Sunday, June 28, 2015

Cleaning carburettor Yamaha LS3

The Yamaha LS3 has a Mikuni VM20 carburetor. It's the same as the Yamaha RS100.  As I couldn't find a repair set for the LS3 I bought the one for the RX100.

Yamaha RX100 with also a Mikuni VM20 carburettor
Yamaha RX100 with also a Mikuni VM20 carburettor

The only difference was the air-mix-screw being a bit shorter. If it's not working I can easily replace it with the old original one.

Carburettor repair kit Yamaha LS3 - RS100
Carburettor repair kit Yamaha LS3 - RX100

Exploded view Yamaha LS3 carburettor
Exploded view Yamaha LS3 carbie

This carb was in desperate need of some TLC.

Mikuni carburettor Yamaha LS3 100
Mikuni carb Yamaha LS3 - left

Mikuni carburettor Yamaha LS3
Mikuni carb Yamaha LS3 - right

Before I opened the carbie I cleaned the outside with wax and grease remover and with a couple of steel wool pads.

Carburettor in need of some TLC
Carburettor in need of some TLC

The bottom of the bowl was filled with gunk and rust, amazing how the bike ran with all the dirt in the bowl and main jet.

Dirty float bowl carburetor Yamaha LS3 100 1972
Dirty float bowl Yamaha LS3 100

After cleaning the bowl and taking out the main jet and banjo bolt I took off the floater so I could take out the valve seat and needle.

New and old valve seat and needle Yamaha LS3
New and old valve seat and needle Yamaha LS3

Carburettor nozzle Yamaha 100cc
Carburettor nozzle


With some compressed air I cleaned all the passages and with a wooden toothpick you can reach and clean all the hard to reach corners. 

Mikuni carburettor with hand choke
Mikuni carburettor with hand choke

Mikuni carburettor with hand choke
Mikuni carburettor with hand choke pulled out

Mikuni carburettor with pushed choke

Original air screw  longer than new one..
Original air screw  longer than new one..

As the carburettor set didn't came with a new nozzle (for some reason they almost never do) I just cleaned it and for now I'll keep the original jet needle. When the bike is running again I'll try both needles and see which one is best.

Mikuni main jet and banjo bolt Yamaha LS3 100cc
Mikuni main jet and banjo bolt

Float and new gasket Mikuni carb Yamaha LS3
Float and new gasket Mikuni carb

Mikuni carburettor with Yamaha Reed valve
Mikuni carburettor with Yamaha Reed valve

Mikuni carb attached to reed valve Yamaha LS3
Mikuni carb attached to reed valve Yamaha LS3

Mikuni carb cleaned and ready to use
Mikuni carb cleaned and ready to use



Saturday, June 20, 2015

Cleaning the Steering bearings

Still had to open and check the two steering bearings. I postponed this for a while because I didn't have a steering nut wrench. That's what I thought... When my pushbike had a flat tire last week I found a combination tool in it's toolkit, including a steering nut wrench :)

The job is pretty straight forward; carefully remove the steering nut while holding the under bracket which can start to drop down. There're two bearings, each existing of two races and 19 steel balls. Over the years the grease in the bearings can become old and hard giving wear and rust a chance.

2 top races with 19 balls partly covered in old grease - Yamaha LS3 100
2 top races with 19 balls partly covered in old grease

Lower race with 44 years old dried out grease - Yamaha 100cc 1972
Lower race with 44 years old dried out grease

Collecting the steel bearing balls with a magnet - Yamaha 1972
Collecting the steel bearing balls with a magnet

When I took of the ball race (bearing) cover 5 balls fell out and it took me a while to find them all..#@!<" Anyway I soaked them in old petrol for a while and cleaned the 4 races with wax and grease remover.


Steering head section - Cleaned lower top race - Yamaha LS3
Cleaned  race - Yamaha LS3

Steel race balls after cleaning -Yamaha LS3 100cc
Steel race balls after cleaning -Yamaha LS3

After cleaning I filled the races with high temp bearing grease which I bought once for the rear wheel bearings of my Volvo 122S. All the 38 balls still look like new, no corrosion and no flat spots. Now it was a matter of simply pushing the balls in the grease filled races.

New fresh grease ready for the top race- Steering head section Yamaha LS3
Fresh grease ready for the top race

In the meanwhile the ball race cover and steering nut where nickel-plated for a bit over 3 hours.

Nickel plating the ball race cover and steering nut
Nickel plating the ball race cover and steering nut

When finally tightening the steering nut after reassembly take care not to overtighten  but make sure you got rid of any play. The steering rod must be able to move freely.

Steering head section Yamaha LS3 1972
Steering head section Yamaha LS3 1972

Steering head section Yamaha after reassembly - Yamaha 1972
Steering head section Yamaha after reassembly

I also started the reassembly of the painted frame. Still a long way to go ;)

Reassembling frame - Middle and side stand - Yamaha LS3
Reassembling frame - Middle and side stand - Yamaha LS3

Reassembling frame - using old shocker to keep it together
Reassembling frame - using old shocker to keep it together