Motorcycle Repair: 78 CX500 Pwr Problems, local bike shop, leakage problems

Question
Hi Bill - I recently purchased a 78 Honda CX500. (600 miles). After having my reseident mechcanic (brother-in-law)mess w/ the floats - due to leakage problems - w/no success to stop, I sent the the carbs out to a local bike shop for a good cleaning. I'm not sure if they ajusted the floats to back to the right level, but the cabs were very clean. I insatlled them back on the bike and it started and ran ok. I'm still in the process of legalizing the bike for the road and want to make sure it's ready. But just the other day I change out the antifreeze and took it for a quick spin and the bike lossed power and even stalled. the bike starts ok but when under power and accelrating the throttle I lose RPMs. not sure it this is fuel or carb related. Also I had teh tank cleaned w/ muatic acid and flushed w/ water and filed w/ gas.  Any help would be greatly appriciated. Thnaks Rob F.

Answer
Rob, I wonder if your bike ever had the 600 mile service? I have to tell you that there were numerous problems with the early CX500s, including incorrect main bearing sizes, bad stators and broken camchain tensioners. There were updates for all those problems, but I doubt that Honda is still offering to fix them for free now.
The 600 mile service would include a valve adjustment and camchain adjustment, as well as fluid checks. I hope you bled all the air out of the system when you chained the anti-freeze and that you used non silicate Honda fluid.

The floats are not adjustable, I think... plastic, at least on the later ones. 15.5mm is the correct height.

Cleaning the tank with muriatic acid will strip the coating off the inside of the tank, so any air space will start rusting right away. Phosphoric acid will leave a bit of a coating on it. Be sure that all the water was flushed from the tank, as it may have been caught up in the petcock or run down the fuel lines to the float bowls, then into the jets! That creates a definite power loss.

There is an air cut valve on one of the carbs, that need to be checked for tears or leaks, as well as an accelerator pump diaphragm to aid in acceleration. The petcock has a screen that goes inside the fuel tank and the mesh is fine enough to trap water/rust and block fuel flow. The ports in the petcock could also be plugged with debris/rust/water, preventing fuel flow for both carbs.

Make sure that the spark plug caps have about 5k ohms in each one and put in a fresh set of plugs, if yours are the originals or are fouled.

Bill Silver