I'm stumped

pscook

pscook

Platinum Level Site Supporter
Okay, I've been fighting (tolerating?) an engine which runs terribly for the last year or two. Yeah, I don't get to ride often enough. But here's what I have gone through as well as the troubleshooting history:
  • New piston
  • New pipe o-rings
  • Lectron 38mm carb
  • Replaced Q Stealth silencer with Leo Vince
Runs like crap. No top end, no snap, it just seems to bog or splutter (excessively) when the throttle is more than 50%. Sometimes I can nurse it above half throttle, but rarely.
Troubleshooting:
  • Reinstalled stock 36mm carb
  • Checked Power valve (it works, verified with cover off and running)
  • Reeds good (very little wear, no daylight)
  • Swapped CDI like for like
  • Verified no rags in the intake or exhaust
  • Timing is still where it should be, no broken or dislocated parts on the stator plate
  • New plug(s), tried two different heat ranges and E, EI, EIX, whatever, no difference
Still runs like crap, no difference.
What I'm doing now:
  • Pulled jug, piston looks good. No wear marks, no scoring, no evidence of seizure or other shenanigans. Carbon on the top, but not excessive (to me)
  • Going to swap Leo Vince silencer back to the Q Stealth, just remove a variable (ran fine before, might be the silencer)
  • Check all grounds
  • Replace ignition coil (you never know)

What else am I missing? I will get some solder and run a squish test, but I'm pretty sure it's excessive, and I don't think the excessive squish would cause it to run poorly. Plus, it ran fine before I got my hands into the engine, so it's something that I did to cause the issue. And it's always had a freshly cleaned and oiled air filter, no rags in the intake.

Lastly, here's a stupid question - With a Wossner piston, the arrow points to the exhaust, right?

Upon reflection, it's really starting to lean towards the silencer.

Thoughts?
 
Have you run a compression test? I was also going to suggest the ignition coil but you are doing that now. I would also try another silencer or run a quick test without a silencer. I had a friend with a KTM and he found that the silicone he used to seal his pipe went inside the pipe and eventually broke off and plugged the spark arrestor. From my experience, the arrow points to exhaust.
 
Sounds like an air flow issue. The other thing that comes to mind is a piston installed backwards. Arrow to the exhaust port is right, maybe the piston was stamped wrong. Do you have the old piston for comparison? Make sure the hole locations in the piston match.
 
If nothing else already identified fixes it you can try the pickup coil and stator.
 
Swapped back to the Q Stealth silencer and swapped out the coil including HT lead and plug cap.

The Lectron was installed at the original point of consternation, but the problem has persisted with the swap back to the AS2 36mm carb.

Wossner piston has the intake notches around the wrist pin, and the arrow points to the exhaust. Ring locating pins are in the intake side as well, so I'm fairly confident the piston isn't wrong way 'round.

I'll give it a run tomorrow morning (well, not too early of course) and report back. The problem is that the, er, problem doesn't show until you are hard on the throttle, which is a bit tricky around here as I don't have trails, but I do have a fair bit of straightaway past the house to give it some throttle.

I'll see about pulling a quick compression test tomorrow before I pop the tank back on, just for info.

Thanks for the inputs, I really hope I have good news to report. I think it's been like this for coming on two years, so to say I'm fed up is an understatement.
 
Make sure you have a resistor type plug cap. I had similar issues and it ended up being a non resistor plug cap fitted by the last owner, 2cdi 's later and she runs sweet.
 
You know, I converted from kick to E Start and had to replace the entire wiring harness. I have checked (and double checked) all of the connections, but if I were to focus on a specific connection, which color wire(s) should I investigate? Also, it seems to run better in "rain" mode, if that matters.

Two different CDIs with same results. But I'll go through the wiring connections later this morning.
 
Well. I don't know if it was the coil or the silencer, but it's a 300 again. Bout tossed me over the high side right in front of my house. I can loft the wheel again (if the tire isn't spinning and smoking, that is).

I'll swap back to the Leo Vince silencer when I get a chance, after I swap in the Lectron. Now that I have a baseline I can start to add bits and bobs again.

Phew! Thanks for everyone's ideas and support. Regarding the compression test, it was 100 psi dead cold and it hadn't been run since I put the jug back on. I'll see about another test later today after I remove the tank to put on the Lectron.
 
Depends on your gauge and length of hose. The 300 has a bleed port (smaller bikes don't). It also depends on how fast you can kick the engine over repeatedly.

100 psi seems way low to me. My 250 gets to 200psi using the estart. A compression test is only useful to track your own bike. When it gets to 180psi new, but after a few years only gets to 130psi, then you know it's time for a top end.
 
I was thinking 100 is low, and I didn't recheck before buttoning it up. It only has 20-30 hours on the top end, I can't imagine that it is worn after that short of at time. I'll have to see about checking it soon, just cuz. Rings are cheap enough (just like me!) that I should have some in the spares bin in case.
 
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