03 Katana 600 High Idle when Warm

[Phantom552]

I just picked up an 03 Katana 600 with 12k on the odometer, and a fresh carb rebuild. During the hour long ride home with my new (to me) bike -- (Approx 20-25min In) it started to idle high at stoplights (3k-3.5k RPM), so I pulled over, shut it off, talked to a fellow rider for a few minutes, and started her up again. Everything was once again fine so I continued on my merry way, and the same thing happened again as I reached my destination.

Anyone have any ideas as to what could cause this?

[arsenic]

Do you have fuel flooding the crankcase? If not, it could be the intake boots / intake boot o-rings. As rubber heats up, it expands. It may be worn and expanding to the point of not being air tight anymore.

[maniac1886]

+1 sounds like a vacuum leak to me

[fahzakat]

I have the same issue on my 06, I bought the O rings but I need to remove the boots but the oil lines are in the way so its a bigger project then I expected. I just did the plugs as number 3 filled with water in the last storm and caused some shorting out. Runs great now but I am not sure how so much water got in the hole since the boot was on and tight. Mine does the same thing, runs great, idles perfect when it gets hot it ramps up to 2k and some times will climb to 3 but mostly around 2. I adjusted the idle when it was hot and it seemed to fix it a little but today out on a run it started it again.

[Phantom552]

No fuel in the crankcase, I did a round of routine maintenance tasks (Oil change, air filter, chain clean/lube) after getting the bike and didn't see anything that the previous owner had neglected really.

I've been adjusting the idle here and there after long rides when the bike is hot enough to start the issue, but its constantly either idling too high or too low no matter how slight the adjustment is, and the idle likes to vary itself a bit when sitting.
A vacuum leak sounds feasible, is there a method you guys would suggest to troubleshoot it and/or eliminate/confirm the issue? Thanks!

[Phantom552]

Also, could the carbs possibly be out of synch and cause these symptoms? Just trying to cover all bases here since this new (to me) bike is my daily ride at the moment, id like to get it ready for prime time ASAP

[Kreylyn]

Also, could the carbs possibly be out of synch and cause these symptoms? Just trying to cover all bases here since this new (to me) bike is my daily ride at the moment, id like to get it ready for prime time ASAP

Yes, out of sync could definitely cause the issue. That is a vacuum/air leak basically.


I'd use a flammable spray, and spritz around all points where plastic or rubber meet metal. If the rpms change when your doing this... that's a leak point.


Krey

[fahzakat]

Bike mechanic told me to use a spray bottle with water in it. Get the bike hot enough to make the idle climb and then spary around the areas that might be leaking air, it will suck in a little water and make it run rough. He said use water is it leaves no residue and doesnt explode or catch fire if you happen to use to much. I have been told to use propane and a host of other combustable materials but water seems the safest He said to look at the stacks that hook the carbs to the block, the end caps that plugs the syncing vacume holes on the carbs and the line to the gas tank. Hope this helps, I may do mine this weekend as I want to get mine fixed as well but been putting it off all summer

[Kreylyn]

Bike mechanic told me to use a spray bottle with water in it. Get the bike hot enough to make the idle climb and then spary around the areas that might be leaking air, it will suck in a little water and make it run rough. He said use water is it leaves no residue and doesnt explode or catch fire if you happen to use to much. I have been told to use propane and a host of other combustable materials but water seems the safest He said to look at the stacks that hook the carbs to the block, the end caps that plugs the syncing vacume holes on the carbs and the line to the gas tank. Hope this helps, I may do mine this weekend as I want to get mine fixed as well but been putting it off all summer

Safer... sure. Effective... not really in my experience. Unless you have a massive leaking issue (not likely) then the very minor water amount getting in isn't going to have much of an affect. On the other hand, the problem with a leak is that the mix is lean. Adding even a little more combustion will show an improvement in running and change the rpms. Never had water make a change by it being sucked in (yes, I've tried just to test it...). The only way I was ever able to notice a difference with water, was to use enough that it actually reduced the air flow as a temp plugging of the leak. That didn't really narrow down where the leak was because of the amount of water being used was everywhere.


The reason a flammable spray isn't a problem is because your using very small amounts, that evaporate quickly, and most of suggested options are not going to leave a residue. For example, isopropyl alcohol... ( rubbing alcohol in a spritzer bottle) is a great example of clean, safe, simple test medium that is easy and cheap to come by.


Note... don't spray gas... that would be dangerous as the fumes do not dissipate easily or quickly and will create a dangerous situation. But a starter spray, or simple alcohol will.


Just my experience....


Krey

[Phantom552]

Finally got some wrench time on the bike, sprayed carb cleaner all over carb boots/ intake boots/ vacuum hoses /top port caps-- no change in idle. I'm going to assume at this point the carbs are out of sync since I'm not sure what else it could be.