Friday, September 9, 2016

Velocette Venom ignition timing and improvements

After the Venom gave British bikes a bad name at the Henstridge Bikers' Blast when it needed a push to get it going before heading off down the airstrip I decided it was well past time to give it a little love.

Given that the starting was OK from cold, acceptable from hot and very poor from warm everything pointed to the mag being the problem. The Venom is fitted with a BTH TT mag with manual advance and retard, a high quality instrument but not immune from fault after some sixty years of regular use.

Though Velocettes have a reputation as an engineer's motorcycle and as being designed by motorcyclists for motorcyclists they obviously never expected anyone to remove the mag, ever. The aft top nut is in easy reach but the other two redefine awkward. No amount of searching through manuals yielded any tips at all and seeking advice from experienced old hands merely confirmed that it is a bugger of a job. In the end a 1/4 drive socket with half the faces ground off did the trick. Luckily neither of the nuts were particularly tight as presumably whoever fitted them last also struggled.

Removing the mag pinion required making a simple puller from a piece of spare steel strip and a couple of bolts from the misc bolts bin.

The mag was taken over to APL Magnetos where Paul turned it around very quickly. Within a few days I had the mag back and ready to fit. Putting it back on the bike was a task only matched in awkwardness by taking it off. Countless times I dropped the nuts down between the engine plates. Occasionally they would have the grace to drop all the way through down to the workbench but more often than not they would find somewhere to get stuck in between.

The best consensus for Venom timing seems to be fully advanced at 38 degrees before top dead centre. Several sources confirmed this as did the Velobanjogent so it seemed like a very good spot to aim for.

In reality rigging up a timing disc and matching it to a point on the cases and checking the opening of the points with a fag paper is never going to be pin point accurate. I can only say at best that the timing is somewhere between 37 and 39 degrees. Either way though it is right and the bike runs a treat.

Mag nut peek-a-boo. (And yes, I did clean up the gasket cement!)

Velocette mag removal 'special' tool.

Homemade Velo mag pinion remover.
Whilst tinkering with the Venom it seemed like a good plan to approach the wet sumping problem that this example has. I had a go at re-seating the ball valve on the original one-way valve but there was no improvement at all. A call to Grove Classics resulted in the below stainless piece of finery arriving at my doorstep a couple of days later for a reasonable 35 odd quid. Problem now completely fixed.

Gove Classics' new anti-wet sumping valve.

Whilst at it and with the bike on the bench I recalled an unused Amal Monobloc that had been hanging around forgotten in a box in a corner of the garage for a good while. The Monobloc came to me in a box of spares with another bike and as luck would have it is the right size for a Venom with the bonus that it is the posh model with a chromed brass slide. The slide makes a very satisfying freshly machined metal on metal whir as it raises and lowers, almost worth the extra money alone! I jetted it at 270 main jet, 106 needle and 30 pilot with the needle fourth position from top as seems to be generally recommended. The float bowl extender is a useless piece of adornment picked up from ebay but it matches the finned inlet manifold so on it went. The bellmouth came from Alan Hitchcocks

Shiny new Monobloc fitted with boy racer floatbowl extension.

And shiny bellmouth.

End result? A bike transformed from a wet sumping recalcitrant starter with a penchant for embarassing the owner before an audience at bike meets into an eager to please puppy dog. Starting is now first kick with a reliable tick over from cold. I wouldn't quite say the bike is like new but a relatively small investment has transformed pleasure and ease of use. So much so that it's taken the position of daily rider bike of choice from my BMW. 

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