78XS400 Posted July 8, 2009 Share Posted July 8, 2009 Here are all the issues I am having - The right cylinders exhaust pipe runs about 60 deg HOTTER than the left at all times - The right cylinder missfires at idle (ONLY after its fully warmed up, it idles perfect when I first start it up untill about 10-15 mins later) - I have it idling at 1500 and sometimes it dies at that (again only after its warmed up) Carbs have been FULLY dissembled and cleaned TWO times now. , new plugs are in. Any ideas? I have messed with the lean/richen screws but had no luck, timing is good, I had it idling perfect for about a week and this popped up, also did a cylinder leakdown test thinking maybe it was a head gasket but that all checked good. Link to comment Share on other sites More sharing options...
Moderator drewpy Posted July 8, 2009 Moderator Share Posted July 8, 2009 Here are all the issues I am having - The right cylinders exhaust pipe runs about 60 deg HOTTER than the left at all times - The right cylinder missfires at idle (ONLY after its fully warmed up, it idles perfect when I first start it up untill about 10-15 mins later) - I have it idling at 1500 and sometimes it dies at that (again only after its warmed up) Carbs have been FULLY dissembled and cleaned TWO times now. , new plugs are in. Any ideas? I have messed with the lean/richen screws but had no luck, timing is good, I had it idling perfect for about a week and this popped up, also did a cylinder leakdown test thinking maybe it was a head gasket but that all checked good. I wonder if the pilot screws have snapped off in the carbs. if you can totally unscrew the pilot screws and they have a blunt end, then thev'e snapped off. If they are as sharp as a needle then your OK on that one. does sound like running weak on the right, some xs's had different size jets etc in each carb to compensate for this kind of thing!! Link to comment Share on other sites More sharing options...
78XS400 Posted July 9, 2009 Author Share Posted July 9, 2009 I wonder if the pilot screws have snapped off in the carbs. if you can totally unscrew the pilot screws and they have a blunt end, then thev'e snapped off. If they are as sharp as a needle then your OK on that one. does sound like running weak on the right, some xs's had different size jets etc in each carb to compensate for this kind of thing!! Yep, pilot screws are good to go... Link to comment Share on other sites More sharing options...
Joshua2 Posted July 9, 2009 Share Posted July 9, 2009 An air leak on the intake manifold ???? VERY CAREFULLY (due to the fire risk) try spraying a mist of petrol or Eazi Start round the intake when its running to see if the engine speed increases. VERY CAREFULLY ! ATB J Link to comment Share on other sites More sharing options...
78XS400 Posted July 9, 2009 Author Share Posted July 9, 2009 An air leak on the intake manifold ???? VERY CAREFULLY (due to the fire risk) try spraying a mist of petrol or Eazi Start round the intake when its running to see if the engine speed increases. VERY CAREFULLY ! ATB J I used carb cleaner and sprayed all over the head (near the spark plug area) and the engine died but did not rev up just died. Manifolds are good, I did a cyl leakdown test @ 80 psi both on a hot and cold motor and heard nothing coming out.... Link to comment Share on other sites More sharing options...
JimR Posted July 9, 2009 Share Posted July 9, 2009 I wonder if the pilot screws have snapped off in the carbs. if you can totally unscrew the pilot screws and they have a blunt end, then thev'e snapped off. If they are as sharp as a needle then your OK on that one. does sound like running weak on the right, some xs's had different size jets etc in each carb to compensate for this kind of thing!! but in time with that (above) insure the dwell is set correctly and the rest of the engine is in good shape XS400's in the UK tended (when new) to give odd results if the bike was not set up as it should be so if you ensure the engine compression is good; the tappits (valve clearance) is correct; Dwell is correct; Timing is correct; Carb balance - correct. The only reason to fit different jets to each carb was to cover up the time the XS400 (in the UK) spent in crates and the carbs got full of the green gunge. back in the day Yamaha (Mitsui) sanctioned this in order to save the factory a bank of carbs before the bike would run correctly .... seems odd. As the bikes have got older I would guess the green gunge would have perhaps of increased. But the above should return an XS400 sohc to running ok, as I have not looked at one of these bikes since the mid 80's my sumission my be incorrect but was well valid then. Regards Jim Link to comment Share on other sites More sharing options...
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