? P.S. The old girl's not running yet, but it can't be long now. is it %^&&88*'s it pees down here all the time !!! the english flag looks better than the union jack flag ,, I guess the welsh would use the Drgon rather than the union flag (scots too). When you set the timming up on the old 175 it was set 1.8mm btdc fully advanced so with no advance and unknown cylinder (jug ? whats that ? US posters seem to use that term) you may need to alter the timing in order to take into account of no advance perhaps .2mm either way may help, but until u get the old bird running who knows !!!! After reading the thread you have a needle jet & jet needle to translate to us in europe !!! Regards Jim Link to comment Share on other sites More sharing options...
Rapco Posted March 12, 2009 Share Posted March 12, 2009 I guess (and surely hope) you have resolved the problem with your dt, but if not, check this. you said the flywheel was loose. the chance are great that you already destroyed the wood-roof(half-circular, moon-key call it like you want) by turning the engine over with the flywheel not tightened enough. That happened to me twice since the idiot who owned the bike before me stripped the shaft where the flywheel is bolted. So you would need a new key, and they are pretty *****ing hard to find in the xact mesure. I had to buy 100 in one shoot! If you flywheel is out, the timing will be wrong, and the bike will kick back when it want the kickstarter, since it not firing at the proper time. After that, check your timing, which can be setted by the point gap(i dont remember the exact gap number) and the thing should run. so as i said, the thing to check is the flywheel woodruff key! And after that set the timing and you'll be good! Rapco! by the way, in which part of canada do you live? Link to comment Share on other sites More sharing options...
little dave Posted March 12, 2009 Share Posted March 12, 2009 regarding the gap on the points. I cant remember what the proper gap is either on my 74 dt175, I was told that a business card would do. but i used a set of metal gap feelers. which brings me to the point of my post, make sure you dont use steel or stainless ones, as they tend to want to jump towards the magnet on the fluwheel instead of going thru that narrow hole and where you want them between the points. Link to comment Share on other sites More sharing options...
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