xs 360 runs on right cylinder only

[joe4g63]

I have a 1977 Yamaha xs 360. If it sits in the garage for about a week I can hop on it and go like crazy with it for about 20 minutes or so, then it will start backfiring on the left cylinder and start to run like crap. When I get back to the house it will only idle with full throttle, so I pulled off the left spark plug wire and the engine did not change at all but the plug is sparking. Just wondering if anyone else have had this same problem? Maybe when the engine gets that hot the valves are out of whack and will not create enough compression on that side, or might be a carb issue on that side.

[drewpy]

I have a 1977 Yamaha xs 360. If it sits in the garage for about a week I can hop on it and go like crazy with it for about 20 minutes or so, then it will start backfiring on the left cylinder and start to run like crap. When I get back to the house it will only idle with full throttle, so I pulled off the left spark plug wire and the engine did not change at all but the plug is sparking. Just wondering if anyone else have had this same problem? Maybe when the engine gets that hot the valves are out of whack and will not create enough compression on that side, or might be a carb issue on that side.

Carb issue, pilot jet

[Stevar]

I smell a dirty carb... there is a screen for the fuel on the reservoir...it may be clogged. Especially if you left gas in the carb over a long period of time. Gasoline tend to build a film floating on top over time and then when you try to turn that on it blocks the pathway for the liquid.

[joe4g63]

Thanks for the replies. I went through both carbs and made sure the pilot and main jets were clean, the only thing I haven't actually done is put a carb kit in it yet. I also checked the compression with the engine cold-the left was 125 with about 10 kicks, and the right was 140 same amount of kicks. Then I got it all put back to together and she ran great, a little hesitation between idle and mid but wide open it ran great. About 20 minutes later though there went the left cylinder again. Could carb sync cause this, cause I have not done that, also how about those plastic adjustment screws( I believe they are for air fuel) I have tried them all the C.W., and CCW no change between idle and mid range. The tank was off this last summer and I threw some rocks in there and rattled the heck out of it hopefully to get some of the rust out. Today I am going to take off the pet cock and ensure the screen is clean, and also buy a cheap paper filter and throw in the fuel line. Any help would be appreciated.

[joe4g63]

Well here is the latest and greatest. Tore the carbs all down, and let soak in carb cleaner-inspected pilot screws and both were bent a little bit at the tips. Found that the pilot screws were about 2 or so turns out, instead of 1.5. I did not check the float height yet though. So I reassembled the carbs and installed them. Also I figured I would make sure I even had the correct plugs in, the guy I got it from said they were. Well they weren't I had br9es in it, when it calls for bp6es so that's 3 stages hotter plug. Well I put the bike back together and so far it has been running pretty good, still a little bit of a bog coming from a stop through midrange which I think might be the pilot screws being bent. Also at idle it still back fires some out of the left pipe. I checked the plugs and the left plug is black, and the right plug looks great. I also did a compression tests with engine hot and got 125 on left, and 140 on right. The wet test was 140 on left, and a little over 150 on the right. So the compression isn't quite up to par (140-170 the manual says) but it is a 1977.

here's the recap

-pilot screws bent----causes bog?

-float height no checked-- causes?

-compression left 125/140wet, right 140/150wet------not igniting everything causing plug to turn black?

-point gap not checked yet--Might cause the spark issue w/ the left plug?

Where can I get new pilot screws at? I have looked on the internet and haven't really found anything.

[yoda]

With the lower compression on the left side, the chances are that it is burning a little bit of oil. Piston ring wear, oil in barrel, burnt on plug.

Things can't be far out because it runs OK, so just needs tickling up.

[drewpy]

Well here is the latest and greatest. Tore the carbs all down, and let soak in carb cleaner-inspected pilot screws and both were bent a little bit at the tips. Found that the pilot screws were about 2 or so turns out, instead of 1.5. I did not check the float height yet though. So I reassembled the carbs and installed them. Also I figured I would make sure I even had the correct plugs in, the guy I got it from said they were. Well they weren't I had br9es in it, when it calls for bp6es so that's 3 stages hotter plug. Well I put the bike back together and so far it has been running pretty good, still a little bit of a bog coming from a stop through midrange which I think might be the pilot screws being bent. Also at idle it still back fires some out of the left pipe. I checked the plugs and the left plug is black, and the right plug looks great. I also did a compression tests with engine hot and got 125 on left, and 140 on right. The wet test was 140 on left, and a little over 150 on the right. So the compression isn't quite up to par (140-170 the manual says) but it is a 1977.

here's the recap

-pilot screws bent----causes bog?

-float height no checked-- causes?

-compression left 125/140wet, right 140/150wet------not igniting everything causing plug to turn black?

-point gap not checked yet--Might cause the spark issue w/ the left plug?

Where can I get new pilot screws at? I have looked on the internet and haven't really found anything.

#

check your valves as they could be leaking/mal adjusted

pilot screws as a keyster kit from sirrius online in canada or I got a set from motoward yamaha dealer (just google)

[joe4g63]

Well hello again, I am still working on this dang thing. Well I checked the valves cold, and all four needed a little fine tuning. Then to the float height, they were really close but a little off, so I corrected them also. Went riding tonight and rode it pretty hard for about 25 minutes and it wasn't running to bad, still a little boggy mid throttle. Then i parked it at a store, and when I came out I had to kick about 15 times to get it to fire, and then once it did it was back to its old tricks-full throttle on the hand grip but was barely idling. I also noticed that the engine felt extremely hot. After about ten seconds of that it finally came out of it, and I could rev it up some, then off I went back home. While going home it was really boggy midrange again, and didn't really want to idle at stops or else it was revving really high. I pulled it into the garage and it wouldn't stay idling for me again. So I am pretty sure that it has something to do with ignition when it gets hot. Until the bike get really warmed up it runs great.

[drewpy]

Well hello again, I am still working on this dang thing. Well I checked the valves cold, and all four needed a little fine tuning. Then to the float height, they were really close but a little off, so I corrected them also. Went riding tonight and rode it pretty hard for about 25 minutes and it wasn't running to bad, still a little boggy mid throttle. Then i parked it at a store, and when I came out I had to kick about 15 times to get it to fire, and then once it did it was back to its old tricks-full throttle on the hand grip but was barely idling. I also noticed that the engine felt extremely hot. After about ten seconds of that it finally came out of it, and I could rev it up some, then off I went back home. While going home it was really boggy midrange again, and didn't really want to idle at stops or else it was revving really high. I pulled it into the garage and it wouldn't stay idling for me again. So I am pretty sure that it has something to do with ignition when it gets hot. Until the bike get really warmed up it runs great.

need to check your ignition coils next:

off the top of my head: 4ohms and 9k ohms (+/-20% @ 20'C) for secondary and primary, these should be the readings you are looking for. The coils could also break down with running, Mine did that.

Also check your battery is charged and charging at 14.5 volts.

did you check that the tips of the pilot needles hav'nt broken off in the carb body? If you take one out, they should have a really sharp needle. Both mine had broken off in the carb body and the spare set were the same.

[yoda]

Sticking valves? Does actually sound like fuel starvation. As demand increases, restricted delivery cannot keep up.

[joe4g63]

So tonight I rode her for a good hour or so, and finally it started to act up. I brought it home and pulled the plugs and did a compression test quick while it was hot to make sure neither of the valves were sticking partly open making it lose compression-they both checked out. The bad part was that both of the plugs were nasty sooty black, not just the left plug anymore. Then I did a resistance check on both coils while still hot,-first I checked with the plug boots on, and I got 14.4k on the right, and 18.6k on the left, so I took the boots off, and the the resistance of both coils were between 9.6k and 10.3k. When I checked the boots themselves the right was about 4k and the left was around 8k which I don't think check out. I am going to search the manual tonght and see if I can find some specs. Also I am going to check the resistance later when both have cooled off.

[joe4g63]

Alright after the bike cooled down I checked everything again. Left coil primary 3.7 ohms, secondary 8.91k ohms----right coil primary 3.7 ohms, secondary 9.73k ohms and the manual says 9.5kohms it should be close to. So ,maybe the left coil is on its way out. I am also wondering if the xs400 coils will work on the xs360, I am looking at a pair on ebay that are off of a 81 xs400. With the caps I still get 4.48k ohms on the left plug cap, and 8.73k ohms on the right. The book says that if the ohms value exceeds 9k then then caps are bad, so I guess my caps are good then. I also ohmed out the condenser and that checked out with the manual. Since I had the coils off I figured I would take a look at the carbs once again. While pulling them apart I found a little fuel on top of both of the diaphragms for the sliders-i am not to sure it there is that was suppose to be there. Just to double check with the position with the needle and the clip, I have it at the middle position which is the 3rd from the top and the bottom.

[Ferg]

Alright after the bike cooled down I checked everything again. Left coil primary 3.7 ohms, secondary 8.91k ohms----right coil primary 3.7 ohms, secondary 9.73k ohms and the manual says 9.5kohms it should be close to. So ,maybe the left coil is on its way out. I am also wondering if the xs400 coils will work on the xs360, I am looking at a pair on ebay that are off of a 81 xs400. With the caps I still get 4.48k ohms on the left plug cap, and 8.73k ohms on the right. The book says that if the ohms value exceeds 9k then then caps are bad, so I guess my caps are good then. I also ohmed out the condenser and that checked out with the manual. Since I had the coils off I figured I would take a look at the carbs once again. While pulling them apart I found a little fuel on top of both of the diaphragms for the sliders-i am not to sure it there is that was suppose to be there. Just to double check with the position with the needle and the clip, I have it at the middle position which is the 3rd from the top and the bottom.

How about swapping your right/left coils and see if the problem changes sides.

Cheers Ferg

[yoda]

Since I had the coils off I figured I would take a look at the carbs once again. While pulling them apart I found a little fuel on top of both of the diaphragms for the sliders-i am not to sure it there is that was suppose to be there. Just to double check with the position with the needle and the clip, I have it at the middle position which is the 3rd from the top and the bottom.

Think you just found the problem.

Diaphrams are bad news when they start to leak. Change these and give it another run. Ensure there is no air leakage around them.

[joe4g63]

So I let the carbs sit in cleaner overnight and reassembled them, and put them back onto the bike. I also bought new plug boots, so I know those are good now. Then I went out riding and same thing happened as usual, riding down the highway at about 60mph/mid throttle, whenever I craked the throttle wide open it would bog out, once i let off and went back to mid throttle it would come out of it and run decent again. When I got back to the house the bike would idle by itself good. I pulled off the left plug wire and no change in the engine, the right wire would kill the engine-so still the left cylinder is getting me. Then I switched the coils and started it up, and pulled the same wires again, and the left cyl would still not change anything-so the coil are good I would say. When it was idling i noticed the right carb had some fuel coming out of the rear of it, and the left carb didn't have much at all coming out (this is after i took off the filters so I could see in there). When I revved the engine both of the diaphrams would lift equally, so I figure the diaphram sliders are good then. When idling I would put my finger in the right carb and lift the slider up and the engine would die when I did this, but the left did not change the way the engine was running. I do have the vacuum line coming off of the petcock hooked up to the left cylinder, and the right port plugged. I figure that shouldn't matter though. I found some 1978 xs400 carbs on ebay pretty cheap and am wondering if I would be able to put these on the bike without any problems.

[drewpy]

So I let the carbs sit in cleaner overnight and reassembled them, and put them back onto the bike. I also bought new plug boots, so I know those are good now. Then I went out riding and same thing happened as usual, riding down the highway at about 60mph/mid throttle, whenever I craked the throttle wide open it would bog out, once i let off and went back to mid throttle it would come out of it and run decent again. When I got back to the house the bike would idle by itself good. I pulled off the left plug wire and no change in the engine, the right wire would kill the engine-so still the left cylinder is getting me. Then I switched the coils and started it up, and pulled the same wires again, and the left cyl would still not change anything-so the coil are good I would say. When it was idling i noticed the right carb had some fuel coming out of the rear of it, and the left carb didn't have much at all coming out (this is after i took off the filters so I could see in there). When I revved the engine both of the diaphrams would lift equally, so I figure the diaphram sliders are good then. When idling I would put my finger in the right carb and lift the slider up and the engine would die when I did this, but the left did not change the way the engine was running. I do have the vacuum line coming off of the petcock hooked up to the left cylinder, and the right port plugged. I figure that shouldn't matter though. I found some 1978 xs400 carbs on ebay pretty cheap and am wondering if I would be able to put these on the bike without any problems.

try squirting some easy start in the left carb, and if it kicks the engine you have fuel starvation (sticking float needle) or a massive air leak. usually the right carb has the vacuum take off, i'm sure yamaha would have done it on the left if they could as it would have saved ££'s on fuel tubing building so many 1000's of bikes.

did you run the bike on prime which bypasses the vacuum system? and cleaned the fuel tap filter?

[joe4g63]

the only way the bike would run is on the pri on the petcock. Also another thing that is kind a fishy is, the manual says to put the petcock to res when removing the tank, well my petcock still leaks when doing that. I put it on the on position and that seems to stop the fuel. I took the petcock apart awhile ago, and am pretty sure I put it back together, but is there a chance that it is not put together correctly?

[drewpy]

the only way the bike would run is on the pri on the petcock. Also another thing that is kind a fishy is, the manual says to put the petcock to res when removing the tank, well my petcock still leaks when doing that. I put it on the on position and that seems to stop the fuel. I took the petcock apart awhile ago, and am pretty sure I put it back together, but is there a chance that it is not put together correctly?

Its possible or the diaphram in the petcock is damaged causing leaks. you can get rebuild kts.

To by-pass that issue: run some tubing from a container of gas (petrol) and place it higher than the carbs, suck on the pipe and let the fuel run down the pipe and quickly push the fuel pipe onton the carb intake. let the spilt gas evaporate and try starting the bike up and see if that helps.

I do that to balance my carbs with the tank off!

do this at your own risk!!!!!!!!!!!BTW

[joe4g63]

So I got good news I finally got the right tools and a friend experienced with the points systems to check the static timing. My left and right cyl timing were both at the "LT and RT" marks. So after adjusting it to the LF and RF marks like the manual says the bike runs great, we think that somebody might have installed a new timing chain and didn't know where to time it at so they timed it to tdc. I still have a little back fire out the L exh pipe still. So my friend held a dollar bill up to the exhaust and said watch this, you would see the dollar move out most of the time but everyonce in awile you would see it get sucked tight onto the pipe meaning the exh valve was to tight, sticking or just leaking to much. I started a new forum about if anyone knew if a 79 xs400 cyl head would fit my 77 xs360, since I found one on ebay for dirt cheap that is in good shape.

[joe4g63]

By the way thanks Drewpy, Yoda, Ferg, and Stevar for all the input.