mtayl125 Posted January 26, 2010 Share Posted January 26, 2010 Hi Folks, After rebuilding a box of bits, I am having problems starting my 78 DT175MX. The bike starts with full choke but revs to 6000RPMish!! Turning the choke off kills the engine & will not restart without the choke. Bike appears to be standard, so suspect a problem with the float level, not sure where to measure float height as manual does not say. Regards Mark Link to comment Share on other sites More sharing options...
Moderator Cynic Posted January 26, 2010 Moderator Share Posted January 26, 2010 Hi Folks, After rebuilding a box of bits, I am having problems starting my 78 DT175MX. The bike starts with full choke but revs to 6000RPMish!! Turning the choke off kills the engine & will not restart without the choke. Bike appears to be standard, so suspect a problem with the float level, not sure where to measure float height as manual does not say. Regards Mark Oldgit (soon to be lucky old git) will hopefully pitch up with one of his pictures soon enough. Its measured from the base of the carb, as in the gasket face WITHOUT the gasket in place. I take it you have done the usual stuff like checking the slide isn't stuck or the cable snagged, fuel flowing ok etc. Stick some pics up, show your work off. Link to comment Share on other sites More sharing options...
Moderator Airhead Posted January 26, 2010 Moderator Share Posted January 26, 2010 Oldgit (soon to be lucky old git) will hopefully pitch up with one of his pictures soon enough. Its measured from the base of the carb, as in the gasket face WITHOUT the gasket in place. I take it you have done the usual stuff like checking the slide isn't stuck or the cable snagged, fuel flowing ok etc. Stick some pics up, show your work off. Here you go Mark, While you have the float bowl off, remove and check the pilot jet is clear because part of the symptom you describe points to this, also you may have an air leak, chech cylinder base gasket, head gasket and rubber inlet manifold by spraying with WD40 when its running Link to comment Share on other sites More sharing options...
mtayl125 Posted January 27, 2010 Author Share Posted January 27, 2010 Great picture, will check this out at the weekend (no garage, so need the daylight) and check the jets etc. Will let you know how I get on. How does spraying with WD40 help? Regards Mark Link to comment Share on other sites More sharing options...
Moderator Airhead Posted January 27, 2010 Moderator Share Posted January 27, 2010 How does spraying with WD40 help? Regards Mark If there is a leak, then if you hit it with WD40 you will hear a difference in engine speed / tone and so its a good tool to find where leaks are. Link to comment Share on other sites More sharing options...
RogerD Posted January 27, 2010 Share Posted January 27, 2010 If there is a leak, then if you hit it with WD40 you will hear a difference in engine speed / tone and so its a good tool to find where leaks are. Great tip on the wd40 leak test - my old DT has the same symptom and I suspected a leak someplace as well. Link to comment Share on other sites More sharing options...
CameronMac Posted January 27, 2010 Share Posted January 27, 2010 Great tip on the wd40 leak test - my old DT has the same symptom and I suspected a leak someplace as well. Great advice here, I took the carb apart on my 79 and the entire jet hole was filled with gunk. Not sure if it fixed my idle problem yet, but I'm sure it helped something Link to comment Share on other sites More sharing options...
mtayl125 Posted February 3, 2010 Author Share Posted February 3, 2010 If there is a leak, then if you hit it with WD40 you will hear a difference in engine speed / tone and so its a good tool to find where leaks are. Cleaned the carb jets at the weekend as best I could, but could do with an altrasonic clean, as there is still some visible residue in the bowl etc. The float seems to be set correctly, but still have the problem. The jets / needle all match with the manual spec, but the manual mentions a starter jet (as well as the main and idle jets). Does anyone know where that is in the carb? Did not have chance to fully test the WD40 trick and may have limited time to check again this weekend, but the carb is a tight fit betweeen the 2 rubbers and does not line up very well so there may be a leak somewhere. I also think the throttle cable may be pulling the throttle open slightly as the cable routing is not quite right under the tank - will need to spend a bit more time on this. Incidently, thats a tidy looking tailpipe on your bike oldgit - who makes it? Link to comment Share on other sites More sharing options...
Moderator Airhead Posted February 3, 2010 Moderator Share Posted February 3, 2010 the manual mentions a starter jet (as well as the main and idle jets). Does anyone know where that is in the carb? Incidently, thats a tidy looking tailpipe on your bike oldgit - who makes it? Here is the starter arrangement, my tailpipe was made by SM (Serval Marketing) back in the annals of history, just dont see them anymore, not even on ebay. You need to sort out that cable routing though as this is likely the problem, you should hear the throttle (clunk) as it bottoms out when you shut it off Link to comment Share on other sites More sharing options...
mtayl125 Posted February 4, 2010 Author Share Posted February 4, 2010 Here is the starter arrangement, my tailpipe was made by SM (Serval Marketing) back in the annals of history, just dont see them anymore, not even on ebay. You need to sort out that cable routing though as this is likely the problem, you should hear the throttle (clunk) as it bottoms out when you shut it off WOW what a font of knowledge you are, many thanks. I will look closely at the cable routing as soon as I can. Link to comment Share on other sites More sharing options...
mtayl125 Posted February 5, 2010 Author Share Posted February 5, 2010 WOW what a font of knowledge you are, many thanks. I will look closely at the cable routing as soon as I can. Yippee!! have temporarily re-routed the cable slightly outside the tank and also adjusted the connection rubber to the filter box as the carb was not square to the inlet rubber. Bike starts OK on choke now but struggles to idle off choke. Will need to check the air screw and throttle stop / idle screw settings but feel like real progress has been made. Need to sort out some gremlins with the lights and horn too but hopefully MOT time will be looming (it was last taxed in 87 so its great to have saved a DT. Thanks to all Mark Link to comment Share on other sites More sharing options...
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