TwinTalon Posted December 5, 2008 Share Posted December 5, 2008 I have a little situation: 1980 XS400, stock exhaust (small hole rusted on bottom left @muffler, not fixed yet), pod filters, stock #135's. It much prefers full choke to even start, though when it wasn't 40 degrees outside, half choke sometimes did the job. Once it's warmed up a bit, the choke can be cut off and it'll idle fine, settles-in right at 1,200. When cold, she stumbles a bit. Once warm, she revs fine. She just doesn't like to Un-Rev. It takes a good 3-4-5 seconds to settle back down to idle. So: What carb situation is indicative of requiring half-to-full choke to start, and what would cause the revs to come down so slowly? I would tend to guess it's a little lean, but it's been a while since i've had to fool with carbs and i'm not quite sure. Any Suggestions? Link to comment Share on other sites More sharing options...
Spraguepsycho1 Posted December 5, 2008 Share Posted December 5, 2008 Definetly sounds like a lean problem, possibly a vaccum leak between the carbs and the heads, or most likely the combination of the extra airflow from the pod filters and stock jets. I know some bikes like the Suzuki Katana's refuse to run right with the extra air gained from using a K&N filter inside the stock airbox, no matter how hard you try to jet the carbs. IF you still have the stock airbox setup, you might want to give tha ta try and see if it clears up the problem, otherwise you may be able to turn out the idle fuel mixture screw a bit and see if that helps the hanging idle and starting problem. My Katana has a V&H full exhaust, along with tons of other mods done to it, and had a slight hang at idle, along with major popping on deceleration. I adjusted the mixture screws out from the stock 1 1/2 - 1 3/4 out from lightly seated to 2 3/4 turns out, and it made a major improvement. Not familiar with your carbs, but the mixture screws may be hidden under some small caps on the underside of the carbs, right next to where the carbs go into the intake boots closest to he cylinder heads. I had to carefully drill out the caps on mine to access the screws. Link to comment Share on other sites More sharing options...
TwinTalon Posted December 5, 2008 Author Share Posted December 5, 2008 Definetly sounds like a lean problem, possibly a vaccum leak between the carbs and the heads, or most likely the combination of the extra airflow from the pod filters and stock jets. I know some bikes like the Suzuki Katana's refuse to run right with the extra air gained from using a K&N filter inside the stock airbox, no matter how hard you try to jet the carbs. IF you still have the stock airbox setup, you might want to give tha ta try and see if it clears up the problem, otherwise you may be able to turn out the idle fuel mixture screw a bit and see if that helps the hanging idle and starting problem. My Katana has a V&H full exhaust, along with tons of other mods done to it, and had a slight hang at idle, along with major popping on deceleration. I adjusted the mixture screws out from the stock 1 1/2 - 1 3/4 out from lightly seated to 2 3/4 turns out, and it made a major improvement. Not familiar with your carbs, but the mixture screws may be hidden under some small caps on the underside of the carbs, right next to where the carbs go into the intake boots closest to he cylinder heads. I had to carefully drill out the caps on mine to access the screws. I've already siliconed the carb holders, so i doubt its a leak there. I'd Really rather not put the stock airbox back on as i'm trying to keep investment to a minimum and the stock filters(There are only cages left in the airboxes... ) are more than I wanna spend. I'm sure the pods have something to do with it, but I dont know if I need to adjust the needles, jets, mixture screws, etc. Stupid Question: When you unscrew/loosen the mixture screws on top of the carb, is it letting more Air or Gas in? I ask because a lean condition would not be helped by backing off the mixture screws. I thought i'd read on here that you usually don't have to mess with jetting on this bike unless you do a full system with pods. Did i misunderstand something? I'm sure there's some adjustment to be made after pods, but I don't know what to adjust. Again, it's been a while since i've fooled with carbs, and i'm a forgetful bloke... Link to comment Share on other sites More sharing options...
Spraguepsycho1 Posted December 6, 2008 Share Posted December 6, 2008 I've already siliconed the carb holders, so i doubt its a leak there. I'd Really rather not put the stock airbox back on as i'm trying to keep investment to a minimum and the stock filters(There are only cages left in the airboxes... ) are more than I wanna spend. I'm sure the pods have something to do with it, but I dont know if I need to adjust the needles, jets, mixture screws, etc. Stupid Question: When you unscrew/loosen the mixture screws on top of the carb, is it letting more Air or Gas in? I ask because a lean condition would not be helped by backing off the mixture screws. I thought i'd read on here that you usually don't have to mess with jetting on this bike unless you do a full system with pods. Did i misunderstand something? I'm sure there's some adjustment to be made after pods, but I don't know what to adjust. Again, it's been a while since i've fooled with carbs, and i'm a forgetful bloke... You're still pulling more air into the engine through the pods than you would with a stock air filter system on it. If you added a ful exhaust it would be even more noticable. It might not be lean enough to damage anything, but would explain needing to use the choke more now. I would guess that to run the pods, you'd probably have to go a little bigger like maybe 2 sizes up on the main jets, but you may be close enough with the stock jets to just raise the needles 1 or 2 notches by moving the clip, and adjust the mixture screw a little for idle and low rpm. The mixture screws all depend on where they are on the carbs, as in are they in the front half of the carb closest to the engine, or the rear half closer to the air filter. Closer to the engine and they are fuel screws so turning them out will increase fuel, if it's closer to the air inlet they would be idle air screws so turning them out would lean the mixture further. On my Katana the screws were right on the bottom just in front of the bowls underneath small round caps, those were fuel screws. Most 4 strokes use fuel screws, air screws are more common on 2 strokes. Would it be possible for you to post a pic of the carbs so I could see where the mixture screw is? Link to comment Share on other sites More sharing options...
TwinTalon Posted December 6, 2008 Author Share Posted December 6, 2008 You're still pulling more air into the engine through the pods than you would with a stock air filter system on it. If you added a ful exhaust it would be even more noticable. It might not be lean enough to damage anything, but would explain needing to use the choke more now. I would guess that to run the pods, you'd probably have to go a little bigger like maybe 2 sizes up on the main jets, but you may be close enough with the stock jets to just raise the needles 1 or 2 notches by moving the clip, and adjust the mixture screw a little for idle and low rpm. The mixture screws all depend on where they are on the carbs, as in are they in the front half of the carb closest to the engine, or the rear half closer to the air filter. Closer to the engine and they are fuel screws so turning them out will increase fuel, if it's closer to the air inlet they would be idle air screws so turning them out would lean the mixture further. On my Katana the screws were right on the bottom just in front of the bowls underneath small round caps, those were fuel screws. Most 4 strokes use fuel screws, air screws are more common on 2 strokes. Would it be possible for you to post a pic of the carbs so I could see where the mixture screw is? Golden. Thank You. I cant really take a pic, not at the moment, but they're on top of the carbs, on the engine side, maybe 12mm from the outlet to the engine. By your description, they're definitely fuel screws. Alright, i'll play with that next. from what i've read, these particular carbs won't let you adjust the needles, not even with shims/washers. You have to go buy aftermarket needles with clips. Thanks for the info. I'll twiddle on the bike in the next few days and give a report. Link to comment Share on other sites More sharing options...
Spraguepsycho1 Posted December 6, 2008 Share Posted December 6, 2008 good luck Link to comment Share on other sites More sharing options...
mark h Posted December 6, 2008 Share Posted December 6, 2008 I have a little situation: 1980 XS400, stock exhaust (small hole rusted on bottom left @muffler, not fixed yet), pod filters, stock #135's. It much prefers full choke to even start, though when it wasn't 40 degrees outside, half choke sometimes did the job. Once it's warmed up a bit, the choke can be cut off and it'll idle fine, settles-in right at 1,200. When cold, she stumbles a bit. Once warm, she revs fine. She just doesn't like to Un-Rev. It takes a good 3-4-5 seconds to settle back down to idle. So: What carb situation is indicative of requiring half-to-full choke to start, and what would cause the revs to come down so slowly? I would tend to guess it's a little lean, but it's been a while since i've had to fool with carbs and i'm not quite sure. Any Suggestions? Hi Ya TT, I had the same problem, In the end i stuffed my PODS (clear flow) with lightly oiled domestic sponge, Figured i was getting way to much air, Worked! Mark. Link to comment Share on other sites More sharing options...
TwinTalon Posted December 7, 2008 Author Share Posted December 7, 2008 Hi Ya TT, I had the same problem, In the end i stuffed my PODS (clear flow) with lightly oiled domestic sponge, Figured i was getting way to much air, Worked! Mark. That would probably work, but i'm betting mixture adjustment via the fuel screws will fix it too. I'll just have to play around with it till I get it right. Thanks for the tip! Link to comment Share on other sites More sharing options...
Moderator Airhead Posted December 7, 2008 Moderator Share Posted December 7, 2008 That would probably work, but i'm betting mixture adjustment via the fuel screws will fix it too. I'll just have to play around with it till I get it right. Thanks for the tip! if i remember correctly from previous threads, the mixture screw on these is a fuel mixture adjuster (instead of an air mixture adjuster), this means that turning anti clockwise will richen the mixture, Drewpy will no doubt confirm or correct this! Link to comment Share on other sites More sharing options...
Moderator drewpy Posted December 7, 2008 Moderator Share Posted December 7, 2008 if i remember correctly from previous threads, the mixture screw on these is a fuel mixture adjuster (instead of an air mixture adjuster), this means that turning anti clockwise will richen the mixture, Drewpy will no doubt confirm or correct this! clockwise weaken (screws in so less fuel). Link to comment Share on other sites More sharing options...
Moderator Airhead Posted December 7, 2008 Moderator Share Posted December 7, 2008 clockwise weaken (screws in so less fuel). so...I was right then! Link to comment Share on other sites More sharing options...
Moderator drewpy Posted December 8, 2008 Moderator Share Posted December 8, 2008 so...I was right then! correctomondo Link to comment Share on other sites More sharing options...
Cy Welch Posted December 9, 2008 Share Posted December 9, 2008 Golden. Thank You. I cant really take a pic, not at the moment, but they're on top of the carbs, on the engine side, maybe 12mm from the outlet to the engine. By your description, they're definitely fuel screws. Alright, i'll play with that next. from what i've read, these particular carbs won't let you adjust the needles, not even with shims/washers. You have to go buy aftermarket needles with clips. Thanks for the info. I'll twiddle on the bike in the next few days and give a report. On the 80 carbs turning the screw out richens the mixture. Also if adjusting the mixture doesn't help the off idle problems you might be able to raise the fuel level about 1 mm. You may have to turn them out a good bit as it sounds like it's very lean. Link to comment Share on other sites More sharing options...
TwinTalon Posted December 9, 2008 Author Share Posted December 9, 2008 Alright, i'll be turning the screws out at 1/2 turn increments and see where that gets me. Thanks for the help everyone. I'll report back how it goes. Link to comment Share on other sites More sharing options...
mark h Posted December 10, 2008 Share Posted December 10, 2008 Alright, i'll be turning the screws out at 1/2 turn increments and see where that gets me. Thanks for the help everyone. I'll report back how it goes. Don`t worry if it seem`s your turning out too much, mine are way outside the usual, MAKE SURE there nice and pointy, Took me days in the end, Just a tweek here and a tweek there, You`ll sort it in the end, Cheers mark. Link to comment Share on other sites More sharing options...
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