decomp lever

i have a '83 honda pa50II, and i was wondering what the decompression lever does? i've noticed that if the moped isn't running that great, i'll hit it, and then she runs better. why is that?

i've also noticed some sparks when the lever is pushed back to whence it came, is that normal?

i think this is all related to when something strange happened to my moped. all of a sudden, she wasn't running great, i thought it was the battery, but it wasn't, and now i just think it's the cold. the decomp is a decent solution for now, i just want to know what it's actually doing.

Re: decomp lever

generally a decompression lever is used for ease of starting a motor, sometimes for downhill running , any sparks when it is returned to its normal state might be from it grounding back to the head, but the motor should run better when it is engaged(off) not in use so something is def. wrong could be a clogged or dirty carb or exhaust.

Re: decomp lever

Ron Brown /

Pat,

Find the source of the sparks. It sounds like your spark plug is shorting to the decompressor valve or cable.

When the decompressor is operated, the engine should run much worse, if at all. You can use it to kill the engine at idle but it is not recomended as it eventually burns the valve. I can only imagine how fast it will burn if you operate it at full throttle.

One more possibility is that you have lost engine ground and it is grounding through the decomp cable.

Ron

Re: decomp lever

Don't know what the spark problem is but it sounds as though the decompressor valve has carbon buildup and when you activate it it gets a little better. You might want to do a top end decarboniqation. I presume you don't mean that you are riding it with the lever pulled .Just a quick pull and release.

Chris

Re: decomp lever

Ron Brown /

Chris,

Don't you think that a fat spark at the decomp lever may cause a weak spark at the plug?

Why ignore this symptom and tear the engine apart first?

Ron

Re: decomp lever

Was unclear about the spark situation. How would pulling the decomp in improve the spark? Other than decreasing the resistance caused by compression? But with no compression it wouldn't run better. Decarbonization is standard mainatanence.

Decompression valves are not designed to be used as an off switch. when they are used as such carbon up real easily.

Re: decomp lever

Ron Brown /

Chris,

This is from Pat's original post:

i've also noticed some sparks when the lever is pushed back to whence it came, is that normal?

This was my original reply:

Find the source of the sparks. It sounds like your spark plug is shorting to the decompressor valve or cable.

When the decompressor is operated, the engine should run much worse, if at all. You can use it to kill the engine at idle but it is not recomended as it eventually burns the valve. I can only imagine how fast it will burn if you operate it at full throttle.

One more possibility is that you have lost engine ground and it is grounding through the decomp cable.

Chris, given that the decomp valve mechanism and the spark plug share the cylinder head, why wouldn't the decomp cable short to the plug wire and cause sparks at the lever, or be working as a substitute ground for the engine.

Call me crazy, but if there is something going on that obviously should not be and could be causing the symptoms, I allways fix that problem before trying to find another.

Pat, how about telling us what happened.

Ron

Re: decomp lever

wow, you guys have lost me completely. too much knowledge for me to handle.

anyway, i don't think anything happened to cause this problem, it just happened one day.

chris had assumed correctly before, i hit the switch for a second, and then she runs better. i'm not constantly holding the switch. so is this a carbon buildup?

and how do i fix the sparks issue? how do i tell if the spark plug is shorting to the decomp valve/cable? and how do i make it ground properly?

you guys constantly amaze me with your waelth of information. thanks.

Re: decomp lever

Ron Brown /

Pat,

I am not familiar with this model, but look at the spark plug cap and wire and see if it is close enough to the decomp valve mechanism to short out to it. If it is, move it. If it is not, look around the engine mounting bolts for a ground wire. There should be a heavy wire or piece of braid between the engine and frame. Make sure this is in good shape and clean and tight at both ends.

BTW, if the "sparks" you are refering to come from the decomp valve on the cylinder head, this is actually fire as you are opening a hole into the cylinder and is normal. If this is the case, forget about the electrical problem but do check to see if the decomp mechanism interferes with the plug or wire.

Ron

Re: decomp lever

actually, the sparks are coming out of the lever on the handlebars. it scared the hell out of me the first time it happened.

Re: decomp lever

Ron Brown /

Pat,

The lever on the handlebars is connected to the engine through a steel cable. Look at the engine end for the problem.

Ron

Re: decomp lever

Ron Brown /

Pat,

How about an update? Did you fix it?

Ron

« Go to Topic — end of thread

Want to post in this forum? We'd love to have you join the discussion, but first:

Login or Create Account