During the restoration of my second-hand Honda NTV650 Revere, I come across the fuel petcock severely damaged. The thank itself were corroded by rust and needed a deep restoration (see this article, in Italian: Restauro con Power Tank di un serbatoio arrugginito).

The original Honda part has code 16950MS9005 COCK ASSY., FUEL, but it is no longer produced by Honda. The body of the petcock is closed by two rivets, so no maintenance is planned. In my case some rust from the tank accumulated into the holes and damaged the 4-holes rubber gasket.

Tank petcock thread diameter	22 mm
Hexagonal nut	30 mm
o-ring petcock - tank	14 mm i.d., 1.40 mm section
Fuel pipe connection outer diameter	10 mm
Distance between rivets	34.30 mm
Screws to replace rivets	3 x 16 mm (1)
Reserve tube lenght	100 mm (protrusion from the petcock-tank contact surface)
Reserve tube diameter	7.5 x 8.5 mm (inner x outer)
Filter base outer diameter	14.2 mm
Filter body outer diameter	13.0 mm
Filter base height	7.0 mm maybe is 8.0
Filter full height	180 mm

1. We drilled two passing holes, the screws were provided with self-locking nuts.

The brass tube of the reserve were severely corroded; I suspect that the previous owner used some sort of acid to clean the inside of the thank, producing even more damages!

I drilled the rivets hand-free; first I removed the rivets heads using a 4 mm bit, so that the petcock can be disassembled. Then, using a file, I smoothed out the parts of the rivets that were protruding from the body of the petcock. I completed the hole using a 2 mm bit, finally I enlarged the hole till 3.2 mm, with the idea of ​​using two 3 mm bolts with self-locking nuts.

1. A thickness of 2.70 mm was measured on a very old and squeezed gasket, probably a new gasket is more thick. The maximum acceptable thickness (calculated upon the available space) should be 2.95 mm. Because the original gasket has a raised outer border as well as raised borders around the holes, an overall thickness of 3.00 mm, that includes the raised borders, is plausible. This way, the compression of the gasket should ensure a proper sealing.

According to this forum post, it seems that the rubber parts (the 4-holes gasket and the o-ring) are the same mounted into the petcock of the Honda quad TRX350, years 1986-1989. User Goober published some nice photos and drawings with the measures of the gaskets; he succeeded to restore the petcock using a kit, despite the measures were slightly different.

In the following image you can see the assembling order of the components, from the inner to the outer: the rubber gasket, the tap body, the washer with two notches, the wave spring washer and the closing bezel:

Finally I re-assembled the petcock using two 3 x 16 mm bolts with self-locking nuts:

As the original spare part is no longer in production, it is possible to buy a non-original one. Unfortunately the quality is by far worse than Honda, and it seems that none of the available items fit perfectly the NTV650, even if the part is advertised for that model. There are a plethora of them available on Aliexpress, the models that can be somewhat adapted are the ones advertised to be compatibile with CBR600F, VT600, CBR400.

Obviously you need a petcock with the tank thread of 22 mm and the fuel pipe diameter of 10 mm, but you must pay attention to the following too:

• The lenght of the reserve tube: the original is about 100 mm out of the body of the petcock. A different lenght means a different fuel reserve capacity.
• The lenght and the shape of the knob pin: the original is 13 mm in lenght, with a square section of 8 x 8 mm with a chamfered corner. Almost all the non-original fuel petcocks I found had a pin that was only 5mm long.
• The shape of the filter: the strainer screen starts at some distance from the base of the filter, this lenght must not exceed 30 mm otherwise not all the fuel can flow out of the tank. The diameter must be 14 mm at the base and 13 mm at the main body.

After purchasing several spare petcocks, none of them fit satisfactorily as the original. Luckily I was able to recycle from them the three defective parts (the reserve brass tube, the 4-hole gasket and the mesh filter) and restore the original item.

The original brass reserve tube is 7.5 x 8.5 mm (inner x outer). Some non-original items have instead a tube of 7.0 x 8.0 mm, too loose to fit the original hole. Luckily I was able to recycle a tube with the correct dimension; wanting to get a more solid fit, I used the soldering iron to melt a bit of tin at the end of the tube to increase the diameter by about a tenth of a millimeter.

The original 4-hole rubber gasket has a diameter of 27.10 mm and probably is 3.00 mm thick when new. Into one non-original petcocks I was lucky to find a gasket of 27.00 mm diameter and 3.30 mm thick. Using fine sandpaper and emery paper I reduced the thickness of the gasket to just 3.00 mm, acting only on the side opposite the knob. In the following images the original face of the gasket and the thinned one:

In the following image there are two non-original fuel strainer filters. The first one is quite similar to the original one, just the base (the part with 14 mm diameter) should be 8 mm lenght instead of 7. The other does not fit because the solid part (non-mesh) at the base is too long:

As an alternative to restoring the original petcock, you can use a non-original tap by modifying the knob pin. In fact with many non original petcocks the main dimensional problem is the the knob pin, wich is shorter than the original. This means that the knob does not fully engage because it contacts the body of the petcock; that contact prevents the knob from rotating.

The original knob pin is 13 mm, while the non-original one is only 5 mm. In the following photos the small extension I built to fit it. The collar made of brass sheet allows for good resistance, but it required to slightly enlarge the hole in the plastic knob.

• TRX350 (86-89) Petcock Rebuild