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Help/ ideas please

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K2-K6:
Thinking about this last night and to pick up on those resistance readings.

From my view it looks like with that 17ohm reading on 4 and because that coil is at the same time firing cylinder 1 it could result in the following effect; I know when a plug is fired under pressure ( compression stroke) it has an effective increase in resistance up until the point where ionisation occurs ( the start of the spark jumping across the plug gap) so if when no4 is required to fire and the wasted spark accompanying it in no1 is under no cylinder pressure, then the combined difference in resistance would lead to most of the coil energy effectively exiting from the combined coil down to no1 plug. This would lead to a very compromised ignition of the no4 cylinder, and to the effects you have experienced. Perhaps Ash, with his electronics hat on, may offer a more technical view of this.

The question about the idle adjust screw (raised on here a fee weeks ago with reference to a thread on the USA site) I believe is as follows; the idle air passage when the throttle slides are closed will be under vacuum, this will pull fuel up through the idle jet into main air stream. The air screw if backed out will allow that vacuum to pull more air from front side of carb and LESS fuel up from the float chambers. If you wind the screw in it will restrict the air bleeding into the passage from carb front side, causing the vacuum to assert greater pull via the fuel jet, so INCREASING fuel delivery.
If you get out of range with the air screw it would indicate you have a idle jet too small or large to work with the setup you have (not the case in your bike) but for those with modifications perhaps.
I think this subject causes debates because people think of throttle slide which as the needle jet moves with the air slide, then as you increase air it also increases fuel at the same time. The idle circuit is a bit arse about face in that you have a fixed vacuum from the engine tickover drawing through the idle passage which uses the air screw as a proportioning valve to bias that pull toward or away from the fuel jet.if that makes sense.

After all that going round in my head I had to go and think of Francoise Hardy (poster girl of CB750) to be able to get some sleep. ;)

AshimotoK0:
Primaries should be around 4.5 Ohms Secondaries 15k (15,000) Ohms for original Tec coils. You must use a decent multimeter on low Ohms range for primaries though. Main thing is to connect meter to secondaries and wiggle the HT wire to make sure inner conductor is not fractured.  On most of my 10 resto's I will be replacing the HT leads, as in my write-up. US bikes (like yours) are the worst for suffering from HT insulation hardening and internal conductor core fatigue. Primaries are very reliable and  not usually the cause of any problems.

RGP750:
Thanks you two.
Results look good in the bench, I have all 4 running now after fitting new NGK plug caps.
Ash the coils are new ones i got from the US as my originals were hardened as you say and i assume shot ,at least the ht leads.
as no OHMS reading across the leads.
I have backed out the mixture screws  1/4 turn. The US site is where the screw in or out issue arose.
Off for a ride to a bike show in 10 mins so report back when i get back this afternoon.
cheers rich

RGP750:
Great ride today and a bonus of a 1st at the show ;D
Bike running fine now and i have learnt about resistance in plug caps '
Thanks all for your input
Rich

Nurse Julie:
Well done Rich. You will need to make a new Trophy cabinet soon 😊😊 x

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