Ignition timg a CB125s

scrimshady · Derestricted Danger Joined: 01 Nov 2009 Karma :

hello all, i am new to this forum and would like some advice please.
i ride speedway bikes and have bought a CB125s Engine that has been tuned to run on methanol but i have no points or generator on it, i have just bought the points and was wondering if anyong could tell me how to do the ignition timng on it.
also i would like a manual if someone knows where i can download from.
thanks
Richard

stinkwheel · Bovine Proctologist Joined: 12 Jul 2004 Karma :

It is very crude. You set the points gap and hope the timing is somewhere close.

If it's been that highly tuned, you might want to slot the mounting holes for the stator plate so you can advance it a bit.

This may however cause problems for the mechanical ignition advancer.

EDIT: There seems little point in setting the timing to the factory setting if you're running a high compression top-end and methanol because it'll all have gone batshit anyway.

Keep advancing it slightly until it either wont start, looses power or starts pinking, then back it off a bit.

At a total guesstimate, I'd start around 4mmBTDC and work from there.
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scrimshady · Derestricted Danger Joined: 01 Nov 2009 Karma :

thanks for that. iwill give it a try...

Blue_SV650S · World Chat Champion Joined: 27 Nov 2008 Karma :

I have a haynes and the points gap is stated as 0.3-0.4mm.

Set the points gap to that and then align the index mark on the points backplate to the index mark on the engine (they are fairly obvious markers).

That obviously only sets it back to factory standard. The better way to do it is to take the rotor plate off (honda cover down below) and reveal the flywheel. On it there will be some markings and an index on the casing. the points need to be just opening as the 'F' mark passes the index. I'd then mark the backplate to have a baseline to work from.

If you are using high octane fuel, you can advance the timing from there - the actual value will need experiment or further research, but I'd try 5deg to start with (that is 10deg at the points)).

But that is for you to fiddle with ... at least you now know how to set back to standard Thumbs Up

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scrimshady · Derestricted Danger Joined: 01 Nov 2009 Karma :

thanks for all your help. looks like i need to get the to do it all properly. does nayone know where i can get a manual from??

Hoffy · Trackday Trickster Joined: 15 Jan 2006 Karma :

Halfrauds ? or contact pyro4lyfe , he had my old CB125s and also the manual. I know he sold the bike, he might still have the manual though Wink

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Hoffy · Trackday Trickster Joined: 15 Jan 2006 Karma :

Halfrauds ? or contact pyro4lyfe , he had my old CB125s and also the manual. I know he sold the bike, he might still have the manual though Wink

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Plagued by 1980s Suzuki 2 strokes !

Blue_SV650S · World Chat Champion Joined: 27 Nov 2008 Karma :

https://www.bikechatforums.com/viewtopic.php?t=140295

https://www.megaupload.com/?d=1HR7J1TE
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The purpose of life is to fight maturity.

scrimshady · Derestricted Danger Joined: 01 Nov 2009 Karma :

thanks for all your help.
so if i set the points to start to open about 4mm BTDC that should do it??
i havent got a flywheel so i cant use the marks on there but i have been thinking,, the piston has been replaced with a non standard one so all the marks wouldnt be of use anyway ..woud they???
thanks all

Blue_SV650S · World Chat Champion Joined: 27 Nov 2008 Karma :

scrimshady · Derestricted Danger Joined: 01 Nov 2009 Karma :

i have a various dial guages for finding TDC, i use it for deisels engine for my company. i dont have any flywheel in the side casing of the engine so i cant align the F mark.
you said about the marks on the points backing plate????? i can see the mark on the plate but not on the casing.... do you have a picture of what i am looking for????
i am with you on setting it back to stock first but like i said i dont have the marks to do that.
Thumbs Up

Blue_SV650S · World Chat Champion Joined: 27 Nov 2008 Karma :

scrimshady · Derestricted Danger Joined: 01 Nov 2009 Karma :

thanks for that. not running total loss, they took it out because they dont need generators in there and it lightens it a little...
makes sense to take it out but wish i got it wheni bought the engine.. thanks for the pic all makes sense now.

Blue_SV650S · World Chat Champion Joined: 27 Nov 2008 Karma :

scrimshady · Derestricted Danger Joined: 01 Nov 2009 Karma :

we run them on a charges battery then when it goes flat we change it for a fresh one

Blue_SV650S · World Chat Champion Joined: 27 Nov 2008 Karma :

scrimshady · Derestricted Danger Joined: 01 Nov 2009 Karma :

aahhhhhh... total loss on speedway is the oil system...

this is my first bike with this system with a battery and its already doing my head in.
so if i set my points to the timing mark on the backing plate then that stock and i cand advance or retard it from the points backing plate???
thanks for your help.

Blue_SV650S · World Chat Champion Joined: 27 Nov 2008 Karma :

scrimshady · Derestricted Danger Joined: 01 Nov 2009 Karma :

the bike is a bit of a make up but all with late 70s parts.... they are brilliant to ride without all the expense of a 500cc.
pm me you emaill address and i will send you some pics, we have a facbook page aswell with some pics and videos, type in lydd speedway and it will come up.
cheers mate.

Blue_SV650S · World Chat Champion Joined: 27 Nov 2008 Karma :