akamor

Oops, I think there has been quite a misunderstanding on my end. What you are calling the idle screw I call the throttle stop screw. Yes, that is on the outside of the carburetor and can easily be adjusted. Currently, I have that screwed in all the way. My understanding is that the idle circuit INSIDE the carburetor has two components. I have been talking about the idle jet and air screw which are pictured here: http://www.dansmc.com/pilot_group1.jpg. My air screw, which is actually accessible from outside of the carburetor is completely seated. My idle jet is 2.5 turns out. I do not believe that I have an air air jet. In this configuration my bike will not idle. When I unseat the air screw the problem becomes even worse. My plan was to adjust the idle jet by unscrewing it more because I thought this would richen the mixture. Once the bike could actually idle I was then going to follow your directions with the air screw and throttle stop screw. Thanks and sorry, Adam

Ok, that makes sense. I am going to unscrew the idle screw a ridiculous amount then incrementally screw it in until the engine will idle. Is it common practice to leave the carburetor on the motorcycle while making these adjustments. I suppose it would be possible with a small enough ratchet to remove the float bowls and make the adjustments? What do you think? Thanks, Adam

How do I get it to idle in the first place is my real question I guess. Should I be adjusting the idle screw? Thanks, Adam

Thanks. That is something I have not yet considered. The problem is only with idling however. I was under the impression that the jet needle only affects the mixture when the throttle is above 15%. Can it also affect the idling circuit? Once I make the mixture richer by adjusting the jet do I need to then mess with the idle settings again? Thanks a lot! Adam

That is what I initially thought so I should have mentioned it, but I have already taken the carburetors apart twice and cleaned them thoroughly. The pilot is definitely clean inside and out. Is it weird that my air screw must be completely seated for the bike to run? Does this mean I should unscrew the pilot even more? Thanks, Adam

Hello All, Thanks for all of the ongoing support. In its current state the bike is very close to being rideable. The motorcycle will idle with the air screw turned in completely and the idle screw turned out 2.5 turns. I am now having a different problem however. The motorcycle idles around 1500 rpm currently, which is too high, and as soon as you touch the throttle the engine will rev up, seemingly without bound, until you throw the kill switch. I cannot think about what would be causing this. Does anyone have any ideas? I was thinking about an air leak, however, I do not believe there are any leaks from the airbox->carburetor->intake manifolds OR from petcock->intake manifold nipple. Could other leaks be present? Thanks as always, Adam

I am a little confused by your instructions. In the bikes current state my air screw is turned in all the way and my idle screws are 2.5 turns out. The bike will not idle with these settings. Should I continue turning out my idle screw until the bike will idle then follow your directions?

Hello All, I am going to purchase a new carburetor for my XS400 because one of the posts supporting the float pin has broken off. I found someone with an old carburetor they are willing to sell. All they can tell me is that the carburetor is for a 1980 XS360/400 Twin. My specific bike is a 1980 XS400G with vin number 3F8. I have not heard of the Twin model, does he perhaps mean a twin carb? Does anyone know if all XS model bikes in 1980 used the same carburetor? Thanks, Adam

Thanks for the reply. I took the carburetors out for one last cleaning. When I put them back together I will give it a try. Stay tuned.

Hello All, First off, thanks to everyone that has been helping me over the past two weeks. I started off with a motorcycle that would not start and it is near running flawlessly now. I am having one problem however. I can only start the bike with the throttle open. Once the bike starts if I do not constantly apply the throttle the bike dies. Between 1200 and 2000 rpm (approximately) the bike sounds weak, however, over 2000 rpm it sounds GREAT. I think the problem lies in the idling circuit in the carburetor. For this carburetor the idling circuit has two components I believe. The air screw and idle jet. Even with throttle the bike can only start when the air screw is turned all in, however, like I said idling is bad. What should I do to adjust the idle jet? Assuming you believe the idling circuit to be the problem. Thanks, Adam

Hello, My 1980 Yamaha XS400 has a vacuum activated petcock. The vacuum line connects the petcock to the intake manifold. The vacuum line keeps undoing itself when I run the engine. I keep the bike stationary and idle the engine and over time (about 15 seconds) the vacuum line on the petcock end completely removes itself from the petcock nipple. Does anyone have any idea what can be causing this? If it helps, my intake boots are cracked and there is probably not a god seal (I have new ones coming in the mail). Thanks, Adam

Ah. I was looking for an unused hole somewhere on the carburetor. Thanks. I suppose the air rushing into the engine from the carburetor creates a vacuum which activates the petcock. Thanks, Adam

I think I am about to seriously embarass myself, but hear it goes. The petcock has two hoses coming out of it. I attached the larger of the two to the carburetor. I assumed the other hose was for gasoline vapor. Is it supposed to attach to something? Where would I attach it? Thanks for such a quick response! Adam

Hello All, I am restoring an old Yamaha XS400G 1980. I think ALMOST everything is in working order, but I am having trouble with fuel flow. If I set the petcock to the prime position for several seconds then switch it to on or reserve the bike will start/run no problem, but then die after a minute or so. When I try to start it up again the bike wont start until after I have 'reprimed' it for several seconds. I went out and bought a inline fuel filter so I could actually watch the fuel flow from the petcock to the carburetor and when the petcock is in the on or reserve position I see no fuel flowing. (The inline fuel filter is see through). My guess is that the petcock is damaged and fuel cannot flow in the ON and Reserve positions. Any advice? Thanks, Adam

I just got a Yamaha XS400 and I need to find replacement air filters. If I get PODS will I have to rejet the carb? I was hoping to avoid rejetting. I have the air boxes, but the filter material is destroyed. I was thinking about just ordering the correct material and making my own air filters with an exacto knife a hot glue gun. Do you know what material I should order? Thanks, Adam

I do not think I can just choose a random filter material. I need to know the exact material to be used otherwise my fuel to air mixture will be off.

What material did you use? I do not have an old lawnmower so I will need to go to my local shop and request the correct type of foam. Thanks, Adam

Could you tell me the kind of material that is used in the stock filters. Before I try to make them myself I need to know the correct material. Thanks, Adam

Hey All, I just bought a Yamaha XS400 1980. I need to replace the air filters that are inside the air boxes. I was thinking about getting air pod filters but I read that I would have to re-jet the carburetors. I am trying to make this as simple as possible so I would just like to purchase the stock air filters. I do not believe that stock air filters are made anymore so I was going to get a sheet of UNI air filter paper and make my own. I do not think it will be difficult because I still have the metal frames that go inside the air boxes so I just need an exacto knife and a glue gun. Does this seem like an OK idea? What type of UNI Air Filter paper should I purchase? I want this to be as close as possible to the stock filter so that I do not have to mess with the carburetor. Does anyone know the porosity of the original air filters? Thanks, Adam