Ok, to start, I did my best to search through the forums for this solution. I have stated that in the past and others have pointed to entries that solved my issue. Maybe I just suck at searching. Regardless, total rebuild of DT400C, a bit of jerking, jumping, surging. Scary on strong throttle, very strong, great power band. First thought was to double check timing and carb settings. Carb has stock needle, 6F9. Main is 160, pilot 40, stock. Needle position had 2 clips, weird but true. First clip at 4, which is stock, other clip at 3, removed tiny odd clip and kept the larger is position 3. Cylinder bored .5 over.

Ok, timing. I set this at assembly but wanted to verify. Pulser plate all of the way to right as i’m facing the flywheel. Zero adjustment left and it does appear it needs to go another millimeter but can’t. Picture attached showing pulser plate securing screw slots. I’m using 2.75mm BTDC. Why would the pulser coil plate be at its extreme? Key on shaft ok, clear indicator Mark on flywheel, big and small as well as mains replaced. Can’t understand why this adjustment is so far off, what am I missing?

So, way long but surge and buck is issue. Typically from my experience carb, (leak down good). Timing is weird but super close, any other suggestions? Thanks all for any help. May have to zoom pic to see extent of adjustment issue.

Isn't the stator plate itself also slotted?

Anyway... looks like you might be a tiny bit retarded and I'd probably leave it there.

Yep, I am... No excuse on the stator plate being slotted. Just set to existing wear marks and forgot about it during assembly. Today I centered the stator plate and re-adjusted timing, did keep slightly retarded. I’m just lucky that pulser checked out fine and CDI is working properly. Really amazed but anticipate future failure.

Just ignoring basic principal of only adjusting one parameter at a time due to laziness, the carb discoveries along with timing settled down the condition to acceptable.

Thanks for the input.

Carb removed, found several issues. Float level way off leaving bowl fuel level way low. 7.5mm off. Also, main jet stated was incorrect, even though highly unlikely to contribute to issue it was moved from a 180 to the stock 160. Removed and validated reeds are ok, not any official test but no petals cracked and functioned with the ‘blow and return’ test. Seems the intake boot clamp was 100% bottomed but not as tight as it should have been, another hasty assembly mistake. Replaced. Actually gapped a fresh plug, verified timing multiple times, viewed condition of piston and cylinder after break in. All good.

After all of these checks and fixes, the surging problem has been greatly reduced and i’m satisfied the remainder is normal. If not normal, I wouldn’t know since this is my first bigger bore single 2C.

Gets up and goes for sure but quite honestly, not some huge difference from my 250. They both seem strong.

I am considering this problem ‘solved’. Maybe some of these notes will help others.

Mark would never be so rude........!!

Glad you got it sorted.