AboutBill Silver Expertise Need help with vintage Hondas from the 1960s? I am an expert with 250-305cc bikes in particular and most all of the other pre-91 models, in general. I do NOT claim to have a great deal of experience on Gold Wings, Cruisers, ATC/ATVs and dirt bikes.
Experience I have owned/ridden/maintained Honda motorcycles for 35 years. I have written five books on Honda repairs and collecting. I was a service manager for two Honda shops back in the 1980s.
Organizations VJMC (Vintage Japanese Motorcycle Club) of North America
Publications VJMC newsletter, as editor for two years and as contributing editor currently.
Question Hello,I hope you can help me out.How do I get the idle to stay steady.I have just restored a 1971 honda ct90.When I bought the bike the carb's throttle valve was varnished tight.The carb's over all condition was the same.I have cleaned the carb.- gas tank,installed a in-line fuel filter.My carb has the square shaped float bowl.I bought a carb kit that included the main-idle -slow jets. (different sized jets)Also included was an air screw and idle screw and float bowl gasket and float valve needle.There also was various O rings.I replaced all the old parts with the ones from the kit.The engine would not start. So I put the old parts back in --except for the gaskets and idle/air screws--I have got the engine to start on the first kick.But the idle seems to slowly go up and slowly go down then stop.I have cleaned all traces of "dirt" and checked the float level and all the jets are cleaned.I have re cleaned the carb-Found dirt in screen.I have made sure the passages were not blocked.The timeing/points/spark advance seem in spec.New honda spark plug.+ new battery As the manual states-The engine is at normal opp.temp while I try to get it to idle. Throttle cable is new.Some sluggish responce at throttle snap-depends on how fast the rpms are.I have tryed all the manual fixes.Air screw turned in then out as manual states.There are no fuel leaks.I must be missing somthing.Sorry for the long story but I thought it might help.
Answer Mike, tell me about the compression readings and/or the valve clearances first. Tight valves and/or low compression will cause all kinds of problems with idling and performance.
Next, be sure that the spark advancer springs are tight, so that the spark timing returns to F mark at idle.
Check the float level... If your bike is a 1971 production, that means that it is a K2 designation and requires a 20.0mm float level. Incorrect float level settings will cause the engine to surge and richen up at idle. Check the plug to see if it is too rich or too lean.
Air leaks at the intake manifold/insulator will cause idle mixture issues, as well. Try raising the clip on the needle up and down one notch to see if that will affect the part throttle response.
