Missing on cbx400?

**lb99** · 16th August 2009, 19:57

missing at low revs and idle, dissapers as you pass through the midrange, seems ok on full throttle, top third of rev range.
40000km, and a cycleworks 4 into 1.
leaving a black stain on swingarm behind the exhaust

i have checked out the leads coils and plug caps, all seem ok.
air filter new
plugs new
fuel flow ok
had a new baffle for exhaust made by cycleworks
carbs have been stripped and cleaned thoroughly, and reassembled as per honda manual

put it back together, still ruff as guts off idle, and hunting a bit as well.
going through the carbs cured the hard starting problems I had been experiencing,(yay) but not the rough idle.
I wound in the idle mixture screws 1/2 a turn (leaner?) seemed a bit better (those things are a cnut to get at)
the float levels are all the same (stupid no adjustable plastic floats), checked with some plastic hose on drain tap.

made up a carb balancer out of some plastic tube and some 2 stroke oil, it works ok, but the levels are all over the place and continuously changing, so you cant set anything accurately, unless you open the throttle a bit to about 4k then it all settles down.

wtf?

**F5 Dave** · 17th August 2009, 12:16

Originally Posted by lb99

. . .
going through the carbs cured the hard starting problems I had been experiencing,(yay) but not the rough idle.
. .

hmm, so you found something there, or just it was better when cleaned?

I was going to suggest pilot jets but you have cleaned them. Like see through hole clean?

Choke operation? It's been more than quite a few years since my CBX (550 with c.works exh) so can't quite remember it., but it sounds like it is running rich if there is a mark being left, mine always ran sweet & clean.

Also check emulsion tubes are round & not slightly ovalised which will foul plugs etc. do a search on factorypro website to read up (will need to dig around). But these carbs weren't that prone & mine had close to 100,000 on it.

**quickbuck** · 17th August 2009, 17:28

I would revisit Carbs, as my first thought was Pilots....

BUT as you have too much fuel (by the sound of it), then check your floats, and make sure one hasn't sunk.... or the float valve seat hasn't perished....

Rough running can be caused by too much fuel as well as not enough.

**lb99** · 18th August 2009, 17:39

typical honda, have to go through back mudguard. ffs

floats are stupid non adjustable ones, levels all the same (checked with clear tube against carb body), I'll crack it, it'll just take time

edit: update, look what I found, could this be the problem?

**F5 Dave** · 19th August 2009, 18:02

Ha yes I remember, was easier to move airbox & virtually everything else to get the carbs out.

Ha! nice find,

keep looking while you have it apart though (often several reasons gang up) but that should screw up the idle mixture nicely.

**lb99** · 19th August 2009, 19:09

well I got some tiny o'rings today, and fittted em after work- no joy, bikr wont even start now. Kinda had my hopes up

carbs in, carbs out, carbs in ........

gave up for tonight

will have a look later

**quickbuck** · 19th August 2009, 19:15

Originally Posted by lb99

well I got some tiny o'rings today, and fittted em after work- no joy, bikr wont even start now. Kinda had my hopes up

carbs in, carbs out, carbs in ........

gave up for tonight

will have a look later

Those are the suckers.... I did mean to say Valve Seat seals....

Anyhow, now you have to ensure the fuel is actually getting from the tank to the carbs...
So, make sure it isn't a "Re-assembly issue".

Fresh eyes in the morning will help....

Oh, and give your plugs a good clean, if you haven't done so.
I know they are new, but 2 &3 may be a little wet by now.

**lb99** · 19th August 2009, 19:31

Originally Posted by quickbuck

Those are the suckers.... I did mean to say Valve Seat seals....

Anyhow, now you have to ensure the fuel is actually getting from the tank to the carbs...
So, make sure it isn't a "Re-assembly issue".

Fresh eyes in the morning will help....

Oh, and give your plugs a good clean, if you haven't done so.
I know they are new, but 2 &3 may be a little wet by now.

yeah, there is fuel in carbs, none in cyls though. the seals were kinda flatish, so the o'rings might be a bit fat, may try to get some tiny fibre washers tomorrow, and try that.

can anyone point me at a parts fiche for my bike, according to the interweb it does;nt exist

**quickbuck** · 19th August 2009, 21:24

Originally Posted by lb99

can anyone point me at a parts fiche for my bike, according to the interweb it does;nt exist

Hmmm, is your bike an NC13? Na, wait, that was the VF400....
Will continue to look...

Used to have a great site, but it is in the history of my other (almost dead) computer....