Anyone know how to fix my problem?

Ragekillen

New Member
Dec 5, 2020
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So backstory about 3 months ago i purchased the bbr stage 4 80cc kit (second motor previously had a 49cc).
Bike ran fine alot more power then my old 49cc. I finished break in and had no noticeable issues with standard mix ratio.

Now for the issue i suddenly have very low power and jerking i removed the exaust baffle for the ability to even use it. due to a accident i left the petcock off when getting on the next ride and right before it ran out of fuel i had a massive power spike it might be more power then i had originally so now i have the petcock set to the sweet spot with the downside being if i have a rather large stretch of wide open i run out of fuel in the line before the drip can replace.

So the obvious issue is its flodding and the carb adjustment screw seems to be doing nothing while moving the petcock to the right spot works i would like to fix the carburetors fuel dumping issue instead of rigging it any help is appreciated.
 

Venice Motor Bikes

Custom Builder / Dealer/Los Angeles
Mar 20, 2008
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Los Angeles, CA.
If you run with the petcock 1/2 shut you are running the engine very lean!!! That's why if feels more powerful, but can easily be burning the engine up!!

I suggest installing a slightly smaller main jet in the carburetor instead. ;)
 

Ragekillen

New Member
Dec 5, 2020
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If you run with the petcock 1/2 shut you are running the engine very lean!!! That's why if feels more powerful, but can easily be burning the engine up!!

I suggest installing a slightly smaller main jet in the carburetor instead. ;)
What size is the stock jet ?
 
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Ragekillen

New Member
Dec 5, 2020
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What size is the stock jet ?
Never mind i figured it out the performace carb has a stock size of .78mm

So i will be ordering a jet kit very soon but what are the other possible issues if this is not solved by raising/ lowering the throttle needle clip and jet
 
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Davideo

Active Member
Feb 25, 2020
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So backstory about 3 months ago i purchased the bbr stage 4 80cc kit (second motor previously had a 49cc).
Bike ran fine alot more power then my old 49cc. I finished break in and had no noticeable issues with standard mix ratio.

Now for the issue i suddenly have very low power and jerking i removed the exaust baffle for the ability to even use it. due to a accident i left the petcock off when getting on the next ride and right before it ran out of fuel i had a massive power spike it might be more power then i had originally so now i have the petcock set to the sweet spot with the downside being if i have a rather large stretch of wide open i run out of fuel in the line before the drip can replace.

So the obvious issue is its flooding and the carb adjustment screw seems to be doing nothing while moving the petcock to the right spot works i would like to fix the carburetors fuel dumping issue instead of rigging it any help is appreciated.
Try not running at full throttle for extended periods. Running with the throttle wide open often does not result in increase speed it only allows excess fuel through the engine. The adjustment screw only affects the idle speed and does not have anything to do with the mixture control.
That is controlled by the movement of the tapered needle valve in the jet.
Fuel running out of the carburetor suggests to me that the float valve is not closing when the bowl if full (sticky valve or faulty float).
 
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Ragekillen

New Member
Dec 5, 2020
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Update:
I realized i had the nt carb that came as a spare i took the jet out of it and replaced my hp carb jet. performance is great again with petcock wide open only noticeable issue as of now is it seems to top out at some point, the engine kinda stumbles for about a 1/2 second allowing rpm drop and it picks back up after until it stumbles again. Im thinking the jet is just a hair or 2 off for the current air density
 

MedicWill

New Member
Oct 25, 2010
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Update:
I realized i had the nt carb that came as a spare i took the jet out of it and replaced my hp carb jet. performance is great again with petcock wide open only noticeable issue as of now is it seems to top out at some point, the engine kinda stumbles for about a 1/2 second allowing rpm drop and it picks back up after until it stumbles again. Im thinking the jet is just a hair or 2 off for the current air density
I had the same problem using cheap stock carbs and HP carbs.
Switched to a Mukini and the problems went away.