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Author Topic: '73 CB250 - Doing it right this time round.  (Read 85533 times)

Offline scott_jangers

  • Posts: 42
Re: '73 CB250 - Doing it right this time round.
« Reply #585 on: May 17, 2017, 03:02:07 »
Hey Green199, I've got my hands on a K4 with a really skanky pair of 725b carbs. I'm going to have to clean them up pretty thoroughly and order a pair of rebuild kits from Silvers but i'm also missing the air cleaners. The plans to run them with something aftermarket, so was wondering how you got on with jetting and tuning with your stack exhaust combo? Are you running the stock jet sizes?

Plus, seen your bike over at the bikes shed forum too, but bit quiet over there of late. Good luck getting it ready for next weekend. I'll come over and say hi...!

Offline Green199

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Re: '73 CB250 - Doing it right this time round.
« Reply #586 on: May 17, 2017, 06:03:02 »
Hi mate, yeah come and introduce yourself at the show!

At the minute I still just have a few things left to do with the loom before going for some proper runs to check the tuning. I have stock jetting and she idles ok, but no proper distance under power yet. I'll let you know when she's finished up (hopefully before the show! haha).
1973 CB250 'Doing it right this time round' - http://www.dotheton.com/forum/index.php?topic=36795.0

Offline scott_jangers

  • Posts: 42
Re: '73 CB250 - Doing it right this time round.
« Reply #587 on: May 17, 2017, 10:45:22 »
Seems to be very little info on anything 250. I guess it wasn't big in the States as there's loads more for the 350. Maybe brits are just restoring them and not customising. Mine is missing side covers, air filters and the filter housings, and it'll be hard and expensive to track them down, so it feels like a perfect donor for a custom build!

At present I'm gonna do the same as you, but if mods look hard to do with the 725b, I may have to save up for the mikuni's.

Anyway, I find having a deadline to work to sometimes energises you to get stuff done, so sure you'll get it all sorted in time. Chuffed for you that they wisely saw fit to include a true shed build in the show. See you then!

Offline Green199

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Re: '73 CB250 - Doing it right this time round.
« Reply #588 on: May 19, 2017, 07:39:45 »
Seems to be very little info on anything 250. I guess it wasn't big in the States as there's loads more for the 350. Maybe brits are just restoring them and not customising. Mine is missing side covers, air filters and the filter housings, and it'll be hard and expensive to track them down, so it feels like a perfect donor for a custom build!

At present I'm gonna do the same as you, but if mods look hard to do with the 725b, I may have to save up for the mikuni's.

Anyway, I find having a deadline to work to sometimes energises you to get stuff done, so sure you'll get it all sorted in time. Chuffed for you that they wisely saw fit to include a true shed build in the show. See you then!

It's also tough finding information about the 725B's. I even contacted David Silver and they just told me that the specs 'should' be the same as other models found on the 250, like the 722A or I think 726?? Would have loved to put some flatslides on to aid in tuning etc. Maybe in future.

Was exactly the same boat as mine. Would have liked to restore it but it was already a hack job to begin with so went down this route.

I managed to basically complete the wiring loom last night, so on Saturday I'll wrap and install it, and hopefully get a nice video to show.
1973 CB250 'Doing it right this time round' - http://www.dotheton.com/forum/index.php?topic=36795.0

Offline scott_jangers

  • Posts: 42
Re: '73 CB250 - Doing it right this time round.
« Reply #589 on: May 21, 2017, 03:49:06 »
Just curious but did you ever set the float levels? The Clymer and Haynes manuals both have 19mm but I've read a couple of threads where the preference has been 25 or 26mm.

Good luck with the loom and getting it started  :)

Offline Green199

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Re: '73 CB250 - Doing it right this time round.
« Reply #590 on: May 21, 2017, 05:25:42 »
Yeah, I went for 26mm. Got the bike running yesterday (video to come soon), and noticed a slight leak from both overflows, so either the float height is slightly out or my soldering up of the crack in the emulsion tube wasn't perfect. I tested it previously with compressed air so i'm thinking its more the float levels.

I believe 19mm is for the bowls which use the black square floats, and 25-26mm (or even 21mm i've seen somewhere) are for the round brass floats, depending on carb model.
1973 CB250 'Doing it right this time round' - http://www.dotheton.com/forum/index.php?topic=36795.0

Offline Green199

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Re: '73 CB250 - Doing it right this time round.
« Reply #591 on: May 21, 2017, 06:17:30 »
Here's a little video of her up and running yesterday. Still got a bit of tweaking to do with the carbs and I've got a bit of tappet noise so I need to redo the valve clearances.




Also, here's a little overview of the wiring. The ignition switch sends power to the coils, and to an 'on/off' switch in the headlight bucket. This is because I want to maximise the amount of juice from the battery to create a spark, so all other electrical systems receive no power until it's up and running.

The switch then turn on all the other lighting systems etc. The voltmeter is included so I can keep an eye on the voltage going back to the battery to check I don't overcharge it as its Lithium-ion. The rear brake light switch just has a loose connection which is why it didn't light in the video. It's now been sorted.



Just a few minor things to do and shes finally finished!  ;D
1973 CB250 'Doing it right this time round' - http://www.dotheton.com/forum/index.php?topic=36795.0