float needles are worn or have a bit of crud keeping them open!
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Bike idles fine but will not rev
- Thread starter moomaster
- Start date
moomaster
XS400 Member
I know there's no junk keeping the float needles open because I had the whole assembly apart yesterday. If the float needles were worn, why would it only overflow with gas after i adjusted the float height?
Also, where is the idle mixture needle I'm supposed to see carb cleaner shoot out of? I know the emusion tube is clean because I had that out before I dunked the whole carb in carb cleaner.
Also also, for adjusting the float height, my whole life up until now I have been bending the little bit of metal the float needle hangs off of, but that picture points to the little bit of bent up metal on the side? Am I supposed to be bending that? How do I measure the height if I'm changing that?
Also, where is the idle mixture needle I'm supposed to see carb cleaner shoot out of? I know the emusion tube is clean because I had that out before I dunked the whole carb in carb cleaner.
Also also, for adjusting the float height, my whole life up until now I have been bending the little bit of metal the float needle hangs off of, but that picture points to the little bit of bent up metal on the side? Am I supposed to be bending that? How do I measure the height if I'm changing that?
jmd_forest
Bldg 1980 XS400 Cafe Bike
I'm pretty sure I bought this bike from moomaster about 2 weeks ago. I just got the chance to pull the carbs and disassemble and there is a touch of crud inside. I doubt the carbs were ever completely apart as the float needle screens were dirty and I needed an impact driver to separate the carbs. It also looks like the enrichment circuit is dirty. I plan to give them an EXTREMELY thorough cleaning and replace the float needles, as well as all the other o-rings and throttle shaft seals. I'll keep the thread updated with how I manage.
lhaolpa
XS400 Junkie
I would say that you should replace the float needle sets,which include the float needle,seat,etc. Mikesx has a good kit which includes all you should need except elbow grease,cleaner,etc. I went through the same thing with both bikes I have,leaking,cleaned seat with Q-tips and acetone,and replaced,it ran well for a while,then started flowing again.Put in new kit,and no more probs with overflow. Don't be frazzled when you read the part about fits 650,they use the same carbs as 400s. If you have an air compressor,blow all the passages until they are clear. lha
jayel
#9 Guru 78 SR500 80 XS11
check the ignition advance, if it's not advancing it won't rev
jmd_forest
Bldg 1980 XS400 Cafe Bike
Thanks for the hints. I plan to replace the float needle and seats. It looks like the PO (or the PPO or PPPO) replaced the diaphrams already so they should be good to go. It makes me a little nervous that someone has already pulled these apart as I don't know what they may have done or if there is anything missing.
Regarding the ignition advance: My experience with advance is limited to automotive vacuum advance in a distributor. I was under the impression advance on this bike is TCI controlled. Could someone elaborate a little regarding checking the advance?
Thanks for the help.
Regarding the ignition advance: My experience with advance is limited to automotive vacuum advance in a distributor. I was under the impression advance on this bike is TCI controlled. Could someone elaborate a little regarding checking the advance?
Thanks for the help.
jayel
#9 Guru 78 SR500 80 XS11
if it's TCI it should be ok, but I would at least look at it with a strobe
jmd_forest
Bldg 1980 XS400 Cafe Bike
Spent all day cleaning the carbs. What I find is a little dirt, bent/warped floats, the idle mixture needle is missing the tiny metal washer and o-ring at the bottom, throttle shaft seals leak a little, gunk in the float needle screen. Other than that they are reasonably clean which is to be expected since moomaster had them off and on a least a few times for cleaning. I'm tearing them COMPLETELY apart and giving them an extremely thorough cleaning with OOO steel wool and carb spray. I'm ordering new throttle seals, float needles and seats, and idle circuit o-rings and washers today.
Just be careful with the steel wool. Cosmetically the carbs might appear dirty, but that doesn't really matter. You just need to be sure there is no gunk blocking any of the passages. Steel wool has a tendency to shed fibers which can fit in the passages you are trying to clean. An air compressor and carb spray is what I prefer. If they are getting completely torn down you could also consider Berryman's dip; it's more expensive than steel wool, but it's nice being able to just let them soak while you do something else.
jmd_forest
Bldg 1980 XS400 Cafe Bike
Thanks for the hints. I use quite a bit of carb spray to make sure any stray steel wool fibers are washed away. I should probably plug in my compressor and use some air too. I've used the same method successfully on the Hitachi carbs on my 85 XJ700. I'm glad there's only 2 carbs on the XS400 or the $55 of carb parts would be $110. Can't wait for the parts to come in. I've never even had this thing fired up yet.
I'm also polishing the hats and bowls. Used 220 then 800 then 1500 grit paper and they came out pretty nice. Guess it time to grab some high cut rubbing compound and hit them with the buffer also.
I'm also polishing the hats and bowls. Used 220 then 800 then 1500 grit paper and they came out pretty nice. Guess it time to grab some high cut rubbing compound and hit them with the buffer also.
jmd_forest
Bldg 1980 XS400 Cafe Bike
Well, its about time to continue this thread. I had a self induced time out to have my left knee replaced with a shiny new metal and plastic one the day before Thanksgiving so things are moving slower than I wanted.
OK so all the parts came in: I replaced the float needle valve, float needle seat, idle mixture screw,spring, seat and o-ring, and the throttle butterfly shaft seals. The carbs were COMPLETELY stripped and thoroughly cleaned, polished the slides and slide chambers. All the jets and tubes that can be removed were removed and thoroughly cleaned, bowl and all bowl passages cleaned, dip tube cleaned. All polished with 000 steel wool blown clean with compressed air and blown clean again with spray carb cleaner.
Float bowl set at 26MM per PM with Drewpy, idle mixture set 3 full turns out.
Assembled with new stainless screws for hats, bowls, and alignment rails. Tightened up the intake manifolds that were loose.
Got the carbs back on today and hooked up a temp gas tank and blocked off the petcock vacuum. Bike started right up but will barely idle and backfires a little more than occasionally. The throttle had no real affect but to kill the engine. It is getting spark to both cylinders since both mufflers get warm. By the way, I did not install the air cleaners and related plumbing for this quick test.
My plan is:
1) Compression test (just haven't had the chance yet). Bad valves could be causing backfire. I probably should check valve timing also. I have no idea what the PO/PPO/PPPO may have done.
2) Check ignition timing ?? Have no idea how to go about it. I pulled off the points cover and found some type of electronic/hall effect pickup that I have seen a picture of in another thread so at least I know its not some third party "performance" part. There are no points or condenser on this bike.
Anyone got a hint on ignition timing?? Anyone got a hint on anything else???
Desperation is setting in. I'd like to have this thing running well when my son gets home for Christmas and we can start our father son cafe build in earnest.
Thanks for any help you may be able to provide.
OK so all the parts came in: I replaced the float needle valve, float needle seat, idle mixture screw,spring, seat and o-ring, and the throttle butterfly shaft seals. The carbs were COMPLETELY stripped and thoroughly cleaned, polished the slides and slide chambers. All the jets and tubes that can be removed were removed and thoroughly cleaned, bowl and all bowl passages cleaned, dip tube cleaned. All polished with 000 steel wool blown clean with compressed air and blown clean again with spray carb cleaner.
Float bowl set at 26MM per PM with Drewpy, idle mixture set 3 full turns out.
Assembled with new stainless screws for hats, bowls, and alignment rails. Tightened up the intake manifolds that were loose.
Got the carbs back on today and hooked up a temp gas tank and blocked off the petcock vacuum. Bike started right up but will barely idle and backfires a little more than occasionally. The throttle had no real affect but to kill the engine. It is getting spark to both cylinders since both mufflers get warm. By the way, I did not install the air cleaners and related plumbing for this quick test.
My plan is:
1) Compression test (just haven't had the chance yet). Bad valves could be causing backfire. I probably should check valve timing also. I have no idea what the PO/PPO/PPPO may have done.
2) Check ignition timing ?? Have no idea how to go about it. I pulled off the points cover and found some type of electronic/hall effect pickup that I have seen a picture of in another thread so at least I know its not some third party "performance" part. There are no points or condenser on this bike.
Anyone got a hint on ignition timing?? Anyone got a hint on anything else???
Desperation is setting in. I'd like to have this thing running well when my son gets home for Christmas and we can start our father son cafe build in earnest.
Thanks for any help you may be able to provide.
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From the Yamaha factory service manual elsewhere on this site:
Now, it sounds to me like it is still lean. Put the remainder of the intake system in place and the filters then try it again.
Are you starting it on full choke (enrichment)? What happens as the bike warms up? It barely idles, but at what rpm? Have you adjusted the idle rpm? Did you visually verify that the throttle butterflies are opening together? It's no replacement for a proper synchronization, but it's a good place to start.
Now, it sounds to me like it is still lean. Put the remainder of the intake system in place and the filters then try it again.
Are you starting it on full choke (enrichment)? What happens as the bike warms up? It barely idles, but at what rpm? Have you adjusted the idle rpm? Did you visually verify that the throttle butterflies are opening together? It's no replacement for a proper synchronization, but it's a good place to start.
mcrowell75
XS400 Enthusiast
Did you say the air cleaners were off when you fired it up?
^^air cleaners off the carbs will give you the symptons you describe
jmd_forest
Bldg 1980 XS400 Cafe Bike
Yes, air cleaners were off for this quick test. I will install the air cleaners and related plumbing and try again tomorrow. I guarantee the throttle butterflys are moving in tandem when I twist the throttle. I Did a bench sync off the bike using a sliver of index card before reinstalling the carbs and the butterflys move smooth throughout their entire range of motion with absolutely no binding anywhere.
I am starting the bike on full enrichment.
Someone was definitely in the spark unit before I bought the bike as the retaining screw is pretty butchered up to the point someone used a hacksaw to cut a slot in the screw since the phillips head had been stripped.
I didn't note the idle RPM. It doesn't really idle for more than 30 seconds to a minute before dieing and using the throttle to ever so slightly increase the RPMs doesn't really work. So, it has only run for a total of 5 minutes or so and never fully warmed up but warm enough for the pipes to get too hot to touch. Regardless, I would expect SOME response from very slowly applying throttle other than dieing. I will use the idle thumb knob to increase idle a touch for testing tomorrow.
Still .... consistant but irregular backfiring should not be related to carb issues. Somehow I'm getting spark at inappropraite time to fire off the fuel charge. I'll try reviewing the manual excerpt provided above with the engine running. I'm not really sure what the "rotor" is on this bike. I'll look around in the morning. At least I do have a strobe light from my younger days. I'd bet most younger mechanics have never had the need to use one.
I am starting the bike on full enrichment.
Someone was definitely in the spark unit before I bought the bike as the retaining screw is pretty butchered up to the point someone used a hacksaw to cut a slot in the screw since the phillips head had been stripped.
I didn't note the idle RPM. It doesn't really idle for more than 30 seconds to a minute before dieing and using the throttle to ever so slightly increase the RPMs doesn't really work. So, it has only run for a total of 5 minutes or so and never fully warmed up but warm enough for the pipes to get too hot to touch. Regardless, I would expect SOME response from very slowly applying throttle other than dieing. I will use the idle thumb knob to increase idle a touch for testing tomorrow.
Still .... consistant but irregular backfiring should not be related to carb issues. Somehow I'm getting spark at inappropraite time to fire off the fuel charge. I'll try reviewing the manual excerpt provided above with the engine running. I'm not really sure what the "rotor" is on this bike. I'll look around in the morning. At least I do have a strobe light from my younger days. I'd bet most younger mechanics have never had the need to use one.
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no, the bike will pop when it's lean and get really hot. my tracker did it till i upped the pilot jet.
jmd_forest
Bldg 1980 XS400 Cafe Bike
Finally some progress:
Installed the air cleaners and intake plumbing but still not getting any throttle response. With the throttle wide open I was idling at 1200 RPM. Pulled the plugs and did a compression test and noted 140 PSI in each cylinder with my POS compression tester (this bike, although neglected for some time, only has 9K miles on the odometer). The spark plugs installed by the PO were brand new NGK B7ES. Spec calls for BP7ES. Not knowing the difference, I cleaned up and installed a set of BP8ES (one step colder than BP7ES) I had laying around from my XJ700. They didn't help.
Pulled the ignition cover, and as noted previously, the screws holding the pickup unit's circular backplate to the cylinder were pretty chewed up. Also, the rotor (figured out what/where it was) retainer washer was definitely not original, maybe the retainer bolt is not original but I can't tell. Upon inspecting the pickup sensors (tiny magnetic "plates" molded into the pickup unit) it was obvious the sensors had come into contact with the rotor at some point but the damage seems inconsequential. I removed and cleaned the rotor and pickup and reinstalled with the same results, no throttle response.
Per one of the earlier posts, I decided to try and adjust the timing even though there are no timing marks to speak of that I can find. There is a "divit" in the flange the pickup unit retaining backplate sits in and 2 "divots" separated by a single "tooth" in the pickup unit retaining backplate.. I simply loosened up the pickup unit retaining screws and rotated the pickup unit by one "divot" clockwise and I immediately started getting throttle response. Moved it another "divot" clockwise and it became much smoother and throttle response and return to idle became much better to the point of "normal".
I've downloaded the manuals from this site but I seem to be in a dilemma in that the 1980 does not have points as described in the SOHC manual (up to 1979) and the other service manual is for the DOHC models, if I am not mistaken.
Houghmade's post earlier is not very helpful since there is no "LF" mark on my rotor and I can't identify any "index mark".
Any hints from anyone on properly timing this thing would be greatly appreciated.
Installed the air cleaners and intake plumbing but still not getting any throttle response. With the throttle wide open I was idling at 1200 RPM. Pulled the plugs and did a compression test and noted 140 PSI in each cylinder with my POS compression tester (this bike, although neglected for some time, only has 9K miles on the odometer). The spark plugs installed by the PO were brand new NGK B7ES. Spec calls for BP7ES. Not knowing the difference, I cleaned up and installed a set of BP8ES (one step colder than BP7ES) I had laying around from my XJ700. They didn't help.
Pulled the ignition cover, and as noted previously, the screws holding the pickup unit's circular backplate to the cylinder were pretty chewed up. Also, the rotor (figured out what/where it was) retainer washer was definitely not original, maybe the retainer bolt is not original but I can't tell. Upon inspecting the pickup sensors (tiny magnetic "plates" molded into the pickup unit) it was obvious the sensors had come into contact with the rotor at some point but the damage seems inconsequential. I removed and cleaned the rotor and pickup and reinstalled with the same results, no throttle response.
Per one of the earlier posts, I decided to try and adjust the timing even though there are no timing marks to speak of that I can find. There is a "divit" in the flange the pickup unit retaining backplate sits in and 2 "divots" separated by a single "tooth" in the pickup unit retaining backplate.. I simply loosened up the pickup unit retaining screws and rotated the pickup unit by one "divot" clockwise and I immediately started getting throttle response. Moved it another "divot" clockwise and it became much smoother and throttle response and return to idle became much better to the point of "normal".
I've downloaded the manuals from this site but I seem to be in a dilemma in that the 1980 does not have points as described in the SOHC manual (up to 1979) and the other service manual is for the DOHC models, if I am not mistaken.
Houghmade's post earlier is not very helpful since there is no "LF" mark on my rotor and I can't identify any "index mark".
Any hints from anyone on properly timing this thing would be greatly appreciated.
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you need to take the left cover off the side.( on main stand) It has 4 screws at 12, 3, 6 and 9 O'clock
you'll see a window with a notch in the middle, the spinning rotor has the timing marks on them which are hard to see.
you'll see a window with a notch in the middle, the spinning rotor has the timing marks on them which are hard to see.
jmd_forest
Bldg 1980 XS400 Cafe Bike
I gotcha ... the round aluminum cover with "YAMAHA" molded into it. That makes sense as it should be direct access to stuff inline with the crankshaft, kinda like timing marks on a car's front crankshaft damper wheel.
I'll give it a whirl first thing tomorrow. Once I get this thing running well I might be able to take it for a spin around the neighborhood to check out the transmission. Hopefully there will be no issues there.
I'd like to thank everyone for their help and patience with an XS400 "noob"
I'll give it a whirl first thing tomorrow. Once I get this thing running well I might be able to take it for a spin around the neighborhood to check out the transmission. Hopefully there will be no issues there.
I'd like to thank everyone for their help and patience with an XS400 "noob"
mcrowell75
XS400 Enthusiast
I'm in to this thread because I think you are close AND you are from Jersey
Can you post pics. I'd like to see good clear pics of this electronic ignition. Is it even adjustable? Does it rotate around the cam lobe so you can make the cylinders fire earlier or later?
I have a video on you tube that shows how to time a points ignition. In it you can see the LF line.
Also, when you bench synched the butterflies did you line them up to the correct two holes. I have a pic in my album showing this.
How are your air cleaners. Are they shot? If the foam is rotted away you may have too much air coming thru = lean condition.
Can you post pics. I'd like to see good clear pics of this electronic ignition. Is it even adjustable? Does it rotate around the cam lobe so you can make the cylinders fire earlier or later?
I have a video on you tube that shows how to time a points ignition. In it you can see the LF line.
Also, when you bench synched the butterflies did you line them up to the correct two holes. I have a pic in my album showing this.
How are your air cleaners. Are they shot? If the foam is rotted away you may have too much air coming thru = lean condition.
