Remove RPS Hawk 250 Catalytic Converter

FrozenSalad · 02-06-2019, 08:25 PM

Hello all, I'm new to this forum but have had my Hawk for about a year now. I was just wondering if anyone that has one has removed the Cat from the exhaust and if so, did it yield any substantial power gains? I know it will need a carb adjustment after, but just wanted to know what others have experienced before I dive in.

Thanks for any feedback!

**JerryHawk250** · 02-06-2019, 08:53 PM

Welcome aboard!

There are a few of us that have gutted the cat. It will definitely help it breathe. Carb tuning is a must do after. The stock carb are tune real lean from the factory. Here's a link to my tread. http://www.chinariders.net/showthread.php?t=17913

Red Hawk · 02-06-2019, 09:33 PM

Definitely a must do. I cut the cat out and tig welded a new pipe section before the first engine start. Spend the bucks and get a new carb. You'll eventually want to port the head it's not hard just be clean with your parts on reassembly. Also recored the stock muffler is much less restrictive and almost too quiet on the road.

I'd say after all that my hawk has about 50% more HP now, it's very close to a CRF 230. But it's still a 230! So keep your expectations grounded. Pure dirt bikes will still eat you alive. But you can run the roads!

There's some good threads on China riders about this.

Megadan · 02-07-2019, 02:40 AM

Without delving into the world of head porting, which is definitely worth it if you have the ability, the single biggest restriction of these bikes from the factory is the exhaust. Two cheap and easy mods to do to the stock exhaust are to decat it and clean up the welds at the head pipe inlet where it meets the head. Combined with an intake upgrade (airbox mod or pod filter and a properly jetted carburetor these engines really wake up in the mid range and top end. As the others have mentioned, the factory carb tuning leaves a lot to be desired, and even with no other mods, having the carb jetted properly makes a big difference on its own.

If you want to take it as far as you can go, the factory ports are the next big restriction to the engine, and with a good port job and larger carburetor you will be able to properly utlize the full top end of the RPM range, where the factory head ports and carb really hold it back.

FrozenSalad · 02-09-2019, 02:41 AM

Thanks for the feedback guys! I had a feeling it was worth doing. I actually have already done the carb upgrade and a 17 tooth front sprocket which helped a lot. But needless to say, I wanted more. I'm able to get to around 60 as an absolute max, but didn't want to get a new rear sprocket with the current power

I'm glad to hear that it was a fair if not big increase in your experience. I hope to have the same luck.

As of now the cat is out and I'm getting ready to weld it in. I just ran out of time for the project today. I'll pick it up again tomorrow and let you guys know how it goes!

Weldangrind · 02-09-2019, 01:23 PM

Welcome FS! Please show us pics of your cat-ectomy.

FrozenSalad · 02-10-2019, 01:13 PM

So I've welded the exhaust and fitted it back on and it fits great and there's a huge power increase (by Hawk standards anyway

It was definitely worth the effort!

I'll post some pics for sure once I finish. While running it, I noticed there's a pinhole leak in the joint, so I'll need to weld that and then do the final grinding and prettying it up. This was my first time welding, so it was a learning experience for sure! Haha, very very fun though. I was hoping to have some more time welding, but it went pretty quick.

To any more advanced welders out there; do you know if the metal's temperature would affect the weld pool? I was getting a lot of heading up of the metal VS a flat and pretty weld like you see a pro do. As a test, I did hold the weld a little longer in some areas and it seemed to flatten out a bit VS beading (as it got hotter I assume), but then it made a little tower of material. Just curious if there is anyone who knows more about welding and might know roughly where I'm going wrong. The surface was very clean and I had flux core wire (.30)

Thanks all!

Weldangrind · 02-10-2019, 01:50 PM

I'm not an advanced welder. I'm just a goofball with a decent MIG.

Without going too far down the rabbit hole, flux core is a challenge when compared to MIG with shielding gas. On top of that, a welder that does not have infinite voltage control is a crap shoot.

Does your welder have four (or five) voltage options, or does it have an infinite control, like a volume knob? Please tell us more about your machine.

To answer your specific question, heat can make a difference but it depends on the material and thickness you're welding. The right voltage and wire speed, combined with the right wire and shielding gas will not be affected by base metal temperature as much. For anything less than 1/4" thick, I'd be inclined to say the base metal temperature is not an issue at all.

As a point of trivia, materials like cast iron require heavy pre-heating before welding. It really depends on what you're welding and what your setup is.

OneLeggedRider · 02-10-2019, 05:52 PM

Flux core isn't going to be a pretty weld. As far as the piling up it sounds like too much wire speed and not enough heat. It should sound like and egg sizzling in a pan and try to take the weld as far around the pipe as you can without stopping, especially with flux core.

Sir kayakalot · 02-10-2019, 09:57 PM

Dan mentioned this, but it’s wirth saying again..... make sure you clean up the factory weld on the inside of the exhaust pipe at the mounting flange. It is ridiculous how much performance can be gained as some of the factory weld jobs are VERY restrictive right there. Cleaning up that weld and removing the cat and re-jetting the carb is by far one of the best mods you’ll do to your Hawk

Tommy

elkhunter338 · 02-15-2019, 12:17 AM

Hmm I am going to have to see if the CSC tt250 has a cat.
The exhaust has a end cap with 3 or 4 bolts, have not removed it yet.

Megadan · 02-15-2019, 12:31 AM

Quote:

Originally Posted by elkhunter338

Hmm I am going to have to see if the CSC tt250 has a cat.
The exhaust has a end cap with 3 or 4 bolts, have not removed it yet.

If I remember correctly, the TT250 does not have the catalyst in the header pipe like the Hawk does, and I believe it is located in the rear section at the very start of the muffler.

The end cap, and more specifically the spark arrestor right behind it is definitely a restriction if flow is what you are after. pcspecialist removed the original spark arrestor on his and replaced it with a straight through tip designed for the pro circuit exhausts as well as drilled out the last baffle in the muffler. See here. http://www.chinariders.net/showthrea...t=16636&page=4
The tip he used. https://www.amazon.com/gp/product/B0...iglink28144-20

If you don't like the tip sticking out so much you could always trim it back to sit flush with the muffler end cap. I did something similar with my ebay exhaust using the factory cap and the ebay mufflers outlet pipe. https://i.ibb.co/7VDc6yL/50243774-10...69349376-n.jpg

02-06-2019, 08:25 PM	#1
FrozenSalad Join Date: Aug 2018 Posts: 3	Remove RPS Hawk 250 Catalytic Converter Hello all, I'm new to this forum but have had my Hawk for about a year now. I was just wondering if anyone that has one has removed the Cat from the exhaust and if so, did it yield any substantial power gains? I know it will need a carb adjustment after, but just wanted to know what others have experienced before I dive in. Thanks for any feedback!
	0

02-06-2019, 08:53 PM	#2
JerryHawk250 Moderator Join Date: Oct 2016 Location: Houma, La. Posts: 11,723	Welcome aboard! There are a few of us that have gutted the cat. It will definitely help it breathe. Carb tuning is a must do after. The stock carb are tune real lean from the factory. Here's a link to my tread. http://www.chinariders.net/showthread.php?t=17913 __________________ 2024 Linhai 300 ATV 4x4 2023 Lifan Lycan 250 Chopper 2023 Venom Evader 2022 Lifan KPX250 2020 Kawasaki Vulcan S (Sold) 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
	1

02-06-2019, 09:33 PM	#3
Red Hawk Join Date: Jul 2018 Location: NEPA Posts: 273	Definitely a must do. I cut the cat out and tig welded a new pipe section before the first engine start. Spend the bucks and get a new carb. You'll eventually want to port the head it's not hard just be clean with your parts on reassembly. Also recored the stock muffler is much less restrictive and almost too quiet on the road. I'd say after all that my hawk has about 50% more HP now, it's very close to a CRF 230. But it's still a 230! So keep your expectations grounded. Pure dirt bikes will still eat you alive. But you can run the roads! There's some good threads on China riders about this. __________________ 2018 Hawk P&P Decked .040 off the head. 17/43 D.I.D. 428, NGK Iridium plug, DeCat, Wrapped pipe, Custom S.S. Muffler core, Nibbi PE30 115/35, L.E.D. Lights, Digital Cluster, USB port, Cutting Bord skid plate, Oil cooler w/ custom CRF oil filter inline, 5Wt fork oil, Rear Shock, CNC Back Rack, 30mm FAT bars, Bark Busters, ProGrips, Adjustable levers, Shinko 700’s lots of Loctite!
	0

02-07-2019, 02:40 AM	#4
Megadan Join Date: Apr 2017 Location: Omaha, NE Posts: 8,110	Without delving into the world of head porting, which is definitely worth it if you have the ability, the single biggest restriction of these bikes from the factory is the exhaust. Two cheap and easy mods to do to the stock exhaust are to decat it and clean up the welds at the head pipe inlet where it meets the head. Combined with an intake upgrade (airbox mod or pod filter and a properly jetted carburetor these engines really wake up in the mid range and top end. As the others have mentioned, the factory carb tuning leaves a lot to be desired, and even with no other mods, having the carb jetted properly makes a big difference on its own. If you want to take it as far as you can go, the factory ports are the next big restriction to the engine, and with a good port job and larger carburetor you will be able to properly utlize the full top end of the RPM range, where the factory head ports and carb really hold it back. __________________ Hawk Information and Resource guide: http://www.chinariders.net/showthread.php?t=20331 2018 Hawk 250 - Full Mod list here. http://www.chinariders.net/showpost....62&postcount=1 2024 Royal Enfield Shotgun 650 https://chinariders.net/showthread.php?t=34124
	0

02-09-2019, 01:23 PM	#6
Weldangrind Join Date: Mar 2009 Location: Sardis, BC, Canada Posts: 25,977	Welcome FS! Please show us pics of your cat-ectomy. __________________ Weldangrind "I figure I'm well-prepared for coping with a bike that comes from the factory with unresolved issues and that rewards the self-reliant owner." - Buccaneer
	1

02-09-2019, 02:41 AM	#5
FrozenSalad Join Date: Aug 2018 Posts: 3	Thanks for the feedback guys! I had a feeling it was worth doing. I actually have already done the carb upgrade and a 17 tooth front sprocket which helped a lot. But needless to say, I wanted more. I'm able to get to around 60 as an absolute max, but didn't want to get a new rear sprocket with the current power I'm glad to hear that it was a fair if not big increase in your experience. I hope to have the same luck. As of now the cat is out and I'm getting ready to weld it in. I just ran out of time for the project today. I'll pick it up again tomorrow and let you guys know how it goes!
	3

02-10-2019, 01:13 PM	#7
FrozenSalad Join Date: Aug 2018 Posts: 3	So I've welded the exhaust and fitted it back on and it fits great and there's a huge power increase (by Hawk standards anyway It was definitely worth the effort! I'll post some pics for sure once I finish. While running it, I noticed there's a pinhole leak in the joint, so I'll need to weld that and then do the final grinding and prettying it up. This was my first time welding, so it was a learning experience for sure! Haha, very very fun though. I was hoping to have some more time welding, but it went pretty quick. To any more advanced welders out there; do you know if the metal's temperature would affect the weld pool? I was getting a lot of heading up of the metal VS a flat and pretty weld like you see a pro do. As a test, I did hold the weld a little longer in some areas and it seemed to flatten out a bit VS beading (as it got hotter I assume), but then it made a little tower of material. Just curious if there is anyone who knows more about welding and might know roughly where I'm going wrong. The surface was very clean and I had flux core wire (.30) Thanks all!
	3

02-10-2019, 01:50 PM	#8
Weldangrind Join Date: Mar 2009 Location: Sardis, BC, Canada Posts: 25,977	I'm not an advanced welder. I'm just a goofball with a decent MIG. Without going too far down the rabbit hole, flux core is a challenge when compared to MIG with shielding gas. On top of that, a welder that does not have infinite voltage control is a crap shoot. Does your welder have four (or five) voltage options, or does it have an infinite control, like a volume knob? Please tell us more about your machine. To answer your specific question, heat can make a difference but it depends on the material and thickness you're welding. The right voltage and wire speed, combined with the right wire and shielding gas will not be affected by base metal temperature as much. For anything less than 1/4" thick, I'd be inclined to say the base metal temperature is not an issue at all. As a point of trivia, materials like cast iron require heavy pre-heating before welding. It really depends on what you're welding and what your setup is. __________________ Weldangrind "I figure I'm well-prepared for coping with a bike that comes from the factory with unresolved issues and that rewards the self-reliant owner." - Buccaneer
	2

02-10-2019, 05:52 PM	#9
OneLeggedRider Join Date: Nov 2018 Location: Stockport, Oh. Posts: 1,442	Flux core isn't going to be a pretty weld. As far as the piling up it sounds like too much wire speed and not enough heat. It should sound like and egg sizzling in a pan and try to take the weld as far around the pipe as you can without stopping, especially with flux core.
	4

02-10-2019, 09:57 PM	#10
Sir kayakalot Join Date: Dec 2016 Posts: 269	Dan mentioned this, but it’s wirth saying again..... make sure you clean up the factory weld on the inside of the exhaust pipe at the mounting flange. It is ridiculous how much performance can be gained as some of the factory weld jobs are VERY restrictive right there. Cleaning up that weld and removing the cat and re-jetting the carb is by far one of the best mods you’ll do to your Hawk Tommy __________________ Hawk 250 Mikuni carb 115 main. De-catted pipe. Air box mod. 15/42 sprockets. Digital instrument cluster, FMF end cap on muffler, handlebar toolbag, Custom foot pegs
	2

02-15-2019, 12:17 AM	#11
elkhunter338 Join Date: Dec 2018 Location: Oregon Posts: 81	Hmm I am going to have to see if the CSC tt250 has a cat. The exhaust has a end cap with 3 or 4 bolts, have not removed it yet.
	0