hellcat carb issue plaguing me

tophattitus · 08-02-2020, 08:44 PM

So to give a little history on my bike I've gone through 3 carbs and I'm on my 4th. the first one had a float stuck, and tamper proof screws. i believe it was a pz19. i replaced it with the same carburetor from a second source. it did not match up with the heat shield on the intake so i had a massive air leak. the next carb i ordered was a vm22 with a new intake manifold and heat shield. i changed the jets and it ran good for a while. eventually i noticed if you twist the throttle very quickly it sounds like its bogging and if i hold it after twisting it fast it dies out. I've tried re jetting it multiple times and cleaning it and no luck. I'm onto my 4th carb now. i ordered a pz25 and a new intake manifold and heat shield direct from taotao. i have the same problem again. except it runs perfect when on choke. so i know its running lean, and i expect a air leak again. however I've tightened every bolt from the intake to the carburetor. I've even tried it with and without the heat shield in between. I'm honestly at my wits end and about to give up on my bike. I am wondering if anyone could give me some sort of incite on what else could be causing this or if they think its a lost cause.

ripcuda · 08-03-2020, 02:12 PM

Stock carb on my HC is the PZ-25 Keihin clone. I slotted the tamper-proof bowl screws with a dremel so I could get to the jets.
The stock jets are 88 main, 32 pilot.
I drilled out the main jet to 90 (mm).

I put one thin washer under the throttle needle (for better midrange).
I also drilled out A/F screw tamper-proof plug and set A/F screw to 1 turn-out.
My HC runs great in stock configuration (w/ stock airbox) with these settings.

But wanting more... I too have gotten a vm22 Mikuni clone carb.
The vm22 fits the stock intake and spacer... but it does have a larger diameter hole than the spacer. I dremeled the spacer to taper the sharp edge where they meet to smooth airflow... but it still necks down a little through the spacer into the stock intake. I've had no air leak issues with the o-rings on the intake/spacer with the vm22.

I have not got my vm22 fully jetted proper yet. Keeping the stock airbox... I did have to lower the throttle needle... as I was bogging badly in the mid range. My vm22 came with a #95 main jet... I drilled this open to ~#98... but it's still not fully reving out for me. Think I need to try #100 next.

tophattitus · 08-03-2020, 04:06 PM

Yours is a 2020, mines a 2019, and they have different parts for their bikes. theres like 3 different headlight controls for hellcats. so a difference in carburetors isn't uncommon. but i know the bikes running lean. ive checked the top of the carb, the carb to intake manifold, and the intake manifold to the head with propane and there's no leak. with the pz25 ive changed needle settings, the top two needle settings the problem gets worse, the middle and the lower two it remains the same. and changing the af ratio richer shows no difference, but leaning it out makes it worse. im about 90% sure its not a carburetor issue.

RedCrowRides · 08-04-2020, 07:41 PM

Man if you havent checked your valve clearances i would spend an hour and do that before i messed with anymore carbs , the valves on all the Grom clones are notorious for being too tight from the factory and it gets worse with more miles.The valves being too tight can cause all kinds of strange running problems that seem like carb / fuel issues but really arent.

Just a thought , i learned this the hard way so believe me it is worth a shot at trying.
Get your valves right and see if that don't help, i bet it will and if not at least you know that isnt the issue , it aint that hard a job. Then you can go back to carb tuning.

08-03-2020, 02:12 PM	#2
ripcuda Join Date: Mar 2015 Location: Spokane, WA Posts: 253	Stock carb on my HC is the PZ-25 Keihin clone. I slotted the tamper-proof bowl screws with a dremel so I could get to the jets. The stock jets are 88 main, 32 pilot. I drilled out the main jet to 90 (mm). I put one thin washer under the throttle needle (for better midrange). I also drilled out A/F screw tamper-proof plug and set A/F screw to 1 turn-out. My HC runs great in stock configuration (w/ stock airbox) with these settings. But wanting more... I too have gotten a vm22 Mikuni clone carb. The vm22 fits the stock intake and spacer... but it does have a larger diameter hole than the spacer. I dremeled the spacer to taper the sharp edge where they meet to smooth airflow... but it still necks down a little through the spacer into the stock intake. I've had no air leak issues with the o-rings on the intake/spacer with the vm22. I have not got my vm22 fully jetted proper yet. Keeping the stock airbox... I did have to lower the throttle needle... as I was bogging badly in the mid range. My vm22 came with a #95 main jet... I drilled this open to ~#98... but it's still not fully reving out for me. Think I need to try #100 next. __________________ '20 TaoTao Hellcat 125 "grommet" '04 Yamaha TTR-125LE '00 Yamaha TTR-90 '07 Kinroad XT200GY Runmaster (sold) '07 KMD GY6 150cc ATV (sold) '07 Kangchao 250cc ATV Monster (sold) Baja Moto DB-30 "Doodlebugs"(x3) (sold) '06 Hi-Bird 200 parts bike (sold)
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08-04-2020, 07:41 PM	#4
RedCrowRides Join Date: Jun 2018 Location: Florida Posts: 759	Man if you havent checked your valve clearances i would spend an hour and do that before i messed with anymore carbs , the valves on all the Grom clones are notorious for being too tight from the factory and it gets worse with more miles.The valves being too tight can cause all kinds of strange running problems that seem like carb / fuel issues but really arent. Just a thought , i learned this the hard way so believe me it is worth a shot at trying. Get your valves right and see if that don't help, i bet it will and if not at least you know that isnt the issue , it aint that hard a job. Then you can go back to carb tuning. __________________ 2001 Mustang GT 2004 Sportster 2018 VADER 2020 Orion RXB250L
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08-02-2020, 08:44 PM	#1
tophattitus Join Date: Aug 2019 Posts: 22	hellcat carb issue plaguing me So to give a little history on my bike I've gone through 3 carbs and I'm on my 4th. the first one had a float stuck, and tamper proof screws. i believe it was a pz19. i replaced it with the same carburetor from a second source. it did not match up with the heat shield on the intake so i had a massive air leak. the next carb i ordered was a vm22 with a new intake manifold and heat shield. i changed the jets and it ran good for a while. eventually i noticed if you twist the throttle very quickly it sounds like its bogging and if i hold it after twisting it fast it dies out. I've tried re jetting it multiple times and cleaning it and no luck. I'm onto my 4th carb now. i ordered a pz25 and a new intake manifold and heat shield direct from taotao. i have the same problem again. except it runs perfect when on choke. so i know its running lean, and i expect a air leak again. however I've tightened every bolt from the intake to the carburetor. I've even tried it with and without the heat shield in between. I'm honestly at my wits end and about to give up on my bike. I am wondering if anyone could give me some sort of incite on what else could be causing this or if they think its a lost cause.
	0

08-03-2020, 04:06 PM	#3
tophattitus Join Date: Aug 2019 Posts: 22	Yours is a 2020, mines a 2019, and they have different parts for their bikes. theres like 3 different headlight controls for hellcats. so a difference in carburetors isn't uncommon. but i know the bikes running lean. ive checked the top of the carb, the carb to intake manifold, and the intake manifold to the head with propane and there's no leak. with the pz25 ive changed needle settings, the top two needle settings the problem gets worse, the middle and the lower two it remains the same. and changing the af ratio richer shows no difference, but leaning it out makes it worse. im about 90% sure its not a carburetor issue.
	0