Ignition point adjustment - Tuning Yamaha RD125

After replacing the spark plugs with new ones (NGK B8HS) and installing a new battery (Yuasa 12N5.5A-3B) I was able to start the Yamaha but it wasn't running very smooth, Idle was ok, but revving sounded like sh!%. So I took off the exhausts to give 'm a clean and also to have a look inside the cylinders. 

New spark plugs B8HS for the Yamaha RD 125A

Marine spark plugs?? Yes, they are the same as the "normal" plugs, only the exterior of the Marine ones have a better rust protection.

Battery Yamaha RD125A 1974 - 12V 5.5Ah

The chrome work of the pipes is still in pretty nick shape but I discovered one of the silencers was missing and I couldn't find them for sale on Internet anymore. The guy I bought the bike form happens to be a boilermaker and offered me to make one. I only had to drill all the little holes (many little holes...), braze a small bar at the end and tap a thread for the mounting screw. perfect fit :)

Fixing a new silencer - Yamaha RD125A 1974

Old and new silencer - Yamaha RD125

The piston in the left cylinder looked OK, but the right one probably has had some kind of meltdown. There was some kind of dip in the middle of the cylinder, the size of a fingertip. This can happen when the timing is too advanced which will give you a way hotter running engine.

Melted top of right hand piston 

When I took off the ignition/flywheel cover everything looked pretty clean and almost untouched. OK, let's see if the timing is still spot on on this bike.

There's more then one way to check the timing of a two stroke Yamaha; The factory mark on the flywheel which has to line up with the static mark on the ignition plate when the contact breaker point starts to open (spark plug will fire). Actually there are two marks opposite each other on the flywheel, one for the left and one for the right cylinder. However there can be a problem with the accuracy of this method because the static mark on the case can be moved by loosening a screw. Maybe your bike was a Monday morning bike or one of the previous owners changed the mark, who knows...

Ignition timing parts - Yamaha RD125A 1974

1. Contact breaker points plate
2. Contact breaker points (Ignition points)
3. Crankshaft which you can turne with a scredriver
4. Ignition timing mark on flywheel (there are two)
5. Static ignition timing mark on case
6. Condensors
7. Arrow pointing in direction of running engine

L and R referring to the left and right cylinder of the bike, seen while sitting on the bike.

Luckily there's a more accurate method to check the ignition timing. For this method you need a dial indicator gauge a dial gauge adaptor to fit it in the spark plug hole and a feeler gauge.

First of all you have to check the max point gap. This should be somewhere between 0.30 and 0.40 mm. On my bike there's a small mark on the end of the crankshaft so you can see where the top of the lobe is (see pic). Normally the max opening point occurs when the piston is in TDC (top dead centre). This is the moment when the piston changes travel direction at the top of the cylinder.
If the gap is out of specs, loosen the screw a bit, insert a 0.35 mm feeler gauge and move the breaker point till you feel some light resistance when moving the feeler blade. Moving the breaker point up will give a bigger gap, moving it down a smaller gap. thighten the screw and check it one more time, also make sure you put in the feeler blade without an angle which will give a bigger gap.

Measuring the max point gap - Yamaha RD125A 1974

In order to set the ignition timing on two stroke bikes most manuals will give you a number BTDC (Before Top Dead Centre). For the Yamaha RD125A this is 1.8 mm BTDC. The spark plug has to fire at exactly that moment in order to give the best engine performance. 

For the next step you'll need a special tool which you can buy online, at good bike shop or you can make it yourself. I made one myself because I didn't want to wait a couple of days ;) 
I used an old spark plug bottom, a piece of copper pipe, some kind of spacer from an old car and brazed them together. Make sure you dial indicator gauge isn't moving in this tool, tighten it!

Ignition timing tool Yamaha two stroke

Ignition timing tool Yamaha two stroke

Ignition timing tool mounted in left cylinder - Yamaha RD

I also had to make a small extension rod for the dial gauge to make it long enough to determine the piston position.

For the next step it's important to look for the normal rotation direction of your engine. For Yamaha RD bikes this is counter clockwise. There's also an arrow on the flywheel case which points in the right direction. 
Make sure you take both spark plugs out before you start the timing procedure! You won't be the first one who starts his lump while checking the timing..
With the dial gauge in the spark plug hole look for the TDC, this is the moment when the dial gauge stops moving up and starts moving down. Now set your dial gauge at zero exactly on this TDC point. 
Now turn the crank with a screwdriver 3 mm clockwise (to get rid of play in the crankshaft) and then turn it 1.2 mm counter clockwise. This is the exact point where you want to have your plug sparking (3-1.2=1.8mm). 

OK, how will you know it's sparking? The spark plug will generate a spark at the moment the breaker point starts to open. You can check this by connecting a simple 12V light bulb. One wire on a ground and the other wire on the orange or grey lead depending on the cylinder you're checking. (left breaker point has a orange lead an right one a grey lead). As long as the point is closed the bulb will not light but as soon as the breaker point starts to open it will light. Don't forget to put your contact on, switch it off as soon as you've done the check. You don't wanna drain your battery. Make sure you do this while turning the crank counter clockwise. If the light goes on too early (more then 1.8 mm BTDC) there's too much advance, if it's too late it's too retarded. Either way you have to loosen the 2 screws of the breaker plate and move the plate up or down till it's right. For the Yamaha RD's moving the breaker plate clockwise will give you more advance, and moving it counter clockwise will give you more retard timing.

How to move the points and breaker plate
Not my best drawing but you get the point ;)

Connecting the light bulb - ignition timing two stroke RD

Instead of connecting a light bulb over the breaker point you can also use a spark checker

OK, sounds easy enough or....@#$!!$# The timing on both cylinders was way out of the 1.8mm specs (hence the melted piston I guess). Way to much advance, over 3 mm! So even while pushing the breaker plate all the way counter clockwise I couldn't get it right... Worn out ignition breaker points! 
There are 3 methods to solve this problem:

1. Buy new points
2. Go for a smaller max ignition gap (let's say 0.2 mm )
3 sand down the brown plastic part that makes contact with the crankshaft lobe

I will go for 1 but for now I'll go with a combination of 2 and 3. Make sure you sand down the plastic part equally (same height  overall) and don't sand too much off, keep it above the fine line.

Finally I got the timing spot on. I had to turn the idle screws on the carbs a bit more in to keep the bike running at idle. And it seems to be that the ignition timing points on the flywheel are in the right position, good to know for the next timing workout. Just for fun I also checked the timing with a strobe light. Perfect! 

Ignition timing spot on - Yamaha Rd 125 A 1974

Still have to replace the burned piston before I take the RD for a spin.

Starting the RD125A after ignition point adjustments

Update 22-07-2016:
Just fitted the new contact breaker points (part 183-81421-10). As you can see in the pic below the teeth of the contact breaker plate are nice in the center of the screwdriver "lobes". This is always a good starting point when adjusting new points and you've set the max point gap around 0.35 mm.

New contact breaker points (part number 183-81421-10) 

Setting the new contact breaker points

Right breaker plate teeth in the center of the screwdriver "lobes

Yamaha RD125A 1974

Searching Internet for some parts for my Yamaha LS3 resto I came across a Yamaha RD125. I've always loved the RD models so I did some research on the bike and according to the colour scheme it must be a RD125A from 1974. The bike wasn't running, has matching numbers and had been sitting in his shed for over 16 years. It was a bit rusty but the engine turned over and it was still in original condition. I couldn't resist buying it :)

Yamaha RD125A 1974

Yamaha RD125A 1974

2 stroke Engine Yamaha RD125A 1974

Carburettors Yamaha RD125A 1974

Only 9904 Km - Yamaha RD125A 1974

Fuel tank  - Yamaha RD125A 1974

Seat  - Yamaha RD125A 1974

Original rims  - Yamaha RD125A 1974

Original Reflector  - Yamaha RD125A 1974 - love the little details

When I got home and unloaded the bike form the van I kick started it one more time just to listen...All of a sudden it was running high revs on one cylinder! Oeps... I quickly switched off the engine before it got damaged inside. You never know what's been growing inside the engine during the 16 years of hibernation...

First of all I checked the inside of the fuel tank; pretty rusty, not rusted trough but more then flash rust.
OK, timer for some chemistry. I've already used electrolysis for rust removal on other bike and car parts, so this should be possible with the inside of a fuel tank as well.

Rusty fuel tank Yamaha RD125 A

You'll need some washing soda which you can buy at your local supermarket for a couple of dollars, a battery charger, a bucket, ductape and a metal rod.

Empty your tank completely and rinse it with water on the inside.

Fill the bucket with water and add approximately 500 grams of washing soda to 10 litres of water. Mix it till it's all dissolved and pour it in your tank. Don't worry about the paint or other parts, like you fuel tap. The solution won't attack it. If you spill some on your paintwork, just wipe it of and rinse with some water if you want. Make sure the fuel tank is completely filled so the inside top of the tank will also get de-rusted.

Making washing soda solution for de-rust electrolysis

Now grab a metal rod, bent it in shape so it will go all the way in the tank and make sure it won't touch the metal parts of the tank. I put some ductape at the end of the rod and around the fuel cap opening.

Metal rod as anode in fuel tank Yamaha Rd125 - tank is the cathode

Connect the Neg (-) black lead of your battery charger to the tank (best is a bare metal part) and the red (+) wire to the metal rod and switch on you charger. I've a pretty heavy battery charger so it started the process with 22 Amps. You'll see and hear the solution bubbling and after a while you'll get some foam forming. After an hour or so the Amps had dropped to 2, so I switched the charger off, took the rod out of the tank and cleaned it. It was very rusty. You can sand it, but the best way I found to clean it is dipping it in hydrochloric acid for a couple of minutes and then rinse it with water before you put it back in the fuel tank.
I repeated this every couple of hours to keep the process going.

Rust removal Fuel tank with electrolysis

Ampere reading at the start

Ampere reading  after an hour or so

Cleaning the metal rod / anode with hydrochloric acid

You'll see that the solution in the tank will get hot after a while.
After 8 hours or so I emptied the tank and rinsed it with water, it was almost rust free but I decided to give it another treatment the next day.

The last minuscule rust parts can easily be removed with some hydrochloric acid (HCL). I used 30% HCL and mixed it with water to get a 15% solution. 1 Litre is enough to clean the tank. Be careful when you pour it in the tank and keep some water nearby to rinse spills on you paintwork. Put the fuel cap on and shake thew tank in all directions for a couple of minutes. Trow out the acid and rinse with lots of water. Try to get all the water out and use a hairdryer to get rid of the last water drops.
You'll see that flash rust will form within 10-15 minutes, so to stop this put some motor oil in the tank and make sure it's covering all the metal parts. I left the oil inside for a day and shook it a couple of times.

Inside fuel tank after rust removal

Inside fuel tank after rust removal with electrolysis

Next thing is to take of the exhausts and check the inside of the cylinders.