Tips

Tips, Tricks and Cool Stuff

Gas Tank

There are a few parts that are next to impossible to find new. In addition many used ones are in pretty bad shape. The first thing that comes to mind is the vintage plastic gas tank.

Mostly they are faded, have deep scars or are stained by gasoline.

Since I was lucky enough (or crazy enough?) to buy an extra gas tank or two, I decided to take the worst one of the bunch and experiment. Unfortunately I forgot to take a before photo, so here are a few photos of better used tanks so you get an idea of what is possible using this technique.

I found that sandpaper and a great deal of patience is the best way to restore plastics.

There are two ways to do the rough shaping and take out the deepest scratches. One is by sanding the other is to use a straight edge razor blade and scrape at a 90 degree angle to the plastic. Depending on how deep the gouges are and the piece you are working on, you may use one or both during your project.

I started using a Sears orbital vibrating sander. Don’t use a belt sander. Well unless you want to have a big pile of plastic dust!

I first sanded the tank with 100 grit sandpaper, then graduated to 220 and then to 320 with the sander.

Every once in a while wipe the sanding dust off the tank and tap it off the sandpaper. If you let the dust build up on the sand paper the dust will put additional scratches into the plastic while you’re sanding.

Use care when sanding your plastic tank. Sand a little at a time, sand with the contours of the tank and use light pressure on the sander. Your goal here is to remove only enough material to remove the deep gouges and scratches.

You want to have a smooth overall finish when you are done with the 320 grit paper. Yes there will still be sanding marks, but no big scratches.

Now it is time to hand sand using finer grit sandpaper. At this stage I used a rubber sanding block with wet/dry 400 grit sandpaper and water with a small amount of dish washing liquid. The block helps to avoid uneven sanding marks caused by fingers and the dish wash liquid helps lubricate the sandpaper.

The cleaner you keep the sandpaper the less time it will take. Change the water often to remove all the grit and sanding dust. Again this ensures that you will not add scratches as you work.

Graduate to finer paper as the tank gets smoother. I started using 400 then 600, 800, 1000 and 1500 grit papers. When you get to this point you will probably see scratches that you want to fix. You decide the amount of time that you want to invest in your plastics.

My bike will be a racer, so I left some small scratches in the plastic. The tank looks almost new now instead of old and beat-up. If you are building a Garage Queen you could put as much time and effort as you willing to restore the plastics.

After all the sanding you will have a dull matt finish on the tank, the next step is to polish it.

I use Gel-Gloss polish on the plastics. I tried a few others but this one works the best. I use my drill with a 6 inch buffer wheel from Sears. Use caution because the edge of the buffer can leave deep marks if it hits the plastic at speed. It will take more time to fix these little marks.

Since I have gotten so many e-mails asking where I got the Gel-Gloss Polish I am posting this link to Amazon.com where you can find a photo of it and order it if you like. I purchased mine at The Home Depot!

Fenders

You use the same technique for restoring the fenders and other plastic. On this fender I used a straight edge razor to take out the deep gouges and scratches. Then I started the wet sanding process outlined above.

It is very difficult to get good before and after photos of plastic parts because of reflections. Please look closely at the photos and the differences should be noticeable. In the first photo you can see that the overall appearance is dull and there is a deep gouge that looks like a snake. Above that are deep abrasions that are at a right angle to the fender.

In the photo of the refinished fender you can see that there are no gouges or scratches and the whole fender is shiny and glossy.

Air Box

The YZ125G air box has a tendency to leak at the rubber boot to plastic air box connection. This is due to the fact that Yamaha did not use any sealant at this critical junction. From the information that I gathered this contributed to piston seizures on this bike.

Do yourself a favor and drill out all the rivets, clean the boot and the air box then use a good silicone sealant (or Yamabond) and re-rivet the boot to the air box. Make sure that you line everything up the same way as you took it apart.

Make sure that you use a high quaility air filter that is well oiled and grease the lip before installing it. If you are going to race use a new Uni Filter. This is one area where the aftermaket part is better than using NOS.

In addition to this the 1981 air box has a better filter mounting bracket and screw than used on the 1980. It is much easier to get the filter in and out using the “larger” 1981 airbox.

Carburetor

The carburetor also caused some issue with seizures. There are two little “tabs” on the bottom of the float bowl. The left tab can come into contact with the center cases. This causes the float bowl to be agitated and can create a lean running condition that can lead to disaster.

To resolve this problem simply file down the left side tab approximately 3mm. If you take off more material than that please use a sealant on the end of the tab otherwise it could leak fuel.

The float bowl on top is stock, the bottom is modified. The photo on the right is a close up of the modified tab.

In addition to this modification I also upgraded to the 1981 YZ125H carb which is 34mm. The standard carb from the 1980 is 32mm.

I was fortunate enough to find an NOS carb intake manifold. I also installed a new set of Boyesen reeds.

Ignition Timing

The standard setting is 2.27mm B.T.D.C. you should change this to 1.8mm B.T.D.C. this was covered by a Yamaha Service bulletin and will result in a less pipey powerband.

Seat

The seat that I found had a good base and foam but the cover was torn and worn. There are a few places to find aftermarket seat covers although I found mine on E-bay from these guys ( http://www.vrmracing.citymax.com/page/page/1518422.htm )

Gee, how can you tell that the seat foam is from a 1980 YZ125G?

Remove all the old staples from the seat base, clean it and then dust off the seat foam. Set the foam into the seat cover and then place the seat base on top. Carefully staple the cover to the base. Make sure that you pull the cover so that there are no wrinkles, but not so tight that you “warp” the name on the sides or back.

Number Plates

I know lots of people that are restoring 1980 YZ125G’s that spend a lot of money on NOS Yamaha Side Panels. This is wonderful if you are looking to show the bike, but why do that if you are going to race it? You could buy used OEM side panels and restore them or you can buy aftermarket side panels.

I decided on using Opaque side panels and front number plates from DC Plastics. These look close to what the early factory bikes used and they only cost $60.00 for the pair. The people at DC Plastics are very helpful and they have plastic available for most vintage bikes.

Drilling the plastic is probably the most challenging part of using aftermarket plastic. The way I did it was to place the plastic in place (hold it in position with duct tape) and mark it from the inside of the screw holes. Drill the holes a little larger than the diameter of the mounting screws and use wide washers.

Foot Pegs

The stock small foot pegs have been replaced with a set from a 2000 YZ125. These were sandblasted and painted with clear paint.

You have to make alot of modifications to make these pegs work on the 1980 YZ. First you have to drill out the pivot pin holes to 10mm. The spring holder area of the pegs have to be cut down to fit into the brackets. I did this on a grinder a little at a time and then cleaned them up with a metal file.

Take your time with this you do not want to make that area too small. You will also have to file a few other areas as needed. Once the pegs will fit into the brackets slip the pivot pin in and try to move the peg through its travel. Make sure that it does not bind anywhere. If it binds file down whatever is cauing the problem.

You will need to cut down the spings to fit the smaller brackets. The stock spring was three winds I cut mine down to two.

Throttle Assembly

Many people use the universal whirlpool throttle assemblies on their vintage racers. Many times these do not fit very well and they tend to break or stick because you need to modify them to work properly.

A 1992 YZ throttle assembly with a 1984 YZ125 Throttle cable bolts right on to this bike. I like the feel of the OEM throttle and it should last a long time.