1972 cb350 idle issues
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From: mwhyte on 14 Jun 2007 17:21 Howdy folks Forgive the newbie, but I've got a dumb question that I can't seem to answer for myself. Here's the thing: I've got a 72 cb350 that wasn't ridden much over the last 10 years (though it was ridden a bit here and there throughout). I had a problem with stalling and the left piston not firing until the engine heated up significantly. So I did the obvious: Rebuilt the carbs -- even replaced both diaphragms -- replaced the air filters, replaced the points, set the timing (all by my mechanic, of course). Both pistons are firing now, but unless the choke is open (minimum halfway) the bike will stall when idling (ie. sitting at a light). Also stalls sometimes on downshift. Is it as simple as adjusting the idle here, or am I missing a more complex problem? Any help would be appreciated. Thanks much, MW
From: Albrecht via MotorcycleKB.com on 14 Jun 2007 17:41 mwhyte wrote: >Is it as simple as adjusting the idle here, or am I missing a more complex >problem? http://www.bikebandit.com/partsbandit/showschematic.asp?dept_id=2316300 The idle mixture screw is shown on the side of the carburetor as 8, 8, and 3. Turning it counterclockwise about 1/4 to 1/2 a turn should make the engine start idling on both cylinder when cold. If that doesn't help, remove the screw after first tightening it until it lightly seats, while counting the turns. Then spray some aerosol carb cleaner in the hole and reinstall the screw the same number of turns out from lightly seated that you counted. If that doesn't clean the idle circuit out, try putting about thee ounces of Berryman B12 Choke and Carburetor Cleaner in a full tank of gasoline and going for a slow ride to clean the gum and varnish out of the carbs. Another possibility is that the floats are set too low, or the float valves are gummed up and stuck shut. -- Message posted via MotorcycleKB.com http://www.motorcyclekb.com/Uwe/Forums.aspx/tech/200706/1
From: paul c on 14 Jun 2007 18:14 Albrecht via MotorcycleKB.com wrote: > mwhyte wrote: > > >>Is it as simple as adjusting the idle here, or am I missing a more complex >>problem? > > > http://www.bikebandit.com/partsbandit/showschematic.asp?dept_id=2316300 > > The idle mixture screw is shown on the side of the carburetor as 8, 8, and 3. > > Turning it counterclockwise about 1/4 to 1/2 a turn should make the engine > start idling on both cylinder when cold. > > If that doesn't help, remove the screw after first tightening it until it > lightly seats, while counting the turns. > > Then spray some aerosol carb cleaner in the hole and reinstall the screw the > same number of turns out from lightly seated that you counted. > > If that doesn't clean the idle circuit out, try putting about thee ounces of > Berryman B12 Choke and Carburetor Cleaner in a full tank of gasoline and > going for a slow ride to clean the gum and varnish out of the carbs. > > Another possibility is that the floats are set too low, or the float valves > are gummed up and stuck shut. > I'm curious whether synchronizing the butterflies/vacuum would have any effect (assuming the carbs can be balanced on this bike).
From: Albrecht via MotorcycleKB.com on 14 Jun 2007 19:06 paul c wrote: >I'm curious whether synchronizing the butterflies/vacuum would have any >effect (assuming the carbs can be balanced on this bike). Mechanic$ in $tealer$hip$ often recommend carb $ynchronization ju$t before Chri$tma$ and April 15th. ;-) Seriously, you cannot synchronize dirty carbs, and CV carbs with shafts joining the two butterflies don't go out of synchronization as easily as the older slide valve carbs with multiple throttle cables. -- Message posted via MotorcycleKB.com http://www.motorcyclekb.com/Uwe/Forums.aspx/tech/200706/1
From: mwhyte on 14 Jun 2007 19:13
Albrecht wrote: >http://www.bikebandit.com/partsbandit/showschematic.asp?dept_id=2316300 > >The idle mixture screw is shown on the side of the carburetor as 8, 8, and 3. > >Turning it counterclockwise about 1/4 to 1/2 a turn should make the engine >start idling on both cylinder when cold. > Thanks a ton for the tips; I'll give it a go and see what happens. >Another possibility is that the floats are set too low, or the float valves >are gummed up and stuck shut. I just got the bike back from the mechanic yesterday after a carb rebuild ... I hate to think this is possible, but I guess it could be ... |