Please help i am at a loss and bike week MB is 10 days out

[big_n84]

i just bought my first xs about a month and a half ago. it is a 1980 xs100sg. i have been trouble shooting and reading the posts and searching for a few nights and have not found the answer to my problem so here it goes. i bought the bike and it had been sitting in a guys garage for about 6 months. he had removed the carbs and then took them all apart in a feeble attempt to rebuild them. i decided to accept the challenge of putting them all back together. i did after buying a set of used carbs off ebay for doner diaphragms. i also used them as a diagram for putting my carbs back together. well i put them on the bike get the fuel going to it and it is only running on one side. i take the carbs back off and check my work and everything seems fine. i put them back on. iam getting fuel as the spark plugs are soaked after i remove them and also raw gas will pour out of my exhaust while the bike is idling. the problem is it is only on cylinders 3 & 4. i did a compression test and its 150 psi across all four cylinder. i tried swapping the plug wires around and still 3 and 4 nothing 1 and 2 cherry. when riding it when i get on it all four kick in when i get on it but at a cruising speed and steady rpm it goes back to the 3 and 4 missing. please all input is appreciated because i have no idea! i am a decent mechanic and this is not my first carb job on a four cylinder bike but the first one i cant figure out. THANKS for any and all input i need to ride!

[ccogswel]

I know there will be a Guru that will chime in but I'll still try to help. When you say they all kick in when riding did you ever look to see what rpm your at when they do kick in. The pilot jet is from idle to 3000 or 4000 rpm when the main jet takes over. Sounds like you have a pilot jet blockage still. You will have to take them carbs back off and clean the pilot circuts. Now this is where a Guru may come in as I may be wrong but you will also want to take out your air fuel screws when you clean the pilots out. That way you can check to make sure it's open and clean in there as well as I think it's all connected.

Also when you say you changed the plug wires around did you switch between 3&4 or did you switch 1&4 and 2&3? As 1&4 run off one coil and 2&3 run off the other coil.

[DiverRay]

Because it's 3&4 that have the problem, it is the carbs. The 80 carbs have an "O" ring to seal the needle and seat. You NEED to replace ALL the parts for the needle and seat, or the floats will not do much good. The second cause of flooding, and you did say it was flooding, is the vent hole being plugged. Since you said you've done carbs before, I'll assume you made sure the spray can of cleaner will hit you in the eye from every hole in the carbs. The 80 models vent through one of the holes in the intake bell. Final thing is VERIFY that ALL floats are the SAME HEIGHT! I would also check for any binding between the float and the float bowl.

[big_n84]

i have the floats set and the needle seals great as i put all new needles and seats in them i was sure of the carbs being the issue due to the way the coils are set up. i will go back in and check the vents. all of the O rings are brand new. i need to go back over the vents and check them again as i have been rushing the project. along with getting the carbs right i have also managed to repaint the entire bike and get it looking pretty good. if i don't get it running thats all it will do though and that is useless. thanks for the input!

[Ken Talbot]

Have a quick look at your fuel line routing too. These bikes are prone to fuel line kinking if you run say the left side petcock to the left side carbs and vice-versa. Most guys end up putting in some longer hoses so they can cross over i.e. feed the left carbs from the right petcock, etc.

As an after thought, you might also want to test petcock operation. Pull the fuel lines from the carbs, put the open end into a jar or can, and check to see if you're getting flow from each petcock when you should.

[big_n84]

i am getting plenty of fuel. too much in fact as it is soaking the plugs and dripping out of the right side exhaust. its not until high rpms that it manages to clean itself out and hit on those 2 cylinders. i kept the octopus but used all new fuel line as the 1980 plastic version just didn't suit me. and i have tried the switching the feed lines thing and nothing changes. i have ruled out fuel delivery. i switched 1&4 and 2&3 plug wires with no change in the status either. i appreciate all the ideas please keep em coming as i am sure someone will stumble over the fix.

[Ken Talbot]

Oops - didn't catch that you've got a special, not a standard. Slight change in direction.

Okay, if you've got fuel flooding out of #3 and #4, you may have buggered-up float valves, and/or mis-adjusted floats.

You said earlier that all o-rings were good - does this include the o-ring around the body of the float valve seat itself?

[big_n84]

yeah when the floats are up on 3 ans 4 they seal. it is new needles ans seats. i put the floats up and blew into the fuel inlet to see if there was a leak and there was none. fyi i blew into it with my mouth very low pressure because i am aware that it is a low pressure system.

[fredintoon]

There's needles & then there's needles

Hi Aaron,
there's the fuel level needles that work with the floats to control the carb fuel height. The '80 carbs should have the ones with rubber points on the ends.
Then there's the idler needles. They are in the top front of each carb down a hole you can reach from outside. (EPA may have plugged yours) There's a needle, a coil spring, a plain washer and an o-ring.
Unscrew the needle, the spring usually comes out with it, hopefully the washer and o-ring will too but if not you can fish them out with a straightened paperclip that as a 1/16" L bent on the end.
Go to MikesXS and see fuel system/slide needles etc items #48-5011 & 48-5012 at the bottom of the page. Pull the enrichener slides out too then spray most of a can of cleaner down every little hole.

[prometheus578]

Ok...
Compression is good.
Spark is good.
(even switched the wires and the spark was still good.)
That leaves carbs.

What do all the plugs look like?
#1 and #2 I can imagine are white or tan.
Now, #'s 3 and 4....
Are they white, but wet?
Are they black and sooty.
Are they black and wet?
If they're black you need to replace them before going further.

Fuel going out the exhaust pipe.
Either it's a spark issue... spark plug not firing and you're just pumping unburnt fuel through the engine, or it's a carb issue.

Float level (and by this I mean fuel level) too high will cause flooding.
Float needles not sealing in their seats will cause flooding. This is also usually evident by fuel dripping/pouring out from the airbox.
This extra fuel can also flow forward into the cylinders and into the crank oil. As you have 'extra' fuel coming out the exhaust, you should check your oil level, as well, as raw fuel in the cylinder will also get past the rings.
I'm afraid it's time to pull the carbs once again. Recheck the float levels. With the bowls still off, hold the carbs right side up and see if all the floats drop the same distance. A float that drops too far, when it rises can cant the needle at an angle and jam it open.
Flip the carbs over on their back and hook fuel to them. 'Blip" the floats to clear the lines of air. Dry everything and then wait and watch. If the needles are leaking, you'll soon see it.

Puttin' a hose in your mouth and blowing... you learn that trick in prison?
Blowing into a hose is not how one checks for a fuel leak at the needle and seat. If just a little air was getting past... how would you know? I don't think your mouth is that calibrated. A little leak of fuel would soon overfill a bowl.

Fred is correct concerning the idle mixture screws. There's little O rings at the bottom. I've seen carbs with broken o rings, or two O rings in that hole as they didn't get the first one out, thought it didn't have one and just put another one on the screw. Need to check there, too.

[RUSH]

All the above plus check that the floats are actually FLOATING. you might find a hole, the tech tips have some good tips. also check to see that they weigh the same.
Check that the oil is all oil too. Sometimes fuel will leak past the rings or breather and down to the pan.

[big_n84]

plugs black and wet. bought new ones tonight no change. the float falling to far thing sounds very plausible. i adjusted the float height upside down to the specs in the clymer manual but am not sure how far they fall or what is too far. i am gonna check the idler needles as well. i noticed the needle not sitting right on the float tabs after running it briefly so that could defiantly be a factor in the problem. if you have any advice on how far they should fall please let me know.

[prometheus578]

Don't need to fall far. Actually, it's not really important... just so that they fall far enough to let the needle drop and open.
Drop too far, and as mentioned, they can put an angle on the needle on the way up and it can stick in place.

[prometheus578]

As per Rush...

If you suspect that the floats might have a hole in them and have fuel inside weighing them down, a quick check.
Heat up a pot of water. Hot, but no need to boil. With a pair of pliers(or just one plier), submerge the float into the water.
Air inside the float heats up and expands. If there's a hole, you'll see bubbles coming out.

[John]

Could I ask what procedure you used to remove the float seats? Did you just grab them with a pliers and twist and pull them out? That can distort the seat, and the needle may not rise and fall smoothly in the seat.