R26 lack of performance

[starfield181]

Hi UK newcomer to this forum with a 1956 R26 on which I would be grateful for some help.

Though its a nice bike to ride it has always lacked performance and this came home to me last Sunday when it would barely live with a BSA C15 ridden 2 up. Top speed is around 55mph with maybe a little more downhill. Will cruise on the flat at 50mph but a strong headwind or going uphill pulls this back quite quickly. A friend with an R26 tells me his runs at 55-60mph quite easily and frankly my 1937 250 AJS is considerably livelier.

I have checked all the obvious things on the bike and found nothing wrong. Carburretor is set as per manual except that it has a 125 main jet. The timing is spot on and the exhaust system is not blocked.

Today I removed the head and found that everything seems to be perfect. New valve guides, valves correctly seated and there is no wear apparent in the bore. In over 600 miles it has not used a drop of oil and never smokes.

The only thing that struck me is the piston which even at tdc is 3.2mm below the top lip of the barrel. Is this normal or could my bike have an incorrect piston giving a lower compression ratio than standard?

Any help appreciated as I love the bike but would like a bit more performance.

A picture of piston and spark plug is at http://www.starfield181.co.uk/DSC_0714.JPG

Thanks

Peter

[Bmwrider59]

Hello Peter and happy Father's Day and also new to the form and have posted a couple of times. I was wondering if you could help me with an electrical issue that I've been having. Is the yellow wire coming out of the back of the transmission case the main battery connection for the positive side?
My R26 has never been disassembled so I still have the original piston perhaps I could take a picture of it if it would help or have you already resolved your issue?

Thanks for the help

Vic