Honda-SOHC

Thanks for the replies Hairy and Mike.
Yes the engine and gearbox has been stripped and checked but the primary chain looked ok so was not replaced and the carbs have been synchronised to less than 1 inch Hg.
 The noise I'm worried about is more of a whining noise (I didn't make that clear originally) like 2 gears not meshing correctly and i think it's coming from the clutch side.
The clunky sound at idle may well be primary chain noise but I don't think that's anything to be concerned about at this stage.

I haven't tried running it downhill without the engine running as Mike suggests but will at next opportunity that's a very good point.

That makes sense and as you say it is a bit of a deterrent, I was just a bit worried that the MOT man might spot it and fail me on safety grounds. I'll just have to hope for the best.

Thanks a lot for that.

When putting in the wiring on the 400 I had a spare green wire from the RH handlebar switch which terminated under the tank along with all other connectors. In thinking that it must be an earth I put a ring tag on it  and connected it to the frame.

When I came to check the ignition timing I found that there was no power to the coils and after tracing the circuit through I found that power for the coils comes directly from the kill switch via black/white wire and should be powered by a black to the live side of the switch.

On my kill switch I have a black/white wire and a green which is the one that I  put to earth. This is clearly wrong as the green wire needs to be live when the ignition switch is on in order to feed the coils via the black/white.

 I thought it would be a simple matter of changing the green wire to live and this worked fine except that now RUN is either of the two stop positions and STOP is in the run position.
 The wires  to the kill switch are both in sleeving and look original but obviously don't match the wiring diagram.

Has anyone come across the same situation? I can only think that the switch has been replaced at some time with one from a different bike. OR AM I MISSING THE OBVIOUS !!!!!

Ran it today and just had a little potter down the road before it started raining but never got out of second gear. It seems to run ok and picks up from idle without a flat spot, but as it doesn't have MOT or Insurance yet and 'plod' lives a few doors away I can't give it a real run. Best of all 'no drips'.

I got the 400-4 engine running last after week after a complete overhaul. I hooked it up to a small temporary fuel tank and all seemed ok initially, it ran on all cylinders although idling was a bit lumpy, however after playing with the air bleeds I settled 2 turns out and went on to balance them with vacuum gauges and it didn't take much adjustment to get a good balance.
After this the engine ran much smoother although there seemed to be a bit of a flat spot on the transition from idle jet to main. I checked the ignition timing with a strobotorch and decided to leave it at that until I get it on the road.
However two of the carburettors started to drip fuel which was really annoying as I was careful to set the float levels at 22mm so I decided to remove the carb's in order to re-check the float levels but after reading some older posts on this forum regarding carb' problems I decided that the floats might not all have the same buoyancy after 40 years so I made a set of adapters to fit into the bowl drains with short clear plastic tubes in order to see the actual fuel level in each bowl.
It was found that on the 2 which were dripping from the drains the level gradually rose whilst the others remained constant and therefore the problem was leaking needle valves, this turned out to be tiny pieces of cotton fluff where I had used a cotton cloth to wipe out the temporary tank and hadn't fitted a filter into the line. Lesson learned, and a quick trip to the local garage for a 2 quid in line filter should resolve the problem.
After checking all the needle valve were free of dirt I re-filled the bowls and this time they were remarkably consistent and settled at about 3mm below the joint so after leaving them for a couple of hours I am satisfied that all is well and I can now re-fit them and prepare for the MOT test.

What I take from this is that it's easy to blame faulty components for some of our problems but in my case it was a very small almost invisible foreign bodies that were to blame.
 

First time I had used it, but all very straightforward.

Thanks Oddjob. I'm not in any real hurry lots to do and I'm away all next week, please let me know if you manage to come up with one.

Also thanks to Chris400

Does anyone have a spare plug from the 400-4 oil gallery points side. Its item 72 in the parts book. Called 'cap B, oil path
Mine had been brutalised by a PO. I managed to get it out but its pretty much destroyed and may leak.