Wraith88 Posted August 3, 2011 Share Posted August 3, 2011 Just bought a 74 DT175 soaked the carbs, sparkling clean now. Replaced spark plug and fuel line, coated tank, new oil. Getting good spark, fuel into carb, oil to cylinder from pump, can hear throttle work properly, set air mix screw at 2 turns out and idle screw at 3 turns out. With choke out starts right up but idles at 8000 rpm. Put choke in immediately dies. No air filter in, I don't know if that would cause any of this. Any help would be great. Thanks Link to comment Share on other sites More sharing options...
nayruf Posted August 3, 2011 Share Posted August 3, 2011 Just bought a 74 DT175 soaked the carbs, sparkling clean now. Replaced spark plug and fuel line, coated tank, new oil. Getting good spark, fuel into carb, oil to cylinder from pump, can hear throttle work properly, set air mix screw at 2 turns out and idle screw at 3 turns out. With choke out starts right up but idles at 8000 rpm. Put choke in immediately dies. No air filter in, I don't know if that would cause any of this. Any help would be great. Thanks Idling at 8 thou rpm, The only time mine has done that has been when I have put the throttle slide in the wrong way round and the slot in the throttle slide has missed the locating pin in the carb barrel. Link to comment Share on other sites More sharing options...
Wraith88 Posted August 4, 2011 Author Share Posted August 4, 2011 Idling at 8 thou rpm, The only time mine has done that has been when I have put the throttle slide in the wrong way round and the slot in the throttle slide has missed the locating pin in the carb barrel. I'm sure it's not that, but thanks. Link to comment Share on other sites More sharing options...
DTGordo Posted August 4, 2011 Share Posted August 4, 2011 Geez, 8K RPM?? Didn't know they went that high. You running nitrous on it? Anyways, can you back the throttle screw out? Sorry that's obvious I know. Is the needle in the right spot on the throttle valve/cyclinder? It'll have a few notches on the needle but I'd be surprised if you get 8000RPM from that. I can't see that there would be much else that would push the idle speed up if everything else was ok. Maybe some seals are stuffed and causing problems. Hope that helps, Gordo Link to comment Share on other sites More sharing options...
Wraith88 Posted August 5, 2011 Author Share Posted August 5, 2011 Geez, 8K RPM?? Didn't know they went that high. You running nitrous on it? Anyways, can you back the throttle screw out? Sorry that's obvious I know. Is the needle in the right spot on the throttle valve/cyclinder? It'll have a few notches on the needle but I'd be surprised if you get 8000RPM from that. I can't see that there would be much else that would push the idle speed up if everything else was ok. Maybe some seals are stuffed and causing problems. Hope that helps, Gordo Tried idle adjustment already and also tried moving the c clip on the needle to lower it, also no effect. So stumped on this one. Really strange behavior. But thanks for your advice. Link to comment Share on other sites More sharing options...
DTGordo Posted August 5, 2011 Share Posted August 5, 2011 I've got no idea now but I vaguely recall something about stuffed seals letting the air in = high revs. Can't remember if that was the crank seals or round the carby. Maybe both. Others here will know much more about that. I've got a 175 old thing (like a '75 farm bike "AG" or something) that was all over the place with the revs. When I took the case cover off to check the clutch I noticed the right crank seal was not seated properly and half hanging out. Pushing it back improved things heaps. You can give them a visual at least? Other than that I'm done....... Hope that helps, Gordo Link to comment Share on other sites More sharing options...
250dt_enduro Posted August 5, 2011 Share Posted August 5, 2011 hi if you want to make sre there not leaking spray brake clean or ether on them in it revs more you know you have a leak. i had a sled once with running problems it would run with the choke on and when i'd take it off it would die, i tried the ether trick and foind it was the crank seals, also if the crank seals are leaking it can lead to the engine running to lean and you will go through pistons in case you did not know that already. Link to comment Share on other sites More sharing options...
Moderator Airhead Posted August 5, 2011 Moderator Share Posted August 5, 2011 hi if you want to make sre there not leaking spray brake clean or ether on them in it revs more you know you have a leak. i had a sled once with running problems it would run with the choke on and when i'd take it off it would die, i tried the ether trick and foind it was the crank seals, also if the crank seals are leaking it can lead to the engine running to lean and you will go through pistons in case you did not know that already. Good advice but generally it can only be done with the 'dry' seal behind the generator, if the other ones duff it will burn oil and smoke some Link to comment Share on other sites More sharing options...
Wraith88 Posted August 9, 2011 Author Share Posted August 9, 2011 Thanks everyone. Was indeed leak at the crankcase to carb joint. One of the little rubber tabs that seat into crankcase was caught under and preventing good seal. runs good now. Thanks for all the advice. Link to comment Share on other sites More sharing options...
dpehrson Posted March 27, 2013 Share Posted March 27, 2013 dpehrson I had a similar problem with a 78 dt125 that I pulled from a scrap yard for $40. The engine would not idle after warm-up without the choke on. The problem... Apparantly someone before me placed a dab of thread locker on the air screw threads... I cleaned the carb about three times due to this problem, After a very careful and timely examination, I discovered that the airscrew was going very snug, which I had previously thought was seated, way to soon. I observed that the needle portion of the airscrew was not observed as even entering the air port orifice on the intake side of the carb. I examined the air screw threads of the carb and noticed debris gumming up the threads. I then continued to force thread past the thread locker and adventually to the real metal seat. At 01:00AM, I assembled and installed the carb and started her up. I warmed it up with the choke on and then pushed the choke in to discover that it purred like a kitten. One final adjustment to the air screw of 1/4 turn in and it idles clean without the choke and accelerates without hesitation. Who would have guessed... Link to comment Share on other sites More sharing options...
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