Bike will not start!

[goor]

Hey all,

I have an 81 xs400 and I just thoroughly cleaned the carbs, checked the diaphragm, blasted everything out with compressed air, I have new carb holders, charged battery, pod filters, I can get it to fire with starter fluid but it won't continue on fuel. I checked the petcock. It flows freely on prime and stops on "on" when the line is disconnected from the carb, I opened the float bowl plug screw and there seems to be no fuel in the bowl, this explains why it won't spray fuel.

If the petcock works, why are the float bowls not filling. What am I missing?

Thanks

 

[only]

the needle not raising out of the seat? stuck float? have you ran it on prime?

 

[goor]

Thanks only but I just made a breakthrough...

holy crap , I'm an idiot! I just took the bowls off to check and reset the float height and I found that I had reassembled the floats on upside down which kept fuel from filling the bowls. I flipped them and set the float height and when I primed the bowls I could hear them fill right up and it started on the 3rd kick!

NEW PROBLEM : it idles pretty well but when I roll on the throttle it doesn't respond, it actually bogs down and loses rpm but if I open it all the way up it ramps up the rpm awkwardly but it is totally non-linear. when I roll on an 1/8 turn or so and it bogs I can hear a hiss coming from the intake side of the carbs... It had the same bogging/power loss problem before I rebuilt the carbs! Any ideas?

 

[only]

is the choke on? sounds either air restricted or too much fuel.

 

[bcware]

Any mods or are you stock?

What did you set the float height to?

How far down do the float needles fall when you hold the carbs right-side-up with the bowls off? I found that if the needles are allowed to fall too far open they can get stuck open or close unreliably.

If you're bogging down at anything below wide-open-throttle you're probably too rich. This makes me suspect float height or float needle action.

Have you looked at the plugs? What color are they?

 

[goor]

bcware,

I have emgo pod filters which may be part of the problem. As in the "emgo pods 'bad' " thread, I put them on the end of the stock H shaped filter to carb rubber manifold thingy like the picture someone posted. I haven't started it yet in this configuration. We'll see in the morning...

I have stock pipes cut before the muffler so, at the moment it's straight until I decide on an exhaust. The carbs are in their stock setup as of now (I have read some of the stuff you have done with your carbs due to changing the pipes and the filters and I figure I will have to make some adjustments)

I read 32mm for stock float height in my manual so, I set them at that height today after I made the discovery that I had installed them incorrectly.

I'll check the float needle tomorrow as you described. That would make sense because, if they go past a given point as they slide through their housing they could get wedged at a slight angle as they slide out of that housing (probably even more so if they have wear on the 4 rounded "ridges" that they have)... good point!

the plugs seem normal, dry but black.

What do the carbs do when the floats allow too much fuel into the bowl in turn making the engine run rich? It is obviously sucking in more fuel than it is supposed to but, how exactly?

Sorry for the newbie question but I am just that, so...

Thank you sir!

 

[bcware]

The emgo pods seemed to cause problems for me when attached directly to the carbs; using the H-shaped inlet should eliminate any issues, however.

What size main jets are you using? pilot jets?

How many turns out are your idle mix screws? Most people seem to suggest starting at 3 or 3.5 turns out.

For my bike the manual suggested float height is wrong. On my 78 I have it set to 25 or 26mm. Your 81 might be slightly different, but 32mm sounds way too high to me. If they are too high you will definitely have problems because you won't have enough fuel in the bowl. Don't take my word for it though because I do not know what yours is supposed to be. Someone else can confirm.

There should be a tang on the back of the floats that rests against one of the "posts" that the floats are hinged on. Bending this tang is how you adjust the float needle action. See the attached photo.

If your plugs are black and sooty you are way too rich. They should appear pretty clean, but maybe slightly yellow-tinged. The sooty carbon deposits weaken spark a lot. While experimenting I use a brass brush to clean the carbon off and they seem to work well again. Once you are done tuning buy a fresh set. For me it was actually my idle mix that was fouling my plugs, not the mains or anything.

If the float needles get stuck open or don't close reliably the fuel level in the bowl rises high enough to flood the venturi through the main jet and emulsion tube. Even though the needle is blocking the emulsion tube at low rpms, the fuel easily displaces it. Even if fuel isn't pouring out your air filters any extra will foul your idle mix. Once your plugs are black and sooty from this fouling you will get all sorts of crazy behavior. This isn't the only way an idle mixture can be fouled, however; the simplest way to foul your plugs is to run choke for too long or to turn your idle mixture screws too far out.

As a reference I attached a photo of a generic float needle. The line represents about how far the needle should drop down when the bowls are oriented right-side-up (floats on the bottom). This doesn't need to be exact and they could probably even open less than this. After you adjust the float height hold the carbs right-side-up and push the float up and down several times to see how the float needles behave.

 

[goor]

Thanks so much, bc! You have been very helpful with this issue.

I don't know anything about my main or pilot jet sizes. They are stock as far as I know. I will have to do some reading and find out.

I have experimented with idle mix screw settings from 1.25 to 2 to 3 to 3.5 turns and didn't really notice much change. I'll look into this more.

I can't wait to see if I can get this old thing running right. info I'll post tomorrow with the results...

 

[bcware]

If you have the carbs open again pull out the main and pilot jets. The size is printed into the metal on the top or side somewhere. It is important to know what size they are to diagnose or fix the issues you're having.

 

[FUBAR]

when i revamped my '81 special carbs last weekend i came across the whole 32mm in the manual also. the correct height is actually 26mm (drewpy) but this is only on models with brass floats.. at 26mm my plastic floats dont pivot correctly, im pretty sure if you have the plastic floats rather than brass, its around 16mm from the gasket surface.

 

[kebabs]

when i revamped my '81 special carbs last weekend i came across the whole 32mm in the manual also. the correct height is actually 26mm (drewpy) but this is only on models with brass floats.. at 26mm my plastic floats dont pivot correctly, im pretty sure if you have the plastic floats rather than brass, its around 16mm from the gasket surface.

this is an old post.but yesterday I adjusted floats to 26mm.bad idea it stopped the float needle from opening no fuel to carbs.reajusted to 32mm .now working good .