I am trying to work out why my bike seized
I have a 2020 husky 150 with a 36mm Keihin carby main jet 178 pilot 45 needle 3rd clip (middle).
New crank and piston replaced at 40 hours bike seized at 43.5
After the rebuild I did 1x 2 minute heat cycle. 2x 5 minute heat cycles in the shed and then jetted it and with plug chops. I went the 178 main as it was slightly rich and I ride in west Australian sand.
since the rebuild I raced slippery but thick muddy clay and also very soupy and boggy loam. Today on a sand track I did one sight lap thenhalfway through the 3rd lap (4th in total) of proper riding it locked up after a roller and then no compression. Checked the plug colour and it was coffee brown with some little specks of metal I’m assuming from the ring nipping up
I know the bike came with a 38mm carby as standard. Could putting a 36mm on it have caused this? I’m lost and need help as I can’t work out why as the plug colour was good and the bike wasn’t overheating. No steam no funny noises it just stopped
The pic is if the spark plug after it seized.
Any help is appreciated as I like riding a small 2 stroke in vets because everyone else has 450s and it’s fun to try pass them.
That main sounds pretty big for a 36mm and 150 engine, very strange it seized.
What needle and fuel? It could be detonation in the midrange, was the bike rattling?
95 unleaded mixed at 40:1 with silkolene pro comp full synthetic
no rattle at all it just stopped.
Needle is NVYA
The sand was wet and deep but I come from Western Australia. It’s deep sand 90% of tracks
178 main seems lean for a 125 stock ktm jetting on the 16 with a 38mm keihin was a 190. Pretty sure my friends beta 125re that has the 36mm keihin stock has a bigger main than a 178.
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Checklist:
Good (91) and fresh (not stale) fuel,
2-storke oil in fuel
Clean filter and intake,
Detonation marks in head/crown?
Air leaks (base gasket, crank seals)?
If all this checks out, likely it's down to the main jet being too small for the conditions (track, temp, elevation, throttle opening).
That's assuming you did your rebuild correctly and your clearances (ring and piston to bore) were in spec.
We’re the rings gaps checked/set?
Let's see the piston
Cast or forged piston? What mfg is the piston from?
All of the above is yes fresh fuel bought that morning, mixed at 40:1, clean and oiled air filter ready for the ride
detonation? Not sure need to take the barrel Off this weekend
will take off magneto and check air leak but it did not rev weird like it was sucking air
ring gap and piston were correct and in spec
wossner piston forged
I have a workshop manual with it not just the owners manual so all torque settings and note settings I checked.
I can’t work out why it did it now and not earliest if the tolerances were incorrect.
only thing I can think of is the 36mm isn’t able to cool it down enough in sand. I’m going to rebuild it and out the stock 38mm mikuni on it and take it back to the same track and see what happens
thanks everyone for their suggestions.
The 36mm carb size wasn't the problem more like you were too lean on the jetting was the problem.
Does the pic of the spark plug show it’s too lean?
if it was lean it would be white wouldn’t it?
that is what is confusing me
When my 250 2-stroke seized, the plug, head and inside the exhaust header were a black ash color. I also had a detonation hole in piston and aluminum specs on plug.
Most cases you would expect white hot if it was lean, but mine ended up black.
Is the underside of the piston crown discolored? Or did it lose a ring locator causing a ring to rotate?
Check your water pump impeller.
Thats what I was thinking too. Cooling issue? Any leaks?
I’ve been away at work for the last 2 weeks and head home this Friday so I’ll strip it down and let you all know.
Thanks for the information
Post pic of piston
Small bore 2 stroke, if you ride fast they are a ticking time bomb....
Pit Row
Do I finally got home after 3 weeks at work this is what I have come across. This is the rear left of the barrel and rear of the piston left side.
Just got home now from work and posted some pics
Just looking at the jetting, NVYA #3, 48, 178, what slide # ? from my perspective, it looks lean, especially in the 1/4- 3/4 throttle range, with the 3/4 to wfo, being a little lean as well, but not as bad as that 1/4- 3/4 range. BTW, That NVYA duel taper needle, is really not what I would be using in that bike.
It looks like the ring snagged a port. Maybe the port edge wasn't chamfered enough or maybe some piece of debris got in there. Are both circlips accounted for? Take the reed block apart and make sure nothing is missing there.
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