A very helpful overview, Jim.

At the last event, I ran with both the standard Vevor TAV clutch and then swopped for the Juggernaut clutch.  Based on what others had said, I was expecting (and got) faster acceleration.  However, what I did not expect was the change in the effective final drive ratio.  From rough calculations using GPS speed and a digital rev counter, I seemed to get at least 10% overdrive from the standard Vevor clutch but still using the same belt I was getting 1:1 drive on the juggernaut at max speed.

I mention it here because if builders are struggling to get their final drive gearing up to or beyond 7:1, fitting a juggernaut has the additional benefit of giving you a good 10% on your final drive ratio.  (That is 10% more revs for the same speed, so better employing the headroom gained by removing the governor and adding various tuning mods.)

Thanks for the feedback and apologies for not spotting the earlier similar query from Scotty.  So, two more pairs of springs arrived today from KKC and I now have four quite different springs including the original from the engine (a Maxspeedingrods GXR212).  See the attached photos.

Original engine spring is 30mm free length, 1.8mm wire diameter and five turns.
KKC Heavy duty Honda GX140/160/200 spring is 34mm free length, 1.9mm wire diameter and 7 turns
KKC aftermarket GX160 G4 spring is 26mm free length, 2.2mm wire diameter and 5.7 turns
Chinese heavy duty GX200 is 27mm free length, 2.4mm wire diameter and five turns

I'm surprised to find such variation in free length. I don't know if this is by design or a nightmare of quality control! The compressed length of any valve spring when installed in the engine is 22mm.  This leaves me concerned that the 26mm Gx160 G4 spring would have marginal pre-compression to ensure the collet cannot come lose under the dynamic loads.  By contrast, the HD GX140/160/200 spring seems unnecessarily long at 34mm.  Although it is made of thicker wire than the original spring, the two extra turn make it soft again.  My best guess that it might be around 20% stiffer than the original, which doesn't seem enough.  The GX160 G4 spring seems at least 50% stiffer, which is about right.  However, as mentioned earlier, it is worrying short.

On balance, the safest bet out of this bunch is probably the long HD GX140/160/200 spring.  I'll give it a try and see what the engine sounds like.  Any other suggestions welcome

How wonderful!  I love it!  I'm also relieved to see all the hot or spinning bits are safely covered!   

Some wonderful action photos!     Thanks Andy for organising a very enjoyable day at the best kart track I've ever seen.

Ade

If you bought the same eBay £45 steering rack as I did, you might be interested in this modification. 

I was a little dismayed to see how much slack there was between the rack and pinion, mainly due to the plastic housing and lack of rear bearing.  When you take the cover off (see first pic) it almost looks as if there was meant to be a bearing there, but was forgotten!  When I test drove my cyclekart, the slack in the steering wasn't that noticeable, but due to the plastic housing, I felt it would wear rapidly and only get worse. 

I was about to order a better quality part when I realised I had left over bearings from my wheels.  They measure 12mm ID x 37mm OD and the housing is 36.5mm ID and the boss on the back of the pinion is 10mm OD.  So with a slice of 12mm OD, 1mm wall thickness tubing and a bit of fettling on the bearing outer race (angle grinder) I had a perfect fit.  What a difference! Plus, I now have confidence the steering rack will not wear quickly.

Camping for me on the Sunday night, please 

Ade

Jay, if no one else has already dived in, I'll take the mesh.  We can sort it at Whilton Mill.
Ade