Fitting the MAR 350 with an OKO K-101
This MAR 350 has an AMAL sleeve mounted 27mm carburetor which is worn out and clogged.   After removing the carburetor and the old manifold sleeve, we clean up the intake and put a new manifold sleeve in place.
The inlet for the fuel on the OKO is a loose fit for a 1/4" hose, so we sleeve it for a nice fit that does not require a clamp.  We use Tygon hose which does not harden and get brittle like regular fuel line.  A good bronze fuel filter is placed in the hose, vent lines are attached and it is ready to be tested.
This 26mm OKO K-101 breathes new life into this old OSSA MAR 350, turning it back into the tractor it was, now with even more grunt.
Fitting the MAR 250 with an OKO K-101
The 250 MAR fitment with the OKO K-101 carburetor is very similar to the fitment on the 350 MAR.  The 350 comes with a spigot manifold, but the earlier 250s have a metal flange to spigot adapter on the manifold.  Originally, we fitted a sleeve to the existing spigot, but this pushed the carburetor back past the point where it could connect with the stock air box.  We found the best solution, which enabled us to use the stock airbox, was to remove the metal spigot and replace it with our rubber flange to spigot adapter, thus eliminating the need for a connecting sleeve.  This pulled the carburetor forward about one inch or 25mm, giving us plenty of room to sleeve the existing airbox hose as we do on the 350 MAR.  Now it is a very neat package, as well as easy to install.  Specify when ordering whether you need the flange adapter or just the sleeve as later models used.
OKO K-101  Carburetor Kits For:
OSSA Plonker, MAR 250, MAR 350 and Pioneer 250
Select the shipping destination and the OSSA model from the dropdown boxes below.  Kits include adapters, hardware and hose clamps for the model chosen, as well as extra jets for fine tuning.
Select Destination, Shipping Included in Price
Carburetor Kit For:
Select Mount type
In stock
Optional clear float bowl
In Stock
OKO K-101 Clear Foat Bowl
OKO offers this clear float bowl for the K-101 series so you can easily check the float level, or see if any dirt or water has accumulated in the bowl.  It attaches with four screws (incuded).  It does not have the bottom nut for access to the main jet.  This may be purchased by itself or with a K-101 Carburetor kit.  Click on the "options" below.
Clear Float Bowl Options Including Shipping To:
Carburetor Size
OSSA Page: 250 and 350 Trials, 250 Pioneer
Above is a 1972 OSSA Pioneer 250 used for road riding; now with a 28mm OKO K-102 (Clear bowl)
OSSA Pioneer now "runs better and idles smoother than it ever has."  (Quote from owner)
The original airbox hose is too small, so we cut it back even with the end of the spigot on the airbox and then sleeve it with hose that has a 2" ID, in this case with clear hose, though we also use black rubber hose. 
Fitting the Pioneer 250 with an OKO
Though we have sold several kits for the Pioneer 250, jetting and fitment had been provided by our customers who were willing to dial the carburetor in themselves.  We provide them with our "best guess" and they take it from there, letting us know if they need different jets, etc... to make it work right.  We do this with any bike/engine we have not had the opportunity to fit an OKO on.  Now, we have fitted an OKO on a 250 Pioneer ourselves and in doing so have gained some more knowledge, especially when fitting to the original airbox.  If you want to connect the OKO to the original airbox, let us know and we will provide an adapter to do so.  This is however, a very close fit and we needed to remove the lip from the airbox to make it work.  The end product looks original and works as it should.  See the photos below.
Below is the bike our customer fitted a 28mm to using a K&N Filter.
Below is the 250 Pioneer we recently fitted with a 28mm OKO, keeping the stock airbox.  Click the thumbnais to see the larger photos.
Fitting the Gripper 250 with an OKO K-101
The 250 OSSA Gripper  uses the 28mm OKO and attaches to the manifold using the 35mm rubber sleeve.