Motorcycle Repair: Honda CT90, honda ct90 motorcycle, carburetor body

Question
Hi,
    I have a 1970 Honda CT90 motorcycle.  When I go to start the cycle it revs up so loud that I adjust the choke but then it dies.  So I bought a Beatrice carb and installed it.  Now when i attach the two gas lines to the carb the gas leaks out the bottom through the drain line.  I tightened the screw responsible for the drain line but that doesnt help.  Only when i turn the gas to off does the leaking stop.  Do you have any ideas why the gas leaks out the drain line?  Does it matter which gas line attaches to which entry to the shutoff valve?  One is for Res and the other for On.  I don't understand why there is leaking.  I am hoping the new carb will resolve the high rpms on start up.  It acts like something is or was stuck making the engine run wide open.  Any ideas are greatly appreciated.
Sam

Answer
Sam, your old carb may have been fine with some good cleaning and adjusting.

The gas from the bottom fitting of the float bowl is due to the float valve not shutting the fuel off when the float has risen up to push the needle tip closed. The needle could have been dislodged from shipping impacts or it may have been assembled incorrectly.

I take it that you bought this item: http://ep.yimg.com/ca/I/dratv_2115_147595878

The carburetor doesn't care which fitting it needs to be fed from as long as gasoline is present.

It is similar to this OEM Honda model..  http://www.cmsnl.com/honda-ct90-trail-90-78-us_model7161/partslist/E++1401.html

Disconnect it from the fuel lines, remove it from the intake manifold, then remove the bowl screws, so you can look inside to see if something is damaged, loose or missing from the float bowl interior.

Fast idle conditions come from numerous sources:
Throttle cable that is coming apart internally,
Throttle cable misrouted causing it to pull on the carb slide when the handlebars are turned.
Spark advancer sticking, causing advanced ignition timing at idle.
Warped carburetor body causing throttle slide to stick in part open conditions.
Air leak at intake manifold flanges and/or O-ring connections.

Start at the beginning. Adjust valves to .002" cold on compression stroke, check compression. If over 140psi, then remove the spark advancer to see if it is sticking/stuck and not able to advance/retard correctly. Then clean points, set them to a maximum gap of .014"-.016" at the highest part of the point cam. Finally, move the whole backing plate until the points just open at the F mark on the flywheel/stator alignment marks.

Make sure all intake manifold gaskets are secure, check carburetor slide fit in carb body and when throttle cable is attached. Check for throttle slide moving smoothly up and down with air cleaner disconnected.

Bill Silver