Britbike forum Forums British Motorcycle specific Brands Bsa bulletin board Weber / Dellorto on Thunderbolt head

I made an adapter to fit a Weber / Dellorto carb to a Thunderbolt head .
This will fit in the original frame , with modification of the oil tank .
I’ll post more photos when it’s fitted , and a write up when it’s running.

totally awesome. Keep us posted!

Maybe weld a couple of tubes straight through the oil tank for the velocity stacks? Would need a rear mudguard to keep them from sucking in dirt thrown from the tyre.

It does actually fit as is , but more space around the inlet mouths would be preferable - maybe even room for a sock filter .

The head is sent off for guides and valves. Hopefully will have it back soon . Looking forward to testing and tuning the set up

That's cool as. Nick does them by welding, but it's pretty long, which suits the tuned length, but hard to fit on a solo.

If you transition through those lovely manifolds to oval at the head you get lots of flow. I'm on the wrong computer to show the oval entry, but this shows a bowl area on a Lightning head. The Thunderbolt has decent ports they are just a bit thin at the pushrod tunnel. But an oval entry means volume without going too high, it's wide instead, and you can have the top in a nice fast curve rather than going down then up.

Looks like you have relieved the head for the piston crowns much like I have.

With big lumps of heat conducting metal as a manifold, you'll need this.
https://www.autosport.com.au/weber-soft-mount-kit
It'll also help with vibration damping/fuel frothing a little.
Although not as pretty, tubes with rubber hose type connections and
a mated manifold on the carb side, are far more practical.
But, looking at the bike it's going on, it probably won't make a difference.

Allan, blending the head like that actually spoils the squish effect to some extent
especially when using the big bore kits.

Not sure why that's like that, it could be to stop them wacking. It looks like it was on a block with central bores. So maybe it was on the smoker I made sleeving a std block. My bores are closer together, plus Paul's were different again. Put it all together goes great but the old iron 750 block is cracked through the pushrod tunnel. So the head is adjusted to where those pistons aim. And it will soon be wrong. Just don't want pistons hitting the head or the gasket.

Std blocks can split there as well. If you have a big oil leak there wash it and have a look. Just under where the rear bolts stop. So when we can get one of John's 750 alloy cyls we can actually use some rego. I washed it threw talcum powder on it when dry and a wet oil seep crack is right across it and at the back as well. didn't even have to start it.

Not sure what John's blocks do around the tunnel but mine are solid. But still 1/2 the weight of iron. I could get one of mine machined and Nicasiled but John's would be cheaper and are class looking.

A Bandit or a Rob North would maybe fit the long set up so would an rgv we were thinking about that. But Thunderbolt head.