Questionhello Bill,I wanted to follow up on my bike.The engine seems a little better here is what I have done... I have checked the compression,It seems to be within limits 10kg/cm2. I had to adapt my pressure guage to fit the spark plug hole- so there is a chance it could be a bit higher.The bike has 3,000 miles on it.I don't know how long it sat idle or where.The valve tappet clearance was tight I could not get the .002" guage to slide in- so I re adjusted ,now guage goes in with a bit of friction there.I have re-cleaned the carb,sealed the intake both where it enters the head and where it enters the carb.Float level 21mm,with a new float needle+ valve.Throttle response seems good now.I do notice a slight miss.Also there is a oil leak directly below the cast iron portion of the head -I'd say where the little silver cam chain bolt is.Not a bad leak but still a leak.I have 10w-40 honda oil in.Spark plug looks dark but not sooty.Looking at the cam chain from out side it looks tight-the tensioner spring length is good.A little smoke in the exaust.I guess thats abut the whole of it.Whats the best course of action.I would like to take her out on a trail ride this weekend to see what she can do...thanks---mike
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Followup To
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.
Bill Silver
AnswerMike, you have been busy. Glad to hear that it is coming around for you.
Honda specs 20.00mm for the float level. First versions were 21.5mm. I know it seems like a small thing, but can make a difference when you are dealing with such a small carb and air/fuel volume. You may want to recheck that and be sure that the measurement is when the float is just touching the tip of the needle, not compressing the spring loaded tip.
Be sure that the spark advancer is free to advance/retard w/o a lot of slop when the springs have the weights pulled in. You can crimp the spring ends very gently to firm the tension up. Set timing by making points open at the F mark alignment, with an overall gap of .014" (.35mm) at the maximum lift. Be sure that the point faces are clean and shiny. If you see excessive arcing from the points while engine is running, the condenser lead to the points may be loose or condenser weakening.
Honda specs compression at 12kg/cm2, so you are a little down from that, perhaps due to sticky rings from sitting so long. Some of the later models had valve stem seals, which could be hardened by now and allowing some extra oil through to upset the mixture a bit. Idle mixture screw setting is suggested at 1 turn out. Tolerances will vary if you are at a different altitude. If the carb has an altitude compensator, check the seal/o-rings for that function.
Spark plug cap may be loose on the wire and/or have some resistance value variances. Early ones had no resistors, but later ones will have about 5k ohms value when checked from plug wire end to sparkplug tip connector.
Bill Silver
