Yamaha TZR125 mixture

Hi all,

My son has a Yamaha TZR125 (G reg) and we are having a lot of trouble
making it run smoothly - in fact, when I just left it, it would not
start at all.

The problems started today when having ridden 10 miles, the bike just
stopped (after popping in the exhaust) and refused to start.

Trying to start it at home resulted in further backfiring in the
exhaust, which I thought was an indication of a lean mixture. Looking
at the plugs though, it is running rich as they are black and oily.
After cleaning, we tried basic tuning of the carb, but this led to a
position where we can no longer start the bike - the only
adjustments undertaken were the air and idle adjustments and they have
been put back into the original positions.

Any ideas of what we should try and details of how to adjust the carb
would be useful as I can find no information on the Mikuni website.

We've yet to get a manual for the bike, but I am sure that we can get
it running well without one - famous last words eh!

Any advice most appreciated.

Thanks,
Mark

 

I believe that's a 2 stroke, if so they all do that sir.

See above.

Did you recite the incantations from the Black Magic Book of 2 Stroke
Tuning, with the bike parked dead centre on a pentangle marked on the garage
floor in goat's blood? If not you haven't got a hope.

If you google for Mikuni one of the sites (the Australian one ISTR) allows
you to download a full Tuning Manual for the VM Carbs in pdf format. I
found this quite a good read, but not a quick fix.

Indeed, I am still trying to get optimal running from the TS since last
November, despite a HBOL and the VM tuning manual..

Paging Lozzo.

--
Dan L (Oldbloke)
My Bike 2000 Honda CB500
M'boy's Bike 1990 Suzuki TS50X (Heavily fortified)

BOTAFOT #140, DIAABTCOD #26

 

Mark wrote:
[snip tale of woe]

I would suggest checking/doing the following:
1. Clean the air filter in petrol and then soak in two stroke oil and
replace.
2. Clean the carb (i.e. dismantle completely and then rebuild get new
gaskets)
3. check the oil pump setting (should be behind one of the engine covers)
4. check the compression.
5. Check the timing.
6. get a new plug
7. Get a manual, if you ask the local yamaha dealer you may be able to
get a copy of their workshop manual, if not Haynes BOL.

Its a two stroke, there isn't much else to them.

Have a look here:

http://www.google.co.uk

http://www.partspartners.com/html/tzr125.html

HTH

 

Hi Oldbloke,

Ah, damn. This is where I went wrong. You see, I don't have a garage
so I used the patio and goat's blood is in short supply so I used the
neighbours cat. Neither the wife or the neighbour are best pleased at
the moment!

Thanks, I looked at another Mikuni manual but it was totally
different. This one looks much better. I think that it is similar
enough and this manual (http://www.mikuni.com/pdf/vmmanual.pdf) gives
some nice detailed information.

Well, if I can get it to run first I will be much happier. I am sure
that this manual will help.

Thanks again,
Mark

 

In uk.rec.motorcycles, Mark said:

Is the oil/petrol mix ok?

I had a similar thing happen to a DT125 many moons ago and the air
filter (K+N) was thick with 2-stroke oil.

 

Oldbloke says...

Get a manual, work from that. If you don't know what's what, you could
end up doing damage.

I'm not much use with TZR125s, the man you need is....

.....Paging Jack Hackett

 

<SNIP>

Have you checked the spark?

And not just the fact that it sparks, but that it is doing it correctly.

 

Many thanks to all.

I've done the filter and carbs and am slowly moving on to test the oil
pump, timing etc., but I really need to get a manual now before
testing these items.

The bike started again last night. When cold (and choke pushed in), it
runs really well at idle and throughout the range.

When it gets hot and choke pushed in it backfires through the exhaust
and fails to idle as well. If you pull the choke out it won't idle,
but it revs throughout the range with no problems. It's almost as
though the choke operates opposite to how I would expect.

It also looks like the carb used to have an auto-choke as there are
two interconnected pipes coming from the back of the choke housing.
I'll take a look tonight as to how the choke should work!

Many thanks,
Mark

 

Yep, there is a nice big fat spark. I want to check the timing, but the
damned bulb in my strobe light is dead - is there another way?

Mark

 

Mark Pate wrote

You /can/ check the static timing with your ears, or by eye, or even by
touch. Far better to use a meter though.

 

Yet another thing that I need to check......why isn't there a manual on ebay
when you need one

 

Hi Steve,

Thanks, but how? AFAIK (as I have no manual), there are no points and the
coil is energised via a magnetic pickup (pulse coil?)...in this case, surely
the only way to check the timing is via a strobe - isn't it?

I've bid on a manual on ebay, so I hope to have one soon.

Damned bikes .... damned kids!

Cheers,
Mark

 

Mark Pate wrote

A little early, even for me.

I don't know a thing about your bike but, and this works for all engines
I think, you can turn it over by hand and see when the spark goes.
This is called static timing, the basic set up. Either a vacuum or a
computer will adjust the dynamic timing, i.e. the one you see with the
strobe.

Although it is worth mentioning that timing tends not to go out of
adjustment of it's own free will, it usually requires interference from
man to do that. Concentrate your attention on the fuel/air issues.

 

Thanks Steve,

I'm happy with static timing on a car engine, where you have points on the
distributer but "this" bike seems to rely on current generated by the
flywheel rotating past a magnetic pickup to generate the spark. The only way
to test the timing is probably via a strobe as you can't turn the flywheel
fast enough by hand to generate the spark and judge the position of the
piston at this point.

Please, someone, tell me if I am talking crap!

Cheers,
Mark

 

If there is anything specific you need to know from the manual, I'll have a
quick flick through mine and e-mail you the appropriate details.

Mine is for the 87-93 models.

 

Hi,

Many thanks for the offer, the bike is 1990, so this is ideal. There
is loads that I need to know, but I guess that most of it is quite
detailed - I've put a bid on a manual, so I hope to have one in the
next few days.

If the manual specifies any way to statically test the timing, this
would be very useful.

It seems like the battery is not charging either. I guess that I need
to check for 14V at the battery whilst at 1/4 throttle or something
like that, but is there any way to test the rectifier if this is not
present?

My email address on this post is wrong (as I no longer use this ISP),
so please feel free to email me at

Many, many thanks,
Mark

 

(Mark) wrote in message

Sorry for replying to my own post, but I have come across a rather
good faultfinding chart for charging issues -
http://www.electrexusa.com/Images/fault_finding.pdf - it may be useful
to someone else!

Cheers,
Mark

 

months ago i posted here for advice on a tzr engine, after lots of faffing
about, it was the stator plate, chap who rewound it said he has done
loads,engine is still working in my kart, and before it didn't, cost me a
tenner to have done at a local motor rewinder,

hope this helps

Gary