idle hunting

evenin' all.

I took ownership of a 1981 Honda CD200 Benly last week. Bit tatty, but
does the job. It's... interesting.

It has an idling problem though. Before I took the carb apart the revs
would kinda stay high then die. Then I bunged the dismantled carb in a
sonic wash for an hour, and it all came up shiny. I was hoping that
would do the trick, but the problem is still exactly the same.

The throttle slider had a couple of dents where the idle control screw
meets it, so I carefully sanded the slope down with sandpaper. There's
still a shallow dent, but not as bad as it was.

I also disturbed the pilot air valve, but haven't got a scooby what this
does! Can anyone explain, or preferably find a cross-section diagram to
explain? It was covered in black gack before I cleaned it.

Anyway, since I threw it all back together the idle's all over the place
like before. The revs just slowly and randomly hunt around. So my
Haynes says that when it's all nicely warmed up I'm supposed to adjust
the pilot valve in the way until it sputters and stalls, then turn it
out the way until it sputters and stalls, then plump for somewhere
directly in between, and that this should be 2 turns out from the
lightly seated position. *Then* you set the idle speed with the screw
stop. But how are you supposed to set the pilot valve if your idle
screw stop's not set and you can't get a steady idle?

I have managed to get it so it doesn't die when you close the throttle,
but it's still hunting around.

Any thoughts? Could it be unrelated to the carb at all, perhaps? An
ignition/timing fault?

cheers
Biz

 

biz says...

Air leak between carb and head? Get it running then spray carb cleaner
on the manifold and see if the revs rise. If they do you've got a leak.

--
Lozzo
Triumph Daytona 955i SE (Black with added black bits)
Suzuki Bandit 600S (Green with added shit bits)
Yamaha SR250 Delusion (It's "Special")
I ride way too fast to worry about cholestorol.

 

Loosen or take off the petrol tank cap and try it...

 

This is your problem. Get another slide or another carb. Some lunkhead
has damaged the slide and also the idle control circuit and it will now
*never* idle properly.

 

Hmm, well I messed around with the pilot air screw and the idle control
screw a bit more, until I decided to take it all apart again for another
look. Noticed the slope for the idle control screw was dented again
from this activity, so set a policy of never winding it *in* without the
throttle wound open.

So I filed back the slope smooth again, blew some WD40 through all the
jet bores to check they were all clear and gave it a good air blow-out.
Then I changed the float height. The Haynes description of this is
pretty hopeless too.

Anyway, I put it all back together again, and Hey Presto! Suddenly I
get a steady (albeit racey) idle speed! So I did the procedure of
winding the pilot air screw to both extremes and plumping somewhere
between the two, then (carefully getting the throttle out the way)
adjusted the idle control screw.

I'm still befuddled about how or why these changes have worked, and
indeed what everything does, but I seem to have fixed it.

I didn't try Loz's or Keith's tricks, as they were next on the list!

 

Back in those days bikes often had a breather hole in the the tank cap, if
that got blocked it would play havoc with the idle and could even stop the
bike from starting or running at all.

 

Neat trick here

http://gstwin.com/float_height_check.htm

 

He's lucky to have drains with extension pipes on them.

 

There is bikes and then there is proper bikes.

One of the reasons I have become a fan of the GS500E is that it is all
so easy to maintain. A good learner machine in many respects.

Although the above statement does not apply to the exhaust header bolts.
A week of soaking in WD40 and gentle persuasion every day and the can on
the donor bike is firmly and resolutely still on the donor bike. I need
a rattle gun.