coachb Posted September 15, 2010 Share Posted September 15, 2010 I recently bought a 1981 DT175. Maybe I'm expecting too much but it seems to be down on power. I ran a compression check and 1st kick had 75psi, 2nd kick 85 3rd kick had 100psi. The bike wont idle and niether screw on the carb affects the idle or performance of the bike. It only had 1800 miles (if odometer is correct) on it. Should this bike have a power band . It doesnt seem to when get the rpm's up. Any advice would help. Thanks Link to comment Share on other sites More sharing options...
blackhat250 Posted September 15, 2010 Share Posted September 15, 2010 Should this bike have a power band . IAny advice would help. Thanks HI " How does it idle ? is i ok wen choke on ? then how is it after warming up, ? air screw [ brass left side small] shud be 1.5 turns out . How long has it been standing without use, ? & air filtre ? [ clean] Power band , depends on what bike you"ve been riding previous, goona feel guttless if you"ve been on modern bikes, 70-75mph flat out, Link to comment Share on other sites More sharing options...
coachb Posted September 15, 2010 Author Share Posted September 15, 2010 It's wierd really, you don't have to choke it when cold. Will start on 2nd or 3rd kick. When you rev it and it comes down to idle it will gradually idle down and quit. Idle screw is all the way in and doesn't effect it at all turning it out. Air filter looks new. Seems like 50 mph is top speed. Rpms arent out the roof.... just doesnt want to go any faster. About 30 years ago I had a Kawasaki 175 that seemed to have alot more zip to it than this bike. It didnt have a power band at all and felt stronger. I also checked the slide in the carb and its in correctly. Haven't torn it down for a cleanibg yet though. Link to comment Share on other sites More sharing options...
Moderator Airhead Posted September 15, 2010 Moderator Share Posted September 15, 2010 Yeah something is awry if neither screw affects idle, either that or you didnt turn the throttle stop (knurled one) sufficiently clockwise to lift the carb slide and increase the engine speed. Either way if you have just acquired the bike I would recommend a full carb strip and proper clean Link to comment Share on other sites More sharing options...
Moderator Cynic Posted September 15, 2010 Moderator Share Posted September 15, 2010 It's wierd really, you don't have to choke it when cold. Will start on 2nd or 3rd kick. When you rev it and it comes down to idle it will gradually idle down and quit. Idle screw is all the way in and doesn't effect it at all turning it out. Air filter looks new. Seems like 50 mph is top speed. Rpms arent out the roof.... just doesnt want to go any faster. About 30 years ago I had a Kawasaki 175 that seemed to have alot more zip to it than this bike. It didnt have a power band at all and felt stronger. I also checked the slide in the carb and its in correctly. Haven't torn it down for a cleanibg yet though. I would check the float height, and your idle jet tbh. You may have a crank seal issue but that generally makes them a pig to start. Whats the old plug like? Don't get hung up on oil or ignition it is very unlikely to have owt to do with it. Primary target for me would be the carb. Has it been stood for any time? Link to comment Share on other sites More sharing options...
coachb Posted September 15, 2010 Author Share Posted September 15, 2010 I dont know much history on the bike. The carb (without tearing it down) looked good inside where the slide is. Works freely also. What should the float height be? Or can you direct me to a sight where I can find carb specs? And also, what is a good compression (PSI) for it. Link to comment Share on other sites More sharing options...
Moderator Cynic Posted September 15, 2010 Moderator Share Posted September 15, 2010 I dont know much history on the bike. The carb (without tearing it down) looked good inside where the slide is. Works freely also. What should the float height be? Or can you direct me to a sight where I can find carb specs? And also, what is a good compression (PSI) for it. Compression is a difficult thing to check on a stroker, if it runs its within limits. The float height should be 21mm, need OG's super diagram for this bit. As any discription i try will only confuse you if you cannot recognise the actual components. Paul.....? Link to comment Share on other sites More sharing options...
Moderator Airhead Posted September 15, 2010 Moderator Share Posted September 15, 2010 You didnt say where you are? I guess its USA as 'tear down' is an American expression, we would say 'strip' here. In the UK we had two different carbs although these were basically the same, they were numbered 2H500 and 3U500, they had different components in them. I 'think' the American one was akin to the 3U500 and had an interference fit emulsion tube (AKA needle jet), when you strip the carb down for it's thorough clean...tap this out from the top (downwards) it will not need much of a tap so take it easy as it's soft brass. You may find it gunked up like this so you have to get it out to clean it. also take out the other jets...main jet...pilot jet and the float needle valve (dont damage or lose the gasket under this)..take out the air mixture screw and dont lose the O ring if it has one (which I think it may well have)...take out the choke plunger and check the rubber seat is not damaged. Clean the carb body with carb cleaner and blow through any little passages with compressed air or an air duster. Re-assemble it all and check the float height is set to 21mm (gasket removed) see picture as has been said set the air mixture screw to 1 and 1/2 turns out from gently closed, then adjust the throttle stop screw for idle at around 1200rpm As fpr cpmpression I reckon 100psi should be fine and did you do this test with hot engine? ...Paul Link to comment Share on other sites More sharing options...
coachb Posted September 16, 2010 Author Share Posted September 16, 2010 I did the compression test cold. And yes I'm in the states. Last night I stripped the carb and cleaned it. Looked pretty good inside. I also gutted the exhaust. Idles now but the screw is all the way in. Ran much better in 1,2,3 gears. Still seems sluggish in the upper gears. Ran out of time and called it quits for the evening. Will adjusting the slide needle help in the upper gears? There is a screw holding the plate on top of the needle that is being stubborn. I will take the carb aprt again and do a more detailed cleanig now that you have given me som edirection. Thanks for the photos. Darren Link to comment Share on other sites More sharing options...
Moderator Airhead Posted September 16, 2010 Moderator Share Posted September 16, 2010 What is the air filter like...does it need a clean? Not sure about the carb on the DT175E ...whether or not the needle is adjustable fot height or not like the UK bikes were What do you mean by gutted the exhaust? Link to comment Share on other sites More sharing options...
coachb Posted September 16, 2010 Author Share Posted September 16, 2010 I removed the baffle and cone from inside, "opened it up". Several forums I've read people commented that due to EPA air regulations in the U.S. the exhausts were restricted inside. The air filter is new. Link to comment Share on other sites More sharing options...
Moderator Airhead Posted September 16, 2010 Moderator Share Posted September 16, 2010 I removed the baffle and cone from inside, "opened it up". Several forums I've read people commented that due to EPA air regulations in the U.S. the exhausts were restricted inside. I dont suppose you have any pictures of that? Link to comment Share on other sites More sharing options...
coachb Posted September 16, 2010 Author Share Posted September 16, 2010 The baffle had 1 screw holding it. Remove it and shine a light down from there and you can see the cone. I cut the pipe with a band saw and removed the cone with a pair of vice grips. Then welded the pipe back together. Link to comment Share on other sites More sharing options...
coachb Posted September 16, 2010 Author Share Posted September 16, 2010 I guess the cone would actually be in the muffler part of the pipe. But some other forums speak of a restrictor in the inlet of the pipe where it attaches to the cylinder, I haven't went that far yet. They say a "washer " with a very small hole in it is there that can be cut out. Link to comment Share on other sites More sharing options...
Moderator Airhead Posted September 16, 2010 Moderator Share Posted September 16, 2010 But some other forums speak of a restrictor in the inlet of the pipe where it attaches to the cylinder, I haven't went that far yet. They say a "washer " with a very small hole in it is there that can be cut out. I havent heard of this washer you speak of, however this is what I found in my DT175 header pipe. Theres no way it is affecting your performance as badly as you report though. Link to comment Share on other sites More sharing options...
coachb Posted September 16, 2010 Author Share Posted September 16, 2010 I just purchased the bike and I'm trying to figure out what my problem may be. Other people have mentioned this may be a factor. I reaaly don't know. I guess that's why I'm on here looking for suggestions. Link to comment Share on other sites More sharing options...
Moderator Airhead Posted September 16, 2010 Moderator Share Posted September 16, 2010 I just purchased the bike and I'm trying to figure out what my problem may be. Other people have mentioned this may be a factor. I reaaly don't know. I guess that's why I'm on here looking for suggestions. Could be any number of reasons, what other forum are you getting help from? Myself I would meticulously clean the carb first and blow through all the little passages in the carb body with compressed air. Re-assemble and set the float height and mixture screw. If that didnt cure it, then I would take meter readings of my magneto coils and ignition coil to see if they are out of spec. How many wires connect to the CDI ? Link to comment Share on other sites More sharing options...
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