gsxr600 idle

[chassisMAN!]

hey guys,

small problem, here is some background.
-our first car.
-we're prepping it for FSAE west.
-running a '02 gsxr600 with power commander
-custom 4-2-1 exhaust.
-all the stock sensors are being used.

now, the engine runs fine with the stock (twin butterfly) intake, revs beatifully and sounds fantastic.


For the new intake we're using one stock throttle body, complete with the electronic butterfly(and all sensors,tps, map...) and the cable actuated one. this leads to the venturi style restrictor and then in to an aluminium intake manifold (5" dia x 13" long). From here all the air is fed into a 4 stripped intake pipes (all holes sealed) and the stock fuel injectors are in place. the engine idles ok( a bit rough) for the first few seconds, then tries to fix its idle and start to pick the revs up very quickly. i've killed the power each time cause i dont want it over revving. any ideas on what may be causing this and how to fix?


sean

[Pete M]

What is your initial throttle opening? Typically teams adjust their idle rpm by varying the throttle opening at idle. If you've got too much air there, it'll idle pretty damn high. The initial normal but rough idle is likely temperature related. If the engine isn't tuned perfectly, it can take a bit of running before it sits at its normal idle rpm.

There are other methods of controlling idle though, such as ignition timing. There was a thread about this a while back.

[Kirk Feldkamp]

You still have an electronically-controlled butterfly in there and functioning? You should check the rules on that one. I have a feeling the rules committee people will flip out over that one.

Having had this problem before myself, it sounds like you have a leak somewhere in the intake system after the throttle body. If it can't be controlled by your low throttle stop position, then that's almost certainly the culprit. It doesn't take a big hole. Try sealing up the whole thing at both ends and blowing air out. Sure it's the wrong direction, but you can probably find the leak pretty quickly that way.

Also, having done this exact intake setup about 4 years ago on a 2001 GSXR600, are you 100% certain the "sealed holes" where the TB shafts used to be are still there? I sucked one into the motor on the dyno because it wasn't in there well enough. The final method I settled on was running a tap through the shaft bore and then JB Welding the holes shut. You MUST use something that hardens up really well (think 2-part anything) or else the engine vacuum will suck it right in.

Let us know what you find.

-Kirk

[Kurt Bilinski]

Originally posted by turbotwig:
Having had this problem before myself, it sounds like you have a leak somewhere in the intake system after the throttle body. If it can't be controlled by your low throttle stop position, then that's almost certainly the culprit. It doesn't take a big hole. -Kirk

What he said - a vacuum leak.

[Jersey Tom]

Slightly unrelated, but that seems like a mighty big plenum volume. How is your throttle response?

[Kirk Feldkamp]

Probably tough to tell if he can't get it to idle yet. http://fsae.com/groupee_common/emoticons/icon_wink.gif

-Kirk

[Mark TMV]

Throttle response is actually pretty good and the car is very driveable. It just doesn't want to idle. That's about all I know, I don't deal with engines.

p.s. everything is BIG on this car...<sigh>

[Kurt Bilinski]

Just keep in mind what you've got. You have a car that idles fast - that takes air for it to happen. If your throttle plate is really closed (is it?) than the air's getting in somewhere else. As was suggested above, remove the intake manifold off the car as an assembly, and blow air into it. Sure as sh!t, you're going to find how air's getting in.

[chassisMAN!]

The plenum is actually 4" in diameter, so its a bit smaller. After some tweaking the throttle response is ok at very low rpm and may also be a cause of the rough idle. At anything above 3.5K this thing just seems to rip! it pulls really strong past 12K. I have a throttle stop, and that is set to keep the car around 3K, when its nice and warm and in a good mood, the car will actually idle at 1000-1200rpm.

when I plug off the intake, the car dies immediately, so im hoping there isnt a significant leak, if any.

for the secondary butterfly, it is actually before the restrictor and the mechanical butterfly. it helps the driveability a bit. I can run the car no problem without that now. so if needed can just unplug it.