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Matt at PCS, the Yamaha dealer, looked at my forks today and determined they are just fine. He said he lubes the fork seals quite a bit before installation so it must have been just that stuff being pushed past the wiper, giving the appearance of leaky seals. I've put another 250 miles or so on the bike since I thought they were a problem and now look to be just fine. If the seals do present a problem I'll bring it back in and they'll fix it up for me.

I did a bit of digging around and it seems I'm about 50mm short for fork oil height, though. Matt set them to 150mm air gap and spec is 100mm, so I'll probably be adding some fork oil sometime. Shouldn't be a big deal at all, just need to snag another container of fork oil, my Rad ate the last one.

Bike seems to be running better, it's improving gas milage every time I fill it up. If it keeps going like this when I fill it up next I'll be getting about 60 MPG, then 75. Or not, depending how I ride it.

Alright my Katana is doing a superb job of "hide the issue" from me. Here are my symptoms: bike has been working great for the past 300 miles or so. Take it out for a ride after riding back from campus, and within six miles it starts acting like it's starving for fuel. More throttle makes it sound louder but no increase in speed. Can barely keep my current speed, ~60 MPH. Moment you let off the gas and pull in the clutch, the engine dies. You can keep that from happening by applying a liberal amount of throttle, keeping the engine speed at about 5,000 RPMs. Anything less and it will die.

So I've been assuming my fuel delivery was the problem. So new, rebuilt petcock, new inline fuel filter (old one was not clogged), polished needle seats inside carbs, float heights set correctly, no sticky floats. I also tried riding with the gas cap open to verify vacuum lock wasn't happening, due to a clogged gas cap vent.

No dice, still has the same problems. Ok, really tight valve clearances might cause that, once the motor warms up. Pull the plastics, gas tank, oil cooler and valve cover off. Nope, every single vavle is spot on!

I've been racking my brain about this for quite a while and the only thing I can come up with is not enough fuel flow from the tank to the carbs. As I probably mentioned before, the '88 and '89 Kats had single outlet fuel petcocks, while the '90+ models received a double-outlet petcock with two lines running to the carbs.

Other than that, I'm just stumped. She ran hard and strong for the past 300 miles, including steady cruise above 70 MPH for, say, five minutes, but two minutes at 60 and she starts acting starved again.

I'm about to just plunk down the cash for a set of '90+ carbs and all the required pieces to rebuild them, this is getting RIDICULOUS.

Replaced my fuel line to the carbs with a straight line, no inline fuel filter. Synched the carbs (pretty bad, the locknut on the center adjuster loosened) and bolted it all back together. Debating a ride before it gets too cold out to see if the problem is gone.

Here are some pictures for your time.




(edit) test-ride went alright. 80 MPH cruise and no issues, bike seems to be much better mannered with balanced carbs. I'll put on a bunch of miles tomorrow to see if the problem crops up again.

Well, she didn't want to play nice this morning. Seemingly random fuel starvation issues at speed. At least, I think it's starvation. I'll be cruising down the freeway doing 60, then the bike would start slowing down, then bucking forward a little bit. Adding throttle made more noise but no more power, bike can barely keep its current speed. If you pull in the clutch and let off the throttle, the engine dies almost instantly. Giving it a decent amount of throttle, say, 1/4, will keep the speed up to 3 or 4k RPMs and it won't die. Only does this when the bike gets warm.

I have a rebuilt '90-'97 600 fuel petcock that flows plenty of gas. I had an inline filter installed but removed it in case it was the problem. After removal I went for a ride and could do 60, 70 or 80 MPH cruise without a problem. Next morning it can't even get around town before starving for fuel.

It ran like a champ for 300 miles, then the issue suddenly cropped up, then went away.

Since the problem seemed to occur when the motor was warm, I assumed seriosuly out of adjustment valves could be the issue, so I checked them. All of 'em were spot-on. Also thinking it could be vacuum-lock in the gas tank, I tried riding with the gas cap open. No change, still starving.

A few things I can think of:

My carbs' vacuum line isn't pulling enough at 60 MPH to allow fuel to pass through the petcock. Apparently this is also a problem around town, but at, say, 80 MPH it pulls enough vacuum to let the petcock work.

OR, the single fuel line to the carbs doesn't provide enough fuel. CyberPoet pointed out Suzuki went to different carbs with a dual-output petcock in '90. This could be my issue, but around town it shouldn't be!

OR there is something wrong inside my motor that becomes a problem when it gets warm. Not quite sure what it could be, though. A compression test might tell me something but I don't have the proper adapter for my bike.

I'm just so confused and don't know what to do. If, say, it was my petcock's spring not being overcome by vacuum, it would have been apparent in the last 300 miles. If it was vacuum lock, it would have gone away with the cap open. If it was the fueling of the carbs being choked due to one input line, that would have been apparent the last 300 miles. If it was an ignition problem the bike wouldn't run nearly as well as it was.

I'm about ready to throw my hands in the air and see about finding a newer motor and carbs for it. This is ridiculous.

Forgive my laziness for not going back and looking myself, but have you changed the emmulsion tubes and needles in your carbs? Suzuki's oil-cooled lumps are famous for wearing these parts out of spec in as little as 5000 miles(seems vibration is the problem), and when they do, proper jetting is next to impossible. I think your probably on the right track by thinking it's fuel or jetting.

The emmulsion tubes will wear into a slight oval shape from the needle flappin' around inside the tube, giving inconsistant fuel delivery from the main jet. You should be able to see this wear by eye if it's there, but you have to remove and strip the carbs to do so. P.I.A.....

You can replace them with stock parts, but they ain't averly cheap or any harder than what you have now. DynoJet makes replacements that are sposed to be much harder and last considerably longer, for just a bit more $$$ than Suzuki parts.

But that's just me thinkin' out loud......

BuzZz wrote:Forgive my laziness for not going back and looking myself, but have you changed the emmulsion tubes and needles in your carbs? Suzuki's oil-cooled lumps are famous for wearing these parts out of spec in as little as 5000 miles(seems vibration is the problem), and when they do, proper jetting is next to impossible. I think your probably on the right track by thinking it's fuel or jetting.

The emmulsion tubes will wear into a slight oval shape from the needle flappin' around inside the tube, giving inconsistant fuel delivery from the main jet. You should be able to see this wear by eye if it's there, but you have to remove and strip the carbs to do so. P.I.A.....

You can replace them with stock parts, but they ain't averly cheap or any harder than what you have now. DynoJet makes replacements that are sposed to be much harder and last considerably longer, for just a bit more $$$ than Suzuki parts.

But that's just me thinkin' out loud......

Yeah, from what I've been reading, and help from a buddy, this is what is sounds like. The way the bike was running before probably isn't a lean condition as I expected, but rather a rich condition due to the emulsion tubes letting too much fuel past at lower amounts of throttle. This would explain why it would work fine at, say, 70 MPH, when the needles should be raised that high and engine have that much fuel, but if the same amount of fuel is passing when I'm doing 60, it could be flooding the bike. Strange how it wasn't backfiring, though.

Found someone selling a set of later-model 600 carbs that bolt right up, for $50 plus shipping. This will clear up the bike's problems if it's the emulsion tubes (assuming the newer ones are better) or if it's insufficient fuel flow (later model carbs have dual fuel inlets).

This bike dares defy me no longer or it might find the carbs at the bottom of a lake and a GSXR EFI setup being strapped to it!

(edit) Decided my symptoms are too inconsistent to be carbs/fueling. Ignition problems are the first candidate, so I'm trying to get a set of ignition coils, new plug wires and a CDI box for a song and dance.

I had weird problems with my 92 kat about a year back that wound up being coil problems. cost me about 180$ for both i think. took forever to find somewhere to get the stupid things in my neck of the woods.

But the problem does sound fammiliar. It sounds like it should be screaming down the road, wont run after it gets warm, no power etc...

Tried removing the sheared off exhaust bolts today. Heated them up real good, drilled a pilot hole then went to town with my shiny new expensive bolt extractor kit from Sears. My drill gave me the finger and started overheating, releasing some white smoke, as the bolt was trying to be extracted. Not to be outdone I let it sit to cool down, removed the bolt extractor with a wrench, per instructions, then tried again.

*snap*

Well that was $10. Let's try the next bigger size. Oh, it's stuck, too. Well, let's remove it and try again-

*snap*

So that last one is stuck in the bolt, flush to the head. Oops. Time to see how much a headgasket will run me, 'cause the head probably has to come off now so a machine shop can take care of this.

My alternative is to find some masonry bits and try to drill it out and maybe heli-coil it.

Drilling out snapped, hardened and uneven bits is a good way to do more damage to the hole your trying to save. Having a machine shop do it might be the cheapest solution now.