Carb help!

[TK421]

I took the carbs off the bike for cleaning, everything looked pretty good.  I reassembled and put back on bike.  When I connected the fuel hose, after a couple of seconds, fuel started pouring out of the carbs.  It was really hard to see where it was coming from, but I eventually discovered the air cleaner was full of fuel!

My first guess is a float or needle valve problem, but I did inspect/clean all of them, and I didn't see any issues.  Also, the bike was running and not leaking before this project.  I took the carbs back off the bike and I'll open up the float bowls again tomorrow and check if I missed something.  Anybody have any other thoughts?  I guess if there's nothing obvious, I'll order some new floats and needles and hope that's it. All else fails I'll take the carb assembly to a mechanic and let them have a crack at it.

Thanks in advance for any thoughts.

P.S. I assume the main jet has larger hole than the starter jet?  If so, one of my carbs had them reversed.

[rider123]

Is your petcock set on the prime position? If so it will dump fuel into the carbs.

[lasa_dal]

hi


i think u miss something  when assembling. check that

[TK421]

Petcock was set to ON, although I have wondered if it might be defective, given the amount of fuel overflow.  Should fuel even be flowing to the carbs with the engine off in the ON position?

I don't think I missed any parts... at least there's nothing on the workbench!  I'll double check when I tear them down again.  Has anybody used the Holeshot carb rebuild kits?  The price of the OEM needle valves is INSANE.

[rider123]

You can test it by doing this, going from easy fixes to harder hopefully you'll stop at step 1 or 2 but if not keep going until your fixed:

Step 1: Check the plugs to see if it's only one carb or all that are causing the problems. Problem carbs will be black and sooty or even wet with gas. So say Number 1 cylinder is black and sooty but the rest are fine then you know that you should concentrate on number 1 cylinder. In fact if it's the outside carbs (1 or 4) you may be able to fix the problem with the carbs still on the bike. If all the carbs are flooding go to step 2.

Step 2:
Unplug the vacuum tube from the petcock and cap it with a screwdriver bit or a bit of tape, but leave the fuel line attached. Start the bike and run it until it starves out of fuel. If that happens then your petcock is fine. If it keeps running after 5 or 10 minutes then you know that your petcock is dumping fuel and not shutting off when the bike is not running. Replace petcock or buy a rebuild kit. If it is fine go to step 3.

Step 3:
If in step 1 you have found that only 1 carb has a problem then you should check what jets you have in your bike in case it has been jetted. Do you have an aftermarket exhaust? If so chances are someone at sometime jetted the bike(or should have). Make sure the Mains and pilots are fully snug, they are soft brass so don't go jihad tightening them in there. The longer emulsion tube will have the main jet and the pilot jet should be next to it depending on what year of bike you have. I have a GEN2 (2001-2005). Also while you have the float bowl off, unscrew the emulsion tube which the main jet is screwed into and check to see if the hole at the end of the emulsion tube that goes into the carb is round and not worn or oblong in shape which may cause richness. If your confident that the jets are not worn and everything is snug and installed correctly go to step 4.

Step 4:
Now you should check the needle valve. The needle valve is basically a fuel cutoff switch for that specific carb. When the fuel fills up the carb it pushes up on the floats which pushes on the needle valve cutting off the fuel. If the needle valve is worn it will allow more fuel then is necessary or if its really worn it won't shut the fuel off at all! So what you need to do is unscrew the screw holding the floats into the carb and carefully extract the float and needle valve assembly and take a look at the tip of the needle valve. If it's dimpled and not straight then the needle is worn and needs replacing. See bad ASCII diagram:

       /\
      /  \
     /    \               <------GOOD
    /      \

      /\
     /  \                      <-----------BAD
    I    I                            
   /      \

If the needle valve is good adn there still is a problem now you have to go to step 5:

Step 5:
Ok now you've done everything possible that you can with the carbs still on the bike, now the fun part starts. You must remove the carb bank no matter what. We are going to check float height on all the carbs. What you do is tilt the carb bank on is side with the float bowl covers off and measure from the bottom of the carb body to the highest point on the float with the floats resting BUT NOT COMPRESSING the needle valve and then bend the metal tab on the floats so that the height is 13mm for my bike (2001-2005). For other years of the bike you can google it. I can't do ASCII that well but if you google "CHecking float height" you'll get better diagrams then what I can produce. Tell us the year of your bike or you can google what your float height should be. I think the GEN 1 bikes (96-2000) use a float height of 14.5 but don't quote me.

Can you tell us what year and CC your bike is?

Chances are that if all the carbs are flooding then its your petcock. If only one floods then it's that carb.

[TK421]

rider123, thanks for the help, you really put some thought into that post!  I have a 2002 1200S, it's never been jetted.  The flooding problem only began AFTER I removed the carbs for cleaning, so I can't help but think it's something I did.  I'll check the plugs, although I replaced them about two weeks ago, and they all looked good. The engine hasn't run since this flooding issue.  I did inspect the needle valves during cleaning, and they all looked good.  I did not check the float heights.

Your suggestion in Step 2 reminded me of something:  after watching the fuel pour out for a couple minutes (trying to see where it was coming from without much success) I removed the tank completely to stop it.  When I did, I seem to remember the vacuum tube was unplugged from the petcock.  I assumed it came off when I lifted the tank to get the fuel line, but now I'm wondering if it had come off before.  Could that cause fuel to flow from the carbs, almost like putting in the the PRI position?  Pardon me if that's a dumb question, trying to reason through this thing here!

I'm going to look over/tighten everything tomorrow, hook it all back up, and hope.  I will check all the things you describe, thanks again.

[rider123]

Well it sounds from your symptoms that your carbs are probably fine and it's your petcock thats wonky. Does the fuel flow out when the tank is taken off the bike? Ie not connected to the carbs either the fuel line or the vacuum line? Ie dribbling fuel right off the spigot?

Also check that when you put the tank on the bike to make sure there is no pressure on the fuel selection lever, if I put some pressure on mine, say bending it a little it will pour out fuel. The only thing that is holding back the torrent of fuel is a little spring loaded diaphram. Any extra pressure loosens it up enough to let the fuel flow. Maybe take the handle off to see if that helps and is not binding up with the hoses or hitting the top of the carb.

If you want to test to see if the tank is wonky just make an auxillary tank and test to see if the bike is fine without the fuel tank.

To make a super cheap auxilary McGuiver-type tank($3? maybe less):

1 get a 1 litre or 500ml water bottle. Empty it out thoroughly.

Cut a small hole in the bottom, just enough to let air in there when the bottle is upside down and feeding fuel. Tape up the hole for now with a little duct tape(handyman's secret weapon)

Go grab some cheap tubing that is thinner than the screwtop of the water bottle.

Cut a hole in the screw top of the water bottle and feed the tube through so it will let fuel come out of the tube.

Either go to a fitting shop or home depot or something to either get a brass tube that is smaller than the fuel line and the auxillary tank line or you can go fancy(the 3$) and buy a tapered fitting so you can now attach the hose from the McGuiver-type auxillary fuel tank to the fuel line using the brass fitting. Tape it up with some electrical tape or masking tape so it won't leak.

Now since this auxillary tank is going to last all of 10 minutes I go cheap and just duct tape around the hose going into the screw top so the top won't leak and it works ok(mostly). Plug the vaccuum hose with a screwdriver bit or a piece of tape.

Start the bike and hold up the auxillary tank upside down and take the tape of the little hole you made in the bottom so that air can replace the gas that is going into the carbs.

IF the bike is now perfectly fine without the tank connected then %99 it's the petcock. You may have bumped it taking it off to get to the carbs and screwed it up. Or the fuel selection lever is binding up on the crazy ass emissions hosing we are subjected to.

If you want to forgo the entire auxillary tank deal you can just start the bike with the vacuum tube plugged up and if it runs fine for the couple of minutes worth of fuel in the bowls and fuel line then it's basically the same thing your petcock is being weird. It's extremly rare that the carbs would go totally wonky just by taking them apart especially the dumping fuel problem. I'm assuming that all of the carbs are dumping fuel and not just one correct?

Also it's kind of bizarre your statement about the jets being switched. Ie one is bigger than the other and in different positions. What number carb is that? If you have the main jet where the pilot or mid jet is theoretically you would horribly overfuel that cylinder however the jets are compeletly different here is a pic of what jet is where. I would recheck that. If it's on the outside carbs you can take the bowls off with a little rachet without taking the carbs off.

Here is a pic:


As you can see the mainjet is screwed into the emulsion tube. And the brass Phillips screw above the main jet holds the floats and the needle valve in there.

Did you switch the main jet with the mid-jet on that weird carb? I hope not that will cause you problems later when the bike isn't dumping fuel. They are marked with the number of the size of the jet.

Also if you have to take the carbs off. Do yourself a huge favour and drill out the A/F mixture plugs. That way you can adjust them and if you get a jet kit in the future it will make it alot easier. Most Bandits are jetted extremely lean from the factory. Sometimes turning out the mixture screws a 1/4 turn really makes a difference in the power and drivability. Stock it's supposed to be 3 turns out, mine we all over hell's half acre from the factory and it was a little wonky driving around. Once I drilled the A/F screw plugs out and set them all the same to 3 turns out(this was before I had a jet kit) it immediately drove alot better and that was bone stock. Not only did it have a little more juice but it was alot smoother. What I did was get a drill bit that was slightly smaller than the plug I put a piece of tape on the drill bit a 1/4" from the tip so I didn't drill to deep into the screws then I drilled carefully to make the little hole in the plug a little bigger so I could screw a self taping screw in there and then got a pair of pliers and pulled the plug out. Trust me you'll thank yourself later. Remeber the plug is soft brass so it doesn't take much to drill out so be careful.

[TK421]

Re: jet confusion.  What you call the "mid jet" Clymer calls the "starter jet." What I mean is that externally the main jet (when removed from the holder) and starter/mid jet look the same.  One has a larger hole, so I assumed that was the main jet.  I didn't know they were labeled (makes sense) so I went and had a look.  Main jet says "100" and starter/mid jet "60."  Clymer specs show "No. 100" for the main jet, so that's good to go.  Carb #4 had them reversed, which maybe explains the stumble under acceleration that led me to tear down the carbs to begin with.  They were worked on by a local shop last year, the price of which motivated me to do it myself!

So that mystery is solved, thanks for the help!  I'll update tomorrow...

[rider123]

Well if that shop mixed the main with the mid(starter) jet I wouldn't go back there! Well it sounds like you fixed it so no sweat. It's on #4 carb so if you're really worried you can take off the float bowl without taking off the carbs. Does the bike run fine when the tank is off and the vacuum tube is plugged up(it's attached to #4 carb)?? You should get a minute or two before the fuel runs out of the fuel line and galleries/float bowl. If you don't want to McGuiver it but want to test it longer you could always buy a turkey baster and squeeze in the fuel in the fuel line which will allow you to run longer then having it run out then having to re-attach the tank. You can run it for a few minutes till it warms up and that will give you a piece of mind that basically all is well with the carbs. My guess is that maybe the handle of the petcock is binding up on the emissions crap or was screwed up somehow. If the carbs were that screwy it would dump fuel for like 5 secs then the floats would be out of gas. You were saying that it was a few minutes which is way more than the fuel line + the float bowls would hold. also it would only overflow enough until the fuel was lower than the top of the floatbowls by gravity so not much would come out.

I would try running the bike without the tank for a few minutes so that will at least let you know that the carbs are fine(using a turkey baster to top up the float bowls). Then take a look at the petcock. My guess is its something stupid like the handle binding up. If the tank doesn't leak while off the bike, take the handle off with a philips screwdriver and pop the tank on like that. I know if you angle it properly you can put the tank on with the handle but if there is any extra pressure on that handle it will flow fuel so try it without the handle then screw the handle back on after it's connected to the bike so you can adjust the emissions crap around until it won't bind the handle.

I find the easiest way to attach the tank so you can remember to plug everything in is work from the front to the back so you don't miss anything. So first tilt the tank up from the back and attach the fuel line and vacuum line then slide the tank forward a bit and attach the fuel overflow lines then lastly plug in the fuel guage level sensor lead and your done. Take off the tank in the reverse order then you never miss a connection.

[TK421]

So, I think the petcock is bad.

Since my tank was already off the bike, I set up a non-running version of the test rider123 described.  I put the tank up on blocks, with the fuel line running into a gas can.  Petcock was set to MAIN.  I slowly poured about a gallon of fuel into the tank, which resulted in a steady trickle into the gas can.  I sealed the vacuum tube with my finger, and fuel continued to run out at the same rate.  I switched to RES with the same result.  Fuel didn't flow as freely as when it was set to PRI, but it was a fairly steady stream.

To my mind, fuel shouldn't have been flowing at all in the conditions I created.  So time permitting, I'll take the petcock apart tomorrow and see if there's anything obvious.  Most likely I'll order a new one.  It does bug me that there was no problem before the tank was removed, but I suppose I could have bashed it (no memory of doing so) or maybe it didn't like being upside down for a week.

Any logic checks on my petcock tests would be appreciated!

[canyonbreeze]

If there is no vacuum and the fuel is flowing on any other position than prime then there is a petcock problem.  That being said, even if the fuel flows through the petcock the float valves should be stopping it in the carburetors.  If BOTH the petcock and the float valves let the fuel pass, then you will have it coming out as you describe.

You could have just knocked a piece of sediment into the petcock that keeps it from closing.  Taking it apart and cleaning it may fix that.

When I rebuilt my carburetors a while back, the rebuild kit had float valves that had clips on the back that were a hair too wide.  That prevented the valves from seating and gas flowed everywhere.  The place I got the kit from overnighted the correct needle valves from Canada to California at no cost to me, even though it had been months since I bought the kit.  Kudos to them.

[rider123]

It could be as the canyonbreeze said just a piece of dirt blocking the stop of fuel. Or it could be the spring in the petcock is tired. I think petcock rebuild kits are like $30 bucks or so. DId you start the bike with the tank off to see if it runs ok with just what's in the float bowl and the fuel line? If it runs fine then at least you know %100 what it is.

How the petcock works is there is a diaphram that when no vacuum is supplied to the vacuum valve there is a little spring that pushes on a valve to stop the flow of gas. When the bike is started the vacuum pulls on the diaphram and fuel begins to flow. If the gas is coming out with it not attached to the bike then the petcock needs some lovin'. Just buy a petcock rebuild kit don't bother buying a whole new one as they are pricey.

Holeshot makes a kit for $38 by the same guys who made the OEM for Suzuki

http://www.holeshot.com/bandit/petcock_reb.html

Even if the petcock is leaking slightly the pressure built up will overwhelm the little needle valves pretty quickly. From the sound of it there was niagara falls coming out of the carbs, I would change the oil to be safe in case it's been diluted from the gas overflow. You can keep the filter just quickly change the oil out for a piece of mind.

Think of it this way we have a 20 litre tank a litre is a 1000ml at 1 gr/ml so 1 litre is 2.2 pounds so a full tank weighs 44 pounds full. I dont know of any motorcycle carb in the world that will hold back 44 pounds of fuel with those tiny float needles. They are designed to hold back whats in the fuel line and when running whatever the diaphram will feed the carbs flowing through the petcock. Higher rpms pull the diaphram more as you are using more fuel but fuel is flowing out the carbs so the needle valve maintain the right fuel level they are not really designed to hold back all of that fuel standing still.

[TK421]

Thanks for the help guys!  The Holeshot kit looks good... saw it when I was pricing needle valves.  Is there anything else that could need replacing in the petcock, or is that kit pretty much the sum total of the petcock guts?

My needle valves look okay, if I get some time tomorrow I'll double-check, blow them out with compressed air, and make sure some crud isn't blocking one or more from seating.  The screws holding down the float bowl pivot pin and the needle valve seat were really corroded and rusty looking, so possibly something got in there.  I'm replacing all of those as well.  My understanding is that while the needle valves/floats regulate the level of fuel in the float bowl, they can't cope with fuel flowing freely from the tank.  As you say rider123, it was niagara falls!  It filled my oil pan to about and inch, and there was about half a liter in the airbox!

Carbs are still off the bike so no run test yet.  Gonna double and triple check everything, and replace the aforementioned screws first.  I'll report results as they come in...

Oh, and definitely going to change the oil, don't want to take a chance on that. 

[rider123]

Gas evapourates quickly so if you want to speed it up a bit just take off the airbox lid and drain the oil and leave the oil cap off overnight and it should be mostly gone as long as there is no liquid left. Take out the airfilter and blow it out with compressed air and leave it overnight and you should be good to go. You may have a little left but one good ride on the highway with all that airflow through the airbox will clean it up in no time.

[TK421]

A quick update, since I know everyone is on the edge of their seats...

There was nothing obvious when I tore down the petcock, but the parts looked pretty knackered so I ordered the rebuild kit from Holeshot.  I finally got around to installing it today.  I bench-tested it as before, and not a drop of fuel came out, so looks like that was the problem.  Carbs go on tomorrow then hopefully some riding!!