TC100 starts but won't run.

[Nathan S]

This is infuriating.

The bike will fire everytime you kick it, and will idle weakly for a second or two, and then stall.

Fuel is clean and fresh.
Carby is spotless.
Spark plugs are both new.
Spark is nice and blue.
The choke needs to be about half-way on, or it won't fire at all.
It spits fuel back out the carby (like a piston port engine would - I thought that the rotary valve is supposed to stop that?).
Compression is good.
Pushing the bike around doesn't help.
Endless fiddling with the idle mixture screw doesn't make any real difference.
The carby is still spotless.
The plugs come out wet with fuel, but not dripping.
Removing the carby cover makes no difference.

[gerpster]

You sure carby is spotless?? Sounds like a blocked idle jet to me...any junk in the tank???
I had the same symptoms with bike only running on choke....cleaned carby at least 3 times but in the end it was the idle jet..just kept getting blocked with minor tank crap even after a tank cleanout. A fuel filter fixed it in the end.

[Lozza]

 WTF is a carby cover?? What happens with the choke on full??I would agree with Greg either to much or not enough air/fuel

[pmc57]

Nathan S,
I agree with GregACT but I would also make sure all the jetting and slide in the carby is as per spec?

[pokey]

poor bottom end seals ?

[Rosco400]

have you had it running prviously, stripped it down at all

[pokey]

Checked the rotary valve at all Nathan and the O ring behind it?

[Nathan S]

Full choke = no go.
No choke = no go.
Half choke = half go.

When it does kinda run, it does feel like the old 'cold engine and blocked/too small idle jet' problem. But in my experience, if you keep kicking it and letting it idle until the engine gets a bit of heat into it, then the bike will run.

Has a clean fuel filter.
When I got the bike on Thursday, the tank was nearly full of old fuel, which I drained before doing anything to the bike, and then I refilled with fresh fuel from a clean container. Tank looks clean inside.

Carby has been apart several times now...
Haven't delved any deeper than that though.

The carby cover is the bit that covers the carby...  Seriously, its the access plate for the carby on the rotary valve motor.

[Doc]

check the flywheel key Nathan TS/TC100's are bullet proof and ultra reliable like most small bore trailies 

was there a story with the bike? Maybe it sat for a mechanical reason. Any engine covers off or loose or anywhere it appears it may have been subject to previous work or tinkerings may give up a hint. Wiring played with? Screw heads worn out from regular meddlings?

the little plastic insert thingy that goes in the carb cracked/broken??..my TS75 had issues with not sealing and would not run until it was corrected.

[holeshot buddy]

check the exhaust is not blocked

[Nathan S]

Bike came from Firko. I don't know the history beyond "It was running, then it wasn't". Apparently the previous (to Firko) owner then lost the cover and the airbox, and Firko never really touched it. The TC90 parts bike that came with the 100 donated replacement parts.

Overall, its a very clean bike, with little sign of molestation - still on the original front tyre, I think (it's a gumby looking 'tractor tread' style of thing). Headlight and tail-light are still intact and still working, etc. The odometer reads 2424kms,and looks believable, although the cable is missing.... In any case, its not the usual flogged out old paddock hack.

Flywheel does NOT spin on the crank.

How blocked does an exhaust have to be before it becomes a problem? If you put your hand near the outlet while you kick it over, you can feel the exhaust coming out.

[Rosco400]

Whack a bolt thru the piston, then reliability wont be an issue

[holeshot buddy]

it may not be exhaust but i have
struck many with blocked systems 
symptoms are it starts but wont rev much above idle
and it will fuel up more than normal :'(
see if you can poke a wire or something down through system
you will still feel exhaust out back when running
but if its blocked it will be weak
just another check to do on the list for you nathan

[gorby]

hello nathan,
pull the carby off and look inside the port as you turn it over slowly.the edges of the cutaway on the rotary disc valve should be square,you can see if there is any damage to the leading edge caused by debris(previous piston collapse etc)
or the valve may be mis-timed,its on a coarse spline from memory and gives much the same symptoms as a four stroke with the cam timing out.
 

[Doc]

Condenser, points?? Nathan it's a hit and miss method when the bike cannot physically be seen. If the motor has compression and turns over fine, if it fires then stops and has blowback from the carb, is unmolested and seems otherwise in reasonable condition I'm inclined to go a timing issue. The flywheel may not feel loose but that's not to say it hasn't sheared the woodruff key and the flywheel jammed in a position where the timing is retarded to the hilt. My TS100 sheared these keys on more than the odd occassion and it sounds very remenicent of your wants to start and fire a few times but will not run I probably have a nos set of points kicking around if you want them (free), I've about 100 sets of misc nos points but mainly for early suzuki's