Calling the Guru's...this should be easy....butt

[humanshield]

Been having a odd problem with the 100cc BBK

It's doing pretty good EXCEPT......

I'll be riding along and it "snarks" or "gasps" or "Wops" on me periodically and I have yet to figure it out.

What I mean by those terms is that I'll be riding along doing fine then all of a sudden, for just an instant, it acts as if it completely dies and makes a duck like noise then resumes.  Nothing I've done seems to help.

I have a new head on it and I would swear the intake valve is sticking now and then.   It happens randomly and mostly at higher throttle during cruise.  It's a similar sensation to a HUGE gust of wind hitting you.  The scooter drops 3 - 5 mph and then keeps going.

Reason I say intake valve is because I believe the noise I'm hearing is coming back up through the carburetor.
The valve doesn't have to stick wide open...juuuuust a teenie tiny bit enough to lose compression on that stroke.
I guess I'd have to slap a different head on there to be sure but I don't have another good head to try on it.

FWIW...it seems to be progressing a bit and getting a little worse with time.

Here's what I tried.....

Different Carburetor (No change)
Removed Muffler (No change)
Adjusted valves (No change)
Jetting changes (No change)
New Spark plug (No change)
New Coil (No Change)
New Spark plug cable (No change)
Removed intake (No Change)
Raised Carb Needle (Ran richer but problem still there)
Lowered Carb Needle (Ran leaner but problem still there)
Prayed (No change)
Cussed and swore at it (No change)

I got the kit from 02Starrider off ebay and his kits are great but I'm coming up empty on this one and my gut feeling is it's a sticking intake valve.  I'm running outta idears.

Anyone got any suggestions on this odd ball issue?

[90GTVert]

Are you running the typical CR7HS or CR7HIX? Tried reducing spark plug gap by 0.010" or so to see if it quits?

Does it do it at any throttle position and speed?

[humanshield]

Running a C7HSA NGK.

Ok...will try reducing the gap by .010
Mostly does it at cruise speed, 3/4 throttle or above and often if I make the slightest movement to decrease the throttle.

Scooter is pathetically weak. 35 is about all it can muster. Seems whatever is causing it is slowly progressing. At first I could hit 38 and it felt a bit better. Feels it's slowly losing any initial power it had. Today I honest thought about putting the 49cc back in as IIRC, it did better. Slightly slower on take off, but MUCH better on top end.


This weekend I may swap the 49cc motor back in just to refresh my memory but I do believe the 49cc motor performed noticeably better than this 100cc motor.   Obviously there's a problem but it may be a bad head that came with the BBK.  Not sure yet but nothing else has helped or makes sense at this point.

[boostnjuice]

I had a similar issues when I first installed my bbk, the added power would cause the clutch to slip when I hit a big bump. Don't over look the CVT.

[Fox]

It sounds like an electrical issue to me. One thing I didn't see in your list of things you have tried is a different CDI.

If the two wire connectors on the coil aren't tight that can cause an intermittent loss of spark. Squeezing them with pliers a little will make 'em grab on tighter.

I read a post recently that stated that a kill switch had started mal-functioning causing a similar symptom.

Stator/pickup coil may be on their way out. ?

I suppose that a weak valve spring could cause a "hiccup" .

[humanshield]

It was the carjuretor

Put a 20mm on it and HOLY COW !

Low end is better.  Top end is WAY better.  Midrange is better.

No more snorking and snorting noises and pulls WAY better

[Fox]

Nice! I was way off thinking it was a spark issue. Must be fun to ride now.

[humanshield]

It's definitely better now. But I think I can find more. With 83cc (actual) it still is lacking.
I need to keep looking for the bottleneck. Maybe need to work on the intake manifold. I wish there was a 21mm carburetor.
Feels like 21mm might be the perfect size for 50mm piston size.

The CVT isn't right. It shifts to high gear too early. Does fine up to 25-27 then seems to go straight to highest gear all of a sudden instead of a gradual shift.

[stevec]

i like 02starider parts, he has never done me wrong, i have installed several kits from him.
i had a taotao GT5-50 that i put the "105" cc kit on, domed 52mm piston, was actually 90cc.
it had the same issue where it would feel like it was cutting out and them come back.
i can't remember if it was a bad carb or CDI, either can cause similar problems.
the carb will if the float is not keeping up and runs the bowl too low momentarily and the CDI can if it doesn't send the juice to the coil every time which is not as common as the carb being the problem.
larger cylinders need more fuel and stock 18mm carbs have smaller bowls which can cause them to have to play catch up with the demand it needs.
it's great that you resolved the issue and have better performance.
a good investment is to get an aluminum intake, much smoother flow than the plastic ones.
with all this new power you should consider a bando belt, my taotao shredded a gates powerlink when i upgraded the engine but the bando held up.