redslayer Posted July 14, 2009 Share Posted July 14, 2009 Hi all, I'm new here and would really appreciate some help. I have a '77 DT 400 that has been sitting in a mates shed for a number of years dormant. I have removed and cleaned the carby, adjusted the float level to manufacturers specs, set air mixture screw at 1 1/2 turns out, checked and cleaned fuel cock, checked reed valves and after reassembly checked for any vacuum leaks ( none found ). I have checked and renewed spark plug and after all this i still cant get the bike to idle smoothly without stalling. The bike runs quite well at anything over 2500 rpm but refuses to idle...... PLEASE HELP!!!!!!! I am running a 32:1 mix as the autolube system is no longer ( not sure if this is relevant??) The exhaust does have a few holes which cause the bike to draw air occasionally and backfire but i am doubtful this is my problem.... Any help would be greatly appreciated. Link to comment Share on other sites More sharing options...
mike1949 Posted July 14, 2009 Share Posted July 14, 2009 Hi all, I'm new here and would really appreciate some help. I have a '77 DT 400 that has been sitting in a mates shed for a number of years dormant. I have removed and cleaned the carby, adjusted the float level to manufacturers specs, set air mixture screw at 1 1/2 turns out, checked and cleaned fuel cock, checked reed valves and after reassembly checked for any vacuum leaks ( none found ). I have checked and renewed spark plug and after all this i still cant get the bike to idle smoothly without stalling. The bike runs quite well at anything over 2500 rpm but refuses to idle...... PLEASE HELP!!!!!!! I am running a 32:1 mix as the autolube system is no longer ( not sure if this is relevant??) The exhaust does have a few holes which cause the bike to draw air occasionally and backfire but i am doubtful this is my problem.... Any help would be greatly appreciated. Idle speed adjustment screw?? Link to comment Share on other sites More sharing options...
blackhat250 Posted July 14, 2009 Share Posted July 14, 2009 Hi all, I'm new here and would really appreciate some help. I have a '77 DT 400 that has been sitting in a mates shed for a number of years dormant. i still cant get the bike to idle smoothly without stalling. The bike runs quite well at anything over 2500 rpm but refuses to idle...... Aye .. the pilot jet must be blocked. also check air filtre, jublie clips etc. try and seal exhaust ,[back presure] all important to running settings,, I take it its a mono shock DT400 [1977] Is it .. WOT ABOUT SOME PICS . Link to comment Share on other sites More sharing options...
redslayer Posted July 14, 2009 Author Share Posted July 14, 2009 Aye .. the pilot jet must be blocked. also check air filtre, jublie clips etc. try and seal exhaust ,[back presure] all important to running settings,, I take it its a mono shock DT400 [1977] Is it .. WOT ABOUT SOME PICS . Thanks for your reply, I am 100% certain the pilot jet is clear ( have had carby off and apart twice now), jubilee clips are both tight and i have replaced the air filter. have replaced O-ring on idle speed screw also, still with no result. will try and migweld exhaust to seal it up . As for the pics, Once I tidy her up a bit i will definately show her off Link to comment Share on other sites More sharing options...
Moderator Airhead Posted July 15, 2009 Moderator Share Posted July 15, 2009 so have you had the pilot jet out and held it up to the light....can you see through it? Link to comment Share on other sites More sharing options...
redslayer Posted July 15, 2009 Author Share Posted July 15, 2009 Yes, I have had the pilot jet out, blown it out with compressed air and looked through it - all clear. Link to comment Share on other sites More sharing options...
Moderator Airhead Posted July 15, 2009 Moderator Share Posted July 15, 2009 Yes, I have had the pilot jet out, blown it out with compressed air and looked through it - all clear. I would continue with the exhaust repair now in case thats the problem or adding to the problem, its not just a matter of adjusting the throttle stop screw though is it? Link to comment Share on other sites More sharing options...
yamadoger Posted July 15, 2009 Share Posted July 15, 2009 check to see if your compression is getting low Link to comment Share on other sites More sharing options...
blackhat250 Posted July 15, 2009 Share Posted July 15, 2009 check to see if your compression is getting low Yip . good comment. if u need rebore " i"v got pistons plus rings .NEW.OLD.STOCK. .25 / .50. .75 1.00 . ALL With rings yamaha original parts .. u can get new small end from Web-moto Also i have many spares here , will help u if i can . Take care of that 400 coz they are extremely rare . Oh just noticed ur in ozz,,, Link to comment Share on other sites More sharing options...
redslayer Posted July 16, 2009 Author Share Posted July 16, 2009 I would continue with the exhaust repair now in case thats the problem or adding to the problem, its not just a matter of adjusting the throttle stop screw though is it? Thanks mate just waiting to get into town and pick up some more mig wire before welding exhaust - hoping this helps somewhat. And no it isnt a simple throttle stop screw adjustment, sure it gives me a quick fix if i want the bike to idle at 2500 rpm but doesnt solve the issue. Link to comment Share on other sites More sharing options...
redslayer Posted July 16, 2009 Author Share Posted July 16, 2009 Yip . good comment. if u need rebore " i"v got pistons plus rings .NEW.OLD.STOCK. .25 / .50. .75 1.00 . ALL With rings yamaha original parts .. u can get new small end from Web-moto Also i have many spares here , will help u if i can . Take care of that 400 coz they are extremely rare . Oh just noticed ur in ozz,,, thanks blackhat but yes i'm located "down under"!! dont think compression is my problem however im starting to suspect faulty decomp valve , could this cause an idle problem??? Link to comment Share on other sites More sharing options...
Moderator Airhead Posted July 16, 2009 Moderator Share Posted July 16, 2009 thanks blackhat but yes i'm located "down under"!! dont think compression is my problem however im starting to suspect faulty decomp valve , could this cause an idle problem??? Surely if your de compression valve is faulty...compression would be your problem! Link to comment Share on other sites More sharing options...
redslayer Posted July 16, 2009 Author Share Posted July 16, 2009 Surely if your de compression valve is faulty...compression would be your problem! Perhaps i should have made myself clear i dont think that lack of compression due to worn rings or piston - requiring rebore, is the problem thinking more along the lilnes of intermittent fault or leak from decomp valve. Link to comment Share on other sites More sharing options...
raining-fish Posted June 7, 2010 Share Posted June 7, 2010 Thanks mate just waiting to get into town and pick up some more mig wire before welding exhaust - hoping this helps somewhat. And no it isnt a simple throttle stop screw adjustment, sure it gives me a quick fix if i want the bike to idle at 2500 rpm but doesnt solve the issue. did you ever find out what the problem was? i have EXACTLY the same problem with mine and have tried the same fixes too, but with no luck. the bike will run {a little roughly} over 2500rpm but dies below this. also many backfires when using the kickstarter. i have tried everything i can think of without taking the piston out. carb-many many cleans, air filter fitted and not fitted, timing- all positions, exhaust is nice and free flowing with no holes, spark plug, cap and ht coil all replaced, crank seals-replaced, decompressor- checked and properly setup. still no solution. anyone got any more idea's? fuel is getting in and it is sparking, but it still won't run. i'm thinking about taking the piston out next to see if the rings are stuck in {the bike has been standing for a couple of years}, failing that.... dunno! Link to comment Share on other sites More sharing options...
Moderator Airhead Posted June 7, 2010 Moderator Share Posted June 7, 2010 i'm thinking about taking the piston out next to see if the rings are stuck in {the bike has been standing for a couple of years}, failing that.... dunno! It would be easier to do a compression test to eliminate this possibility Link to comment Share on other sites More sharing options...
raining-fish Posted June 8, 2010 Share Posted June 8, 2010 i put my thumb over the spark plug hole and turned the engine over- virtually no compression! the head and barrel are off now but the piston looks really good and the rings are nice and free. while i was sitting there feeling puzzled, i saw that the decompressor valve doesn't seem to go back all the way in when the kickstart returns to the top. so a quick rebuild {again} and we'll see what happens. Link to comment Share on other sites More sharing options...
raining-fish Posted June 8, 2010 Share Posted June 8, 2010 nope, it wasn't that...b****r! when i kick it over, smoke comes out of the exhuast, but still no starting! i,ve just noticed that my CDI has eight wires coming out of it where-as the manual only shows six. there is an extra black and a white and green{striped} un-used wires. it is a mitsubishi one, perhaps off a later model? time for a beer?....oh yes. Link to comment Share on other sites More sharing options...
raining-fish Posted June 8, 2010 Share Posted June 8, 2010 it is a mitsubishi one, perhaps off a later model? it looks like, after a trawl of the internet, the CDI unit of a yz490. Link to comment Share on other sites More sharing options...
blackhat250 Posted June 8, 2010 Share Posted June 8, 2010 Raining -fish? :huh:Ithot it was redslayer? that posted this. anyway wrong box, you"l be lookn at £100. for a new CDI. model F8T 00172 [MITSABUSHI] part no. 445-85540-22-00. And thats a long drawn out repair:) Link to comment Share on other sites More sharing options...
raining-fish Posted June 15, 2010 Share Posted June 15, 2010 Raining -fish? :huh:Ithot it was redslayer? that posted this. anyway wrong box, you"l be lookn at £100. for a new CDI. model F8T 00172 [MITSABUSHI] part no. 445-85540-22-00. And thats a long drawn out repair:) got one this morning {ebay} many dollars! but, success! cdi fitted and easy starting accomplished! brrrum! the only thing i can think of with the last one was it must have been sparking much later than TDC- hence all the backfires! thanks for your help. Link to comment Share on other sites More sharing options...
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