small bog down in first.

[AkBigN]

I have a pre 98 with pods and full V+H SS2R exhaust and a dynojet kit installed. Whenever I am going into first gear from a stop the bike will start to go and then bog down for a split second and then come right back up with no problems in any gear after that. I can rev it up to 7k and let the clutch out and it still does it. It was really hurting my times at the drag strip.

I was searching for a solution to my problem when I came across this thread.

http://www.katriders.com/forums/viewtopic.php?t=9149&highlight=hesitation

I don't know if this "cutting the springs" solution applies to me because I don't remember if the dyno jet came with different springs or if the stock ones are still in there. Any suggestions?

[pmkls1]

well your jet kit should have come with different springs in it. I did cut down my stock springs and reinstall them but I seem to have a similar problem still. I can pretty much attribute my problem to a slightly rich mixture because in cooler ambient temperatures the problem almost disappears. I have yet to do any tuning on my needles but I suspect that I can at least lessen my problem some with a little fine tuning. Im not sure which direction to point you in because revving mine up higher when taking off helps my problem some. If you can find the stock springs give it a try, if you cant find them you can get new ones for like $4 each if you wanna. One other suggestion I would make is if you do start playing with the springs in it start off by trimming them a little and then if you notice a difference but it isnt enough then cut off more but dont go and lop off a full inch at once cuz you can always cut off more but you cant add length.......

[The CyberPoet]

Order a spare set of springs (suzuki OEM springs) and cut the ones in there now. Also check your carb slides very closely -- the bog comes from the slides not moving up quickly in response to the change in vacuum as you roll on the throttle; this may be spring tension, or it could just as readily be a problem with the slides being dirty, gummy, or having a small vacuum leak somewhere on a bike as old as yours.

Cheers,
=-= The CyberPoet

[md86]

Well , mine did that , and I turned the pilot screws out a bit and it went away . Not sure if that's the problem YOU'RE having exactly , but that's what I did . Takes all of twenty minutes to try anyway . Does it lurch or hesitate a bit coming back on the throttle after a corner , too ? That's another problem that turning the screws out a bit fixed for me . Just my experiance ...

[AkBigN]

It doesn't have any hesititation at any other time. Only going into first (as far as I can tell). If the slides aren't opening fast enough shouldn't I see this problem at idle also? Also, would changing the springs effect all the rev range or just down low.

[The CyberPoet]

It doesn't have any hesititation at any other time. Only going into first (as far as I can tell). If the slides aren't opening fast enough shouldn't I see this problem at idle also? Also, would changing the springs effect all the rev range or just down low.

The gear is irrelevant -- it's what the engine is doing coming off of idle. Odds are that you never go back down to totally static idle with flat vacuum at any time except when stopped, so it's the only time you notice the issue. As for the slides, they may have issues with the initial movement as a result of vacuum issues -- as the RPM's increase, the vacuum increases, which would offset any minor vacuum leaks.

Cheers,
=-= The CyberPoet

[pmkls1]

CP I have a question for ya though ? Isnt air velocity also in question here ? I mean these engines dont develop much vaccum I would assume and they have large carbs vs. the engine size so I would think that velocity would play a large role in all of this since it is a major factor in how a carb works. I am bringing this up because when I experience a bog I am experiencing an overly rich condition which would lead me to believe that my slides are opening but I dont have enough air velocity to correctly atomize the fuel coming out of the carbs. However, even though I am experiencing a rich condition during a bog I am running a little lean during normal operation which would suggest that my needles are adjusted properly. Please correct me if I am wrong though but those were just my thoughts.......

[AkBigN]

I called dynojet and they said the 90-97 katana 600 jet kit doesn't come with new springs. I guess I can try to cut the stock ones anyway.

[pmkls1]

If you do I would suggest getting a spare set just in case it doesnt help. And I would still recommend cutting them down in increments so as to avoid cutting them down too far......

[Black_peter]

CP I have a question for ya though ? Isnt air velocity also in question here ? I mean these engines dont develop much vaccum I would assume and they have large carbs vs. the engine size so I would think that velocity would play a large role ..

Dude... Bernoulli!!

[The CyberPoet]

CP I have a question for ya though ? Isnt air velocity also in question here ? I mean these engines dont develop much vaccum I would assume and they have large carbs vs. the engine size so I would think that velocity would play a large role in all of this since it is a major factor in how a carb works. I am bringing this up because when I experience a bog I am experiencing an overly rich condition which would lead me to believe that my slides are opening but I dont have enough air velocity to correctly atomize the fuel coming out of the carbs. However, even though I am experiencing a rich condition during a bog I am running a little lean during normal operation which would suggest that my needles are adjusted properly. Please correct me if I am wrong though but those were just my thoughts.......

Air velocity is a really weird event in a modern motorcycle carb at low RPM levels. The velocity goes from static (intake valve close) to rising quickly (intake valve opening and exhaust valve still open), to slightly less (intake open, exhaust closed), to zero and back to negative flow (intake valve still open, piston rising). As the RPM levels increase, the velocity of the inbound charge becomes sufficient to over-come the piston rising, cramming more air-fuel mix in there inspite of the piston coming up and cramming the stuff together. The big power surge you feel around 7200 RPM on a Kat engine is when this cross-over starts happening in ernest (more mix loading into the cylinder in spite of the fact that the piston is heading upwards before the intake valve closes).

BUT the velocity of the inbound charge does not control the slide movement directly at all (since all it would do is push the slide forward, not upwards); the slide's upward movement is controlled purely by vacuum and opposed by the spring strength. Thus the existance of the right amount of vacuum is critical to get the slide moving upwards, especially close to idle where the vacuum levels are their lowest (and a minor leak will be enough to disrupt it).

To try to put it another way (half-baked, not clear enough for my satisfaction):
You have a big container about half-full (say a 5 gallon plastic thermos like they use on football fields). At the bottom is a spigot that is always open. At the top is a facet that is constantly pouring in more water, at the same general rate as the spigot is draining, so the whole system is balance. Floating in the water is a tennis ball. This is a good parallel for your vacuum system (the thermos), the water stored represents the vacuum level, while the spigot is the airbox opening (always open to the air) and the facet represents the vacuum source at the engine. About 1/2 of the way from the bottom of the container is a net that has been glued in, and floating on the water is a tennis ball... The tennis ball represents the carb slides, and the net represents the lowest possible postion for the carb slides (because it will support the tennis ball even without the water, just as your slides come to rest in the down postion without sufficient vacuum).
Now punch another hole in the bottom of the container with a metal spike... water starts flowing out of the new hole as well. The whole system is no longer in balance, and if you don't turn up the facet to compensate, the container will empty itself out soon enough. This is what happens when you get a minor vacuum leak in the system. Now, when you turn up the facet (raise the RPM rate up off idle), it takes a while for enough water to build up in the container to float the ball upwards again (i.e. - to build enough vacuum to raise the slides).

Now given this lag of time for the slides to rise, the vacuum is high going through the carbs to the intake valves, but too low initially at the sliders to raise them. This condition causes the mix to go rich, because the excess vacuum pulls more fuel out of the pilot circuit while starving the engine for sufficient flow (because the slides aren't moving out of the way).
Like I said, there are other reasons the slides might not be moving upwards other than a minor vacuum leak (such as gummy residue build-up that takes quite a bit of vacuum power to break free of), or overly strong spring strength (again, which takes quite a bit of vacuum to overcome), but the complaint in general seems to be based on the fact that the slides aren't rising up in an reasonably timely manner coming off the static "down" position at idle. An exhaust analyzer can easily confirm this...

Dude... Bernoulli!!

The slides do not move from Bernoulli's primary principle (that air increases in velocity through a restriction in the opening), but the fueling mixture being drawn into the air from the jets is controlled by it.

Cheers
=-= The CyberPoet

[pmkls1]

Well in short response to your very detailed answer, which i appreciate, I was talking about velocity in relation to fuel atomization rather than slide movement. Like i said before i am sure that my slides are opening but i dont think there is enough velocity for the fuel to atomize properly thus causing a fuel puddling effect. I just had my airbox off while doing my 7500 mile service and I did check my slides for proper movement and I didnt see anything to cause them to stick and I have also already trimmed my stock springs down to 3 inches. I know that I am experiencing a rich condition in my case because I dont have the problem unless it is hot out and I have been riding for a while and the engine is good and hot. In these conditions the engine will actually sputter under 3k rpms. Anyways it seems to me that the problem is related to the engine not producing sufficient vaccum to provide the proper velocity to operate the carbs correctly once the intake and exhaust have been altered from a factory state.

[The CyberPoet]

Anyways it seems to me that the problem is related to the engine not producing sufficient vaccum to provide the proper velocity to operate the carbs correctly once the intake and exhaust have been altered from a factory state.

The change in the intake filtration can make a huge difference, as the vacuum levels from the airbox forward drop with an air filter that flows more. That change indeed has to be compensated for at the jetting (or by returning to the OEM filtration, which is usually my preference). All of the designers for 98 - 05 jet kits that I have spoken with said the same basic thing -- given their jetkits, there is no performance improvement by switching to an aftermarket air filter, and in many cases there is specifically a decrease in performance. Ivan even posted that publically on his site: see

http://www.ivansperformanceproducts.com/Kat600.htm

(same info is also duplicated in his 750 page).

Cheers
=-= The CyberPoet

[pmkls1]

I have read his site and find it quite interesting and it may be cause of SOME of the problems experienced by kat owners. Although my jetting has been changed to compensate for the altered air filter, the change may be a cause for the whole problem like you suggest. I have debated changing back to my stock air filter but then i would have to re-jet and I am too lazy to do that right now but I may in the future just to see if it helps...............

[AkBigN]

Yeah, I don't want to go through the re-jetting process again. I cut the spring and that didn't work. I can tell it does it when the clutch lever is released about 90%.