|Tech Tips by Randy Pozzi|
|#3 Startability & Driveability Problems|
Any of you who have CH150/250 Honda Elites with any miles on them undoubtedly will have at some time, hard starting characteristics.
Assuming you have good fuel, battery, starter, fuel tank ventilation, and fuel shut-off valve operation, cleaning the carb and servicing the choke will give you enhanced startability.
Honda uses the Japanese Keihin Constant Velocity (CV) carburetor with a starter valve set or electric choke.
On conventional carburetors, the throttle cable is connected directly to the throttle slide.
When you twist the throttle, this lifts the slide and immediately increases the size of the carb opening letting in more air/fuel mix and increasing the speed of the motor.
On CV carburetors, the throttle cable actuates a butterfly valve and, as the throttle is opened, the air pressure difference between the sealed chamber above the vacuum slide and the inside of the carb venturi forces the slide up and down.
On the upside, this carb adapts greatly to altitude changes and touring but, on the downside, exhibits lack of immediate throttle response and leisurely acceleration compared to a conventional carb.
The amount of hoses Honda likes to attach to their carburetors and accessibility to it is astounding.
Once removed, the carb is quite easy to service.
On the bottom of the carb is the float bowl held by four screws.
Removing the bowl gives access to the plastic float and valve, main jet and the jet holder.
Higher than expected gas consumption or dripping gas means the float valve needs replacement.
Brand new, the main jet and jet holder looked like a shiny penny.
Tarnish probably has darkened and possibly closed the tiny holes in each. Clean the jets with 0000 steel wool, open the holes with a fine sewing needle and clean.
Next to these jets is the slow jet which has very tiny openings.
If your idle over time has deteriorated, this is usually the culprit and if any replacement jets were considered, this would be the one.
On the top of the carb is the vacuum slide and diaphragm.
Your finger should be able to move the slide up and down.
The only resistance is the spring in the diaphragm chamber.
Once disassembled, the diaphragm has a rubber sheath around it and should be free from tears.
On the back side of the carb is the air cut-off valve held together by two screws.
Inside is a vacuum piston and a tiny rubber o-ring.
Check to be sure the vacuum piston rubber sheath also has no tears.
I like to clean the carb parts in diluted ZEP or CLR calcium/lime/rust remover and dry with compressed air prior to assembly.
Without doubt, the best enhancement to startability is to replace your starter valve set.
The autobystarter as its sometimes called, is the black tubular shaped thing with the wires coming out on the carb.
Held by two screws and a plate, its job is to enrich the carb upon cold start.
When cold, it's needle piston is retracted cutting off the air mixture circuit.
After a few minutes, it electrically extends its needle into the valve body opening up the air circuit.
Regardless of how nice it looks, over time, electrical resistance builds and the valve piston looses its effectiveness giving you hard cold starting.
To measure the resistance of the bystarter, place an ohmmeter between the two wires.
A new bystarter reads 0.5 ohms.
A bystarter with a reading of 7.0 ohms is weak and may give poor performance.
Replace any bystarter with an ohm reading near 10.0 ohms.
The valve starter plates (autobystarter) for the CH150 have a short needle piston and the CH250 a long piston.
They are not interchangeable.
Honda has discontinued all the 1985-88 CH250 starter valve sets.
However, the 1989-90 CH250 and all CN250 Helix valve sets (P/N 16046-KS4-840) will work for the CH250 with some end plug connection modifications.
The CH150 starter valve set for the 1987 model ( P/N 16046-KV7-673) will work for all CH125/150 models and is still available.
Once you have a clean carburetor and a fully functional electric choke, starting your scoot will be a button push away.
Randy Pozzi (Rev. 10/2005)
and maintained by doug Elam