Fill up the oil tank with 2-stroke oil and open up the bleed screw.
Open it and wait until you see the oil coming all the way through before closing the bleed screw.
And yes, the routing of the oil line is correct according to Suzuki. If you have routed the oil line the other way around the oil pump, then you have done it wrong.
Copy from the GT380 service manual:
And later on from Suzuki, the Tune- Up Specifications:
Since I have both the GT750 and the GT380, the specifications for these models are highlighted in the Tune-Up specification.
Before doing anything, take a deep breath and relax. This can be very frustrating if you are unfamiliar with the procedure, but it becomes quite straightforward once you understand how to do it properly.
First of all, you can almost disregard the exact numbers in the Tune-Up specification. In practice, you will rarely achieve them precisely due to mechanical play and slack in the engine. Also keep in mind the tolerance specified in the Suzuki service manual—it is quite large: B.T.D.C. 3.0 mm (allowable range 2.52–3.76 mm).
Some basic info:
From my previous posts for both GT380 and GT750
On my GT750 I used a single test lamp connected in parallel with the points, as shown in the diagram below. When connected this way, the lamp will light when the point (circuit breaker) is open.
If you are using the original Suzuki test instrument with its built-in battery, the lamp is connected in series with the points (not in parallel). In that setup, the lamp will light when the points are closed.
Note: This difference is important to be aware of.
This time I did it differently on my GT380. I made a small box with a battery and three LEDs that show the status of all three points (circuit breakers) at the same time.
Instead of fiddling with the test lamp on each point, I made a small box with a connector that plugs directly into the wiring harness.
Schematics:
PCB:
In this configuration, the LEDs are connected in series with the points and light up when the points are closed. The LEDs are powered by the built-in battery in the box.
The box has a built-in magnet, making it easy to attach to the frame. The black wire goes to ground.
Instead of this box, any test lamp can be used. However, remember that the function is opposite: the test lamp will light when the points are open, not when they are closed.
Adjustments procedure GT380 (not GT750):
Read the Suzuki service manual and my previous posts.
This is my way of doing it:
DO NOT TURN THE ENGINE FROM THE NUT IN THE CENTER OF THE TIMING PLATE. Doing so may break the nylon gear behind it.
Turn the engine using the kick starter. For fine adjustments, use the generator bolt on the left side of the engine.
You can also put the bike in gear so you can see that the rear wheel is turning in the correct direction. If you look at the nut on the timing plate, the rotation is opposite, so it is easy to get confused. Make sure you turn the engine in the correct direction.
Step 1: Mount the timing plate roughly as indicated by the blue arrow.
Step 2: Turn the engine and verify that the point gap at its widest opening is close to the Suzuki specification, about 0.35 mm. Loosen the screw indicated with the red arrow if need and adjust to the the correct distance when it reach the maximum gap. Note, this is not the timing adjustments BTDC.
The gap is not the most critical measurement, and there is little you can do to correct it after the timing has been adjusted. If it is far outside the specification, the points must be replaced. In the worst case, the cam may be worn.
Step 3: BTDC adjustments.
Remember, this the distance before the piston reach the top in the cylinder, about 3mm from top.
Turn the engine until the mark indicated by the yellow arrow aligns with the mark indicated by the green arrow. Note the label L, indicating the left cylinder.
At this moment the points should open and break the current to the coil, and the spark will fire. When using a test lamp, the lamp will go on at this position, but when using the Suzuki test instrument or my box, the lamp will go off. And of course, there is no spark when using my test box, since the current is not flowing through the coils, only through the LEDs and the points.
Do this for all three cylinders (L,C and R) and adjust using two screwdrivers, as shown in the picture below.
Step 4, fine adjustments.
Don’t jump down this rabbit hole if you have mental issues about perfection. You can drive yourself crazy because you will never get it absolutely right. If the bike doesn’t start after aligning the marks as described above, the problem is something else. The fine adjustments are only for fine tuning, and normally you won’t notice any difference in performance.
But here is how its done:
I 3D printed an adapter to fit the 14 mm × 1.25 spark plug threads. Make sure to adjust the distance to the gauge so it contacts the piston slightly before BTDC, allowing you to clearly see when it touches the gauge.
Verify the measurement against the Tune-Up specifications and adjust until you feel comfortable with it. You will never get it exactly spot on.
Points VS electronic timing:
Let’s talk about the elephant in the room: points vs. electronic ignition. First of all, there is nothing wrong with swapping out Suzuki’s magnificent electromechanical ignition system. But for me it’s simply not necessary and feels very much wrong too.
If you struggle with the adjustments, feel free to install an electronic system and get the bike on the road with something easier to set up. But the original system is not difficult to use as long as you know what you are doing.
And keep in mind: most electronic systems use Hall sensors with only one reference point for adjustment, so they can never be as accurate as adjusting each cylinder individually. You can buy systems with optical sensors, one for each cylinder, which improves things, but they are just as tricky to adjust as the original ones.
And honestly—why mess up an old classic with modern parts if it’s not needed? If the points fail, you can usually adjust them on the roadside and get home. If the electronic system fails, you’re stuck.
A friend of mine had major issues with an electronic ignition system that was adjusted according to the procedure using one cylinder as the reference. One of the other cylinders ended up far out of timing, causing vibrations and, in the worst case, a possible engine breakdown. After switching back to points, the timing was correct and the vibrations disappeared.
That said, many people have good experience with electronic ignition, so use whatever solution suits you best.
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The throttle cables are now installed and fully synchronized according to the service manual, along with the oil pump cable.
This was my first time doing this job. The synchronization went smoothly, but the installation itself was quite a challenge.
The real challenge was attaching the cable to the piston — as shown in the photo. The J model uses a smaller piston, while my bike is fitted with K model carburetors, which have longer pistons.
That extra length made it very difficult to get the cable all the way down and properly secured. In the end, I used a piece of dental floss to guide and pull the cable into position. A simple trick, but it worked.
Synchronizing:
I adjusted the alignment according to the service manual. Make sure that all the punch marks line up at the same level when you slightly twist the throttle.
Oil pump wire:
The throttle cable has four inner wires — three for the carburetors and one for the oil pump. The longest one is for the oil pump.
I followed the procedure according to the service manual, but take a close look at the photo below. There are two additional small punch marks, in addition to the one described in the manual.
The manual states that the red punch mark (No. 3 in the photo above) should be aligned with the green mark (No. 4) when the punch marks on the pistons are at the top position.
This is one way to do it. However, you can also align the smaller punch mark (No. 2) with No. 4 — but in that case, the punch marks on the pistons should be positioned in the middle.
I tried to follow the instructions in the manual, and afterwards, when lowering the piston mark to the center position, I noticed that punch mark No. 2 was aligned with No. 4.
In other words, both adjustment methods will work fine.
Olil Pump Wire Retainig Clip:
The plastic retaining clip was missing. Originally, the clip was made of metal, but all aftermarket replacements are produced in plastic.
I had no idea where to buy one, so I used my 3D resin printer and made a batch of them in tough plastic resin.
With resin printing, the height of the part is what determines the print time. A part like this takes about one hour to print — whether you make one or a hundred.
I printed 25 in one go. I’ll be giving them away at the Classic Suzuki Rally in Norway to anyone who dares to use one 🙂
All done:
The bracket for the choke lever was broken. Could I make a new one?
Yes, I did:
How it was done: First, I drew the model in Fusion 360 and used my CNC machine to mill the part from 1.2 mm thick steel.
3D model:
Machining:
Thereafter, I bent the part and nickel-plated it as the final step.
Mounted on the bike:
I’m pleased with the result:
I found this knob om ebay, but decided to make my own.
I’m not 100% sure about the dimensions, since I had to rely on the photo from eBay and measurements of the axle from the speedometer. However, it fit well once mounted.
Feel free to download the STL file if you would like to 3D print your own knob.
The old rubber cushions were almost completely worn out. I found one on eBay but decided to make my own. Using the old ones and photos from eBay, I created this part in my CAD system:
The part I made:
Please feel free to download the STL file:
You need to 3D print it using a rubber-like resin. Use a heat gun to warm up the part before mounting. This will make the rubber part soft and easy to install.
3D printed cushion:
J–K models use the black plastic version of the chain guard. I was fortunate to obtain one of the last remaining original parts from the 1972–1973 production years.
Item No. 14, the metal reinforcement plate, was missing, so I had to fabricate a new one.
The part should have been made in steel, but I chose to manufacture it in aluminium, as shown in my CAD model. After a trial 3D print in PLA to verify the dimensions, I machined the final part from 3 mm aluminium on my milling machine and tapped M6 threads.
Please feel free to downlad the STL file.
For extra strength, I added a nut to improve clamping, since the part was only 3 mm thick.
The chain guard is now mounted on the bike. The screw in the frame will be replaced with a countersunk version at a later stage.
I made the best out of the old exhaust pipes, and the bike looks pretty good with all four pipes mounted. Really happy with how it turned out.
Rear view
Right side
The chain was cut and mounted on the front and rear sprockets.
