question on geometry on my 350x transplant [400ex]

[Rocks&roots]

OK fellow tricksters here is a weird situation, I noticed when I sit on my 350x the chain instead of getting tighter like it should it gets looser which @ times when I get on it the chain wants to skip over the rear sprocket,not all the time but its bugging me and one thing came in to mind,if I had the rear shock bottom linkage in upside down would this cause my issue?? or is it a geometry problem where the motor is sitting up to high? but I cant see how I mounted it the same way matt350x did using the same brackets! anybody feel free to tell me your thoughts on this fluke issue! thank yopu

[oldskool83]

$20 says your front sprocket is not inline with the rear sprocket. Most guys fail at that thinking all sprockets just line up...they wont. Get a straight edge and check. Sprocket spacers will need turned at a machine shop. They do not line up with a 300ex motor so they will not line up with a 400ex motor.

[thomaskwar]

If your chain is getting looser when you sit on the bike, it’s likely a geometry issue. The rear suspension travel should normally tighten the chain as the swingarm moves, so if it’s doing the opposite, something’s off.

If the bottom linkage on your shock is flipped, that could absolutely mess with the geometry by changing how the swingarm pivots. I’d start there—flip it back and see if it changes anything. If that’s not it, the engine placement might be the next culprit. Even if you mounted it like Matt350x, small variances in how high or low the engine sits can change the chain angle, especially if it’s slightly out of alignment with the swingarm pivot point.

Another thing to check is your rear axle carrier—make sure it’s seated properly and the chain adjustment isn’t out of whack. Also, double-check the alignment of your front and rear sprockets. (https://boomerangbet.one/) If they’re not in a straight line, it can cause weird tension issues too.