Hard starting and running woes

[rbmgf7]

I've managed to get the majority of the bike together and now I'm to the carbs. I have a Maxim but it's using carbs from an 80 or 81 XS. I managed to get the bike going a few times starting it with ether and that's apparently the only way to get it started. when i get it started, it takes a little work and warm up to let it finally idle on it's own. it idles right at 1k but when it's warmed up it'll hover around 1.5k. all cylinders seems to be firing except #2. it's warm but not hot like the others. i checked and it has a strong spark and is getting gas.

when i go to throttle, it takes a little jiggling to get the RPM's up but it can reach redline. it also "pops" on the throttle down. my guess it's #2. it also blows smoke whenever the popping is made. it just idled with intermittent throttling for a good 10 minutes but died and now it won't start. i had a box fan blowing at full speed to get some circulation going. i haven't caught it but i think it also pops through the carbs. lean? i checked all the plugs and they're saying a little rich except for #2. #2 is wierd, it's half white and half a little black/gray. i guess #2 works whenever the mains kick in. i plugged the vac spout on both the carb and boot for #2 since i wasn't using the octy.

i've cleaned the carbs numerous time, making sure all the orifices are clear. i blew them out with cleaner and ran my carb wire tool through them. took some small wire to the tubes that run down into the bowl that lead up to the choke. they all seemed good.

the carb has 115 mains and the slow jets are unplugged. i bought plugs and tried running it with them installed and nothing could get it going (well, ehter but it could only run on the ether and anywhere above 4K when gas could get into the mains). i checked and rechecked the float height. i'm just stumped on this outcome.

thanks

[prometheus578]

" You won't want to hear it, but...."

It's still the carbs.
Starting it with ether....
well then..."ether" your enrichener/choke circuit is plugged, or the idle circuit is plugged.

when i go to throttle, it takes a little jiggling to get the RPM's up

You're running on three cylinders, which you already know.
Yeah, it's number 2 carb..., though it also could be a vacuum leak at #2's manifold.
Yeah, carb backfire could be a lean condition... could also be a bad valve adjustment. Vales too tight, as in remaining open would pop back out the carb, as well as not drawing in enough fuel to run at idle.
I suggest also re-checking your valve clearances.
Yes, you've cleaned the carbs several times already, and I'm not doubting your competence... but do it again.
Check for a broken pilot screw tip lodged in the hole...
Check that the jet... in the float bowl for the enrichener/choke tube isn't plugged.
Float level radically wrong could have the same effect.
You're not getting fuel to number 2 cylinder at start up and/or idle.
Time for a re-look.
Carbs need a re-look.

[psycoreefer]

edit :
Never mind I just re-read the post and It seems your on a Maxim - don't think those had a vacuum advance.

i plugged the vac spout on both the carb and boot for #2 since i wasn't using the octy

The vac port on the carb body should be going to the vacuum advance.

[TopCatGr58]

Hey Psyco,

The Maxim DOES have a vacuum advance "SENSOR" box, labelled the boost sensor, above the carbs under the tank, and IF he wants the rideability that the XS is capable of, he should connect the #2 carb BODY port to that boost sensor box/nipple!

IT has been shown that since the XJ as well as the 81XS's TCI has the cent. adv. curves programmed into them, they CAN run without the vacuum advance unit connected, but will cause it to use more gas during cruising speeds!

Rbmgf,

Prom covered it, it's still the carbs as the most likely culprit. You need to spray carb cleaner into the hole in the float bowl, and you should see it spray out the little pressed in jet opening...IF you don't then it's not open and can't supply fuel for the starting/choke circuit!

Aside from the plugs for the pilot jet tower which you've found out that you DON'T need for this style of carbs....were there any brass caps on the top front tunnel of the carbs which is where the PILOT jet SCREWs are? IF the brass caps are still there, then you really haven't cleaned the carbs completely, you need to remove those caps and then the pilot jet screws....careful, small metal and rubber washers under the pilot screws. THEN spray, clean the pilot circuit again.

T.C.

[rbmgf7]

thanks guys, i have the carbs off and now i'm gonna go through them again.

topcat: there were no brass caps. they're all open and i didn't see any washers underneath the pilot screws.

[prometheus578]

"Pilot screws washers,etc."

Those pilot screw washers and O rings probaly are still in the holes.
The o-rings sort of flatten over time and tend to not want to leave their homes.
The small flat washers... being close to the O-rings, in a move of solidarity, often stay with their o-ring pals.
Use a dental pick to probe around that cavity, either till the O-rings come out, or you hit a nerve.
Order of re-installation would be, O-ring, washer on top of it, and then the spring pushing things all together.
Carb spray, or a blast of air from a compressor will move the o-ring and washer from the hole.. and send them flying out of sight.

See bottom picture:
http://www.xs11.com/tips/maintenance/maint17.shtml

[planedick]

Nobody mentions

There is still the synching problem. All of those things they tell you are all good and need to be done, but if you don't do a carb synch, it will never run right.

[tarzan]

You probably alrerady know this but the float level on the 80 and 81 should be 23 mm.On older carbs it is like 25.7.Any way if your floats are set to the old carb settings it would run real lean.JAT

[rbmgf7]

prometheus, my pilots look nothing like that. the ones that came out of my carbs look like small main jets. they have 180 punched on the head.

i figure that's the way it should be, shouldn't it? air flows into the carb, goes into the pilot hole which leads to the bowl. causes an increase in pressure in the bowl which forces fuel into those small tubes which lead up to the chokes....sound right?

[prometheus578]

Nope

they have 180 punched on the head

Talk about needing to be punched in the head....
Ok, let's get the terminology straight.
Three things to concern ourselves with here:
What you have in your paw is a "Pilot Air Jet". This came from the intake/rear of the carb. The #180 is correct.
There is also a "Pilot Jet". This little bugger lives inside the float bowl, in a tower... or more apt, down a tower well, next to the tower for the main jet.
Lastly, we have our elusive friend, the "Pilot Screw". I say elusive, because you haven't seen it.
Lots of people know about "Pilot Screws"... mostly stewardesses, but we can talk about that later.
Anyway... the pilot screw on your model carbs is at the other end.. the engine end.
Now, if you look where the carb goes into the engine manifold, you will see a little tower-looking thing. There will also be an aluminum plug plugging the tower hole. This means that the carbs have never been cleaned, at least, cleaned properly.
The "Pilot Screw" lives in there.
Here's how to evict him.
Get a drill(yes, and a small drill bit) and drill a hole in that plug.
Not too much pressure and do not go too deep. The pilot screw is underneath the plug.
Anyway.. make your hole, then stick something in there and pry out the plug. One can also thread a sheet metal screw in the hole and pry it out with that.
either way.. the plug must come out. (And don't go pryin' like a madman and break off a piece of the tower.(seen it done)
Anyway... behold, the Pilot Screw... friend to many, enemy to some.
Ok, here's how the thing works: (The pilot circuit)
Air rushin' through the carb body causes a low pressure area in the throat.
This low pressure area(vacuum) does several things.
Look in the engine side of the carb throat. Up at the top, you'll see a hole. You may even feel, with your finger, a little nub sticking out of that hole. That's the tip o' the pilot screw.(Further back, you'll also see three more holes, by the throttle plate. They get fuel from the pilot circuit also, and help with transitioning from idle to midrange, etc)
Anyway... back to the vacuum.
When that low pressure area passes that pilot screw hole, it causes a vacuum in the system. Fuel then gets sucked up through the "Pilot Jet" that's in the float bowl area.
Oh, but there's much, much more....
Looking at the "pilot jet" you'll notice a few holes in the side of it.
The vacuum that causes fuel to rise and passe through the Pilot Jet... also sucks air through these holes.. air that comes through a channel from the Pilot Air Jet... those little things that were in your hand earlier.
Now then.. cleaning.
(You have removed the pilot screw, the spring and the washer and O-ring already, and have also removed and cleaned the Pilot Jet. You can put the Pilot Air Jets back in, as they're #180, quite large and never plug up.)
Anyway.. take your can of carb spray and stick the straw in the pilot air jet and give it a blast. You will see... Uhm, wear safety glasses as when this stuff hits your eyes.. you will see nothing for a few minutes.
As I was saying... squirt in the pilot air jet and you will see cleaner come out the tower where the pilot jet once lived. This is good.
Now then...
Place your finger over the pilot jet tower and squirt cleaner again. You will now see cleaner spray out the pilot screw tower.
Now.. here's where all those Clarinet lessons you were forced to take as a kid really pay off....
Take another finger and also cover the pilot screw tower opening and squirt again. Juice now comes out the little hole in the carb throat... the one that the pilot screw regulates.
If you have any fingers still free, you can cover that last hole, and the stuff will come out those three holes by the throttle plate.
Won't really spray out, most likely drip, but it shows that the passages are clear, which is what is important.
Questions?

Oh yeah, that air jet is to provide air to mix with the fuel before it gets to that hole by the pilot screw.

[rbmgf7]

ok good. i wasn't 100% what the other posts were talking about but now i got it.

got 'em all but #2. it didn't want to unsrew all the way out so i left it and did my best at cleaning it. put them back in and turned them 1 1/4 out.

i think i'm getting closer. it can idle as long as it's on choke. turning the choke off or throttling it will kill it immediately.

i have the floats on 23mm.

[prometheus578]

Ok, now it get's interesting....

Or confusing.
We need to properly identify which carbs you have.
On the one hand, you say you have #115 main jets... this would mean 80/81 year carbs.
On the other foot, you say that your pilot air jet is a #180... this would mean 78/79 year carbs. (Later carbs had #185)
Now then, you also state that your main jets are #115. Is this 115 for all carbs?
Carbs of those years had #115 in cylinders #1 and #4, and #120 in the carbs servicing cylinders #2 and #3.
If you have #115 across the board, that means someone has already been dicking inside there...and who knows what we've got.
Having the right carbs, with the right jets, with the right float level, with the right...
OK, back to basics.
Need to find out which carbs you have.
easiest way, look at the airbox side of the carbs.
On the 78/79, there will be three orifaces.(Air jets for the main, pilot, and a hole for air for the choke system.)
On the 80/81, there will be four holes.(the ones already mentioned, but also a hole to vent the float bowl. 80/81 didn't have that hose from the carbs to the airbox.
So... which carbs do you have?
Another difference, which is important...
The 78/79 carbs have a screw or plug, blocking the pilot jet tower. The pilot jet gets it's fuel through a tunnel to the main jet tower. That's why the main jet is so large(#137.5)
The other carbs... the pilot jet tower is open, it get's it's own fuel, so the main jet doesn't have to supply two circuits, hence, it's only #110, #115 or #120, depending on which carb set-up you have.
Either way...
Your bike will only run with the choke on. That means it's still not getting fuel at idle for some reason.
Need to identify which carbs you have, as that'll determine which jets are needed and what float level to use.

[rbmgf7]

i think i have a frankenstein set. the PO had a box of carbs all taken apart. i was able to put one complete set together. i identified the other to be the XJ carb. it was missing some crucial parts so that's why i went with the XS.

there are 4 hole on the airbox side however it only appears two of them are functioning. one for the breather the other for the air jet. there is a Tee to connect the 1-2 and 3-4 bowls. maybe like a breather or over flow. i haven't connected those yet so i left them open to the atmosphere. when i did plug it, my bowls flooded.

yes, there's 115 all across.

yes there was a plug over the pilot screws

i experiemented and installed the rubber plugs over the slow jet in the bowl. seems to have no effect.

[prometheus578]

"Pictures.. where are the pictures...?"

Ok, all is not lost.
(but it's not crystal clear yet, either)


What a minute.. wait a minute.......
You're not counting that big, cresent shaped channel as a hole, are you?
That's to allow air to stabilize the vacuum diaphram... we don't care about that.

Here are 78/79 carbs. Note the three holes.



Here are 80/81 carbs. Note the four holes. I forgot to label that fourth hole. That vents the float bowl




Here's also a front view with the differences.

there are 4 hole on the airbox side however it only appears two of them are functioning. one for the breather the other for the air jet. there is a Tee to connect the 1-2 and 3-4 bowls. maybe like a breather or over flow. i haven't connected those yet so i left them open to the atmosphere. when i did plug it, my bowls flooded.

Now then... firstly, all holes must function. If the Pilot air jet is plugged, you get no idle.
If the main air jet is plugged, you get no mid-range or top end, etc.
If the choke tunnel is plugged , you get no choke.

Unplug the danged holes!

As shown in the pics...
If you have a three-holer, you will have two "T"s. One for the fuel, the other is the bowl vent.
If you have a four-holer, you only get ONE "T", and that's fer the fuel.

Anyway.. take a look at my great pictures, excellent graphic artwork... and make sure we're talking the same language, etc.

Four holes and a pilot screw down in the tunnel means an 80/81.
Two "T"s means a 78/79.

Unless, you've got some weird, transitional 79/80 carb. (it's not unknown to happen)

[rbmgf7]

excellent diagrams.

ok, so i have an 80/81 due to the 4 holes on the airbox side (not including the cresent) and idle screw was capped and down in the hole.

now the tricky part. i have the Tee's between 1-2 and 3-4 which you say are fuel inlets on the 80/81 but i'm using those as vents. i fuel the carbs by a Tee between 2-3 which then send fuel to 1 and 4 via the tunnels within the carbs (on the 78/79 where it says fuel inlet, it's a solid tube for me. these tubes send fuel to 1 and 4).

i'll get some pics later today when i can get ahold of a camera.

i don't know what i did but i managed to get it to idle a little. i can use the choke lever as a throttle but when i use the the actual throttle it'll die. i see what happens at what throttle position so i'll thoroughly go through again. i just don't see how it could go from working to non working in a week, lol. i appreciate all the help you've given.