1967 CB450K0 Black Bomber Rebuild - By Royhall

[royhall]

Hi Mo.

Yes they are a 500T carb experiment that so far is not going too well. Hopefully removing the air cut off valves will cure the problem. Just re-looking at the advice that Ash sought on Facebook, and I'm not sure I agree with what was said. They mentioned that the cut off valves introduce extra air on the over-run to stop exhaust popping, that's not my understanding. I'm fairly sure they introduce extra petrol to enrich the mixture past the point of ignition so it cant burn in the exhaust header. Hence my running rich problem, and why I'm removing them. Will find out once the jobs done and the weather allows a run out.

On the other point about the tank. Bombers don't have a cross pipe to level the fuel, they just use the braking and accelerating of the bike to slosh the fuel to the other side. Typical 60's Honda.

[mo goldie]

Hi Roy

Thanks for that I thought having that blanked off bolt in the tank was it should have had a crossover pipe of some sort to get the fuel over the other side of the Tank where the Tap is,

oh I got some carb kits from wemoto and have put them in so hope they ok as some things did look different to the old ones, and the old ones things like the needles were bent so did Not know where to go to get some originals ones...... don't know how she will run with the new ones as they had needle clips so I have put them on the middle position.

Ashley

did get back to me about the rectifier and said the one I put on the link was good to use.... how all go`s well with that too....can`t try it all out till my cases come back from the sprayer.     

[AshimotoK0]

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Hi Mo.

Yes they are a 500T carb experiment that so far is not going too well. Hopefully removing the air cut off valves will cure the problem. Just re-looking at the advice that Ash sought on Facebook, and I'm not sure I agree with what was said. They mentioned that the cut off valves introduce extra air on the over-run to stop exhaust popping, that's not my understanding. I'm fairly sure they introduce extra petrol to enrich the mixture past the point of ignition so it cant burn in the exhaust header. Hence my running rich problem, and why I'm removing them. Will find out once the jobs done and the weather allows a run out.

This is what Cycle World said about the carbs in 1975 (plus the whole article if anyone is interested in the CB500T itself).


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[royhall]

Thanks Ash. According to that article the removal of the air cut off valves shouldn't make any difference to the rich mixture problem the bikes suffering as it only occurs over 4000 rpm. At least I was understanding it's operation correctly. The removal of the diaphragm housings are done now and I am about to check the float heights are correct then I can reassemble the bike and test what has changed. If nothing has changed, I may end up looking for some decent 450 carbs after all.

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[royhall]

Just been studying the schematic of the diaphragm housing and my plan to remove and blank the ports wont work. Without the housing the slow running circuit will not flow air. It appears that the housing will have to go back on with the diaphragm in place to hold the spring plate open, but blocking the vacuum tube will keep the system locked in that position. Either that or a much more powerful spring to prevent the diaphragm moving. This is all too complex to be worthwhile so I am on the lookout for a good pair of CB450 carbs. Shouldn't have tried this in the first place really, I would rather the bike was ready for spring than be in the garage with some experimental nonsense going on. Plus running as rich as it has been will eventually trash the engine.

Ash. Putting that aluminium disk in wont work either as the plate valve behind will stay in the over-run position and be horribly over rich all the time. You just need to blank the small port above that disk with a piece of rubber the same diameter as the o-ring, then reassemble the valve as stock with the diaphragm in place. That's job done.

[AshimotoK0]

Must admit ...not honestly  studied it in any depth Roy .. I just went on what the FB gurus told me    ....  My own 1st instinct was to simply fit a spring that was far too stiff for the rubber diaphragm to deflect enough under the high vacuum to open the cut-off  valve. This wasn't really an option though because the diaphragms on my 500T carbs were not in particularly good nick and I didn't want to spend loads of money on those carbs as I suspected they might never get fitted anyway. Never heard since if they worked OK or not.

Mick Taylor on here got hold of a 2.5k mile only '67 Bomber a few years back and after he balanced the carbs with some flow-meters, he had that bike ran beautifully if I remember correctly. So the 14C carbs can be made to operate nicely, particularly with the Honda UK mod kit that I sold you to cure the 4k flat spot.

[royhall]

I have got a set of 450 carbs on the way (not sure which model will see when they arrive) so I am going to strip all the new bits back out of the 500 units to reuse. I will order two genuine seal kits from DSS at some point. Also got an ultrasonic bath coming so I can save having to pay people to do them. Cheeky to ask, but are you still doing your own zinc plating as I could do with some small carb bits doing.

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[AshimotoK0]

I have got a set of 450 carbs on the way (not sure which model will see when they arrive) so I am going to strip all the new bits back out of the 500 units to reuse. I will order two genuine seal kits from DSS at some point. Also got an ultrasonic bath coming so I can save having to pay people to do them. Cheeky to ask, but are you still doing your own zinc plating as I could do with some small carb bits doing.

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Think I have a load of 450 carb bits I had replated at Allenchrome .. may have spares ... I will check.

[royhall]

Thanks Ash that would be awesome.

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[royhall]

The replacement 450 carbs have arrived from Germany and don't look in too bad a condition. They are very dirty but should clean up okay. I will give them a good manual cleaning first with a paint brush and cleaner, then a good soak in the ultrasonic should do the trick. Ash, did you find those replated parts that I could buy off you?

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The new carbs are 14H models originally off a 450K1. After a good bit of checking there are a fairly large number of different 450K carbs all with slightly differing internals (and externals). So I have ordered some service kits from 4into1 in the States that are made specifically for the 14H. Failing that I will have no idea if the parts I'm fitting are correct. I am done with experimenting with these carbs and just want a good standard set. I was a bit worried about the right hand carb as the H next to the 14 has been removed with some sort of gouge. But after much checking of 14H pictures on the internet, I am happy that it is correct. There are also other things that indicate they are off the same bike as both carb vacuum bowls have the same rusty cap head screws. Will see how they come up.

[AshimotoK0]

Still need to look Roy.

I would be inclined to fit the genuine Keihin brass-ware I sold you. Lot of bad reports about pattern parts , particularly needles.

[royhall]

Weren't those needles specific for the K0 carbs Ash. The K0 carbs are very different to the K1 to K4 carbs. The 4into1 kits appear to have good reviews that's why I chose them over the DSS kits.

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[AshimotoK0]

Possibly .. theory was if people use those brass parts on 500T  carbs on Bomber K0s then the same for K1 carbs. What's wrong with the parts in the K1 carbs then?

[royhall]

To be honest these carbs are so easy to get on and off I think I will give the kits a chance first. I can always use the other parts if things don't go so well. I will be fitting the springs on the pistons though.

Ash, don't know if it matters but those service parts are for 14C carbs. I am assuming the later carbs already came with the modified parts but I have no way of checking that. I have options here, I will try the kits first and if that's problematic I will fit the genuine bits, then I could clean and try the bits that are in the carbs now. The last option is not a good one as I have no idea if they have been messed with in the past.
I still haven't read anywhere about the vacuum springs, looks like a mod that not many do.

[mo goldie]

Hi Roy and Ashley

got all my cases back and now on looks great.... just got her up and running but Not to well, both carbs set up of the bike and then put on and set mix screws 1 1/2 out runs but when you rev it up and revs come down it hangs around the 2.000 mark then come down to settle around the 1,000 to 1,200 mark............. have you got any Ideas what it might be..... oh I have set it up with a colortune and got it a lovely blue with the mix screws both out around the 1 turn out mark Now.

also Not sure if its charging changing the subject as battery go`s flat after a few go`s on the starter Button..... I Know its Not the battery as that has been checked out ............. so Not sure about any probs with the Rectifier or maybe the stator .... don't Know how to check them out Not up on electrics to be Honest  :'(

Cheers

Mo