BBK bogging down

[Geos]

I upgraded my scooter to a motofine 72cc BBK. It was an easy install and it ran great for about 70miles. Then it started to bog down when i try to get past 20 mph. If i keep gasing it it will get past the bogging some times, but it takes a lot of work to get it there. I had a 85 jet in it, so i tried putting in a 90 and there was no different. I have the stock air box still on it.
Could I have lots some compression? I am using the head that came with the kit. Should i try putting the stock head back on?
I am grateful for any help.
 

[skippy]

try a plug chop to see if running lean or rich. this will show if the jetting right but would think you will need to change to open filter to get more air into the cylinder you will also have to up jet the fuel as well prob 100- 110 jet when after market filter.
 soundes like you need more air and fuel.

[Geos]

I know that i will need to upgrade the amount of air and gas. but the part that i can't figure out is why it ran fine before. I can't really do a plug chop if it can't get it up to wide open. I could understand if it was to lean befor the new jet, but with the new jet and the same amount of air, wouldn't it be richer?

[skippy]

richer mix yes but not enough oxygen. you need the correct balence.befor the ballence was prob about right but to lean. now you up jetted to 95 still low oxygen so you need to rase the air intake. most on hear run 90 -100 jet just on after market filter. so with your bbk kit you will need a higher jetting still.

the reason it prob ran befor is the fuel and air mix was balanced but way to lean. now you up jetted to much fuel to air.

[Geos]

i didn't upgrade the jet til afte i had problems. I will try giving it more air

[streido]

Im still 50cc's and run a 92 jet with an open filter.

Could be you were running lean and now you got compression issues from that but you'd need to do a test to check it.

If compression is ok it prob is too small a jet or too little air or both. The bbk will need more of both to run im sure. It does sound like its maybe not getting enough air in to me, had to tell tho without seeing it. You can take a drill to the air box of you want to keep that instead of going to an open filter. I did that a while ago and drilled about 10-12 1/4" holes in mine on the front cover which did let in more air, had to upjet with that so it def worked. Just need to watch that water doesnt get in.

[Geos]

I tryed a differnt air filter (less resistance) and tryed it with no air filter in the box. It acted the same.

[mono]

My 72cc ran fine with the stock airbox and an 86 jet for a long time...

It's only with a 85cc that I found the stock airbox too restrictive to get a reliable jetting, although even then it would run all the way to it's top speed, and even with an 85cc it proved to be sufficient to just open up the narrowest passages in the airbox and run it with a 92 jet....

I think your problem is not the size of the main jet since it it was running fine before, have you tried cleaning the carb and checking for air leaks, like a cracked manifold ?

[streido]

Also check the main jet isnt blocked or dirty.

[wordslinger]

but it takes a lot of work to get it there. I had a 85 jet in it, so i tried putting in a 90 and there was no different

..do you mean that your scoot is revving relly high? or very low...

[wordslinger]

..i would think a 72cc needs more air than a oem airbox can deliver...

..aaannnd closer to a 100 jet should definately be in order....

[thebatman]

I agree. Probably a little lean. I was running a 90mj in mine..with an open air filter
Where are you located?
Are you still using the oem exhaust?
Did you check for air leaks?....re-torque after the 1st heat cycle?

[Geos]

I changed the gas and cleaned the carb. I did a plug check after i babied it up to wide open, the plug was light tan. we also recheck the valve clearance. it seems to be a little better, but it still runs ruff. My friend that has been helping thinks it sounds more like it isn't firing and there for bogs down. When it is running ruff it seems louder. As it got cooler tonight it was very hard to start.

I do still have stock exhaust. And I live in southern michigan. I am not sure how to check for air leak other than i sprayed some starter fluid are round the carb while it is running and saw no change. I have not tryed re-torqeing it. I will try that tomorrow.

[mono]

Maybe your CDI is on its way out ?

Does the engine rev up all the way when you put the scoot on the center stand, or does it bog down at a certain rpm as well then ?

[Geos]

It revs up all the way on the stand. there doesn't seem like a problem on the stand