Post by davet on Mar 5, 2016 17:01:44 GMT
I thought I'd start a thread on how to rather than add to another thread. So here goes with another picture story. Having heard of the benefits of powerjet on carbs and seeing how they can be retro fitted to many carbs, I thought I'd have a go myself. After all I've destroyed engines in many different ways over the years so nothing to lose then!!
I researched the existing powerjet kits available and realised they were similar to miniature fluid handling systems. After many hours google searching I eventually found a company in the US who manufactured parts very similar to the powerjet kits on the market. In for a penny in for a pound, I found a UK supplier and ordered enough parts to build 15 kits.
BEFORE I START I'VE GOT TO SAY THIS IS MY WAY OF DOING THIS, OTHERS MAY KNOW A BETTER WAY, SO BE WARNED.
Like I said in the previous post you'll need the following parts:
Clippard MNV-3K-M5 - This is the main unit (needle valve) which will eventually be fitted to the carb body.
Clippard 11752-3-M5 - Two of these are needed to connect the fuel pipe from the float bowl to the main unit.
3mm outside diameter brass tubing with an inside diameter of 2mm, so it's 0.5mm wall thickness. More on this later.
5mm petrol resistant tubing.
Some M5 fibre washers.
Quality 3mm drill bit.
M5 tap and matching drill bit.
Two part epoxy.
Good quality threadlock.
Small blowtorch (craft type).
Fittings solder and flux. Do not use electricity solder, you'll need a good quality fittings solder for brass on brass soldering.
To start you'll need to drill a recess with the 3mm drill bit into the needle valve body. This is best done with a drill press because you must ensure the drill bit is dead centre. I centred mine up by putting a smaller diameter bit in the press to centre up the needle valve by putting it in the existing hole.
Next you'll need to cut your brass tube. Use a fine cutting blade and ensure you cut it at 90 degrees. De-burr the tube and clean it with some brake/carb cleaner. It will need to be spotless ready to solder. NOTE the length of your tube will be dependent upon the size of your carb venturi and don't forget to add the 3mm for the recess into the needle valve.
Powerjet tube length is a topic for discussion on its own. I make mine slightly shorter than 1/2 the venture size. So on my 30phbh it is 16mm in length, 13 plus the 3 for recess. I haven't had time to experiment on a dyno with regard to the benefits of specific lengths of powerjet. Amal carbs have small powerjets, Mikuni are longer.
Before soldering make sure you fully wind out the screw of the needle valve. This makes sure the Viton seal on the end of the screw is as far away from the soldering heat as possible. Make sure both surfaces are spotless to enable a good seal with the solder. Practice first with the tube into the side of a brass nut first if you're unsure.
Use a small paintbrush to paint flux onto the tube, not too much just a thin layer. Put the valve into a small vice to hold it firmly vertical. Place the tube into the recess. I found cutting small piece of solder and placing it on the edge where the tube meets the valve to be a successful method. You don't need too much just a sliver. Direct the heat to the tube and valve area, not too close and watch for the solder to melt and disappear around the tube. You don't need to place heat all around the tube as the brass will soak it up and the flux will transport the solder around the tube.
Let it cool and check for a firm seal. Check that the screw can smoothly go in and out.
Some photos of parts.
Sideways reading time. 1. Main needle valve. 2. & 3. fittings for fuel line. 4. Petrol resistant tubing. 5. Rubber cap for screw. (this is dellorto choke/throttle cover cut down). 6. M5 tap and drill.
Better photo of complete assembly.
Now for the fitting. Sticky has done this in scootering a few years ago fitting one to a VHSB carb. These photos are for a phbh. First to fit the pipe connector to the float bowl.
Prepare a clean dust free area to work away from where you're going to drill holes.
Remove the float bowl from the carb. Drill the hole in the bowl where indicated. Don't attempt to do it with the bowl attached, as you'll end up putting a hole in the floats. Mark carefully and check where the connector will come out
The float can be seen through the hole. Make sure the connector does not interfere with the float. If it does use an additional fibre washer to space it out. Be careful when cutting the thread with the tap. Also take care when tightening up, don't use too much force as you may strip the little thread available.
Once fitted use a small amount of epoxy resin around the connector to secure it in place.
Put the float bowl aside to allow the resin to set. Even quick set resins should really be left overnight before using.
Now to the more difficult task of fitting the powerjet to the carb body.
First strip down carb, making sure you take note of where everything goes. Photos always help.
Use a fibre washer to position where the powerjet is to be fitted. You need to leave enough room for the powerjet to rotate as you screw it in to the body once the thread has been cut.
Use a centre punch to mark where you are going to drill and punch ONCE. Be careful when drilling don't force the drill let IT do the work.
Make sure when you drill that the drill is exactly vertical the the surface. The bit needs to go in at right angle, otherwise the powerjet will not sit centrally in the body.
You're now ready to cut the thread. If you haven't done this before, practice on another piece of aluminium, drill the hole and use the tap. Get used to feeling for the tap beginning to bite. There are some good videos on you tube.
Once the thread has been cut, test fit the powerjet and note where it needs to stop where you need to put the connector. It should rest facing backwards, with equal distance between carb body and petrol inlet.
Screw the powerjet in, but do not fit the connector yet. As with the float bowl connector, it is advisable to use epoxy resin to secure the powerjet in place. Once the resin has set, you can attach the connector. Please note it is easier fitting the connector with the petrol pipe fitted to it, like a socket on an extension bar. Before fitting heat the pipe end, it makes it easier to fit over the barbs.
Screw the connector in to the powerjet using the pipe to assist. Do not tighten the connector too much or you may damage the Viton seal (small black washer). Just past finger tight is enough. You could use a small amount of threadlock here, but not too much.
Use the pictures to work out how long the petrol pipe needs to be and cut it to the desired length. Check with the carb on the scooter that you've got enough clearance.
Some photos with the pipe and jet in place.
On this one you can see I've marked the screw with some red paint. It makes it easier when setting it up. The clear pipe will show the height of fuel in the float bowl. It is advisable to get the powerjet set up on a dyno. Once the correct setting has been reached you can use the rubber cover over the screw. It will prevent vibration moving the screw.
MOST IMPORTANTLY, REGULARLY CHECK THE POWERJET AS WE ALL KNOW VIBRATION IS A KILLER OF SCOOTER PARTS. CHECK THE CONNECTORS AND THE TUBE ITSELF.
