mc125 no start HELP

[penton117]

Hi fellow Poggers,
Please help. A friend just bought a 1976 MC125 on e-bay from "MX wife" it was "restored" but when we received it, we couldn't make it run. It has a fat blue spark and it's timed at 1.7 mm BTC. It had a bad head gasket leak (you could see fuel spit out above the exhaust) So we took the top end off and resealed the base and head gaskets, retorqued and still no start. Not even a pop. The plug is coming out wet, as well. The coil wire is black (although it had been painted red) and it has the original Bing with the choke in the slide. I have never had a simple 2stroke be so stubborn. What am I missing? Any ideas?

 

[AndyL]

Two items that come to my mind are that you may have flooded the crank case with fuel, an now it wont fire until you drag it around in second gear for a while behind another bike/car/atv and clean out the crank case.

The other thought was that did you maintain the same dimension (or check it) of the base gasket?  The dimension between the top of the piston and the top of the cylinder with the head off sets the port timing.  Maybe it is off.

my $0.02

Andy

[Rocket]

Make sure if you kick it over with spark plug removed that you ground the plug wire or you may ruin the motoplat.  Timing should be advanced a little more, probably around 2.8mm - 3.0mm, but even where it is, it should start.
Rocket

 

[penton117]

Rocket
Re: timing, I thought 1.7 was a bit retarded, but the manual that came w/ the bike said the same thing.

 

[hrbay]

I never have any human motors available when I'm flooded but sometimes just turning off the gas and holding the wick w/o for half a dozen kicks  will get it cleared out  and it will start popping to life. GC

GC

[Rocket]

penton117
I'm at work and don't have a manual here, I was just assuming that the timing would be a little more advanced, like a 175 or the smaller Sachs motors.  If the book says 1.7mm, I'd stick with that.  Might be a misprint and should read 2.7mm.
Rocket
 


 

[Dwight Rudder]

It is possible you have a cracked case. This model was bad about cracking cases and seizing.
You can find several excellent examples of this model around due to the fact they didn't run long. I would also be suspisous of the coil . I thought they were supposed to have the red wire coil.

Dwight Rudder
7 time ISDT / E medalist
7 time National Enduro Class Champion.

[James]

E-mail me if you need a coil. I have one. I have no way of testing it-nor do I remember where it came form-or the application. It is a red wire motoplat coil and is yours if you need it. Thanks, James

I have bike parts in the kitchen cabinets where most people have dishes..