Carb Overflowing & Hanging/Surging Idle

[Zurkite]

My heads been spinning lately & I need some help figuring out my problem here...

I've been having an issue with the carbs overflowing, not right when I turn the fuel on, but after about an hour or so it's start pouring out of both sides...

I've changed the float height to 26mm, tested the float needles to make sure they were sealing (which they are) but they keep on overflowing.

And yes, im turning the petcock off its not sitting in prime.

Im thinking my issue might be a faulty petcock? I'm running out of ideas I've went thru these carbs almost 10 times & they are squeaky clean

Now I'm having an issue where I kick start my bike the first time and it starts, not amazing because I haven't balanced them yet, but the right cylinder isn't firing correctly.

So I shut the bike off, try to kickstart multiple times, then theres no spark.

Texted both sides by holding onto the engine to see spark and nothing... these are brand new NGKs btw



Faulty coils? This is a brand new battery so no way it not getting enough power.

Send help before I lose it lol. Sorry for the long thread.

 

[Revvy Kevvy]

I set my floats to 20mm, they used to overflow at 27mm as you describe and as for the spark, is 12VDC actually getting to the coils? there are multiple switch between the coils and the battery and if the points are both closed then nothing will fire. Stick a multimeter across the points and make sure you are getting 12V when they open.

Not likely to be both faulty coils but if the points are set really wrong they can both be closed.

 

[Zurkite]

I set my floats to 20mm, they used to overflow at 27mm as you describe and as for the spark, is 12VDC actually getting to the coils? there are multiple switch between the coils and the battery and if the points are both closed then nothing will fire. Stick a multimeter across the points and make sure you are getting 12V when they open.

Not likely to be both faulty coils but if the points are set really wrong they can both be closed.

I Haven't checked with a multi-meter yet but I will do that tomorrow. Where exactly are the points I should be checking? Clearly inside the coil pack where it makes contact with the spark plug, but where else?

As for the float height, I will indeed try 20mm!
I've done multiple tests on the float needle & I even sank the float in gasoline overnight with a wrench holding them down and they didn't sink or have any gas inside.

Thanks for the info, I'll adjust those in the morning aswell and get back.

 

[Zurkite]

Morning everybody, I made some progress!

Regarding the coil issue, I found that when it's switched to ON from the OFF in the right pointing position it didn't give me any spark...

But when I had it in OFF on the left pointing position then turned it to ON... THERES SPARK!

Super weird I have no idea why this happened but who knows right

I also went ahead and adjusted my valves since I haven't done them yet, Left side was totally off , clearance was too small, Right side was slightly off.

Adjusted my floats to 23mm, 20mm seemed a bit too low for my brass floats.

23mm should work, when I first ever adjusted the floats they were sitting around 30mm+ I believe, clearly too high so I set to 27mm, now that's not working so 23mm seems right.

Will throw on carbs later today & get back to the forum & let you all know how the bike is running.

I've had this bike for 4 months and it hasn't had any riding time

I'll post some pics right now.

(1978 Yamaha Xs400)

 

[Zurkite]

 

[Zurkite]

Recently decided to put the rack back on, for some reason it gives the bike its own distinct look.

Incase anyone is wondering too I shaved down the OEM seat that why it's not as bulky as they regularly look, used a cake cutter knife to do it, fairly easy tbh.

 

[Revvy Kevvy]

Very nice looking bike, mine is red and I dont have the little dinky seat but I would like one.
My floats are not brass they are like plastic, so perhaps its different. There is a test well detailed in the manual and also in my blog on all the issues I had with my carburettas and this test using a clear pipe from the bottom of the carburetta bowl to the top of the bowl seems to be the test that all the manuals give in the end. The float sizes seem to vary from 20mm to 32mm with a few sizes inbetween but doing that clear tube test was why I settles on 20mm in the end.

Glad you found the electricial issue, the run/stop I think you describe. But, the question you asked where to measure the voltage its right across the contact points. When they open you should get 12VDC.

Happy riding, its a nice bike

 

[Zurkite]

Very nice looking bike, mine is red and I dont have the little dinky seat but I would like one.
My floats are not brass they are like plastic, so perhaps its different. There is a test well detailed in the manual and also in my blog on all the issues I had with my carburettas and this test using a clear pipe from the bottom of the carburetta bowl to the top of the bowl seems to be the test that all the manuals give in the end. The float sizes seem to vary from 20mm to 32mm with a few sizes inbetween but doing that clear tube test was why I settles on 20mm in the end.

Glad you found the electricial issue, the run/stop I think you describe. But, the question you asked where to measure the voltage its right across the contact points. When they open you should get 12VDC.

Happy riding, its a nice bike

Thanks for your help, to be honest I don't own a multimeter WHICH I SHOULD but I will get to the voltage testing across the whole coil system.

Battery is new also not sure if I threw that in there, but upon typing this I forgot that I was supposed to check all the wiring & connectors incase of any damage upon them, also check the fuse box possibly.

I'll check when I get home & throw the carbs on to see if I can get this baby to run right...

We will see. Be back in a few hours

 

[Zurkite]

Thanks for your help, to be honest I don't own a multimeter WHICH I SHOULD but I will get to the voltage testing across the whole coil system.

Battery is new also not sure if I threw that in there, but upon typing this I forgot that I was supposed to check all the wiring & connectors incase of any damage upon them, also check the fuse box possibly.

I'll check when I get home & throw the carbs on to see if I can get this baby to run right...

We will see. Be back in a few hours

Forgot to add, is there anyway dirty contact points in the coils could cause some issues? Mine seem to be a bit greasy or something.

 

[Revvy Kevvy]

Points are fairly forgiving except for water. I removed mine completely cleaned them up with some old points files I had and washed them in petrol (gasoline) remember to add some light oil to the wick in the centre to help it spin and go through the process of setting them all back up.
Its in the manual,

Remember, points systems survive the EMP of atomic warfare so our little team of XS400 warriors will be roaming the wastelands with the lord humengeous and mad max looking for fuel to power our machines.

How to know TDC
The valve on the LHS will open then close, the next time it passes the LT I mark it is on TDC
set up the timing
Rotate to LF I
the points must open when the I is lines up. as soon as the points open the spark will fire.
Spark plug setting 0.7/0.8mm
Contact 0.3 to 0.4mm max open

 

[Zurkite]

I have come back with new information

So I set my floats to 23mm, threw them back on the carb & let gas fill up the bowl, and no more leaking!

But now I am still facing the spark issue. I realized I get spark the first time I kickstart and then there's no more spark after that.

Idk if this is relevant but I the kickstart when starting the bike, I never use electric start because its faulty & last time I used ignition it drained my battery badly (swapped with a new one)

I've been reading on setting the points & testing the there, but that would only matter if I used the electric start, correct?

Getting me a multi-meter today to check if I'm even getting power to the coils after that initial first kick, then I'll work my way backwards to check for any bad connections or fault grounds.

Since I'm kickstarting, is my process of diagnosing any different? Specific things I should check?

I remember a while back when I had the bike running (not very good at all) one of the coils would get super duper hot compared to the other one, could this be an indication of failing coils?

I'll be back with more info in a few days, I really want to get her on the road soon!

 

[Zurkite]

I know I'm the only one really on this thread but I've been doing lots of testing with a Circuit light & multimeter and I've realized that the killswitch was broken!

I opened it up and peices fell out like the bottom of a chips bag

The things you find am I right...

Multimeter had no change when switching OFF to ON, which had me suspicious, and I hooked up the circuit light to the ignition coil wires (red & white) that hook up to the switch, and nothing changed when going to ON.

Bypassed the wires by tying them together, and light turns on when testing with circuit light on ignition coil wires (red & white)

All this time I had no spark it was because of this.

I'm guessing the times I had one little spark when I first kick started the bike was the point making a very small bridge, which showed me a small spark but then nothing after.

Getting everything assembled tomorrow, seems I overflowed my carbs by trying to kickstart to much...

Oops

Will reassemble in the morning and see what I got!

 

[Zurkite]

Soldered the killswitch wires together to bypass kill switch.

Putting together tmrw to see if everything is dialed in.

 

[Zurkite]

Going to send an update in here incase this information is useful for anyone experiencing the same issue I have.

So great news, no more surging idle, bike starts up wonderfully.

I was having an issue with it dying when given throttle, so I stripped the carbs down once again, cleaned every hole with cleaned + 100psi compressed air for certainty, and changed out the pilot jets since they were dirty (the only jet I forgot to clean last time they were off, silly me)

As far as the surging issue goes, I realized that the throttle cable was setup in a way that the "fully closed" position when the throttle snapped back, wasn't actually fully closed.
BIG FACE PALM!

I loosened the cable, and watched the throttle slowly move downwards... I was in shock lol how could i have never caught this.

My guess is that the "idle" was already high from the cable and the surging that was happening was either the throttle cable being opened from the bikes vibraton, or it throwing off the mixture + the revving.

Got it idling at a beautiful 1200RPM, played with the mixture screws to get the best steady idle speed, while also adjusting idle screw.

So glad I got this finished, the smile on my face when started it up today is something I haven't experienced in a while.

I got some rubber float needles & a gravity fed petcock on the way just incase, rather have the parts then deal with the vacuum operated stock petcock.

 

[Durney]

My heads been spinning lately & I need some help figuring out my problem here...

I've been having an issue with the carbs overflowing, not right when I turn the fuel on, but after about an hour or so it's start pouring out of both sides...

I've changed the float height to 26mm, tested the float needles to make sure they were sealing (which they are) but they keep on overflowing.

And yes, im turning the petcock off its not sitting in prime.

Im thinking my issue might be a faulty petcock? I'm running out of ideas I've went thru these carbs almost 10 times & they are squeaky clean

Now I'm having an issue where I kick start my bike the first time and it starts, not amazing because I haven't balanced them yet, but the right cylinder isn't firing correctly.

So I shut the bike off, try to kickstart multiple times, then theres no spark.

Texted both sides by holding onto the engine to see spark and nothing... these are brand new NGKs btw



Faulty coils? This is a brand new battery so no way it not getting enough power.

Send help before I lose it lol. Sorry for the long thread.

Check the tiny "O" ring around the needle and seat where it sits in the carb body. Fuel can leak even with the floats set properly.

 

[kodiak]

Recently decided to put the rack back on, for some reason it gives the bike its own distinct look.

Incase anyone is wondering too I shaved down the OEM seat that why it's not as bulky as they regularly look, used a cake cutter knife to do it, fairly easy tbh.

That looks so nice. Is that rack stock? My wife would love it if I had one of those.

 

[Zurkite]

That looks so nice. Is that rack stock? My wife would love it if I had one of those.

Yes the rack is stock. I've probably only seen one video on youtube with someone who has the same rack. I actually took it back off, not sure if I like the look or not.

 

[Zurkite]

Update: Took the bike for a good 15 min ride today after syncing the carbs with my own DIY tool, and it rides great!

Really pushed it to high RPM & high speeds, performed just as it should.

I want to list some quick tips I forgot to mention in this thread when I was diagnosing my main issue with rough start.

After I got spark back from bypassing the killswitch I was having a rough time starting it (seemed like a weak spark) so I went to the points and I put a peace of sand paper between both contact points for each side.

FYI; When looking at the points, Left side is for LS, Right side is for RS. You'll know which side you're in because it'll have play when you pull on it. To get to the other side rotate the engine by pushing down the kick starter, then it'll become free.

So right after I cleaned both point for each cylinder with sand paper real good, I kicked it and damn it started so quick!

Dial everything in place when diagnosing an issue, the little things matter!

Hoping this thread will be helpful to someone one day.

Play with the mixture screws and see how it runs. Theres a lot of good videos on youtube showing how to set it right. DONT FORGET TO SYNC THEM EITHER! It makes a HUGE difference trust me.

 

[GuyS]

I have come back with new information

So I set my floats to 23mm, threw them back on the carb & let gas fill up the bowl, and no more leaking!

But now I am still facing the spark issue. I realized I get spark the first time I kickstart and then there's no more spark after that.

Idk if this is relevant but I the kickstart when starting the bike, I never use electric start because its faulty & last time I used ignition it drained my battery badly (swapped with a new one)

I've been reading on setting the points & testing the there, but that would only matter if I used the electric start, correct?

Getting me a multi-meter today to check if I'm even getting power to the coils after that initial first kick, then I'll work my way backwards to check for any bad connections or fault grounds.

Since I'm kickstarting, is my process of diagnosing any different? Specific things I should check?

I remember a while back when I had the bike running (not very good at all) one of the coils would get super duper hot compared to the other one, could this be an indication of failing coils?

I'll be back with more info in a few days, I really want to get her on the road soon!

I kinda thought that 20mm was incorrect. That height would keep the float needle open longer before it closes of the gas, which may have resulted in your intermittent flooding issue?