Tuesday
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Posts posted by Tuesday
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First guess is it is just a tiny 50cc engine and the compression is just fine.
Second guess is the piston barrel seal.
If you stick a dribble of 2-stroke oil down the spark plug hole to coat the
bore and rings. Put the sparkplug back in and turn the engine over.
If there is more compression (even just at first) you have traced the problem to the piston barrel seal.
A time ago I had a knobend rebore my bike engine, The tit-head bored the barrel out to the
maximum wear limit.Hope this has not happened to you.
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Biggest performance boost with the TZR50 is sorting out the exhaust.
It could be that all the restrictions have not been sorted.
Poster in another thread had to split the standard pipe to remove the
restriction and then weld back up again.
Have a look in the airbox for any other restrictions.
On my TZR50 I have a 110 main jet, needle jet at mid position.
Arrow Exhaust.
Front cog 11 teeth, back 47 teeth.
Spark plug BR9EIX
More holes cut in airfilter frame, see pic below.
top gear 50 MPH at 9500 RPM and reves passed 12000.
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Is it electronic or mechanical drive?
Had a problem with my TZR50 that turned
out to be the electronic sensor at the hub.
Put some info in the forum at
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If it is poor compression, I would expect it to be hard to start but at least show some signs of life.
The lack of petrol mixture being pulled through the engine is a big clue though. Crank seals,Bottom Barrel gasket?
Unlikely but is it possible the spark timing is wrong (Don't know if it is adjustable on this engine)
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Couple of tips for getting seized brake pistons out of calipers, add yours.
Opposed piston brake calipers, Oh yes.
Usual story, piston on one side gums up and the other one does all the work.
Time to split the caliper and get both pistons moving freely.
The stuck piston tends not to want to move and offers little material to grab onto.
1/ Before caliper dis~assembly , remove brake pads and caliper from wheel.
Clamp the free piston into the body of the caliper with mole grips but leaving
space for the jammed piston to move.
Pump the brake at the pedal/lever, the jammed piston may come free. Up to you if
you push it right way out and spill fluid, or leave it sticking in a bit and hope to
remove it completely later.
2/ If step 1 does not work to free the piston enough and you have split the caliper and
are looking at a gummed in piston that is not moving. Don't grab it with mole/pipe grips
as you will cuff the surface that the forms your brake seal.
First tip is pretty messy but works sometimes.(Brake fluid is nasty stuff, be careful).
You need a high pressure bike pump (180psi+) and an old inner tube. Cut the valve out the tube but leave some rubber round the base.
Secure the caliper and pressurize the brake fluid/air by pushing the bike valve onto the caliper surface over the fluid feed hole (the one that passes fluid between the caliper halves).
If you are working on the caliper side that has the connection to the master cylinder, block this up with an appropriately sized bolt.
Might shift with the bike pump pressure.
3/ If the piston still refuses to move and you are on the point of chucking the caliper, the following worked for me:
Fill the caliper completely with an appropriate fluid, I will suggest water here.
Cover over the fluid feed hole with a small piece of inner tube rubber.
Clamp the rubber to the caliper using a big vice and squeeze up as much as you dare to seal the fluid hole.
Fun bit - get a blowtorch to the back of the caliper and boil the "fluid" inside.
Pascal alone knows the pressure it will get to.
The combination of heat, pressure and bad language managed to pop out the one I worked on.
Might work for you too.
ps. (Brake fluid is nasty stuff, be careful)
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Hi sooty.
Best guess is the mixture is wrong at midrange engine speeds (too rich if main jet has been upped).
Stick the standard 195 main jet in and set the needle jet at mid way.
Give it a blast and if OK check the plug colour too black (sooty ha.) and the mixture is too rich etc.
Some stories of power valve set up causing poor performance are on this site and could prove instructive.
all the best
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Thanks everybody for the welcome.
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Hello folks.
Picked up my 7th Yam last month and joined the Yamaha club tonight.
Present bike is a TZR 50 rescued from under a pile of crap in some blokes garage.
MOT failed today on the drive chain being too tight, a first for me but in all
honesty it was the correct call by the garage. Sprocket set bought on ebay was
3 links too short!
Live and learn.
Just dropped a fix for the wee bikes digital speedo repair in the garage forum.
Hope it will be of use to someone.
Tuesday
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Found a fix for my broken electronic speedo sensor.
Bike is a TZR 50 but I guess same fix is suitable for similar speed sensors
on other models.
The sensor is on a small PCB buried in a plastic plug that is held in place by a small metal pin in the
front wheel speedo assembly.
If the wiring is OK and the sensor is the suspect it can be changed out if you are good at soldering small
stuff and up for giving it a bash yourself.
Replacement part is a small 3 leg IC made by Allegro Microsystems, part number A1220EUA-T costing a couple of quid.
Data sheet on the net.
Part needed center leg bent underneath to match PCB. After testing shows it is working, best to cover in glue to secure and encapsulate the circuit.
see http://www.louiiv.pwp.blueyonder.co.uk/Speedo_repair/repair.html
yamaha dt50cc.mx lack o compression.
in Yamaha Workshop
Posted
Another thought.
If the exhaust port has been raised by a previous modder, this will drop the compression ratio.