running rich question (06 GSXR 750 stock)

[maddstork]

Hey guys here is a good one for you to bust your brains over. I am running rich on my second cylinder. I know this from my spark plug and the smell. I have changed spark plugs and switched around the coil and same problem. I am wondering if it could be the injector. Thing is there are two per cylinder right? Anyone have any suggestions what it could be? I used to be able to get 120 miles per tank until my light comes on, now I can just get 100 miles tell light is on.

p.s. When I start her up it has to turn over longer to fire or I have to give it some throttle. It use to fire up instantly. But after being warm the start is a lot faster and no throttle needed.

[earz]

Correct, two injectors per cylinder. Primary injector and secondary injector (flows more for higher RPM). Normally, an injector will fail or get plugged up resulting in a lean condition.

I'm assuming you replaced the plugs and used the proper heat range and type of plug recommended by Suzuki. I'm also assuming that you have been using a sufficient octane fuel and running the engine to operating temp before shutting it off (short run times can mimic a rich condition).

A rich condition can be caused by:
1) too much fuel
2) not enough air

I'd start by replacing your air filter (or cleaning if it's a K&N or BMC). Ram air bikes get dirty filters very quickly due to force feeding dirt into the airbox. If your filter is really dirty, I'd guess that will fix your problem. If it's only slightly dirty, there may be other causes. Check to make sure the ramair tubes are not obstructed.

Not knowing the mileage of the bike, one other thing to consider is valve clearances. If the valves are tight, the valve doesn't close all the way, which results in incomplete combustion, which results in not all the fuel being ignited, unburnt fuel deposits on plug and exits thru exhaust, etc. A valve clearance issue can affect one cylinder or all cylinders. If your air filter is really dirty, it may cause premature wear on the intake valve faces by sucking dirt out of the filter and into the engine.

Let us know what you get figured out.

[earz]

For those not familiar with valve clearances and adjustment on sportbikes, I found this illustration which is very informative. Enjoy.

[ryoung57]

D, how would any issue with the air filter only cause a single cylinder to run rich? I would think it would have to be an issue with the individual injector and/or valve.

[earz]

It probably wouldnt affect just one cylinder, but they may all be running a little rich and just #2 is the worst. This could be caused by a number of things (valve clearance, lower compression on one cylinder, improper plug gap, plug not tightened completely in cylinder, throttle body sync (or lack thereof), etc.). I'm just throwing out suggestions on a few things that I would check without actually seeing the bike. You'd be amazed at how many bikes have not been properly/regularly maintained. No matter what the problem is, with a dirty air filter it will never be able to be tuned/diagnosed properly. Kinda like trying to adjust carbs to run right when there is water in the fuel. It'll never run right. The air filter change/clean is a starting point to begin the diagnostic process, but may actually remedy the problem.

[desmo2]

Dustin, I bow to your motor smartness. You da man.

[04StretchedGSXR]

if you think it is your injectors Russ at Russ Automotive in Millersburg will flow them, clean them, and put new o-rings on them for 25 dollars an injector. You would be suprised at how fast they can clog up.

[maddstork]

This actually began before the plug change. The filter is clean too. Do you think it could be from a misfire? It does seem to idle a little odd when cold then seems to smooth out when it warms up. Thanks for the diagram about the valve clearance. Ill be sure to check into that.

[earz]

Another member here suggested checking if the injectors are bleeding down. Some of the early FI bikes (CBR600F4i was bad about it) would allow fuel to bleed through the injectors, effectively flooding that particular cylinder which would cause that cylinder to run rich. To check it, you need to remove the airbox, but leave the tank/fuel pump hooked up. While looking down over the throttle bodies, open the butterflies (may have to do by pushing them with your finger as the throttle cable will not always open them fully without the help of servos). With a paper towel, dry any residual fuel/moisture off the walls of the throttle bodies. Now, turn the ignition on until the fuel pump stops running. Turn off an repeat a few times. This will build pressure in the fuel rail and if an injector is bleeding, you will see it running down the walls of the throttle body. This may not be the cause, but it's something worth checking out. Keep us posted.

[earz]

Originally Posted by maddstork

Thanks for the diagram about the valve clearance. Ill be sure to check into that.

Not knowing how comfortable you are with tearing into an engine: checking the valve clearances is one thing, but unless you are totally confident in removing/reinstalling/timing camshafts and have the appropriate sized shims, I would leave the actual adjustment to someone else.

And...in case you don't have one, here's a service manual to guide you. Valve adjustment starts on page 2-7.
http://www.servicemanualsgsxr.com/75..._K6-K7.pdf.zip