XS360 fuel/carb questions

B

b5iveS4

Been Around the Block
This is a '77 XS360
Ok, so i adjusted my points and kicked it over and it doesn't want to start.
I pull off my pod filters and the one on the right has gas in it. What could that mean?


While i had the filters off, i decided to spray a little carb cleaner and kick it so see what would happen.
I could hear it starting to fire so i kept kicking and it started running and pretty steadily too.


Soooo...I decide i should probably ride it and see how she does. Not great...real poppy and hesitant until it starts
climbing up around 3k and keep in mind the filters are still off and it's got stock jetting as far as i know.
Well...it died and wouldn't restart so I had to push it home. It only made it a block and a half away so it wasn't a big deal.


It only starts when i spray carb cleaner in it so what does that mean? I primed the carbs so it should have fuel.
Seems that that would mean somethings wrong with my carbs. I rebuilt them before i ever started trying to run it.
Nothing is clogged and the diaphrams inside aren't ripped in the carbs.
I have a fuel line from the petcock into the left carb and then the fuel line in between the carbs to draw fuel into the right.
Thats the only line that's run to the carbs. No vacuum lines are connected...where would they connect to. There's one on
each carb boot off the head and then theres a vacuum line on the petcock and they are just open. Should there be a line off
of the petcock that Y's into the carb boots?


Also, what does the plunger do on the carbs, is that the choke?
One more question, when i got the bike started, i put it into first gear and it died like i hit a kill switch.
I could start in 2nd gear but in 1st it just shuts off. Is my neutral safety switch toast?


Sorry for all of the questions, it's my first carbureted bike and it's confusing coming from an R6.
I've started to think it's a fuel issue instead of electrical. I just can't tell if it's running lean or flooding.
Thanks in advance, you guys are always really helpful.
 
I had a 77 XS360.

Step number one: Replace the fuel petcock. Do not use a repair kit.... replace the vacuum petcock with a manual bog standard petcock. This is an very common problem on the 360 and sounds like you have it considering you have fuel coming out your pod filter which is the result of carb flooding. In the meantime before you replace the petcock you can use a clamp on the fuel line under the petcock when the bike is not in use. You should notice an improvement pretty quickly once the excess fuel is drained from your flooded carb(s)

I am not sure what plunger you are refering to? There is a lever on only one of the carbs, the left I believe that is the choke. You want to make sure you check your manual to be sure this is appropriately set, as well as your air/fuel mixture screws on both carbs.

Also the vacuum lines do not go into the carb boots. Those noosles are for draining the carbs pretty much. Something you should do with your flooded carb. I can't remember off the top of my head where the lines go. I seem to remember there being a connection in the middle connector of the carbs? I am sure someone will correct me.

If I still had my 360 or the manual I would look it up for you, but this is all I can say from memory. I am not an expert, in fact I know very little. I read everything in shop manuals or google. Thats the best way to learn and work your way through issues.

Cheers,
 
thanks, i'll definitely replace the petcock. I had planned on it anyway since i'm missing the tube that allows me to regulate between when i switch to reserve.
How do i drain the bowls? I have unscrewed the bolt in the bottom of the carb bowls and let the gas drain out of there many times.
So the little hard lines on the boots that connect the carbs to the head aren't supposed to be connected to anything? one is capped right now but not the
other. I've got a shop manual and have been through that thing a bunch of times but i'll look again closer at the carb section.
 
Also check your float height. If you have brass floats, sometimes they can get holes in them and fill with gas causing them to flood. Take it out and shake it to see if there is any fluid in it. Or, submerge it in water and see if any bubbles come out. The plunger is the choke. Pull it out to open it, in to close it. It sounds like you need to adjust your clutch. Do you have a manual? What carbs do you have?

Both barbs need to be capped.or else you will be extremely lean on that side. To drain, just unscrew the plugs.
 
what's kind of weird is that I seem to be running lean on the right cylinder but that's the one thats capped and the left cylinder is seemingly running rich but it's open. I took the carbs apart yesterday and the floats seem fine but i can take another look.

I was talking to this guy at cycle gear yesterday and he has like 4 older cb's and he asked what my stock jetting was but i don't know what comes in these old mikuni's. Anyway, he recommended 130 main's but only had 132.5s. I put those in and it's not wanting to start unless i spray carb cleaner in the intakes again but once it's running its very responsive like a bike should be but that's only from 3k and up. Seems to rich to start but great higher in the rpm's.
Is there a way to fix this with the air screws or will i need different jets? What does the pilot jet control and what does the main jet control?
Also, would pulling the choke when starting help this issue?
 
First, what size carbs do you have? If you don't know, post a pic of the backside where the filters mount.
Then find out what size jets you have now. You will have a pilot jet, needle jet and needle,and main jet. They all have numbers on them. The mains only get used when you are at 3/4 throttle to full throttle. The pilots are used up to around 1/4 throttle. Needles between these. You should need your choke for cold starts. Once warm, you shouldn't need it. It sounds like your pilot circuit is plugged up. Could be your mix screw settings. Depending on what carbs you have, will depend on what the settings should be and what size jets you need.
Like GroovyAardvark said, definitely change that vacuum petcock to a manual one. They are nothing but trouble.
And get those barbs capped. You can buy caps at any auto parts store.

Questions that need answered.
What are your floats set at?
What size carbs?
What size jets are in them?
What kind of air filters and exhaust are you using?
Are you using inline fuel filters?
 
Also, while your at it, check your diaphragms. To do this, there is an oblong hole at the top on the backside above the intake opening. Cover it with your thumb and lift the slide. It should drop slowly. If not, take it out and check for holes in the light.
 
let me check those things out and get some photos and i'll let you know.
I checked another forum and one guy gave the carb specs...not sure if
they're right but that's all i have to go on before i go outside to check for myself.

XS360
Main jet: 135
Air jet: .06
Jet Needle: 4FP21-3
Needle Jet: X-6
Needle Position: 3
Throttle Valve: 145
Pilot Jet: 17.5
Starter Jet: 40
Air Screw (number of turns out) 1 to 1.5
 
If that's correct, i shot myself in the foot with a smaller main jet haha.
I am running pod filters from dimecitycycles and when i got the bike,
my exhaust was chopped pretty much right under my feet.
 
i can get it to run, and when it does, it is kinda rough below 2k rpm and won't idle now with those new jets. When i rev it, it revs quickly and sounds good and backfires little flames out of the right pipe only. If i open the throttle to hold it at about 2k rpm, the air coming out of the exhaust on the right side is strong and warm but the air coming from the left pipe is weak and cool
 
i also put seran wrap around my pod filters and just cut a small hole to draw air into them to sort of mimic a stock air box if possible. Pipes are still dumped under my feet. I'd like to put pipes on it but theyre so damn expensive. I'd like it to run like it is for now if possible. I don't mind being obnoxiously loud if it helps people watch out for me
 
With those filters and exhaust, you are more than likely running lean. You will need to go up one or two on the pilots and maybe one on the mains. It's really just trial and error until you find the best setup. Also, I don't know about those filters you have, but some filters (like the cheap ebay ones) will block the air vents on the mouth of the carb. But you still have to find why your carb is overflowing. What do your plugs look like?
 
The filters i have are just the cone filters from dimecity's site. I don't think they cover the air vents on the carbs but i can trim the inside lip of the filter just in case. What happens if they're blocked? I pulled the plugs, the right cylinder plug is clean but the tip is white like its running lean. The left cylinder's plug is black and looks like maybe it's fouled?
 
so I'm thinking of going to a 137.5 main jet, a 20 pilot jet and moving the clip on my needle up one notch to bring the overall fuel mixture a little more rich throughout the throttle range. Does anyone see a problem with this?
 
Moving the clip up will lower the needle, making it leaner. I would buy one and two up sizes on the jets.
Also, you could be leaking fuel into the body because of a worn out needle jet o-ring. It is worth the extra few bucks to go ahead and replace them while your in there.
 
cool, i'll try and replace everything i can if i can find all the parts. Ordered the jets today. 20 pilot, 137.5 and 140 main. I did a compression check on it today too. Left cylinder read about 152 and the right was about 146 so the compression seems good. It will now start by just kicking with the choke on, no carb cleaner needed to be sprayed in the intakes. the left cylinder is still misfiring but actually firing strong when it does. It doesn't want to fire under 3k and when i give it a little throttle, it climbs up and as the left cylinder starts firing, the bike revs quickly to like 4k with barely any throttle. It responds well to throttle, and feels strong as long as its over 3k. below that, the left cylinder is quiet and hardly moves any air out of the exhaust. this is still on the stock jetting though so i guess that's normal for having pod filters and chopped pipes. It will almost idle now too, actually will idle but theres a noticeable difference in the cylinders when idling.
 
they are not synced, i don't have the carb sync tool to do it with. I haven't messed with the mix screws much but i have a little. I would need to adjust them in to richen the mixture correct? you think that could bring the left cylinder to fire at idle?
 
Turn the mix screws out to make rich, in to lean the mix. Turn them in all the way, until they just seat, then back them out 1 1/2 turns to start with. This should be close for 34's.
You can make a manometer to sync your carbs for about $10. Here's how.
Buy about 10-12 ft. of 3/16 ID clear tubing from hardware store.
Fold it in half without kinking the tubing and tape it in a few spots to a yard stick or board or whatever that is about three feet long, leaving a loop on the bottom.
Fill it with ATF or 2cycle about a foot up.
Connect each side to your barbs on your carbs or manifolds.
Start motor. If one side rises quickly, shut it off before fluid gets sucked into the motor. You want the fluid to be the same height in the tubes. So, if one side is higher, adjust sync screw a little at a time until they are the same. Then you are done.

Here is a link to a manual for your 360 if you don't have one.
motour.hu/sunburst/dokumentaciok/service/Yamaha_XS360_400_Service_manual.pdf

Looks like you will have to copy and paste it.
 
I have that manual, just haven't really read a lot of it in depth. I do have a question about my petcock and those barbs you're talking about.
When you say to connect that clear line with atf in it to sync the carbs, are you talking about the little vacuum barbs on the rubber pieces
connecting the carbs to the head? There aren't any other vacuum lines on the carbs. Also, is that where the vacuum line on the petcock is
supposed to attatch? Was that vacuum line split and run to each of the barbs originally? When i replace the petcock, i'll just be capping those
barbs on the boots.

That brings me to this, my boots are super dried out and cracked and really need to be replaced. On mikesxs.net, they have the carb holders
that i think replace mine but i want to make sure before i purchase them. They are on this page http://www.mikesxs.net/products-40.html#product-20-6038
2nd item down #20-6038. It says it replaces part numbers 13586 and 13596 and the original part numbers for those holders were
1L9-13586-02-00 and 1L9-13596-02-00. Seems to be the direct replacement. I just wanted to check.

As far as replacing my petcock, it needs to be a non vacuum type, can i use any one pretty much? I'd like to avoid drilling into the tank and risking metal shavings in it if i can or is that unavoidable? Can i get a male to male threaded connector from my tank's stock outlet to the petcock? Seems like it would be considerably smaller going into the tank than into the petcock. Then i'd just plug the other two holes with screws i guess.

Thanks for all your help, I feel like i'm closer to getting this little bastard on the road with every reply i get.
 
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