Persistent exhaust leak, BMS Heritage 150, GY6

[SpectreGadjit87]

Ok, so, I’ve gotten some invaluable advice off this site but it’s my first time asking the scooter universe for advice.

I recently replaced the head on my scooter, due to stripped out spark plug threads. In doing so I had to remove the exhaust pipe, which was rusty enough for the weld between pipe and muffler cracked about 70%. After trying about 6 different quick-fixes from the auto parts store, and then chipping and grinding them off, I re-welded it. Did the soapy water test and didn’t get any bubbles so I reinstalled it.

Now here’s where it gets interesting.

I got a stock replacement gasket and put it in, and there was an obvious leak. Long story short, the flange of the exhaust pipe is warped long-ways from bolt hole to bolt hole. I’ll go ahead and say I’m planning on getting a new exhaust, however my question is this: If the timing is off by, say, a single tooth, could that mimic an exhaust leak? ie: a slight, short bogg at wide-open throttle? I ask because before changing the head I forgot to set it at TDC and had to fiddle with it a bit to get it running (I assume) correctly. Look forward to your wisdom, thanks!!

[SpectreGadjit87]

BTW: scooter starts great, runs great up until the highest rpm, then gives a short hesitation, almost like a street racer shifting gears. I’m 99% sure it’s the exhaust not sealing right at the head. Any tricks or tips are appropriated

[Roscoe]

Yes, one tooth off on cam timing will cause problems. Here ya go ... https://www.buggydepot.com/tech-cent...ad-center-tdc/
When you get the new exhaust, make sure the exhaust pipe flange to the head is parallel when the whole assembly is hanging in place on all the brackets. You'll be able to slightly bend a new pipe, once it's been through some heat/cool cycles the pipe will be much harder to bend. When it matches up as designed the exhaust should last a long long long time, Check those exhaust bolts frequently till you are satisfied they are staying tight. If you can get the scooter up waist high when working on the exhaust it makes the job a lot easier.