Motorcycle Repair: idle problem, clymer manual, manifold gaskets

Question
The motorcycle is a 1972 CL 175 Srambler.  However, the engine is not the original but a 1974 CL 200 E engine.   The mileage on this replacement engine is unknown.  After several years of storage I decided to get the cycle running in order to sell it.  I have been working on it off and on for about three years. I during this time I had disassembled the carburetors and found no plugged holes and replaced the float bowl gaskets.  I got it to run but it had no power.  So late last summer I bought a "Clymer" Tech Manuel, and followed the tune up sequence replacing the condenser, points, and set the timing and so forth.  That solved the power problem, but the idle was somewhat erratic, and only the idle air mixture screw on the left carburetor (choke lever side) had any effect on the idle speed.  The main problem was after warming up when idling the engine would die.  Also, when I had disassembled the carburators the first time, I noticed that the left intake manifold had a gasket, so I replaced that with one that I made.  So with the Clymer manual in hand I decided to follow the detailed instructions and disassemble the carburetors again--this time I removed the floats which I did not do the first time.  I made some slight adjustments to the floats by bending the tab but they seemed fairly close to the 21 mm height to start with but I tried to fine tune it even more.  I made two more manifold gaskets but did not replace the "O" rings because I thought that the gaskets would seal the manifolds.  When I put everything back together and started the engine the idle speed jumped to 600 or so and as it warmed up it increased.  Initially a lot of smoke came from the exhaust and when I slightly opened the choke the RPM shot up towards the red line and I finally had to shut turn off the engine as the idle RPM was uncontrollable.  I talked to the local Honda Service people (They don't work on old cycles) about this problem, and they said that it was probably an air leak somewhere and that I could take carberator cleaner and spray it around the manifolds.  If the idle changed then that indicated there was a leak.  Also, I asked about the gaskets I had installed and they said that gaskets should not be required because the four "O" rings (two on each carburetor)should seal the manifold.  I went home, started the engine and it idled so fast that I could not use the carburetor cleaner because the torque of the engine moved the cycle. After several tries I finally managed to spray around the manifolds and on the left one the idle did slow for a few seconds.  I then decided to disassemble the carburators again.  I went to the local hardware store and found matching "O" rings.  I cleaned the surfaces of the intake manifolds, replaced the "O" rings, checked the carburator jets again, and reassembled them.  I had a lot of trouble reinserting the jet needle on the left carburetor.  One thing I did not do was remove the throttle cable during when I disassembled the carburetors.  But I finally got the jet needle in and I could feel and hear them spring back into position when I released the throttle.  So, I started the cycle and the idle RPM shot up to about 500 rpm's---not as bad as the first time but not the result I expected. I sprayed carb cleaner around the manifold and did not notice a significant change in rpm.  It smoked initially and when I opened the choke slightly the rpm shot up again towards 1000.  When I tried the throttle during this process, it had no effect.  From the fully closed position to the open position it did not seen to change the rpm---it was as if this engine had a mind of its own.  Since the throttle cable is frayed where it splits into two cables, I decided to use a little tape to hold it in place at that point, and when the engine is off the throttle appears to work as it supposed to.  Anyhow I am at a loss.  The more I work on this cycle the worse it performs.  Also when I pulled the spark plugs, saw that the left one was totally black and the other was more or less brown. I cleaned both and reinstalled them. But this had no effect on the problem.  Also, turning the idle and air mixture screws has absolutely no effect on the idle speed. I hope you can help.  Sincerely, Mike Sullivan  

Answer
Mike, it is not clear if your engine swap included the carbs from the 200 or not. Float level settings are both 21 mm but the main jet sizes are different and the needles may have a different taper.
First, be sure that both cylinders have the same compression before you continue. A tight valve or burned valve/seized piston will cause you to waste a lot of work on something that will never run properly. Check the valve adjustment and set to .002" cold on the compression strokes of each cylinder. They fire alternately, so do one, turn the motor over one turn and then do the other side.
Next, pull the point plate and check the mechanical spark advancer for sticking and proper operation. IF you have to take the point cam off do it gently and then clean and lubricate the shaft and hole with point lube. Lube the point cam itself and reinstall it all. Set max gap to .012-.014" and then move the plate until the points just open at the F mark alignment on the flywheel. You can do this with a 12v test light for accuracy. Be sure the point faces are clean and smooth, of course.
Putting tape on throttle cables isn't a very good idea. You need to be sure that both cables are pulling at the same time and closing at the same time. Be sure that there is enough slack in them so they don't get pulled when you move the handlebars or that it isn't getting caught on something under the fuel tank.
Be sure that both needles are on the same clip setting. Try the middle one first.
To synchronize them, leave the float bowls off and remove the main jet holders. Watch the tips of the needles and adjust the cables until they both raise/lower at the same time. Make sure that your needle isn't damaged on the one that you had difficulties with. If you knock the retaining clip off the end of the needle inside the carb slide, the needle will bounce around inside and carburetion will be inaccurate.
Also be sure that you haven't dislodged the needle jet in the carburetor body. If it drops out then you will have a really rich mixture on that side.

Any vacuum leaks are of course not a good thing. If the manifolds and carb bodies are sealed well with proper O-rings then any gaskets are not necessary. The o-rings are metric dimensions, so US O-rings may not be of the proper sizes.

Bill Silver