Honda-SOHC

Hi Kev, welcome to the forum and I am sure you will find this forum a great help to be part of.

That's all good progress Ash. It may have taken a while to set up but making sure the frame is correct is key, too many people focus on the shiny bits and leave the basics. I always get my frames checked, for the £125 it's piece of mind. My Moto Morini frame was both out of alignment and had a crack in a frame tube just forwards of the rear shock mount. The 400/4 I restored for the wife was twisted by 3deg at the headstock. Thankfully 'Ratty' had a clean bill of health.
The 250RS decals from Piki are first class (as all his decals are). Are you spraying the centre stripe on the tank or has Piki made you a decal? Menno painted mine. To be able to paint is a real skill, I remember painting lessons at college, I still have the panel hanging in my garage that I painted in the lesson when I was 17. I had to sign write 'Vellocette and Classic Bike' on the panel as part of the lesson. I was actually employed as a coach painting apprentice at London Transport's bus overhaul works at Aldenham back in 1978. Within a year I had become a Coach Trimming apprentice at LT's train overhaul works in Acton because it was found I had a really bad allergy to cellulose!

Not owning a 500, I've not that specific experience to offer.

A big BUT though, genuinely I've never had problems with plug "fouling" on four stroke engines, that's across all bikes and cars I've looked after since early 1970s.

Another observation, the Boyer ignition is very, very competent in it's delivery. I've no problem working with the std system, believing it to be mechanically almost peerless in it's design, application and component specification .... the Boyer i can see by comparison does offer tangible benefits if that's chosen by the owner though.
Among those benefit appears the ability to fire more adverse mixture range more of the time with exceptional repeatability.  This seems to support a more optimum idle mixture that may give benefit in any residual unburnt component/fuel that may be affecting the fouling determination this topic is about.

Very loosely, NGK plug heat range on these engines could be approximated to continuous load under wider throttle for extended periods of time.
 A 7 giving ROUGHLY decent coverage for 7000 rpm running.
Likewise, an 8 for predominately covering an 8000 rpm consistent load type riding. Etc, etc
Basically its a balance of number of actuation per minute against heat clearance from the engine, ambient air temp also playing a part in air cooled motors too.

Hi, I have just joined the group to get more experience from other members I currently have a Honda cb550f2 in blue have been working on it for sometime now it’s nearly finished but still jobs seem to pop up but looking foward to getting advice from the group

Aha, that is valuable information. I had not seen this half-grade mentioned before. In Holland the general advice was to have the D8ES-L. Let me put it like this: if the D8ES-L fouled, than a "7" also did.
Now that we're older  and also have a lower national speed limit than back then, both the 7 and the D8ES-L can be used no prob.
I am curious if the D8EA is identical with the D8ES-L and if the D7EA also has a tip that protrudes just a fraction more than the D7ES. I have tried to see the difference myself, but I'm afraid the difference is minor and... older eyes don't help either.