CB72 - It lives!
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From: Mike Buckley on 19 Mar 2010 03:55 In message <hnuoa6$u4b$2(a)news.albasani.net>, crn(a)NOSPAM.netunix.com writes >Mike Buckley <Mike(a)hotmail.com> wrote: >> >> Bad form etc. The pilot jet fixed the idle problem but can anybody >> explain when ignition advance should kick in? The CB has a spring >> mechanism on the cam shaft which advances the ignition, on mine it >> appears to be advancing as soon as you open the throttle, I thought >> advance happened higher up the rev range? > >What are you using to test it, this does not sound right. >You need a proper strobe timing light, there will be timing marks ISTR >under a cover on the LHS but ICBW. >Do you have a Haynes or similar BOL ?. > I have a proper strobe light (tenner from Amazon), and it shows my static timing was pretty much spot on, but the slightest rev increase and it advances quite a lot. Weak advance springs seem to be a bit of a problem on these. They can be replaced, possibly without removing the camshaft, but even so the engine has to be dropped in the frame. Electronic ignition is available (for about $300!!) but it still relies on the mechanical advance on the camshaft, so in this case I might get some benefits but not really the one I'm most after. They also recommend going to Dyna coils at the same time, so even more expense. I'll see how it goes on the road before deciding what to do. -- Mike Buckley RD350LC2 CB72
From: Tim on 19 Mar 2010 04:02 In message <mLmtFJO00qoLFwzh(a)hotmail.com>, Mike Buckley <Mike(a)hotmail.com> writes >In message <1qa5NiI7N6nLFwqX(a)hotmail.com>, Mike Buckley ><Mike(a)hotmail.com> writes >>In message <n13vp5p45f1nq9729e6h7o9ksacmv496io(a)4ax.com>, Austin >>Shackles <austinDITCHTHISFORBETTERRESULTS(a)ddol-las.net> writes >>>On or around Fri, 12 Mar 2010 14:53:36 +0000, Mike Buckley >>><Mike(a)hotmail.com> enlightened us thusly: >>> >>>>Moved under its own power for the first time in at least 25 years: >>>> >>>>http://www.flickr.com/photos/39665805(a)N05/4426557037/in/set-7215762250 >>>>1687588/ >>>> >>> >>> >>>bloody hell, you've dnoe a nice job on that. Looks better than new! >> >>Wish it ran like it. Hopefully new genuine pilot jet arrives tomorrow. >> > >Bad form etc. The pilot jet fixed the idle problem but can anybody >explain when ignition advance should kick in? The CB has a spring >mechanism on the cam shaft which advances the ignition, on mine it >appears to be advancing as soon as you open the throttle, I thought >advance happened higher up the rev range? > If it's the same as on my old CB250-K4 then the spring has weakened and the cam is going to full adjust too early. There were a pair of springs on my one. -- Tim
From: Tim on 19 Mar 2010 04:03 In message <1DRp3IPp3yoLFwQN(a)hotmail.com>, Mike Buckley <Mike(a)hotmail.com> writes >In message <hnuoa6$u4b$2(a)news.albasani.net>, crn(a)NOSPAM.netunix.com >writes >>Mike Buckley <Mike(a)hotmail.com> wrote: >>> >>> Bad form etc. The pilot jet fixed the idle problem but can anybody >>> explain when ignition advance should kick in? The CB has a spring >>> mechanism on the cam shaft which advances the ignition, on mine it >>> appears to be advancing as soon as you open the throttle, I thought >>> advance happened higher up the rev range? >> >>What are you using to test it, this does not sound right. >>You need a proper strobe timing light, there will be timing marks ISTR >>under a cover on the LHS but ICBW. >>Do you have a Haynes or similar BOL ?. >> > >I have a proper strobe light (tenner from Amazon), and it shows my >static timing was pretty much spot on, but the slightest rev increase >and it advances quite a lot. Weak advance springs seem to be a bit of a >problem on these. They can be replaced, possibly without removing the >camshaft, but even so the engine has to be dropped in the frame. > Drop the engine just to reach the timing adjust springs? Yeuk. On the K4 they were under a nice shiny cover held by two 8mm bolts. -- Tim
From: Champ on 19 Mar 2010 10:18 On Thu, 18 Mar 2010 22:46:12 +0000, Mike Buckley <Mike(a)hotmail.com> wrote: >Bad form etc. The pilot jet fixed the idle problem but can anybody >explain when ignition advance should kick in? The CB has a spring >mechanism on the cam shaft which advances the ignition, on mine it >appears to be advancing as soon as you open the throttle, I thought >advance happened higher up the rev range? Yeah, but only a tiny bit higher up; my dim memory says that full advance should be at about 2,500 rpm, or perhaps even a little lower, so you don't need hardly any throttle (in neutral) for that. -- Champ neal at champ dot org dot uk
From: crn on 19 Mar 2010 10:22
Mike Buckley <Mike(a)hotmail.com> wrote: > > I have a proper strobe light (tenner from Amazon), and it shows my > static timing was pretty much spot on, but the slightest rev increase > and it advances quite a lot. Weak advance springs seem to be a bit of a > problem on these. They can be replaced, possibly without removing the > camshaft, but even so the engine has to be dropped in the frame. It should be on the static marks at tickover and then advance progressively, reaching the full advance marks at typically around 2800 rpm [1]. > I'll see how it goes on the road before deciding what to do. If is advances too early it will lack torque at low rpm for pulling away. [1] 2800 is from memory, RTFM if you have one, someone will doubtless tell me that I have it rong <B-). -- 03 GS500K2 76 Honda 400/4 project 68 Bantam D14/4 Sport (Classic) 06 Sukida SK50QT (Slanty eyed shopping trolley) |