Gs500 problems...won't start

[RossLH]

Thank you for the help! Just one question: how might I check floats without having that drainage nipple on the bottom of my carbs?(It's just flat with a hole) Should I just measure the distance like it says herehttp://cgi.stanford.edu/~sanjayd/gs500/Maintenance/FloatHeight?

Ah, I didn't realize your float bowls didn't have drainage nipples on them. Sorry if you've already mentioned that, I might have skimmed over it. You'll have to do it the old fashioned way, which by the looks of it you've got the hang of.

As for running the petcock with no vacuum line, you can do it, but I'd recommend getting a new petcock sooner than later. First off, you have to keep a close eye on your mileage, as you will no longer have a fuel reserve--prime is fed by the reserve line. Also, you'll have to cap off the vacuum nipple on the petcock, otherwise fuel will go through the diaphragm and leak out. It's kind of a half-assed fix, but it will work for long enough to order a new petcock.

[cmat1120]

I was thinking about following a tutorial another member posted on here about replacing the petcock with a manual one. It would be cheaper and I don't have to worry about a broken diaphragm. To be honest I do like the vacuum feature though(not having to turn it off every time I finish riding). The only issue I have is I have no idea if the diaphragm in one I buy will be ok and I don't really have the money to buy multiple petcocks.

I might look into fixing the diaphragm on my petcock actually. I've got a whole lot more time than money(summer vacation) so I'd rather do that.

[RossLH]

The only issue I have is I have no idea if the diaphragm in one I buy will be ok and I don't really have the money to buy multiple petcocks.

If you buy new and it arrives defective, send it back and get a working one. I'm not sure I get your logic there.

[cmat1120]

Sorry I didn't mention that I would probably buy a used one. A new one is $87 +shipping(at least where I found it). I'd rather just give up the vacuum system then pay that much. It might be me being cheap, but I'm a high-school student and don't have a whole lot of cash to spare. I understand that theres an inherent risk in buying used, but that's my choice. 

[Snake2715]

Isn't it just a gasket? I mean would a universal gasket work in that area?

Also contact say Adidasguy he probably has one he could sell you.

[cmat1120]

It's like a rubber circle with a smaller plastic circle on it. I'll post pics of it tomorrow. I'll send him a message once I have more money, but for now I'm just going to cap all the vacuum ports and just run it on prime. Since I have the floats set now there shouldn't be any problems and I can remember to turn it back to ON when I turn it off.

[Snake2715]

Oh that's right I had forgot, only been in there once.

Good progress on the bike for sure.

[cmat1120]

So I cleaned the carbs, set the floats, capped all vacuum ports  and then turned the bike to prime and it still wont run. it seems like it almost starts to run when if i hold the throttle down at the same time, but it doesn't go. The spark plugs are still black(I clean them, put them back in and they come out black again). The spark plugs still spark, but maybe they aren't sparking enough? I don't know what it could be at all at this point. There is also a little smoke coming out of the exhaust when I try to start it. I set the mixture screws to exactly 2.5 turns out so I'm not sure why it would be running rich still. I do have a 40 pilot jet in there, but I thought the bike just ran pretty lean from the factory so a 40 was a good replacement. I'm pretty stumped at this point...

[RossLH]

Do you have an aftermarket intake or exhaust? Rejetting the carbs on a stock setup may not be optimal.

How old are the spark plugs? If you bought the bike and never replaced the plugs, I'd go ahead and do that now. It's cheap and easy, and it cant hurt.

[cmat1120]

The actual exhuast is stock with a voodoo muffler. Intake is stock. From what I've read 40 is the "stock" stock pilot jet size and it was only changed to 37.5 in the US version of the bike. The spark plugs are only a couple weeks old they were the first thing I replaced. Other than maybe the spark plugs these things don't seem like they should stop the bike from starting. They seem like they should just make it run lean, rich or rough. Or maybe they are that important...  ... I'm the newbie here lol.

[Kerry]

So I cleaned the carbs, set the floats, capped all vacuum ports  and then turned the bike to prime and it still wont run.

Hmmm ... back to basics I guess.

AIR

I can't think of any potential problems with the air supply, especially since the filter is off.  I mean, ideally you would have a clean one in place, but the bike should at least run (if not perfectly) without it.

FUEL

• (I can't remember if this was already discussed.)  Since you're using the PRIme setting exclusively now, it's imperative that the hose from the longer, front-most outlet on the tank outlet is routed to the rear-most inlet on the frame-mounted ON/RES/PRI switch ... especially if there isn't much fuel in the tank.
• Can you tell whether fuel is actually moving through the RES line from the tank as you try to start the bike?

SPARK

• Your bike ran fairly well recently, using the same (I assume) plugs.  Still, it might be worth a few bucks to buy a backup pair and swap them with your "fouled" pair.  (Sorry - someone else mentioned this while I was typing.)
• Whether current or new, make sure the spark plugs are "gapped" correctly.

Keep talking ... we're bound to latch onto some clues that lead us in the right direction. 

[cmat1120]

So I cleaned the carbs, set the floats, capped all vacuum ports  and then turned the bike to prime and it still wont run.

Hmmm ... back to basics I guess.

AIR

I can't think of any potential problems with the air supply, especially since the filter is off.  I mean, ideally you would have a clean one in place, but the bike should at least run (if not perfectly) without it.

FUEL

• (I can't remember if this was already discussed.)  Since you're using the PRIme setting exclusively now, it's imperative that the hose from the longer, front-most outlet on the tank outlet is routed to the rear-most inlet on the frame-mounted ON/RES/PRI switch ... especially if there isn't much fuel in the tank.
• Can you tell whether fuel is actually moving through the RES line from the tank as you try to start the bike?

SPARK

• Your bike ran fairly well recently, using the same (I assume) plugs.  Still, it might be worth a few bucks to buy a backup pair and swap them with your "fouled" pair.  (Sorry - someone else mentioned this while I was typing.)
• Whether current or new, make sure the spark plugs are "gapped" correctly.

Keep talking ... we're bound to latch onto some clues that lead us in the right direction. 

The fuel is moving(I can feel the tubing pulse when trying to start the bike).
A new set of spark plugs seems like a good idea since these ones have probably been pretty abused by my vacuum issues from before. I'll get a new set as soon as I can.

One thing I noticed that may mean something is I was trying to adjust the idle screw while trying to keep it running and somewhere down there I thought I felt a puff of air or something on my arm when it died...

[cmat1120]

Another video! This time showing the sparks. If someone could tell from the video if the sparks look okay that would be great. Hopefully it is clear enough. Also another thing I've noticed is that the bike seems to get much closer to starting after it sits for maybe 20- 30 minutes without me touching it.

(also I apologize for the video's orientation, I forgot to turn my phone sideways.)

[Kerry]

Can you tell whether fuel is actually moving through the RES line from the tank as you try to start the bike?

The fuel is moving(I can feel the tubing pulse when trying to start the bike).

The main reason for my question was to make sure the hoses are attached right.  If they're switched, then the ON hose (on the tank end) matches with the PRI position, and if that hose is empty because of a low fuel level in the tank, there's nothing for the engine to burn.  (Meanwhile, the RES hose would be attached to the ON position which has now been disabled.)

One thing I noticed that may mean something is I was trying to adjust the idle screw while trying to keep it running and somewhere down there I thought I felt a puff of air or something on my arm when it died...

Hmmm ... that might turn into something.  Seems like you could only get air "puffs" in that area from one of the carburetor "boots".  Can you pin it down any further?

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Regarding the "spark" video....  I can't tell from here; would you say the spark is more yellow or more blue?  (It should be closer to blue.)

Oh, and is there any chance that the "smoke" you're getting from the exhaust is unburned fuel vapor?  (Fairly white mist, smells like gas.)

[cmat1120]

The hoses are attached correctly I checked them. To me the spark seems more yellow, but it's hard to tell. And as far as the unburned vapor, that is very possible I can't tell if it smells like gas(everything smells like gas to me right now), but white mist could definitely describe what is coming out the exhaust.

Here is a picture of where my carbs meet the boots. Are they not in far enough?

[Kerry]

Here is a picture of where my carbs meet the boots. Are they not in far enough?

I'm gonna say "No" to that.  Here's an old picture from my '99 ... ignore the caption unless you get the carbs all the way into the boots and then you eventually arrive at a "hanging idle" or other lean condition.

[cmat1120]

ok thank you, Ill go try to push them further on then.

[RossLH]

Wow, that's not on at all. Loosen up the clamps and get the carbs seated all the way in the boots, that should definitely help.

[cmat1120]

Ok I have them all the way on for sure now. No change in anything else though, its acting exactly the same as before.

[Kerry]

That's OK - I didn't expect the "incomplete carb seating" to be the difference between starting and NOT starting.

Hmmm.  Assuming that the plugs themselves are good (which you'll be testing with a backup set shortly) and gapped properly,  I'm about ready to turn to some deeper electrical tests.  Do you have a decent multimeter with voltage (V) and resistance (Ω) settings?

I'd like to start by checking the resistance values for the "pulse generator" coils and the actual ignition coils.  For the former, locate a 3-wire connector on the left side near the battery.  (Check the wire colors in the diagram below.)



Using the appropriate resistance range on the meter, measure the resistance between a Black/Blue connection and a Brown connection.  Then test between Black/Blue and Green/White.  Both measurements should be between 250 ohms and 420 ohms.  If either of them measures higher than that (or "Infinite") you may need to make your way toward the signal generators one connection at a time until you find the "culprit" wire or connection.  (Hopefully the coils themselves are good!)

I've been "bitten" myself by some corroded connectors in this circuit.  My bike wouldn't start, and I was getting a nice-sized spark, but yellow instead of blue.  Fixing the "at fault" connections got me going again.

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If those circuits look OK, carry out similar measurements on the ignition coils themselves, like so:



The "Primary" measurements should be between 3 and 6 ohms and the "Secondary" measurements should be between 18,000 (18K) and 30,000 (30K) ohms.