Scooterotica

Hi Guys,

I've been having some problems with my Li the last two weeks.
I've tried a few things, changed some things around and can't find the problem (for now).
I would love the engine gurus, the riders, the experts...well...everybody if someone can give me an idea of what it can be.

First the specs:
Li 125 engine
Used to have a Gori sport (modified by Gori himself) kit, but managed to destroy it,
so now i have an unworked cilinder, basically a stockDL bored to 66mm, no tuning, stock portings
60mm GP Crank
Li150 gearbox, 15/46, MB selector
LTH chainpuller
Surflex B clutchplates with stronger springs
Gori Sport exhaust (36mm) slightly modified with bigger silencer (These are LOUD)
Keihin 28PWK on MB intake, normally with LTH elbow and remote filter
I run 3% Motul 800 (maybe a bit too much)
Variotronic at 23° at 2000 to 4000rpm with NGK B9ES (maybe i should go down to 21° or less)
If i've forgotten something, please ask

Now the problem(s):
Engine always ran well, pretty torquey for a low power engine.
A few weeks ago i had to re-weld the exhaust because of poor fitting. I also checked piston, head, cilinder
(light scoring around exhaust port after less then 1000km with this cilinder)
The base gasket is 1mm aluminium, normally i put some sealant on it, but because it was al clean i put it on whitout (maybe one of the problems)

Two weeks ago i went for a longer ride. Noticed it started not on first or second kick with choke, like usual.
Thinking the mixture screw or pilot jet maybe wasn't perfect after i've put on the bigger silencer i didn't think much of it.
When cold the bike ran as usual, except maybe a bit less smooth...
Then after a couple of km's the engine began to rev high when letting loose of the throttle, changing gears and standing still at lights.
Pulled aside and it looked like the rubber on carb maybe was a little bit loose, or it was the mixture screw.
Turn off lammy, fettle a little, starts perfectly, first kick, runs great....form a km or so!
Then it starts again.
I carried on to where i was going, and checked everything. After sitting a while (cooling down)
everything seemed normal...then it started again...worse and worse.

In the week i changed the rubber carb mount, checked that everything was tight, changed sparkplug etc.
Then checked jets, mixture screw and did some adjustments. Tried it a few times on the streets and everything looked good.

Next day on a longer ride...again!! High revs and shaking when letting go of throttle, changing gears and standing still.
If i let go of clutch a bit when standing still it lowers rpm a little (i now, not so good for clutch)


I've checked everything i could think of: gaskets, rubbers, bolts, checked for oil/gasoline leaks etc
I don't have a tool for an air leak test, so do the old school way with brake cleaner

btw, no blue smoke!
Anyone that has worked on same kind of problem?

Sorry for the long text

Gio

My money is on the base packer/cylinder/case joint, jointing compound is essential if not using a gasket. You can make a usable leak down kit using a mountain bike inner tube and a pump. You won't get a pressure reading as the tube will expand but you can check for bubbles with a spray bottle filled with soapy water.

I was thinking of that, but wouldn't the gasket leak some mixture in this case?
Or would the slightess leak just pull in air?

PS can you explain how to use the innertube to test for leaks? Maybe a link or so?

gio695 wrote:I was thinking of that, but wouldn't the gasket leak some mixture in this case?
Or would the slightess leak just pull in air?

PS can you explain how to use the innertube to test for leaks? Maybe a link or so?

Take the mountain bike inner tube (got mine from Asda for about £2.99) and cut it in half opposite the valve. Now attaché one end to the inlet manifold and the other to the exhaust manifold using hose clips to secure. Inflate using a foot electric pump until the tube has expanded quite a bit don't go mad here. Now spray some soapy water around all the joints, head gasket, base gasket, inlet and exhaust flanges, mag flange. spark plug. In my case the exhaust flange leaked so bad I couldn't get the tube to inflate and had to file it flat before I could check anything else. I have read recently that the test works best with the piston at bdc.

This test won't be as good as a proper leak down kit which uses solid bungs and a pressure gauge but is well worth doing.

Colin

coaster wrote:My money is on the base packer/cylinder/case joint,

Mine is on the exhaust gasket face post the "re-weld the exhaust because of poor fitting" Which gio965 does not show a weep in many cases an d BTW burning gear oil produces white not blue smoke....

PS. I like the gheto leak test Coaster!

Thank you for explaining the leak test with the inner tube.
Great system for someone who doesn't have the right tools.

The exhaust flange is tight and looks ok. The gasket is pretty new.
Its an MB one ( i know thes blow as soon as they get some air)

Like i said, every tip is welcome!

Colin, what a brilliant cheap tool. Off to Asda later to get a tube. What PSI do you go up to and how long do you leave it?
After all these years I think I will for peace of mind start leak testing after rebuilds.
Presumably you could leave it overnight?

Chris.

Today i had a bit of time to check some things.
Re-checked carbfitting, gaskets etc... nothing to see.
So wanted to do air leak test, but because i didn't have the material i decided to start and strip some parts of the engine.

One of the things was ignition.
This is what i found behind the stator:







Grease, and something that looks like oil/mixture or melted grease??

So i guess this is the problem...
I'll replace both seals, and best to check all other while i'm at it.

How can this much grease pass two pretty new oil seal and a new crank?
Bad quality?
Difference in size? (somebody maybe had this problem?)
Or maybe just bad luck?

btw. could it be there was too much grease or the wrong type between the two seals (for the bearings) and now its being forced out at high temps?
I don't remember what type i used...

Also, could this give the high revs? Or is this not possible?

The grease will only be getting past one seal not 2 and does not necessarily indicate an air leak. The grease will expand when it gets hot and force its way past the seal especially if there was too much put in. That looks like it has squidged out rather than being blasted out by combustion forces. The leak down test will confirm.

[quote}....What PSI do you go up to and how long do you leave it?[quote]

Like I said above, this is a cheap and cheerful test. A proper kit as sold by Darrell Taylor uses solid bungs for the exhaust and inlet one has a tyre valve in it and the other a pressure gauge. I've heard figures of between 6 -9lbs which slowly drop away over several minutes. Because you are using an unsupported inner tube it will just expand as you try to build up pressure and you will never reach a high enough pressure to register on most gauges. That doesn't really matter though, there will be enough pressure to check for leaks big enough to have caused your problem.