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#1 |
Join Date: Sep 2023
Posts: 5
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Weird Exhaust heat
I'm new so if I post in the wrong place sorry.
At night I realized when I'm cruising 55 on the gas going up hills or on the gas hard for a while my exhaust starts slowly getting red hot but only at the back of the "expansion" part and starts to creep halfway up it. When I look down it's not hot at the header close to the motor. I thought it had to be lean but I'm running 40 pilot with a 120 main, I had a 125 main and thought maybe it was too rich I have a hawk 250 with Nibbi 28fl carb, needle at middle notch, nibbi filter, and ebay exhaust. I've check the valves too and set at . 05mm. I can't figure it out?? |
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#2 |
Join Date: Aug 2020
Location: Australia
Posts: 1,329
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Seems like the catalytic converter is doing some converting and forming hot spots. This could be a location of more/less flow obstruction.
Might have been fouled under a rich condition and then burning off buildup under a lean condition. Check the spark plug to get a glance at the general lean/rich condition. |
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#4 | |
Join Date: Feb 2021
Location: Kansas City
Posts: 2,440
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Quote:
But, an open resonator chamber is supposed to reduce back pressure at the head pipe, which would be great if that's what it is.
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-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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#5 |
Join Date: Apr 2017
Location: Omaha, NE
Posts: 8,067
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It's not a cat on the cheap pipes. I have had 2 of those systems, and it's supposed to be a "power bulge" used to manipulate resonant wave tuning on the head pipe by creating an anode at a given distance from the exhaust valve in order to aid scavenging at a certain RPM point.
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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 |
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#6 |
Join Date: Sep 2023
Posts: 5
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Thanks for the help, after riding it some more the 130 seemed to do the job. I had searched the forums for hours and seen no one else had that problem so I thought something had to be wrong. Bike runs great and exhaust doesn't heat up. I just thought it was odd it was just the bulge heating up
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#7 |
Join Date: Aug 2020
Location: Australia
Posts: 1,329
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if there is no catalytic element installed in the chamber then perhaps the empty expansion section is creating a turbulent hot spot...
Are you sure the 125 was rich...? Think my 28fl carb on stock cylinder with head port/no cat was 38 or 40pilot/130main mid clip... |
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#8 |
Join Date: Apr 2017
Location: Omaha, NE
Posts: 8,067
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My experience with tuning the PE28FL having moved from a PZ30B, was that the pilot jet size remains the same (38 for mine with a ported head, standard bore, cam, exhaust) the idle mixture adjustment was actually very similar too, even though one is and air screw and the other is fuel - approximately 1.5 to 1.75 turns out - and the main jet needed to go up 1 full step (5 numerically).
Others have reported similar, using a 120 main jet on a bike with just basic bolt ons type upgrades, with some people at sea level jumping to a 125, but also stating it was a bit rich. A PZ30 with those same mods will almost always be around a 115 main. Even with the big bore cylinder my pilot jet and idle mixture really haven't changed. I have no doubt the main jet is too rich at a 125, especially given the description and the scenario. It is also worth keeping in mind that the PE carbs have a more aggressive needle taper than the PZ carburetors, so the mid throttle mixture can also be tricky to get right, often just slightly too rich in the middle slot. I have had great luck with moving the clip up one slot to the second from the top to lean it out. EDIT: Just thought of this too. What is your sprocket combination? If you are on a stock 15/50 sprocket setup, cruising at 55 means you're RPM's are getting up around 7500-8000. High RPM, wide open throttle, for a sustained pull, will absolutely start heating up the head pipe like that too.
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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 |
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#9 |
Join Date: Sep 2023
Posts: 5
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My sprockets are 17 and 45 or 46 whichever sounds right, it's turning 6500 at 55, I tried the 115 and it was definitely to lean so I tried a 130 (the only thing I haven't tried) and it barely gets hot after a big hill. It keeps pulling fine with a 130 and doesn't bog. That's gotta be to rich though? There's no engine work done so I don't see why it would want that much fuel? I'm in Arkansas at about 600-800 elevation
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#10 |
Join Date: Sep 2023
Posts: 5
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I've sprayed carb cleaner around the carb to make sure there's not an air leak, it idles great too. I'm trying to think of anything that could be wrong because a 130 theoretically has to be to big. Its only the "cat" part that gets hot. I made sure it doesn't have one before I put it on. It's the same ebay exhaust I've seen everybody else put on
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#12 |
Join Date: Feb 2021
Posts: 961
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Maybe the chamber /bulb is just way thinner walled than the head pipe.
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#13 |
Join Date: Apr 2017
Location: Omaha, NE
Posts: 8,067
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The 130 may very well be the right jet for your bike then. No two engines and situations are the same. I was running a 145 on my PE28FL with my cam and port work. The only real way to know would be to do a WOT plug chop and read the plug, or install a wideband.
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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 |
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