Honda-SOHC

Obviously no options with std piston to change compression specifications.

It is though a consideration, in that a camshaft with extended overlap /duration will lower the effective compression ratio, all things being equal.

The geometric ratio of combustion chamber volume to swept volume remains the same, but with valve opening moved then the active ratio will usually be reduced (assuming longer opening etc) which will reduce the torque at lower rpm.

The changes effectively push the torque peak upward to occur a raised rpm point but looses combustion effectiveness at the lower speeds.
It gives something of a " false" gain, in that the brake horse power is a calculation involving rpm as a factor in projecting work rate.

Net effect is that you have to rev it to get to torque peak by using lowered gearing, seems more dramatic peak as the reduced torque in low rpm range has greater contrast to the high rev performance.

Itll be faster by the effect of fitting in more power stroke to a measured distance that before (lower gearing, higher revs) but at the same low range rpm it will be correspondingly slower from less real torque. In other words, you've always got to ride it at revs to see an increase in power.

Lifting the static compression ratio is a way of compensation to avoid some of this.

You'd probably need a dry build though to assess piston clearance to head and that to valves at the cam duration specification used.

Yes, Nigel is correct.

Probably worthwhile looking through them again. Youjust gain more experience in doing this, a very pedantic/ critical eye in evaluation of them will often turn up something that may be causing an issue.

They are just plain fiddly to get right if there's any impairment etc, that's carburettor in general, even for experienced practitioners of the art. Can go round and round until finally sorting them. A friend runs a garden machinery business and hates the run around that inevitably comes with sorting out simple problems.

The bench sync is absolutely fine to run the engine without problem from tbat aspect. It has the major advantage of knowing they are mechanically in synchronization and helps in diagnosis of other faults if you don't try and sync them after installation.

The carb rack should allow for adjustment of the major rpm stop screw to fully lower the slides after setting them (if you use the drill method on here) which ensures that the slides have the capability of full restriction once set to parity.

You can then connect them to cables, without installing on engine, to ensure the cables definitely don't conflict with that function.  Emphattge slides should sit at rest on that master tickover screw stop, and nothing else should impede that operation.

Adjustment of the airscrew idle function when running is then where the attention should be. The suggested opening point 1 1/2etc should be seen as competent start point, from which you need to test what exactly is needed.  That method is in the Honda manual officially to instruct you.

Effectively, it gets you to adjust leaner until that cylinder falters, this  is the air fuel mixture just going past its technical ideal of 14.7 to one ratio. Thats pertinent to the hardware in place AND the fuel in use at the elevation you are working.
Then it requires you to make it richer by adjustment to bring a 100 rpm drop (multimeter with frequency will register this if you've got one) to bring that carburettor and cylinder to ideal operating point.
Later Honda manual detail recording that absolute setting in service notes as baseline for the operation. It can be different for each of the for cylinders. If you don't get something competently in range at that point, this suggests something else maybe wrong, or some impairment is still there withing that idle circuit.

Yes to special, in tbat they were homologation issue often. Production based race series dictated limited modifications to factory production line vehicles and usually a minimum number available for public sale. These type of "special" vehicles were the result, with enhanced elements that would be useful to racing modifications, whether used on road vehicle or not.

Quite valuable now as they are the desirable limited run specification.  Probably in the region of £50,000 upward for one of those if genuine manufacture with traceable records etc.

13" wheels do look quite small now against general modern stuff. F1 was still on 13" until 2021 though, with small rim and big tire being considerably lighter than the current 18" they've moved to.

I've watched that one recently, interesting outcome and he's quite "investigative" showing his steps etc throughout. Could be skew on cam grind or some rock in rocker arm, or previous wear to give some taper in follower pad. Probably worthwhile using engineers blue to asses wear pattern in those cases. Some camshaft have the lobe peak deliberately ground "skew" to rotate the follower/bucket in distribution of wear pattern between the component.

Have to fast forward through some waffle, he does say that to himself as criticism some times "stop waffling Jim" but leaves you to zip through them yourself to things you find important.

Recently watched a plug re thread in situ as he approaches it differently to other, more common suggestions. Worthwhile watching that one too if you're contemplating the same.

The missing valve spring support washer, as already noted above, won't change how far it moves but, it will decrease spring preload on the valve with the possibility of valve bounce at high rpm.

It may have been affected by that and just touched a piston, that's a possibility. Anyway, a new valve should sort it.

You can check a valve for being straight by just rolling if on stem and head periphery on a piece of glass to see of the mid part of the stem runs true.

A cooker hob, if glass, makes an easy "surface plate" to roll it across. Dont get caught by owner of surface plate though 

Are correct springs still available?  I'm not sure I understand everything you've said there K2-K6

Supply, as Bryan notes, can't see any springs available.

Apologies for confusion.

To clarify;- the molded springs currently fitted should have nil effect on the idle issue you are chasing. They effectively (by tightening) make the retarded position more positive which would only enhance stability and repeatability at the tickover rpm. I'd dismiss them from suspect for this cause.

Two things to check though. Is the A/R mechanical not impeded by friction itself, all appears to rotate freely if you exhamine it ? And, have you checked that the static timing is definitely at the F mark accurately to make sure its getting that aspect right ?

Shortening springs is not to delay curve but to stop erratic advance at tickover, or at least thats the way i see it

Yes, I can see why they've tried to correct if it's obviously slack or showing advance down below about 1500 rpm but not considering it'll increase the spring rate, which will have more influence on delaying the onset of advance.