akamor

Hello all, I might be buying a 1981 XJ750 Seca. How is the parts availability on these motorcycles? Thanks, Adam

Hello all, I have the option to buy a 1982 Yamaha Virago. The bike is currently not running and will need some work. Most likely just carburetor rebuild, but who knows, it could need more. I am new to this bike (my last yamaha was a 1980 XS400 which I loved), what is the availability of parts? Are they easy to come by? Are they relatively cheap? This bike was made well before I was born. What was its reputation for reliabilty and quality? Thanks, Adam

That sounds good. I did that tonight but I am still having problems with the bike. The darn thing wont idle without a choke. I think I am going to move on and reclean the carburetor and recheck for vacuum leaks. Thanks, Adam

Hello All, I have a general question about valve clearances. On a four cylinder engine you must rotate the crankshaft 360 degrees between measuring 'partner valves'. When I say 'partner valves' I mean something like Intake on Cyliner 1 and Intake on Cylinder 4. Or the exhaust on cylinder 2 and the intake on cylinder 3. My understanding is that the camshaft lobes are 180 degrees apart on these 'partner valves', does this mean that a 360 degree turn of the crankshaft corresponds to a 180 degree turn on the camshaft? This is a 4-stroke engine, btw. Also, how do you verify that you are at TDC of cylinder 1? Is it when the cylinder is at its highest position. I was checking by sticking a screw driver down the spark plug hole and moving the back wheel in 5th geer. When the screw driver was sticking out the most (i.e. the cylinder was at its highest) I assumed it was TDC. Also, if cylinder 1 is at TDC does this mean cylinder 4 is at TDC? Thanks as always, Adam

Thanks. That sounds like a great place to start. 1) I have already tuned/synced the carburetors, so that is out of the way. 2) The valves are definitely on my to-do list, I just need to muster the courage. 3) In regards to timing, however. According to my manual my model (1980 XS400G) has transistorized timing as opposed to break point ignition, which means timing need only be checked if the unit is removed from the motorcycle, which has not happened. What is your opinion on this matter? 4) I do not believe fuel delivery to be the problem. I should have given more details when I first made this post. Let me explain further. After the bike has warmed up it ONLY has trouble going up hills. If I start at the bottom of the hill I cannot get up the hill unless I keep the rpms high. I have no problems on flat ground. Do you still believe it could be a fuel delivery problem? The mechanic that sold me the bike says it could be an electrical failing that only manifests itself once it becomes hot. What is your opinion on this statement? Thanks, Adam

Your bike looks awesome. May I ask where you found your exhaust piece? Adam

Hello All, My 1980 XS400 starts up and runs great for the first 15 minutes of driving. After that the bike will randomly lose power when in motion and will sputter and eventually die unless I put the clutch in and come to a stop. The problem is especially bad when going up hill. Since it only happens after the bike is warmed up I suspect an electrical failing because I figure the electrical components are more sensitive to heat. Does anyone know where I can start on this? My initial thought is something is wrong with the timing. Thanks, Adam

Thanks. I did as you said and traced all of the connections and made sure everything was hooked up properly. After fixing a couple of connections everything works great. Adam

It is both front and back. I am not sure if it is the left or right side because I am sure at some point I messed up the wiring. However, it is only 1 in the front and 1 in the back. Adam

Hello All, I am working on the electrical system on my 1980 XS400. I am trying to figure out the problem with my turn signals. I have several questions for someone with a working XS400. 1) When I turn the key should the turn signals light up? Currently when the key is in the ignition but the engine is NOT on my turn signals are on. When the bike is running the turn signals remain on continuously and using the turn signal control on the handlebar has no effect? Is this normal. 2) Only 2 of my turn signals light up. The other two are off, regardless of whether or not the engine is on/off and regardless of what I am doing with the turn signal controls. Any advice on where to begin looking would be appreciated. Thanks, Adam

Could you explain what you mean in more detail? One end of the ground wire should attach to the frame. Where does hte other end attach to? Thanks, Adam

Thanks for the quick response. Regarding my other questions: Why does the manual state the regulator is mechanical? Is it possible I am missing the screw? Adam

Hello All, I am trying to figure out why my battery is not charging on my 1980 XS400. I have tested the alternator and rectifier according to the manuals specifications and everything seems okay. I am having some trouble testing the voltage regulator. According to the technician manual the regulator should be mechanical with some sort of adjusting screw somewhere on the body. My regulator does not seem to have an adjusting screw and I do not believe it is mechanical. It looks like the part in this ebay auction: http://compare.ebay.com/like/120578199689?ltyp=AllFixedPriceItemTypes&rvr_id=&crlp=1_263602_263632&UA=L*F%3F&GUID=831f21641280a0e205467ac6ff344981&itemid=120578199689&ff4=263602_263632 How do I test this unit? Can I follow the instructions in the manual and just ignore the part about the adjusting screw? If it is actually a semiconductor and not mechanical I do not believe it makes sense to measure resistance between different leads. Also, the replacement I have found for the bike are quite expensive. I have a lot of experience in electronics and I was wondering if I can just make my own voltage regulator unit. Does anyone know the specificiations? Thanks, Adam

Hello All, Thanks in part to everyone on this forum my 1980 XS400 is running strong. Now that I have the mechanical issues figured out I need to work on the electrical system. The biggest problem is that after riding the bike for only about 30 minutes the batter begins to die and it becomes hard to start with the electric start. I am fairly confident the issue lies in the alternator. When I put the engine at 2000 rpm and measure the voltage across the battery terminals I typically see it jump to about 12.8 volts, but never higher. To me, this implies that the alternator is not performing properly. What steps should I take to troubleshoot the alternator? Thanks, Adam

Hello All, I have a general question about interchangeable motorcycle parts. If I go to a website like www.bikebandit.com and look in their OEM parts sections for the same part from two different bikes and they have the same part number does this mean they are interchangeable? What is a general method for checking part interchangeability? I need to buy a new carburetor on Ebay but it is for a different year motorcycle. According to www.bikebandit.com they have the same part number (and same cost). Does this ensure compatability? Thanks as always. Adam

Great, thanks. Does this apply to XS400 Special carburetors as well? I have a 1980 XS400 Standard and I found some really cheap carburetors for a 1981 XS400 Special. I wanted to make sure they worked before I spent the money. I was really trying to avoid having to do any modifications besides tuning. Thanks, Adam

It is okay. I understand you. I will adjust the pilot screw to 2.5 turns then possibly adjust the need when I get home from work today. You will probably be asleep by then so we can discuss more over the weekend or on Monday. Thanks! Adam

I will do all of this, but first I have another question. The 'H' shaped hose that connects the two airboxes to the carburetors seems to be far too short to work well. I can connect it securely around the mouth of the carburetor but then it is not securely fastened around the airbox or vice versa. Are there any tricks for making it all connect well. I can almost definitely feel air flowing around the hose-airbox connection. Could this have an affect? Adam

I got the motorcycle idling properly which is awesome. Now I am having another (more serious?) problem. When I keep the bike under 2000 rpm the throttle response is great. When I bring it over 2000 rpm the engine will rev up uncontrollably to 3000+ rpm then SLOWLY come back to an idle. I have no idea what could be causing this. Where should I start looking? I had a pretty serious backfire last night and a friend suggested that my butterfly valves in the carburetor are getting stuck? Is this possible? I was going to check it tomorrow morning. Another friend suggested it could be a vacuum leak. To me that sounds more probable.

Ok, I think I got it now. The pilot screw is located outside of the carburetor on the mouth on the engine intake side. It should be turned out ~1.5 turns. When you guys have been talking about the idle screw, I thought you meant the idle jet which is inside of the float bowl. What you call the idle screw, I call the throttle stop screw. Does all of this make sense? Adam

Gothca. Thanks for all of your help. When I get home today I will try it out. Will keep you updated. Adam

Oh ok. So the idle jet, which is inside of the carburetor, should be seated. The pilot screw is actually the air screw, and that is what needs to be adjusted? Is that correct? That would make a lot more sense because now I would not need to remove the carburetor each time I had to make a simple adjustment since the air/pilot screw is outside of the float bowl. Your really saving me here. Thanks, Adam

Perhaps I misread my manual actually. I have attached a snapshot of the tune-up page. I highlighted in red the section I am referring to. It says to adjust the pilot screw which is fitted to each carburetor. Is that not the same as the idle jet? Where would the pilot screws be located? Are they inside or outside of the carburetor? What is their purpose?

The manual for the bike says it should be at 1.5 turns. Obviously that was not working. Why do you say it should be screwed in completely, why the manual says it should be out 1.5 turns. I am not doubting you, because the manual has not helped me one bit, but I would like to understand this process better.

I will do this the moment I get home. Can you explain to me the purpose of the idle jet. My understanding was that it controls fuel supply during idle. Turning out = more fuel, Turning = less fuel. Is this correct? Can you explain why turning in the idle jet could potentially fix the bad idle? Thanks, Adam