CB360 K0 Not well

[nairb]

Hello, I have had this cb360 for 3 or 4 years and after its restoration have done some 3.5 k on it without any issues....... except for now.

It starts ok and pulls off ok but now won't rev over 5k in any gear.  Seems fine in the lower revs.  SO, before I start to investigate, I thought I would ask the obvious questions......

1.  Blocked main jet?
2.  Ignition Advance not working.? Stuck.
3.  Points gone duff.  Not looked yet.
4.  Some other mysterious and daft issue.

Ta
Nairb

[Bryanj]

3.5 k is dounle the service interval for points and timing PLUS points can, and do hort out on the cover

[Johnwebley]

Does it have single coil?


With twin leads?

Have you renewed it?

I had a similar issue with my CB200

turns out the primary resistance was to high,
Needed to be about 3.5 ohm

Revs OK now

Sent from my SM-A546E using Tapatalk

[nairb]

Well, I have begun the investigation.  Does a cb360 ever go pop.  Apparently so. 

It's a twin coil/points setup.  All original as far as I know. 

So a quick and simple test is to change the plugs.  And with a new set of sparkies I went for a spin.

It's still unwell.  So those points will be looked at next when it's cooled down.  Maybe a set of points from DS is in order.
Time to check the advance units as well.

[Oddjob]

If ordering points, I'd strongly advise buying original, not copies. Copies just don't seem to work as well these days.

[nairb]

If ordering points, I'd strongly advise buying original, not copies. Copies just don't seem to work as well these days.

Yup. I do this with Brake cables and clutch cables as well.  Altho if DS stock an alternative, are they OK?.
Anyway..... its now being prodded to see what's wrong.

[Oddjob]

If the alternatives all there is then I suppose you have to buy them. Try and find genuine first though. Should still be some around. Ask on site and see if anyone has some stored away.

[nairb]

An update.  Points off.  Looks ok.  Advance unit out and seems to be working.  It's free to advance and spring back.
Compression tested.  Cold engine, throttle fully open, I get about 150 (psi?) per cylinder.  So they seem ok.
All back together and points set up as manual says.  New spark plugs.

NO improvement.  Still won't rev and in holding back.  LH plug is very sooty and black. 

Wonder if it's the condenser/coil.

More investigation required...........

[cbxman]

nairb,

Have you checked the diaphragms?  Similar problem back in the day with my CB250s

Sooty plug, I would having those carbs apart.

Good Luck.  Keep us briefed

Jerry

[K2-K6]

nairb,

Have you checked the diaphragms?  Similar problem back in the day with my CB250s

Sooty plug, I would having those carbs apart.

Good Luck.  Keep us briefed

Jerry

Well spotted, it does sound like that in characteristic and worthwhile checking.

If diaphragm is compromised it leaves the airline down (or below optimum height) with vacuum going really high underneath the slide it pulls fuel through the jet way in excess of target to make it like it's running on choke for that carb.

Obscure note, I use exactly this train to tune SU carbs on modified engine, thicker oil viscosity in air damper tube to cause the slide to stay below target and force rich mixture for acceleration while not having to change the main jet from optimum.  Quite a powerful effect overall.

[nairb]

Before I spotted the info on carb diaphragms, I thought a cheap test would be to switch the coils over and see if the RH plug became very sooty.  There is only one condenser and if at fault would apply to both cylinders. 

So with coils changed over and spark plugs cleaned of soot, it started fine and idles good.  But on a 2-mile run, the problem still exists - unsurprisingly.

Anyway, the LH sparky is very sooty again.  SO it's probably not the coils.....

Right, let's have a look at the LH carb......

I will report back

[nairb]

Well the 1st prize goes to ......

Here is a pic of the LHS carb diaphragm.  Not the best pic but...

[ Guests cannot view attachments ]

Its a hole in the diaphragm.

I hope the spare carb diaphragm is still ok

[Bryanj]

Dave Silver does a pattern part but has no stock at moment BGACC-369-004P but its £55 plus drat and postage

[nairb]

Final report.
Spare carb diaphragm was ok and fitted.

Bike now back to its rampant best. 

Good to see that DS has spares.

Thanks
Nairb

[Bryanj]

CMS  has 3 original ones 16022369004 but guess what £135 plus postage.

Have you stopped gibbering yet?