2000 Katana 600 erratic vacuum?

[kelso38]

First time poster, so I'm looking forward to seeing some good replies (which seem prevalent throughout the forums).
I'm currently working on a 2000 Katana 600, here's the breakdown of parts replaced and procedures performed to this point. New battery installed, and voltage tests confirm alternator works properly. Rebuilt carbs (bench synched) installed. I have also double checked jet size, placement and cleanliness, all good. Existing K&N air filter, cleaned and visually inspected. Checked all lines (fuel and air) for cracking or misplacement. Ignition system tested and working properly. Ohmeter test of TPS reads within limits.

Now, here's where the problem is. Bike has poor acceleration and you can hear it *popping* out of the exhaust on initial startup. Also, it is impossible to redline it. Once bike is running for about 10 minutes at operating temperature the *popping* stops, and there is a noticeable difference in exhaust temperature coming out of the pipe. At this point you can redline the bike, but with a horrible lag at 4-7K RPM. Tried to sync the carbs today after warmup and the needle was all over the place at idle. It was still erratic at high speed idle (2-3K RPM), and the value dropped at 4-5K.

I'm really looking for a confirmation of my current troubleshooting. My conclusion to this point is that the valve seats are toast and I'm stuck doing a top end rebuild . I considered the possibility of a warped head or blown head gasket, but I've never had one act "better" after running at operating temperature. Usually just the opposite.

If I'm ignorant, help me. If I'm stupid, shoot me. Thanks!

[CDNbakn]

First things first, ditch the K&N filter immediately. I have read it does no good for our bikes. Not exactly sure why, but the majority vote says ditch it! Also, bench syncing is no good, and is generally used to have the carbs synced properly right after with a manometer (it's really just to get them GENERALLY close). Any slight difference (may not even be visible by the eye) will mess your stuff up. Due to valve seals wearing differently for every cylinder, there may be different vacuum amounts for each cylinder (even with the carbs synced 100% the same), the point in using a manometer is to find the equivalent vacuum on each cylinder. I highly recommend against using any vacuum gauge that has a needle, as they do produce the symptom you mention and that is jumping all over the place. The cylinder will only produce a vacuum every 4th stroke. I find that making your own manometer works best, and will cost you less than 5-10 dollars.

Popping out of the exhaust on a cold startup, to me, signifies either a misfire or bad fuel/air mixture. Are you sure that your carburetor pilot jets are 100% clean? Soak them for 24 hours in carb cleaner solution, "spraying" them with carb cleaner just won't cut it in this case if there is major build up (again, may not be visible to the eye). What are the small numbers printed on your jets? That will tell you a lot about what has been done to the carbs (say, a jet kit installed?). Do you have any grooves with an e-ring on the jet needles? An easy way to tell if you have a jet kit.

Something that can greatly affect performance of an engine is float levels in the carburetor bowls. Ensure that they are all set correctly, and at least within a close proximity of each other. You'd be amazed at how the float levels affect the richness of a mixture. If the hangup at 4-5k rpm is under WOT, then that sounds like the main jet to me, since that is only under operation around 3/4+ throttle. Clean it real good.

Do all this before you dig into an engine and do valve work.

[kelso38]

Thanks for the reply CDN! The carbs are a set of rebuilds and float height was set to factory specs. I believe 13 mm? I did indeed take the float bowls off and inspect everything to make sure the proper jets were installed (115-main on 1 and 4, 112.5-main on 2 and 3). I also removed jets and checked to make sure something didn't get sucked in after initial reinstall. All are perfectly clean, including pilot jets (which were also the right size). I have heard the K&N filters are not much improvement though, but it was already there and in good condition. To be a little more specific though, the lag range is more like 4-7K RPM. Sorry for misleading everyone on that one. Then it cuts loose to redline. I had reviewed the motion pro manometers, and didn't see anything favorable about them anywhere. Depending on who you were talking to, they had to be calibrated every time before use and if you weren't careful you'd pull the fluid right into the carbs as well. Plans for a homemade version would be much appreciated though! Thanks again
P.S. - I edited the lag range in first post. Sorry

[Wild-Bill]

You're trouble is in the mid-range. That's the point where the slides are supposed to be drawing up and starting to open the main jets. This is done by vacuum and that is affected by your air filter. Get rid of that K&N and go back to a stock-type paper element filter before you touch anything else.

The problem with the K&N filter is that it flows air too well. Constant Velocity (CV) carbs rely on some intake resistance in order to develop a vacuum (pressure differential for the physics snobs). This is used to draw the needle up, out of the main jets and make that transition between low engine speed fed from the idle jets and high engine speed fed by the mains. Mess with the intake resistance and you've just FUBAR'd your mid-rpm transition.

[HighRisk]

Sorry to jump into this thread but i've been looking to replace my K&N airfilter anyone got a link to a website to buy the proper one?

[Stumpy]

http://www.ebay.com/itm/HIFLO-AIR-FILTER-fits-Suzuki-GSX-750F-KATANA-1988-2006-/350840646030?pt=Motorcycles_Parts_Accessories&hash=item51afbb698e&vxp=mtr

No idea of the quality of the Hiflo - I use Emgo's, but probably better than the K&N on the Kat. I like K&N's and have used them on all my previous bikes, just they don't seem to play well with our particular machines. I had one for a while.

[HighRisk]

Thanks a ton Stumpy

[TRPUT]

Hi-Flo are good filters. Apparently related to K&N but OEM spec.

Syncing carbs with a needle gauge is not the best method. If it's jumping that much, you probably haven't installed resistors / dampers in the line. But a unit like the motion pro will give you much better results with less angst. Don't be afraid of calibration - it's essential to get good results. There are many home made versions if you want to take that path - just google "carb balancing tools" or search this forum.

(Just too tease you) ... unfortunately, the tool I use - called a Harmonizer - is now out of production because the designer and manufacturer has gone on to other interests. I'm glad I have one - it really is the duck's guts. A lot of guys don't like it because it only has 2 ports (2 carbs at a time) but anyone who has used it swears by it. It's electronic, self calibrating, deadly accurate, super easy, super fast, idiot-proof and displays RPM also - so all the info you need is on 1 screen.

[Jman2343]

Though the gauge your using isn't the best Id say excessive flutter would point toward running rich over filling bowls. I've been there a few times with my motion pro fluid really low and jumping on one or all cylinders.

I usually find wet throttle plates after pulling the air box and lifting the slides.

[kelso38]

That's the kind of helpful info I was looking for. I'll start with air filter and move forward I suppose. Does that fit the bill with the initial startup problem as well? Why does it actually work better after running at operating temp for a while? Just a few factors that are eating away at my sanity. By the way, I hated physics in high school. We'll stick with "vacuum".

[Wild-Bill]

...Why does it actually work better after running at operating temp for a while?...

When the engine is cold it needs a richer air/fuel mix than after it's warmed up. The air leak/high-flow filter leans out the mixture, making the mix too lean for a cold engine but enough for idling a warm engine. That's in addition to the vacuum issues.

Does that help with the sanity issue?

[indianboy7]

try to partially block the air filter opening with a rag when you have the k&n installed. If it starts up easier, you'll know the problem right away....

[kelso38]

Oh yeah, thanks TRPUT! Never, ever tease me with tools! Especially if they're discontinued!!! That Harmonizer (cr) does indeed sound like something I'd put my money into and be justified in buying 3 other bikes *cheap* that are just not tuned worth crap. I have a "minor tool addiction" that affects my bank account every chance it gets!
Sue me, I have a penis.
If I'm ignorant help me, if I'm stupid shoot me.

Me with my beer
goggles on

Also thanks Bill and indianboy. That makes total sense on both counts.
I've been doing nothing but automotive for the past several years, so bear with me please as I get back into the swing of small engines. I appreciate all tips and ideas on here. And yeah, Bill you saved me just enough sanity for the time being to keep working on it. I'll let everyone know when the fresh batch runs out!