Griffon Airbox with Mikuni

[jefe]

I recently bought my first Greeves, a 73 250 Desert Griffon. the previous owner swapped out the amal for a mikuni and replaced the original airbox with a custom airbox.

Does anyone know if the stock airbox can be readily fitted to a mikuni?

Does anyone have a source for the rubber inlet manifold that would fit a 73 250 for the mikuni?

Photos of my bike as purchased

Photos of custom airbox added by previous owner

Photos of the rubber inlet manifold and carb, with lettering on the rubber reading: A9 v34-200 M Kogyo Japan

Thanks
Jeff

[Kim275]

Jeff,

In answer to your questions

Does anyone know if the stock airbox can be readily fitted to a mikuni?

Yes - I have a 36mm Mikuni fitted on my QUB with the stock airbox. on the airbox side it is a tighter fit than the Amal and the inlet extends into the airbox - but just requires a little hot water treatment on the rubber and it fits.
Suggest you use twin foam filters on both sides of the airbox...and note the smaller one on the RHS is harder to find!

Does anyone have a source for the rubber inlet manifold that would fit a 73 250 for the mikuni?

I got a flange for mikuni connector from Surrey Cycles in the UK - (same as for an Amal mk2) - but you can find on ebay in US - this is what you will need

http://www.ebay.co.uk/itm/2928-121-3-mikuni-Amal-MK2-34mm-Rubber-Adaptor-carb-930-mk-/400513776808?pt=Motorcycles_Parts_Accessories&hash=item5d407b3ca8

This one looks identical to the one I use on my 250 Griff with a Mk2 Amal.

To fit the Mikuni with this flange and the standard airbox you will need to get rid of that lump of ally and connect the flange directly to the barrel.
It will also get your length of inlet tract closer (but not as close) as original design.

Hope that helps. BTW assuming you are US based- Kenny of Nicholson motors also a good contact for advice on Griffons and may well have some of the bits you may need for your re-build. He is Bearingman on this forum .

Cheers and good luck with your re-build - look forward to seeing the After photo's
Kim

[dave higgins]

Hi kim, agree with what you say, & as you know we were discussing the mikuni carb replacement a while back.
I found the inlet tract on my t/port to be very very rough in its finish, it had been left as it was cast, & measuring the two inlet ports on the liner, i can see no reason why, with opening the tract out & polishing, that you could not use at least a 38mm carb.
Which is what i have done, its a full 38mm inlet width now,with a symetrical polished finish around the bridge, also cleaned up the exhaust ports, so it will be interesting to see how it has altered the characteristics.
As for the air filters themselves, i made up a couple of cages & used twin foam, both the same size, i`ll let you know how it goes soon....

[Brian Catt]

Which desert will you try it in Dave?........

[dave higgins]

Nice one Brian... do you think i might need a bigger tank.....

[Brian Catt]

Was thinking about Weston Desert race!........Probably need bigger jets as well!

[Kim275]

Hi Dave - will be interesting to see what difference it makes.........I suspect the biggest difference will come from polishing and making the ports symmetrical - especially the top of the exhaust ports and the bottom of the inlet ports...... and of course the Miki gives you smoother throttle off the bottom - so should be sweet !!

I am fitting a 38mm Mikuni to a Monty Cappra 414 at the mo.....down from the stock 40mm Bing - but is suppoed to be a better performer - so as they say (apparantly) Size isn't everything
Happy fettling
Cheers Kim

[jefe]

Thanks Kim!

I bought the airbox on ebay in the UK and had it shipped to one of my friends there for me to pick up the next time I'm in London, might be a few months.

In the mean time, before reading your message I bought this mikuni flange, which in theory should work temporarily with the aluminum manifold, and I'll use a pancake filter and no airbox temporarily until I pick up the airbox next year. The carb is a vm32, the orifice in the aluminum manifold is 30mm. I understand from your message that I'll later need to remove the manifold and buy the amal flange adapter in order to fit the mikuni with the airbox installed, but who knows, I may end up back with an amal, I run amals on my '60 interceptor, my 74 trident, my 54 matchless, all run very well although the monoblock on the interceptor is a tough start!

thanks again, and any further advice appreciated!
Jeff

[Kim275]

Hi Jeff ,
Whether you go for an Amal or Mikuni main thing is to ditch That ally connector and connect them closer to the inlet
Cheers Kim

[Terry Sewell]

Griffon Airbox

OK fitting carb close to barrel, but it will need some sort of heat shield, ie a tuffnel spacer to stop the carb getting warm.

As for the small sponge filters for the QUB air box, I have some in stock that will do the job.


Terry Sewell TDS Offroad Motorcycles. ( sponser of greeves championship)