problems with scooter after head replacement By delta9 (Read 424 times)

[delta9]

I just replaced the head yesterday due to broken exhaust stud. I replaced the exhaust with a performance exhaust from ebay. Also rejetted from 108(stock) to 120. Now it kinda bogs when I rev it and when I go WOT and hold it, it acts like I'm going open/closed/open/closed. In the video I go immediate WOT and hold it until I stop video.



Any ideas?



Here is youtube video.

[Alleyoop]

Is it a stock motor 149.6cc's or does it have a Big Bore Kit? If stock no big bore kit the 120 main jet it to big for a stock motor 110-115 the max and that is if you have a Free Flow Filter and Free Flow muffler.
Alleyoop

[delta9]

Free flow filter and exhaust. Stock bore size. Performance cdi and coil. 12g weights.

[delta9]

Just changed to 114 jet and no change in symptoms

[Alleyoop]

It could be the Performance CDI plug in the OEM CDI and see if it stops the Surging. If same with the OEM CDI put in the 108 Main jet. You did not change the carb did you and get a bigger one.

Also are you sure you are not off on the timing? Very easy to get it out of time if your not careful when replaceing cam or top end.

[delta9]

Ok put 108 jet back in and it's better. CDI was installed before the head replacement and working properly before. I can't do any testing it just started raining. Stock 24mm carb. The stock idle jet is 40. I didn't change it.

Now working properly but there's a little popping when giving a tiny throttle 1-2% from a stop. Just enough throttle to engage the clutch. I'm thinking low speed needle needs leaning.

Elevation here is 1,096'.

Does 108 jet sound right for mods? Everywhere I researched showed 120-130 for intake and exhaust.

[Alleyoop]

The popping is because of the Pilot Jet being a #40 it should be a #35 40 is to much fuel that is what is causing the popping.
Alleyoop

[delta9]

As for the timing, I had the new head on but not fastened and pulled up to see piston. Moved fan to where piston was at maximum top. Then installed the cam and chain where it was supposed to be. I moved cam 1 tooth in either direction to make sure I wasn't off and the 2 small holes on cam didn't line up. I lined it up and bolted head down. I did valve clearance before releasing the cam tensioner but after letting it tighten I checked the clearance again and it was still good at .005.

Bike starts right up within 1 second of pushing start without touching throttle. I would think bad timing would cause hard starts

[delta9]

It wasn't popping at all before I pulled the head and installed the new exhaust. There was a small exhaust leak because of the broken stud at the time. The carb low speed fuel screw was turned all the way in clockwise though. I adjusted it out about 1.5 turns and was running fine about a week ago before the mods. This is the way I got the bike. Why would 40 jet be installed from the factory if it was too big?

Can I just turn the screw all the way in and if needed, take washers out of the needle?

[Alleyoop]

The BRAND NEW SCOOTS with 24mm carbs DO NOT come with a #40 pilot jet someone slapped that in either that or the SCOOT IS NOT NEW. That is a lot of fuel, just so you understand my motor is the same as yours a 157QMJ but it has a 62BBK with a 60mm Stroker crank and a 24mm carb with a #38 PILOT JET and a 122.6 Main jet and all the performance goodies you can think of. So as you can see I have 30 more ccs than you do and It only takes #38 Pilot a #40 is to much even for my motor.

So all I can tell you is the #40 is to much fuel and is causing the popping. Change it or live with what you have.
Alleyoop

[delta9]

It is an old scooter. ~2500 miles 2005 model year. I just inherited it from previous owner a couple weeks ago. Sat in his garage for about 5 years because he couldn't get it started. I traced it to a bad coil and started right up. I pulled the carb and cleaned it and everything was good on the bike except for the exhaust leak. I could get it to 45 on the chinometer, 50 downhill. I figured it was corked up for emissions so I started modding it.

I'll try leaning it out when the weather clears up in a couple days. Thanks for your help

[Alleyoop]

Ride safe,
Alleyoop