'95 kat 750 wont idle down

[GaryS-NJ]

I've worked on a few bikes before and before I pull these carbs off ideas?

I bought this bike not running with the carb butterflies stuck. So I cleaned the carbs and loosened everything up and reassembled. Mounted up the carbs with funnels fueling the two carb lines and she started right up but raced to 4000 rpms. I bought the idle screw down and she would only drop a little and then played with the idle to see where the screw would engage and increase.. So I know the idle screw is off. I also verified the chokes are all closed and verified the throttle cable is loose. Bench synch I get it to carbs 101 and know the butterflies are all snapping closed (I can see that whacking the throttle).

All but one of the mixture screws were set at 2.5 turns out at disassembly but #3 was set at 3 turns out. I reset them all to 2.5 turns. The only real change I did was reset all the float heights much higher to make the seams parallel with the gasket surface. But this should drop the fuel level in the bowls and only affect midrange.. Right? Any other ideas before I pull the carbs? Oh and I did put the vacume hose back on carb 4 and plug the end going to the peacock. Side note, as long as I have power to the bike even with key off, the side fan is running..

[92xjunker]

Float height is critical for proper operation through the entire rpm range. A proper sync will be needed and the airbox and filter installed before any further advice can be given. If you still have high idle then it may be a vac leak, cracked boot, bad O-ring at the head, loose boot connections at the carb to head or airbox, missing hose or cap on the airbox. If that proves fruitless then you may need to reclean the carbs. Side note: do a drop down A/F adjustment after you sync. Overly rich A/F will also cause high idle.

[GaryS-NJ]

high idle

Thanks again 92junker for your help here and on my previous posts.


I have the airbox on with the stock airfilter installed and clamps tight. the bike is responsive for the 4500 rpm idle and up and I thought with a vacuum sync that would only increase the idle. I know my bench sync is pretty good but to do so I couldn't do the sync to the first little hole per the carbs 101 instructions.. I think I ended up doing it to the second up little hole which would have the butterflies open a tad. I wouldn't think this much butterfly opening this much account for an idle at 4000 rpms?


also seeing as I actually increased my float height measurement, wouldn;t this actually drop the fuel level? but then I guess that would make it run leaner and perhaps increase the idle.. but up to 4000 rpms? when checking the float heights, I found that the float weight alone was not enough to compress the little float needle pistons at all so I didn;t have to put the carbs on an angle to "just touch" the float tangs to the needle tips. I set the float height with the full weight of the floats on the needles.. On the bench I did put fule to the carbs and verify that the floats were cutting off the fuel (and also allowing it in with the drain screws open). I had no overflow.


The sync caps are in good shape and snog onto the carb tops. Is there a vacuum measurement I can check on the #4 carb vacuum port that gives vacuum to the petcock? I can go back out there and check that at well as spray carb cleaner around the boots and head to check for air leak.. Also, seems all carbs have the vacuum port on top right side (not left side per carbs 101) but I assume all but number 4 are plugged internally (I'll check that too).


lastly as far as the mixture screws, I know the wiki says 1.6 turns out and carbs 101 I think said around 1.75 turns out but all but number 3 were originally set at 2.5 and I posted on here and got a response saying 2.5 turns would be fine. But don't we always adjust mixture screw for highest idle? Again, I understand that we might have to have the idle screw set high until the sync and mixture are set to bring the idle up in which case I would then bring my idle screw down.. But right now my idle screw is completely disengaged from the throttle tab (and my throttle cable also is not holding the butterflies open).


I'm thinking if WOT (butterflies rotated 90 degrees) will bring the bike to 10000 rpms, then to get to 5000 rpms, I might actually have the butterflies open 45 degrees and thus 4000 rpms where I'm idling is not the butterflies open a hair but would be like 40 degrees. I'm sure with no load this is on a straight line and a small opening might get a good jump in rpms. any guess at what throttle opening would be required to bring rpms to 4000? Like I said, I've worked on a few bikes and the only time I had the idle hanging so high it was die to a frayed throttle cable not allowing the throttle butterflies to close.. On my bike I actually grabbed the throttle cable at the shaft actuator and loosened the cable adjuster until the cable went slack.


One Idea I just had totally unrelated to carbs and intake was the ignition advance.. if the ignition advancer was stuck on advance (recall that I never saw this bike run), could that hold my idle up at 4K? http://katriders.com/wiki/index.php?...ition_Advancer

I could get a timing light on it assuming there is a port but at 4000 rpms, I'd assume the ignition would be full advanced.. can I disconnect the ignition advance??

thinking a little more about the ignition advance, if it was somehow stuck advanced (actually, the advance is probably controlled by the CDI and the cdi is just detecting crank position from a sensor and rpms to set the timing advance..). this is feeling more and ore like a carb issue.. perhaps related to my work to free up the butterflies..

[92xjunker]

Pre Kats don't require the carbs to be tilted to set the float height, the post kat does. With no load very little is required to increase the idle speed. A bench sync only gets the carbs to a running state so a full sync can be done. The katana advance is electronic, done through an rpm/timing program, no mechanical advance. Do a full sync, it's needed and has remedied the high idle many times. As for A/F adjustment, yes...a drop down adjustment could and in my mine should be done.

[GaryS-NJ]

full sync.

I'm headed back out there with and will check the sync. and probe around for vacuum leaks.. I did change all four of the diaphragm cover orings to and the orings between the slide guide and body to standard metric orings.. guide orings looked the same but the little diaphragm orings looked thicker.. I figured they would crush into seal.. Oh and for the fuel mixture, I don't really see myself getting a tool in there to adjust while it's running but if the carbs come off should I drop from 2.5 turns to 2 turns (but that does lean it out and again, I thought mixture screw is set for highest idle..).

[GaryS-NJ]

The carb sync was off with #3 pulling almost 15" while #4 was about 8 and 1/2 both about 12" I evened it out and the idle went up to 5000 rpm. Then I checked for intake leaks and found the #4 airbox boot loose/leaking but snugging it up didn't change things. I'm really thinking i have the butterflies a tad open even with the idle screw disengaged as a result of my work to unstuck the throttle shafts. Like an idiot I was tapping on the butterflies and on the throttle cams. When I was done bench syncing the plates looked closed though and all pretty flat. One thing though when I had trouble bench syncing, I swapped the synch screw springs to put the light ones on the screws and heavier springs between the throttle cam tabs. With throttle closed should I be able to just see all three carb body holes (what I looked at to bench sync) or should the butterflies close much further? To my recollection, the throttle plates looked like they were snappi,g totally closed.

[GaryS-NJ]

idle still way too high at 3000 rpm

Float height is critical for proper operation through the entire rpm range. A proper sync will be needed and the airbox and filter installed before any further advice can be given. If you still have high idle then it may be a vac leak, cracked boot, bad O-ring at the head, loose boot connections at the carb to head or airbox, missing hose or cap on the airbox. If that proves fruitless then you may need to reclean the carbs. Side note: do a drop down A/F adjustment after you sync. Overly rich A/F will also cause high idle.

I swapped the sync screw springs to their correct position and then did a bench sync to the first bypass orifice and now my idle came down from 5000 rpm to 3000 rpm. but that is still way to high


I'm sure I don't have a vacume leak.. I pulled the carbs and the pilot circuit seems clean. I removed two pilot air jets to check their size (previously, I had trouble getting them out so I just sprayed them, but this time I really wanted to check sizing and so used a heat gun followed by freeze out penetrating oil and got two of them out so far). the PAJs are labeled 1.3 which I think is stock for the USA 1995 katana750.. The mix screws had been set to 2.5 turns out so I reset them there.. I guess I could turn them in to 2 turns but I thought mix screws were supposed to be set for highest idle.. either way, I cannot see a mix screw bringing the idle up to 3000 rpm with the idle screw backed all the way off.


The only major change I did when reassembling the carbs was to set the floats much higher... They were all around 13mm and I set them up to almost 14.7mm.. But here I am raising the floats which actually reduces the fuel level in the bowls and I would think this might lean out the pilot circuit and logically raise the idle.. but I'm just bringing the floats up to where they should be.. note that at 14.7, the floats were sitting such that the float seam was about parallel to the gasket surface. Is it possible that my bike and carbs just want a bowl fuel level so high such that the 13mm float eight is correct? so for this next trial, I could bring the floats all the way up to 14.7mm (making it leaner) and/or turn the mix screws in to 2 turns making it leaner (both of these things I thought should raise the idle) or set the floats back where they were to get a higher fuel level and make it richer)..

[92xjunker]

Stick with the required float high for your model. Float height IS critical for proper operation. Measure at the highest point on the float to the carb body.

[shpielers]

Was 3000 after synching after you made those latest changes? If you haven't synced again yet, you'll probably fine after you do.

[GaryS-NJ]

I pulled one spark plug and is didn't look excessively lean nor did it look excessively rich. it had some soot on the threads but the center ceramic was still clean . all in all it looked like a pretty new spark plug (not aged and tan) so it didn't tell me if I'm running way lean or way rich. I cleaned it up and will look again after the next trial with the floats set to 14.7 and the pilot circuit sprayed out (again).// As for syncing, after I made the last change correcting the sync screw springs, yes I did a bench sync and on start up it ran about 3000 rpms. I then did a running sync and it only required very fine adjustments which didn't really change the idle..

now to be clear, I've posted this stand alone high idle post but in a previous post with questions on carb cleaning (yes, after reading carbs 101), I made clear that while trying to unstick my butterflies and throttleshafts, I was soaking, spraying several different penetrating oils, and gently tapping on the throttle shaft levers (the cams that cable and sync screws activate) and tapping on the butterflies, and I even loosened one of the throttle shaft nuts.. none of that did much except slightly bend my butterflies which I have reformed to pretty much flat. the only thing that did loosen the throttle shafts was an overnight chem dip soak.. now I imagine that might attack the throttle shaft felt washers but seems they are not sucking air and I've sprayed them with penetrating oil.. I don't see anything like a bent open butterfly (they are all closing same and syncing to the first orifice) or a shaft/cam that is out of wack...

so my plan is to follow advice here, bring the floats all the way up to 14.7mm and reset all the mix screws from 2.5 turns out (that's where they were except for #3 which was 3 turns out) back leaner to 2 turns out (wish I had a color tune or tiny fingers and extended mix screws). I did look for advice here and on a previous post I was assured that thee 2.5 turns out would be close enough.. and then if my idle still isn't right, I'll look at that spark plug again. putting the carbs on and off is getting easier anyway,.,

can anyone comment on how many turns after touching that the idle screw is typically turned to get the 1200rpm idle?? I have mine completely disengaged with my 3000 rpm idle.

[B-Man]

Speaking from experience, setting the mixture screws to 2 turns on my Kat resulted in a high idle and a slow to return to idle condition. When I rode the bike it would pull like crazy but when I let off it took too long to return to idle.

I bought a MotionPro carb adjustment tool for ~ $25 and it allowed me to adjust the screws back out without removing the carbs.

If those carbs were gunked up and you cleaned them with spray cleaner, they are likely still dirty. Soaking them or using a sonic cleaner is the only way you are going to get all of the tiny passages clear and flowing correctly.

Set the float height as per Suzuki specs and don't mess with it. Everything you alter creates a variable that can have other effects on how the carb functions. If you want them to work as designed, assemble and adjust them to the designer's specs.

[GaryS-NJ]

Thanks B-Man. no for sure my carbs are clean. I removed all jets, soaked them in super clean and chem dip and sprayed and blowed and used a guitar screen.. and jets got soaked and cleaned with the high e string.

so your bike ran high idle at 2 turns out vs factory 1.75 turns out?? had someone been in there before you to adjust the mix screws ? how fast was it idling with the two turns out and then what did you leave them at (BTW, did you use color tune or ear? because I thought mix screws were set to obtain highest idle?)

I might be onto something right now though.. On reassembly after verifying PAJ's to 1.3, and respraying the pilot circuit (it was clear) and preparing to bring the floats all the way up to 14.7mm, I found one oring on float choke tube had a pinch in it and on removal, it broke. some of the floats didn't snap in tight enough too (they did seem tight on the first reassembly) so I'm getting orings for both sides of the float assy (fuel and choke). I'm hoping /wondering if it was pulling fuel into the choke tube and idling high because of that. I'm getting the orings from grainger (saving $25 and will have enough orings for a few lifetimes, anyone need orings??)

[GaryS-NJ]

#1 and #3 not firing

I got the carbs assembled again with new float O-rings and also checked and sprayed the pilot circuit (and soaked the pilot jets). pilot circuit looked clean and clear. I tweeked the floats to 14.7mm (turns out only two floats needed minor adjustment as all the floats had one high side which I used to adjust height..). got them on the bike and she's idling right but was very touchy on the sync screws and the idle screw (on the idle screw, she was high and I could bring it down to idle nice but then she would sputter and die.. while she was running, I used an infrared thermometer to check exhaust temps up high at the bend (hoping to see similar temps, similar mixture..) and I found #1 and #3 cold. couldn't be a coil as one coil fires 1 & 4 and the other fires 2 & 3.. So I changed plugs and then #1 seemed to be warming up but 3 wasn't so I pulled #3 and verified spark with another plug. but then running it again, I had #1 and #3 cold.. I'll start another thread on this because it seems like an oddball problem but any ideas here??