Honda CB750K5 Restoration by Royhall

[Johnny4428]

Lovely looking bike Roy great work! Came from the same place as mine.

[davidcumbria]

Congratulations Roy that’s a beauty 👍👏👏👏

[AshimotoK0]

WOW!  that looks fantastic Roy

[Trigger]

Stunning build Roy. Looks like the same colour as my old K6. Did the bike not come with a original K5, K6 fuel tank ?

Thanks for that Trig. That's the tank it came with. Didn't notice until it was painted that it was an earlier item with the tap on the wrong side. K0/K1 maybe?

Edit.
Just checked photos of all models and you are of course correct Trig that only K5/K6 had the tap on the left. First time I have checked that as it was already painted so it was going on whatever. It's not 100% correct anyway, although the Boyer ignition dates back to when the bike was new so probably counts as classic (digital classic).

The fuel tap was on the right for the K0, K1, K2 up to 1973 in UK. The tap was moved to the right for the K3, K4 and still using tap 16950 and then went on to the bolt on tap K5, K6.

It must be a pain in the butt Roy as, your idle adjustment must be sitting right on the back of the fuel tap. When they moved the tap from right to left, they also moved the idle adjustment to the opposite side on the carbs.

[royhall]

That's very interesting Trig, my idle adjustment is conveniently on the left. Meant to be I guess. It's definitely not as it left the factory.

[royhall]

Just a quick update on the K5. It's been sat unused for over a year due to having way too many bikes to keep running them all. Have kept this one back for a retirement project, and that time has now arrived. Yesterday I got it out of the garage and gave it a good clean and changed the petrol for fresh. Battery was good as it has been kept on an optimiser. The good old girl fired into life first time which is unbelievable.. So took it out for a 50 mile run this morning, bearing in mind it's only had a few runs around the block before. Earlier in this post is a question about the battery charging or not and we established that it was charging. Unfortunately after the run it appears that the battery is not charging, so that's the first job to sort. Will have to go back over the advice given at the time and see if I can locate the fault. The other things that became clear this morning is the squealing front brake (what's the cure for that), plus the normal clutch rattle in neutral. Other than those three things it ran great, light clutch and perfect gear change (bit of a gearbox whine in third gear). Quite pleased overall.

[Skoti]

Just a quick update on the K5. It's been sat unused for over a year due to having way too many bikes to keep running them all. Have kept this one back for a retirement project, and that time has now arrived. Yesterday I got it out of the garage and gave it a good clean and changed the petrol for fresh. Battery was good as it has been kept on an optimiser. The good old girl fired into life first time which is unbelievable.. So took it out for a 50 mile run this morning, bearing in mind it's only had a few runs around the block before. Earlier in this post is a question about the battery charging or not and we established that it was charging. Unfortunately after the run it appears that the battery is not charging, so that's the first job to sort. Will have to go back over the advice given at the time and see if I can locate the fault. The other things that became clear this morning is the squealing front brake (what's the cure for that), plus the normal clutch rattle in neutral. Other than those three things it ran great, light clutch and perfect gear change (bit of a gearbox whine in third gear). Quite pleased overall.

Good to learn you've finally got it on the road, hopefully you'll iron out the teething problems and have a fun summer.

Somebody will be along shortly to advise on your charging problem no doubt, but as regards your brake squeal EBC FA13V sintered pads sorted it for me.


ATB

Skoti 

[royhall]

Cheers Skoti will give them a go. Cant be doing with all the people turning round to see what the noise is.

[royhall]

Tested the charging on the K5 this morning. With the engine running I jumped the white (disconnected) field coil wire to battery positive and it immediately showed 14V at the battery terminals. So the charging/rectifier side is okay. I checked the black cable and it shows battery voltage with the ignition on. Now's the bit I have no idea how to do. How do I check the regulator side? Cheers.

[K2-K6]

There's a comprehensive (with pictures  ) walk through in early 750 Honda manual Roy.

Should be available in Ash's stash, but if not I can copy and post picture for you. It'll be rudimentary but should be legible/functional.

Let us know if needed.

[royhall]

Thanks for that. Would the test be the same for the regulator side of a modern reg/rec that is fitted to mine. I noticed this problem because I keep all my bikes on optimisers. Usually after a run on the other bikes (all same optimisers and batteries) it takes about 10 minutes for the optimiser to run through it's thing and top out the battery. On the K5 it took over three hours to recharge after a 50 mile run pointing to failure of the charging system. As stated earlier, on jumping the field coil wire (white) from the battery it then gave a good charge at 14V, the black from ignition on gave just under full battery voltage. To my mind that provers the charging circuit and the rectifier side of the reg/rec and points to failure of the regulator side. Am I correct in this. Cheers Roy.

[Bryanj]

It sounds like it to me Roy.
The black wire into reg should be within 0.5v or less of battery voltage with ignition on, i would turn kill switch off for this.

Then check again with engine running.

More than that reduction says bad connection at one or more on the many contacts between battery positive and black at reg, usually ign switch or one of the bullets.

Then try testing voltage on white wire out of reg, this should vary from low volts if battery charged to full battery volts as battery looses charge NOTE NOT 12V BUT BATTERY VOLTS

Then as you say if you jumper the white to battery pos this bypasses the reg and the battery voltage should keep going up and up-------not a good idea for extended use.

There used to be a 500 about called gentlemans rocket or something like that, i think Steve D had it for a while and the owner/builder designed his own breadboard electronic reg and posted the diagram which i did have but its gone in one of the many puter crashes over the years.

Hope that helps

[royhall]

Thanks Bryan. With ignition on and kill switch off it is 0.4 V lower than the battery at the black wire. With ignition on the white wire is putting out 0.22V. Does that sound right. Battery is a fully charged AGM.

[Bryanj]

If the voltage on white wire goes up as the battery discharges then yes all is ok BUT i suspect that the white wire voltage will stay low which means the regulator part has failed

[royhall]

Yes I agree. Unfortunately I need a discharged battery to test that, I shall ask around. Failing that I have a spare battery that I can stick a bulb on until it drops below 12v.