Idle problem (wont) after carb cleaning....

[Phil_B]

XS 400 special

Looking for some help...very much an amateur but got up the nerve to clean my carbs. The bike seemed to be suffering from a blockage. I believe only the left side was firing. At first, it ran fine but it had no power, full throttle was a very slow acceleration. The get-up and go, got up and went. Then something changed for the worse and I could get it to idle fine and go, but I would get lurching and then it would die.

The cleaning seemed to go well, sure enough, there was a blockage (a pretty good one) under the right passage below the pin that controls the float. I believe where the fuel passes from the first to the second carb. Also, the little pin holes on the brass tube were blocked up a bit. Carb cleaner seemed to make it through every passage and I think I managed to do a decent job. Though i definitely got carb cleaner on the rubber bits, including the diaphragms.

Anyhow, now the bike seems much better, but even with the idle adjustment screw all the way in, it is just getting to 900-ish revs and dies after a few seconds. If I hold the throttle at 1500-2k it seems to be fine. But at lover revs it sort of chugs every fourth or fifth beat. like I get 4 nice cha-cha-cha's then a longer glug. But as long as I keep it idling slightly higher with the throttle everything seems to be fine. I'm just not sure why the idle screw now seems to be below the height range where I can adjust my idle?

It's like the idle screw got shorter, even with it all the way in/up I'm just at the beginning of the 900 rev range, and that's not enough to keep her going.

Any ideas what I might have done? Any advice would be appreciated.

PS. I'm very new to all this so my terminology might not be up to par....so please feel free to speak to me like a child.

 

[NewHavenMike]

When you do a carb clean, its a good idea to check the valves and get them in spec. Timing needs to be checked too.

My bike has a points ignition and has very similar problems you describe when the timing was way off.

Then the carbs need to be synced. If you do not have a manometer, you can use a thin wire like a guitar string to get the carbs matched closely... i made my manometer out of air supply tubing and beer bottles.

Its always valves, timing, carbs.. except for when its a bad spark plug wire..

 

[XSLeo]

It sounds like when you cleared that passage the gunk that came loose plugged up somewhere else, usually the idle circuits.
I do most of my forum stuff over on our sister forum, XS650.com
The 80 up XS650 uses a BS34 carb very similar to the BS34 used on the XS400. The carb guru's over there put together this www.amckayltd/carbguide.pdf It comes in very useful when cleaning carbs.
In these carbs fuel is drawn out of the float bowl through the pilot jet. This fuel gets mixed with air at the jet. This air fuel mix flows up through a passage to the mix screw and those tiny holes. Part of the idle mix flows out those tiny holes. Part flows up to the mix screw then out a large hole on the engine side of the throttle plates.
The engine idles mostly on the air fuel mix from the mix screw, with the tiny holes helping just a bit. As the throttle plates open they uncover those tiny holes more and as the revs climb they work more.
When this passage and holes are plugged up you can see why it won't idle.
When cleaning carbs you need to remove the idle mix screw. This way when you use a spray carb cleaner you can better tell when it passes through the passages and tiny holes in the carb. With the mix screw out, pilot jet out, throttle plates held open. This way you can see the tiny holes by the throttle plate.
When you use your spray cleaner place the tip of the spray tube into the hole where the mix screw goes. Spray, as you spray cleaner should come out at the pilot jet and all those tiny holes by the throttle plate. It might not at first, it flows out the pilot jet hole easier, once it comes out the pilot jet hole hold a fingertip over that hole. This forces the cleaner out the tiny holes.
This should get a lot of the crud out. Once you get plenty of cleaner in the passages you can let it soak a bit. If you have an air compressor use it with a rubber tip to blow through the same way you did with cleaner.
Those tiny holes may be plugged solid. Take the twist tie from a loaf of bread, the kind with a plastic or paper cover over a thin wire. This thin wire is soft and you can CAREFULLY probe those tiny holes. You don't want to damage the holes.
Probe once then spray the cleaner through. to see if that helped. You can also spray from the pilot jet side. this help back flush the gunk out.
The carb guide has the steps to follow to tear down, clean and inspect the carbs. The inspection will reveal if any parts are needed.
Once you determine what parts if any need changing, you follow the steps to reassemble the carbs. Checking adjustments as you go. Things like float height.
There is a section in the guide "How To Tune For Mods" this section will help you tune your carbs. Remember to make one change at a time then test. Doing more than one change makes it hard to tell what change made the difference.
Leo

 

[Phil_B]

Thank you, this helped!

Now I find that I'm missing a tiny washer from one of the pilot screws. Just need to get hold of that and then it will be on to tuning!!!