Honda Z50 - 1976

Quick notes on rebuild (not restoration):

The piston and cylinder was badly scored, valves receded badly, and cam lobs worn flat. The cylinder was able to be bored "1 over" to .050 oversize and a good used original cam found and new valves to installed in the head.  The headlight, taillight, kill switch and light switch did not work, and headlight missing. There was no spark, with points badly pitted and spark plug cap missing.  The carb was badly corroded internally. The air filter housing is stock and foam filter element is new.

Important - The carb for 1976-1978 is a Keihin PA03, and finding info on settings for the '76-'78 is a challenge with most references using early model settings rather than later models. I found that the Clymer and Z50R '79-'82 service and owner manuals having good (best so far) info on the PA03. The Z50R also has a PA03 carb (B, C variants) and the initial pilot air screw setting is given as 1 1/2 for the '79-'82's. The Clymer manual says 1 7/8 for the 76-78 PA03 and I can't find the source of that, but ultimately 1 1/2 ran best (a Z50R '79-'82 setting). I used a remote digital tach to measure RPM for setting pilot air screw and idle rpm. The slide needle clip is set to the 3rd groove (stock position) for "best" response so far - it still bogs slightly when opening throttle quickly in mid-range but in testing it also did it in 4th and 2nd groove clip positions (from the top), so I focused on idle and throttle crack-open response, and starting consistency from hot or cold (usually one kick).

About the starting "procedure", it took finding an original owners manual to see that one starts the Z50 with full choke on (lever all the way up), then lever moved down (off) more and more as it warms up.  Jetting and float height (mm to come) is stock, so following the stock startup procedure seems to work best for my Z50. Usually 1 kick starting cold or warm/hot.  I did see some examples online of Z50's not needing choke, or partial choke etc but they didn't explain their carb/filter/other settings.

I am at sea level, temps for setup and testing ranged from 50 to 80 degrees, with 50-90% humidity. I tested over a several week period after arriving at settings (and left them alone after making final settings) to see how it started/ran.

Idle RPM 1600. Carb float height 14.5mm. Spark Plug NGK CR6HS .028". Points gap setting .014" and points opening timing set to F mark with Gardner Bender GCT-304 Continuity Tester light tool (light bulb method). Intake/Exhaust valves gap .05mm.

Sources for NOS parts:

NOSPartsNow.com (various parts and original parts manuals)

NipponMoto.com (gaskets)

Hondanuts.com - Northeast Vintage Cycle (various parts)

DML Moto in Coos Bay did the cylinder bore/hone and valve job - excellent work!

CMSL worked well to confirm part numbers, both NOS and superseded.