1967 CB450K0 Black Bomber Rebuild - By Royhall

[Oddjob]

498

[royhall]

You are correct. Unfortunately I have tried float heights both ways, it makes no difference to the running. Possibly a problem using 500 carbs on a 450, although it has genuine 450 needles and jets.

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[McCabe-Thiele (Ted)]

The float height is measured from the join between the bowl and the body so if you reduce the level it  closes off the fuel the float sits higher not lower, higher means more fuel in the bowl, of course I may be on the road to senility 😀😀

I'm talking about the height of the fuel in the bowl so we are at cross purposes with the same outcome.

[K2-K6]

Are they carbs with coil spring above slide ?

If so, a weaker spring will give more air to same throttle opening that will draw less fuel under same rpm. It'll trim it to run leaner even with the same jet and  needle.

There may be an alternative ftom another carb to fit and try.

[AshimotoK0]

Those 500T carbs originally had air cut-off mechanisms on them Roy. Did you remove them and make blanking plates for the diaphragms and block holes etc so that the whole accelerator pump function is blocked off? I did this to a set of carbs for Honda guru Bernie Saunders last year and also donated the carbs themselves. He was feeling really low at the time as his wife had passed away and a customer had lumbered him with a problematic CB450K0 to fix, which was also getting him down. I tapped  balls of solder to block the surplus holes and made really close fitting thin alloy plates to replace the diaphragms. I got the ultra thin alloy sheet  from the outer cover of an old laptop CD drive.

Pretty sure I got advice off Facebook 450 group on this too ... will check.

https://www.vintagehondatwins.com/forums/index.php?threads/cb500t-carbs-on-a-bomber-k0.4360/

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[royhall]

Thanks for that Ash. My carbs were done by Matt Harper who cannot now remember what he did. At the time he said he deactivated the valves whatever that means. I had some new genuine 450 carb parts from you that he fitted but don't know if he changed the mixture screws for 450 type. According to the site you sent me the 450 screws don't fit correctly. I don't suppose you can remember what parts you sent me Ash, I know it's years ago. I cant recall what parts there were at all. I may be best just looking for some decent 450 carbs and rebuild those. Do the 500 carbs have springs on the diaphragms, I seem to remember you sending me a pair of those. Before I go any further I think I will have a scan through the photos, it may help.

[royhall]

I may have discovered something in the photo's. These are some of the new parts that I got from Ash. They are mixture screws for a 450 that don't fit correctly in 500 carbs. I have a horrible feeling they were fitted at the carb refurb. Could be the smoking gun. That would be nice as they are easy to change. It would also explain why moving the mixture screws appears to make no difference.

Long search in a cold damp lockup coming my way. The old 500T carb parts are in there somewhere. If I can find them I can take one out of the bike to compare.

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[AshimotoK0]

The kit I would have sold you Roy was the late 1960's kit issued by Honda UK in Nottingham's Service department to fix a flat spot on the Keihin 14C  carbs and this included a return spring for the piston.

It didn't include those air screws and the airscrew on the 500T is totally different from the original 450K0 one.

Please see pics of the Honda UK bulletin and the parts I would have sold you.

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[royhall]

Morning Ash. Blimey you have a good memory. I must have got the screws from somewhere else not knowing at the time that they wouldn't work. This is definitely the first investigation into what's happening. I will still have the old parts in the lockup, question is where. If all else fails Silvers do a kit for the 500 for £20.

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[AshimotoK0]

Here is the American Honda Bulletin and the parts

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[royhall]

Ash. When you did the 500 carbs for that guy what internals did you use. Were they the standard 500 jets and needles or did you swap in the 450 bits just leaving the mixture screws as 500. Did the guy ever get back to you to say how it was running.

[AshimotoK0]

Ash. When you did the 500 carbs for that guy what internals did you use. Were they the standard 500 jets and needles or did you swap in the 450 bits just leaving the mixture screws as 500. Did the guy ever get back to you to say how it was running.

I fitted the NOS parts from the same kit I sold you and 130 main jets. But obviously the air screws were different style to the K0 ones .. so I cleaned up the original 500T ones, and fitted a new(tiny) O-ring.
Annoyingly, after considerable effort I suspect he has never tried them. I really must call him.  I went to all of the effort because his friends rallied round  told me he was feeling really low and badgered me to put a set of carbs together.

[royhall]

That's annoying Ash. If he doesn't want them I can give them a new home.

[royhall]

Finally got around to the Bomber carb job. Started by stripping the diaphragm housing off the side of the left hand carb as that one can be done with the carb in place. As the carb man said he had deactivated the unit I was a bit surprised at what was in there. It was a fully functioning valve complete with brand new diaphragm.

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The silver centre part of the casting is actually some sort of valve that the diaphragm rod presses against. After a bit of cogitation I decided to leave the diaphragm housing alone. So instead of trying to randomly block off holes and make a mess, I decided to make an aluminium plate to cover the three ports and just leave the casting off. This has the added benefit of being easily reversed should needs arise. It also makes the carb look a bit more like a 450 item.

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That's the easy side done, the right hand side needs the carb removing to get at it as the diaphragm housing is on the inside between the carbs. That's a job for another day.

[mo goldie]

Hi Roy

I thought the Bomber did Not have them ? thought that they were the later Carbs ?

Oh can I ask might be a silly thing but how do the petrol Tank feed each side of it as seems to leave loads in the left side of it when the right is empty ? there is a blanked off bolt in the left side but how do that link to the right side ? have you got any pictures to show how please. also still need some help on what rectifier to use as well ?

Cheers Mo

Oh just seen the rest of the thread..did Not Know you were trying out 500T carbs sorry Roy.......but help with the other would be great