Snap throttle engine stalling, but bike runs fine

Matt6288 · Today, 08:54 AM

Hello,

I've got a brand new '24 Hawk 250 with less than 600 miles on it, and I installed a brand new PE28mm Nibbi carb to upgrade it. I didn't notice this for the first few rides but not long after upgrading the carb, I noticed a weird problem.

The bike idles and runs perfectly. On the highway, it has healthy acceleration and will reach top speed no problem. If I rev the engine gradually up to full throttle, it revs up just fine. But if I snap the throttle, from closed to fully open instantly, the engine stalls.

Now I have no prior experience working on carburetors, but I'm learning. I've read lots of things and watched lots of videos, and have been playing with my adjustment screws, but no matter what I do, the problem isnt going away.

Any suggestions?

Dusman · Today, 09:33 AM

This can be normal with carbs, especially those without accelerator pumps and are a “round slide” type of carb, which the Nibbi PE28 is. You may be able to remedy this with going up one size on your pilot jet, as an off-idle bog is usually caused by a pilot jet that’s too lean. If your bike pops a lot on deceleration, then you definitely have a lean pilot jet and I would look there first.

red2003 · Today, 10:17 AM

Raise the needle (drop the clip). This is the most likely cause. If you don't know what that means, there are tons of videos on the tube to show you how to do it.

Thumper · Today, 10:57 AM

I jetted a bike too rich and had those symptoms. It tolerated gentle changes, but coughed with a quick blip.

Take a look at your plug. Blackened?

Matt6288 · Today, 12:54 PM

it looks pretty normal to me, but again, I'm no expert.

Also, I've never heard any deceleration popping. But if I had a rich condition, shouldn't the problem go away if I were to back the air screw way out? No matter how I adjust it, whether obviously way too far out or in, the engine still dies with a snap throttle.

**JerryHawk250** · Today, 01:43 PM

The idle mixture screw only effects the idle mixture. As red2003mentioned. You might try raising or lowering the needle to see if that clears it up.

Today, 08:54 AM	#1
Matt6288 Join Date: Apr 2024 Posts: 4	Snap throttle engine stalling, but bike runs fine Hello, I've got a brand new '24 Hawk 250 with less than 600 miles on it, and I installed a brand new PE28mm Nibbi carb to upgrade it. I didn't notice this for the first few rides but not long after upgrading the carb, I noticed a weird problem. The bike idles and runs perfectly. On the highway, it has healthy acceleration and will reach top speed no problem. If I rev the engine gradually up to full throttle, it revs up just fine. But if I snap the throttle, from closed to fully open instantly, the engine stalls. Now I have no prior experience working on carburetors, but I'm learning. I've read lots of things and watched lots of videos, and have been playing with my adjustment screws, but no matter what I do, the problem isnt going away. Any suggestions?
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Today, 10:17 AM	#3
red2003 Join Date: Jan 2007 Location: Northern Vermont, USA Posts: 1,230	Raise the needle (drop the clip). This is the most likely cause. If you don't know what that means, there are tons of videos on the tube to show you how to do it. __________________ First Chinabike: 2006 Roketa RSX200E Current Chinabikes: 2023 Titan DLX & 2022 Lifan KP Mini w/ 210cc BRT kit, 22 RWHP!
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Today, 10:57 AM	#4
Thumper Join Date: Feb 2021 Location: Kansas City Posts: 2,340	I jetted a bike too rich and had those symptoms. It tolerated gentle changes, but coughed with a quick blip. Take a look at your plug. Blackened? __________________ -2022 5 speed Templar X Orange, OEM 51T rear sprocket, 14T front sprocket -NOS 2020 KTM 250SX (2-stroke motocross), less than 10 hours on it
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Today, 12:54 PM	#5
Matt6288 Join Date: Apr 2024 Posts: 4	it looks pretty normal to me, but again, I'm no expert. Also, I've never heard any deceleration popping. But if I had a rich condition, shouldn't the problem go away if I were to back the air screw way out? No matter how I adjust it, whether obviously way too far out or in, the engine still dies with a snap throttle. Attached Thumbnails
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Today, 01:43 PM	#6
JerryHawk250 Moderator Join Date: Oct 2016 Location: Houma, La. Posts: 11,572	The idle mixture screw only effects the idle mixture. As red2003mentioned. You might try raising or lowering the needle to see if that clears it up. __________________ 2023 Lifan Lycan 250 Chopper 2023 Venom Evader 2022 Lifan KPX250 2020 Kawasaki Vulcan S 2004 Honda ST 1300 2016 Black Hawk 250 (sold) Keihin PE30 carb,125 main,38 slow.Pod filter,ported & decked head 10:1 CR,Direct Ignition Coil,15/40Sprockets,NGK DPR8EIX-9,De-Cat,Dual Oil Cooler,Digital Cluster 2016 Cazador180 XL 2014 Coolster150 JerryHawk250.com My YouTube Channel
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Today, 09:33 AM	#2
Dusman Join Date: Jan 2018 Location: NC Posts: 217	This can be normal with carbs, especially those without accelerator pumps and are a “round slide” type of carb, which the Nibbi PE28 is. You may be able to remedy this with going up one size on your pilot jet, as an off-idle bog is usually caused by a pilot jet that’s too lean. If your bike pops a lot on deceleration, then you definitely have a lean pilot jet and I would look there first.
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