Viherkogen Posted June 30, 2010 Share Posted June 30, 2010 I just finished, for the most part, at getting my first bike. I had a friend who gave me 78 DT175 for free after it had sat under a lean-to for the better part of this decade. He parked it when it lost compression on it one day and he's not much of a mechanic. Turns out he blew a hole in the piston, but the most costly problem was letting the case fill up with water from sitting so long. Well, after a brief binge on ebay, the bike runs again to the surprise of everyone. She cleaned up decent. Had to replace the original rear fender with one off a 81' Honda 500. I'll try to get the pictures of the before from my phone. It runs, but it refuses to idle. It bobs from 3k to 4k rpms with the choke on, and it rides nice, but as soon as the choke is off, it needs constant revs and dies. The carb has been cleaned thrice and fully rebuilt, along with new gaskets on the whole engine. I think it might be an air leak, but I'm at wits end. Link to comment Share on other sites More sharing options...
Moderator Airhead Posted June 30, 2010 Moderator Share Posted June 30, 2010 It runs, but it refuses to idle. It bobs from 3k to 4k rpms with the choke on, and it rides nice, but as soon as the choke is off, it needs constant revs and dies. The carb has been cleaned thrice and fully rebuilt, along with new gaskets on the whole engine. I think it might be an air leak, but I'm at wits end. Needs constant revs unless the choke is on? This sounds like a blocked pilot jet, can you see daylight through this jet? Welcome to the forum Nice trainers...where did you get them? ...Paul Link to comment Share on other sites More sharing options...
Viherkogen Posted June 30, 2010 Author Share Posted June 30, 2010 I've cleaned out the carb thoroughly, and all the brass is new. The only hole I have worries about, is a port that sits above the fuel bowl. it looks identical to the fuel supply port but it doesn't lead anywhere. The body was submerged in this goopy carb cleaner for an hour. The rpms even during choke will drop from 4k to 3k and slowly come back up and sit there for a min. before repeating. The only thing I can figure, is that air is being pulled in between the reed block where i put a gasket but no silicon. What sort of symptoms are caused by reeds that have a small gap? Link to comment Share on other sites More sharing options...
Moderator Airhead Posted June 30, 2010 Moderator Share Posted June 30, 2010 reeds that have a small gap wont cause an air leak so it's not that. If you are concerned about an airleak you should investigat the magneto side crank seal. Remove the cover and start the engine; then spray WD40 through the slots in the magneto towards the crank seal. Listen for any change in engine speed / tone, a change means you get to replace the seal. Link to comment Share on other sites More sharing options...
Viherkogen Posted June 30, 2010 Author Share Posted June 30, 2010 I'm no stranger to seals going bad during installation in cars, but the bike has 1.4 miles on it. I did a complete rebuild that involved splitting the case and replacing all seals. Are there any other places before I start my hunt? Link to comment Share on other sites More sharing options...
Moderator Airhead Posted June 30, 2010 Moderator Share Posted June 30, 2010 ok for that matter...while your'e busy with the WD40 try spraying around the reed block to cylinder joint, the crank seal mag side, the cylinder base joint, the cylinder head joint. Thats about it. Link to comment Share on other sites More sharing options...
Viherkogen Posted July 1, 2010 Author Share Posted July 1, 2010 ok for that matter...while your'e busy with the WD40 try spraying around the reed block to cylinder joint, the crank seal mag side, the cylinder base joint, the cylinder head joint. Thats about it. Found it. WD-40 to the cylinder base caused the bike to bog and the dead giveaway...the temporary stop of a whirring noise I assumed to be case noise. It was actually air moving through the base. It sounded a bit like a quiet air compressor or vacuum pump. The right side didn't seal due to a bit of the old gasket. It took 2hrs, but I pulled the cylinder up and added some hi-temp RTV silicon. hell, I even sealed the reed box since the carb had to come out. I'm giving it 24hrs to cure, which it about when I get back from school. Link to comment Share on other sites More sharing options...
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