Carburetor throttle opening more than half way does nothing.

[katt]

My carb gives full power when throttle is open 55%, opening more does absolutely nothing.

Needle goes all the way up when on 55% open, tested this with air filter off on the stand.

Is this normal?

This is how butterfly looks when throttle is 55% open.

[Happypancake!]

Might need to grind down the stop the the butterfly opens 110% Take a pic of the side of the carb at 55%

[katt]

Another problem i noticed when i set idle rpm screw to 1900RPM and close idle mixture screw shut it idles fine.

Observation, when on center stand and air filter removed needle goes all the way up at 55% throttle.

[GrumpyUnk]

Either you lack fuel flow to keep the mix good past the 55% mark... or there is an obstruction further on, past the butterfly, that is limiting the induction flow into the engine.
I think I read that the slide is opening 100% when the throttle is at 55%. That means there's vacuum in the venturi, past the throttle plate/butterfly, that works the diaphragm and pulls the slide open.
Is it possible the exhaust is blocked such that your engine is huffing and puffing and not able to flow past that 55% amount of air?
tom

[tortoise2]

Missing needle seat?

[scooterpimp]

Check needle & slide for sticking..or diagram issue..

[katt]

Aug 24, 2018 12:14:17 GMT -5 GrumpyUnk said:

I think I read that the slide is opening 100% when the throttle is at 55%. That means there's vacuum in the venturi, past the throttle plate/butterfly, that works the diaphragm and pulls the slide open.
Is it possible the exhaust is blocked such that your engine is huffing and puffing and not able to flow past that 55% amount of air?

Yeah i checked with air filter removed for observation, could this make slide move at wrong time?

Exhaust is stock and i had 47mm BBK installed before (thought i had 39mm), should i try with muffler removed?

I will also check air box for obstructions.

Aug 24, 2018 17:35:19 GMT -5 scooterpimp said:

Check needle & slide for sticking..or diagram issue..

Needle Jet (seat) is there and diaphragm okay needle moves i confirmed visually with filter off.

Installed 50mm BBK and rebuilt carb i think my scooter might have been capped at 35mph with small main jet, however it makes no sense otherwise it would have run lean when opening throttle more, however i ordered a set of main jets and will see soon.

Now i am getting problem when i twist wrist fast from full stop to WOT engine dies, i had this before when my filter was dirty and i had little gas left, low fuel pressure from main jet?

[GrumpyUnk]

I think if you were experiencing 'leaning-out', the engine would start to run poorly as it transitioned back and forth from 'good' to 'too lean'.
If the CDI were limited, spark would get intermittent above a certain rpm. Again, that would cause intermittent firing.
The slide moves in response to vacuum level in the venturi. Is there a spring atop the diaphragm? There should be. Have you operated the slide manually to insure it moves freely without binding? It should drop back down quickly if you lift and then let go.
Another thing that could limit the engine is a poor alignment of the elbow and the insulator with the intake port. If badc enough, restriction can occur that definitely limits power and rpm.
tom

[SMALL CC TEK]

You have some good leads in here . I like the diaphragm or needle theory , i had several of the Chinese needles with the non adjustable needle loose the top retainer . So when you go a quarter throttle it works you chop the throttle full and no power at all or your diaphragm is not in properly and it is sucking air from the venturi not the Vacuum port so it wont lift all the way .

If it is one of the two i fixed them like this epoxy loctite the non adjustable clip or Diaphragm : Just install it right if it seems too small and you can't get it fitting right take some rubber cement and cement it into the groove of the carb works every time . You would be surprised at how many carbs i have done this way . In fact Kymco Chinese factory did it on all of the Agilitys in 2012 i found out by accident when i pulled several apart for a dirt issue under warranty .

[katt]

Aug 26, 2018 9:11:13 GMT -5 GrumpyUnk said:

I think if you were experiencing 'leaning-out', the engine would start to run poorly as it transitioned back and forth from 'good' to 'too lean'.
If the CDI were limited, spark would get intermittent above a certain rpm. Again, that would cause intermittent firing.
The slide moves in response to vacuum level in the venturi. Is there a spring atop the diaphragm? There should be. Have you operated the slide manually to insure it moves freely without binding? It should drop back down quickly if you lift and then let go.
Another thing that could limit the engine is a poor alignment of the elbow and the insulator with the intake port. If badc enough, restriction can occur that definitely limits power and rpm.
tom

Lol was pretty certain i had spring over needle until i randomly found it on the floor by my table, i left it out after i raised the needle all the way, my needle has 5 positions it was middle position, that was after i created thread though so not related to original problem i were having.

Checked for restrictions in elbow and air box all looks good, elbow gasket is almost straight.

My elbow is 16.5mm inner diameter on the engine and carb side, is this okay?

Head mean engine head opening is about same diameter.

Is this a air restrictor?

[katt]

Received new main Jets kit today will try different setups and let you know if it was a jet limitation, my old main jet size was around ~83 installed on 47mm (70cc) its not too small considering default main get for 50cc is size 75, i installed 50mm (80cc).

Changed to 92 and everything works fine power is there however still not much difference after 55% throttle, perhaps i try bigger jet, i also moved needle back in the middle as i was getting over reach condition on slightly open throttle like around 10% open to the point engine was stalling if i open 10% and hold it there.

I'll use my RPM for reference of main jet, right now with size 92 i open throttle all the way from full stop and getting instant 7000 RPM guess thanks to carb acceleration pump giving more gas, but it goes down to 6500 slowly (used to go to 6000 RPM slowly on 83 main jet) and then back up to 7000 RPM and higher, so i guess need bigger main jet.

[katt]

I put main 98 main jet and RPM drom to 6500 is still there, perhaps it comes from a CVT, but i did notice slight power increase, i will keep main jet at 98 while i am breaking in my 50mm BBK and check which main jet gives me more top speed later got to work on 10% problem there's 2 solutions move needle lower if its needle or i am using size 40 idle jet perhaps too large supplying too much trough idle transition ports.

[katt]

Someone with 70cc or 80cc kit and Keihin CVK carb can you please check when you put on middle stand how much you have to turn handle bar (throttle) to reach 8000 rpm?

I am getting to 8000 RPM exactly on 1/4 of the throttle when on center stand.

Also my throttle valve starts to move up at 1/8 throttle then its half way up on 1/4 throttle and on 1/2 throttle its all the way up.

[katt]

Okay tried main jets sizes 85-98 top speed staying at 35mph @ 8000 RPM, only feel no power when i switch to 78 main jet.

My variator weights are 8.5g (currently at 8.3g worn out), i thought 8g is kind of heavy and should give better top speed.

Nailed it down to transmission, contact pad is glazed up and was not providing a good contact, same happened to my rear brake shoes contact area they were not worn, but were like glass.

Will rough it up and try tomorrow.

Another problem i found bell has some thing spot welded on top and its not straight its out of balance?

Ive seen some people remove this part of bell to make it lighter, why do they have it in the first place?

[katt]

I noticed on variator it has grooves along rotation all around the outside area where belt comes in contact, and its flattened out in the are where belt moves, could it cause belt slipping trough variator?

Also my new belt got shrieked on the top side somewhat and deformed way too quick.

Clutch has one of the contact pads worn unevenly and wear on the bell is slightly more closer to center.

Man roughed up clutch contact pads with 220grit sand paper also metal where belt comes in contact on clutch and variator and still cannot beat 35mph barrier on 80cc kit!? What can it be?