Hesitation On Acceleration

quadzilla570 · Joined: 23 Sep 2007 Posts: 6 Karma: 0

I have a chinese scooter 150cc gy6 bms

The scooter hesitates upon hard acceleration. The thing is it only does it at a certain point while accelerating, then it pulls away no problem. When I let off the throttle at lets say 35-45mph and try to hit the gas again it does the same thing at the same point in the throttle range.

IT DOES NOT HESITIATE AT FULL THROTTLE THOUGH ??? IT ONLY DOES IT FOR A SECOND OR SO WHEN I HAMMER THE THROTTLE HARD.

I tried everything cleaned the carb, checked for vacuum leaks, moved the needle on the carb, checked gas filter etc. etc.

The only thing I didnt do was upsize the main jet. Do you think this would do it. I'm hearing that going to a 110 or 114 main jet might work??

Any suggestions

larry8 · Posted: Mon Oct 15, 2007 12:15 am Post subject:

My 125 does the same thing and I thought at first it was dirty jets. Still could be. But I put in oversize jets (both) and it still does it at about 30 MPH with light throttle. If I give it more throttle it takes off.
What I think happens is the engine runs rich right at the point where the main jet starts to work. The idle jet is pumping gas and then the main jet starts to pump gas and the mix becomes too rich till it starts to suck in more air when I open up the throttle a little bit more.
This winter I'll put back in the original idle jet and see if that cures the problem.

_________________
Mybabies:
'67 BMW R69S-"Toots" in rehab
'09 SC250
Previous rides:
'04 Chinese 125
'06 X9-500
'08 MP3-400
'06 BV500
'09 Mana

Fox · Posted: Mon Oct 15, 2007 12:26 am Post subject:

Is your air filter dirty? You didn't mention having cleaned it. Dish soap and water is good for that. Maybe a free flow air filter might be an answer.

The next thing I would check is the carburetor diaphragm. Take it out and put it up to a light to see if it's cracked. If it is, you need to get a new one. A little rubber cement might hold you over till the new one arrives.

A brand new spark plug always improves things. Check the plug cap to make sure it is firmly holding the plug, and that it is screwed on tight to the HT lead.

Valve lash is something else to consider.

Cheers Cool

quadzilla570 · Joined: 23 Sep 2007 Posts: 6 Karma: 0

I went with an ngk plug, it has a brand new filter (the scoot only has 300 miles), I checked the diaphram, I cleaned the carb completely, and it still does it.

I hate taking the carb off and on, and hate to change the jets to find that its making no difference.

Valve lash - What would this do if it wasnt set right. Its weird because it only happens at the same exact point when applying the throttle, even if your going fast then let off and reapplying the gas, or taking off at a standstill.

Maybe it just does this, I'm clueless - theres a guy down the road with an old scoot in his yard with a gy6- I should try his carb and see if it changes anything

Fox · Posted: Mon Oct 15, 2007 1:58 am Post subject:

I say try a different carb if you can. It cant hurt to try it.

My scoot has all kinds of quirks. I just learned to live with them. As long as it runs and moves, I'm happy. A little stutter here or a stumble there doesn't really bother me. I just don't pull into traffic unless I have plenty of space in case it decides to stutter with an oncoming car. Wink

jpmacd733 · Posted: Mon Oct 15, 2007 2:05 am Post subject:

It may be that your scoot is geared for fuel economy and just shifts to a higher gear a little too soon for best performance. I think I would try just a little lighter rollers so the engine will be reving a little higher as it passes through the 30 mph range. The higher revs will give you a little more horsepower in that midrange speed.

Joe

_________________
If your not on two wheels, your wasting gas.

Fox · Posted: Mon Oct 15, 2007 7:04 am Post subject:

Can You Say: "Accelerator Pump?"

Do you have a carb with the thing on the bottom that looks like a flying saucer? This is what pumps that little extra squirt of gas when you hit the gas suddenly. Maybe yours is not up to par....... Icon_dunno

quadzilla570 · Joined: 23 Sep 2007 Posts: 6 Karma: 0

I have 11 gram weights and a mrp racing variator, large yellow torque spring and yellow clutch springs.

I noticed this hesitation alot more since installing these items. Could the weights be doing something different casuing the motor to bog for a sec or two.

Fox · Posted: Sat Oct 20, 2007 3:19 am Post subject:

Are the 11 gram weights lighter or heavier than the originals? Joe mentioned that lighter rollers may get rid of the hesitation. I just put lighter rollers in my 50cc, and it no longer stumbles off the line and throttle response has improved dramatically.

quadzilla570 · Joined: 23 Sep 2007 Posts: 6 Karma: 0

they are lighter than the originals so I am thinking maybe a bit heavier will make a difference.

No matter were I am or how the throttle is applied (light or heavy) the scoot bogs once or twice then takes off at the same point during acceleration.
If I accellerate very slowly when I reach that spot it bogs, if I crack the throttle it goes then bogs then goes again.

larry8 · Posted: Sat Oct 20, 2007 11:41 am Post subject:

jfp350 · Posted: Fri Dec 14, 2007 9:12 pm Post subject:

my 50 does the same thing but it was when I got a freer flowing air filter that it started

_________________
silver lifan 50QT-2A

yellow lifan 50QT-2A (busted parts bike)

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