Rough idle, possible vacuum leak? Hawk 250

Desuboi941 · 05-15-2023, 12:02 PM

So I installed my nibbi or 28fl and the bike idles really rough. It’s as it the bangs of the engine are inconsistent as if one stroke it wants to die, other stroke too much power. I just went from a 40 pilot down to the 35 and the 112 main to a 115. Pilot jet is on the way. I accidentally bought mikuni jets and had to reorder. I’ll have to upload a video so you can hear it run, revs don’t hand and it doesn’t bog anywhere in the throttle. There is some popping though. All of this was happening before I changed the jets btw. Anyways, I was wondering if any of you had a paper gasket and a black thermal spacer between the intake and the head. On min it seemed like they were glued. I ended up taking them off due to my air box not lining up with my new carb. I ended up switching to a pod filter and I left the paper gasket in there but left the black spacer out because my dog ended up chewing it up… some of you have said I don’t need the spacer between my intake and carb, but I couldn’t get the carb to fit on all the way without it. Also ended up getting a quick turn throttle and my cable is too short. New cable is on the way but for now it’s not too bad. I’ll be doing the valve adjustment either today or tomorrow because I feel like that could be causing the rough idle as well. Basically I’m asking for a direction to look in. Does this sound like jetting, vacuum leak, valves or all of the above? Sorry for being such a nuisance, I’m learning as much as I can on my own, but I also don’t want to damage my baby. I absolutely love this bike…. I just wish I could get her running smooth.

Megadan · 05-15-2023, 12:22 PM

All of that and no mention of your idle mixture adjustment. Have you set it at all? Know what it's currently set to?

Desuboi941 · 05-15-2023, 01:03 PM

Quote:

Originally Posted by Megadan

All of that and no mention of your idle mixture adjustment. Have you set it at all? Know what it's currently set to?

About 3/4 of a turn out on the air mixture. I have to play with the idle screw a tiny bit so it changes, but if I turn the air mix screw out at all it seems to idle worse. Also been trying to run on the rich side till I know what I’m doing.

Texas Pete · 05-15-2023, 03:44 PM

Preface: This is all on an OEM factory carb.

Don't have a hawk but all the times my idle is running really rough and then every few cycles wants to quit and die but the momentum in the fly wheel keeps it going again is always been on my bike due to a vacuum leak and a lean condition causing that behavior. This also when quite bad will show up as lean popping well into the throttle/main and trying to get it to idle will run a bit then hesitate on a cycle and die. My culprit most of the time is the choke because my bike's carburetor has a choke cable and it screws down against the carb body using a crush washer. When I'm doing lots of tuning and taking the carb in and out frequently every once in a while I will finger tighten the choke cable and then work on installing the slide and fuel hose and everything else and forget to come back and wrench tighten the choke cable crushing the washer. Over time the vibrations back my cable out until air leaks into the choke circuit in the carb and creates a bad lean condition. If I didn't have that then having a bad seal on the engine side of the carb allowing an air leak would have done similar. To date I have never had it be the jets that have done behavior as you described with my non hawk bike. The air/fuel adjustment screw being set for the previous pilot jet I removed and went to different size usually manifests itself as hesitation just off idle and onto adding in the main jet tube circuit but everything above and below that runs fine. When I take the bike around the streets and beat the snot out of it to bring it up to full temperature and then set the idle between 500-1000 wherever it is just about to die and then do my air/fuel adjustment routine and dial it in I usually dial that behavior out. If I couldn't then I'd look at moving a size in jetting.

But bottom line is if you have removed and reinstalled the carburetor you need to check everything that is supposed to be sealed either with rubbers and clamps or crush washers or whatever is sealed and that includes the exhaust side of the equation. Only then can you start to work on tuning your settings and dialing things in. And if the bike rides decently well after you put it all back together but then like ass the next time you ride it suspect vibration has loosened something somewhere related to the above during that first ride.

Desuboi941 · 05-15-2023, 04:13 PM

Quote:

Originally Posted by Texas Pete

Preface: This is all on an OEM factory carb.

Don't have a hawk but all the times my idle is running really rough and then every few cycles wants to quit and die but the momentum in the fly wheel keeps it going again is always been on my bike due to a vacuum leak and a lean condition causing that behavior. This also when quite bad will show up as lean popping well into the throttle/main and trying to get it to idle will run a bit then hesitate on a cycle and die. My culprit most of the time is the choke because my bike's carburetor has a choke cable and it screws down against the carb body using a crush washer. When I'm doing lots of tuning and taking the carb in and out frequently every once in a while I will finger tighten the choke cable and then work on installing the slide and fuel hose and everything else and forget to come back and wrench tighten the choke cable crushing the washer. Over time the vibrations back my cable out until air leaks into the choke circuit in the carb and creates a bad lean condition. If I didn't have that then having a bad seal on the engine side of the carb allowing an air leak would have done similar. To date I have never had it be the jets that have done behavior as you described with my non hawk bike. The air/fuel adjustment screw being set for the previous pilot jet I removed and went to different size usually manifests itself as hesitation just off idle and onto adding in the main jet tube circuit but everything above and below that runs fine. When I take the bike around the streets and beat the snot out of it to bring it up to full temperature and then set the idle between 500-1000 wherever it is just about to die and then do my air/fuel adjustment routine and dial it in I usually dial that behavior out. If I couldn't then I'd look at moving a size in jetting.

But bottom line is if you have removed and reinstalled the carburetor you need to check everything that is supposed to be sealed either with rubbers and clamps or crush washers or whatever is sealed and that includes the exhaust side of the equation. Only then can you start to work on tuning your settings and dialing things in. And if the bike rides decently well after you put it all back together but then like ass the next time you ride it suspect vibration has loosened something somewhere related to the above during that first ride.

Thanks for all of that, I’ll definitely check everything, I did just reinstall my exhaust with a new Crush gasket, and the exhaust flange wouldn’t tighten down all the way but there doesn’t appear to be any leaks. It’s probably on the intake side, probable between the head and intake manifold. Hopefully adjusting my valves clears a little bit of the vibrations up.

Desuboi941 · 05-19-2023, 03:31 AM

So I wanted to say it’s definitely a vacuum leak, I tightened the bolts where the leak was and it ran a little better. I ordered the gluey-aluminum and black plastic intake gaskets off Amazon and am getting them tomorrow with another new throttle cable. I bought the 40.3” nibbi nc style throttle cable because the stock throttle cable was too short after my carb upgrade and quick turn throttle and it was way too long. I ended up ordering the cb style throttle cable from nibbi 36.8” and I hope this will help the issue because at the moment the bike is out of commission. Before I took the old throttle off, it only revved when turning the bars full lock right, but not it’s anywhere I turn the bars, even straight. I’ve also made sure to see that the throttle cable is fully seated in the carb and throttle itself. However, the throttle cable is bending against the gas tank and am racking my brain for the perfect solution. I’ve thought about bending the gas tank but want to stay away from modifying it too much. I really want to just get this thing running right and be able to ride it more than a day in a row�� I love this bike so much I wish it wasn’t like every corner I turn I hit another dead end. Also working on getting the valve cover off as the factory must have over torqued them and the bolts are camming out of my wrench. Hopefully I just need a better wrench cuz idk what to do if I round these off.

05-15-2023, 12:02 PM	#1
Desuboi941 Join Date: Apr 2023 Posts: 32	Rough idle, possible vacuum leak? Hawk 250 So I installed my nibbi or 28fl and the bike idles really rough. It’s as it the bangs of the engine are inconsistent as if one stroke it wants to die, other stroke too much power. I just went from a 40 pilot down to the 35 and the 112 main to a 115. Pilot jet is on the way. I accidentally bought mikuni jets and had to reorder. I’ll have to upload a video so you can hear it run, revs don’t hand and it doesn’t bog anywhere in the throttle. There is some popping though. All of this was happening before I changed the jets btw. Anyways, I was wondering if any of you had a paper gasket and a black thermal spacer between the intake and the head. On min it seemed like they were glued. I ended up taking them off due to my air box not lining up with my new carb. I ended up switching to a pod filter and I left the paper gasket in there but left the black spacer out because my dog ended up chewing it up… some of you have said I don’t need the spacer between my intake and carb, but I couldn’t get the carb to fit on all the way without it. Also ended up getting a quick turn throttle and my cable is too short. New cable is on the way but for now it’s not too bad. I’ll be doing the valve adjustment either today or tomorrow because I feel like that could be causing the rough idle as well. Basically I’m asking for a direction to look in. Does this sound like jetting, vacuum leak, valves or all of the above? Sorry for being such a nuisance, I’m learning as much as I can on my own, but I also don’t want to damage my baby. I absolutely love this bike…. I just wish I could get her running smooth.
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05-15-2023, 12:22 PM	#2
Megadan Join Date: Apr 2017 Location: Omaha, NE Posts: 7,976	All of that and no mention of your idle mixture adjustment. Have you set it at all? Know what it's currently set to? __________________ 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
	1

05-15-2023, 03:44 PM	#4
Texas Pete Join Date: Nov 2022 Location: Dallas TX Posts: 578	Preface: This is all on an OEM factory carb. Don't have a hawk but all the times my idle is running really rough and then every few cycles wants to quit and die but the momentum in the fly wheel keeps it going again is always been on my bike due to a vacuum leak and a lean condition causing that behavior. This also when quite bad will show up as lean popping well into the throttle/main and trying to get it to idle will run a bit then hesitate on a cycle and die. My culprit most of the time is the choke because my bike's carburetor has a choke cable and it screws down against the carb body using a crush washer. When I'm doing lots of tuning and taking the carb in and out frequently every once in a while I will finger tighten the choke cable and then work on installing the slide and fuel hose and everything else and forget to come back and wrench tighten the choke cable crushing the washer. Over time the vibrations back my cable out until air leaks into the choke circuit in the carb and creates a bad lean condition. If I didn't have that then having a bad seal on the engine side of the carb allowing an air leak would have done similar. To date I have never had it be the jets that have done behavior as you described with my non hawk bike. The air/fuel adjustment screw being set for the previous pilot jet I removed and went to different size usually manifests itself as hesitation just off idle and onto adding in the main jet tube circuit but everything above and below that runs fine. When I take the bike around the streets and beat the snot out of it to bring it up to full temperature and then set the idle between 500-1000 wherever it is just about to die and then do my air/fuel adjustment routine and dial it in I usually dial that behavior out. If I couldn't then I'd look at moving a size in jetting. But bottom line is if you have removed and reinstalled the carburetor you need to check everything that is supposed to be sealed either with rubbers and clamps or crush washers or whatever is sealed and that includes the exhaust side of the equation. Only then can you start to work on tuning your settings and dialing things in. And if the bike rides decently well after you put it all back together but then like ass the next time you ride it suspect vibration has loosened something somewhere related to the above during that first ride. __________________ 2022 1/2 Templar X 250 - 6 gear model - 13 Front / 40 Rear Sprockets - #42 / #120 Jets - 1mm thick nitrile O-ring needle shim (removed) - Kenda K761 Dual Sport Tires - Sedona Standard Thickness Inner Tubes - Stock OEM battery, carburetor, spark plug still going strong - https://youtu.be/dhAYEKH-jFQ Texas Pete's Templar X 250 Torque Specifications Sheet Texas Pete's Engine Displacement Calculator Texas Pete's Tire and Rim Compatibility
	1

05-19-2023, 03:31 AM	#6
Desuboi941 Join Date: Apr 2023 Posts: 32	So I wanted to say it’s definitely a vacuum leak, I tightened the bolts where the leak was and it ran a little better. I ordered the gluey-aluminum and black plastic intake gaskets off Amazon and am getting them tomorrow with another new throttle cable. I bought the 40.3” nibbi nc style throttle cable because the stock throttle cable was too short after my carb upgrade and quick turn throttle and it was way too long. I ended up ordering the cb style throttle cable from nibbi 36.8” and I hope this will help the issue because at the moment the bike is out of commission. Before I took the old throttle off, it only revved when turning the bars full lock right, but not it’s anywhere I turn the bars, even straight. I’ve also made sure to see that the throttle cable is fully seated in the carb and throttle itself. However, the throttle cable is bending against the gas tank and am racking my brain for the perfect solution. I’ve thought about bending the gas tank but want to stay away from modifying it too much. I really want to just get this thing running right and be able to ride it more than a day in a row�� I love this bike so much I wish it wasn’t like every corner I turn I hit another dead end. Also working on getting the valve cover off as the factory must have over torqued them and the bolts are camming out of my wrench. Hopefully I just need a better wrench cuz idk what to do if I round these off.
	0