TOPIC:

Hi All.  So I was out on a lovely ride a few weeks ago when my bike started bogging down whenever I opened the throttle.  Basically, it would idle fine, but wouldn't go beyond that without choke.  It had been running perfectly for a long time before that ride and hadn't sat for more than a few days.  I assumed something was clogged in the carbs, so took them out and cleaned them thoroughly this weekend. Was surprised today to find the bogging/stalling problem is still there. I have a zr550 with Keihin cv32s. 
I cleaned the carbs thoroughly, including the pilot jets.  The only part I didn't touch was the idle screws just because I didn't think that circuit was relevant to the symptoms...but maybe it is? I suppose I'll go in one more time with the circuit diagram in hand but I guess I'm just wondering if that could really be it.  I did notice the spark plugs are pretty fouled with oil and I'm a bit worried there's something more serious going on - like worn valve seals letting oil into the combustion chambers. The bike does have ~75K miles on it, but as I said it was running great before.  It's also possible the oil was overflow from the crankcase breather. I think I overfilled the oil the last time I changed it.  Anyway, I'm open to any words of wisdom and/or encouragement. I hate it when my bike's not running. 
 

Having to use the choke certainly means you have a fuel starvation or air leak issue.
If you hadn't already check the carbs and the issue came on suddenly i would have said blocked pilots etc.
Have you tried riding with the fuel tap on prime as a split in the taps vac hose or faulty tap diaphragm can cause your issue.

I did try running on prime. Also replaced the in-line fuel filter and made sure gas was flowing. Neither had an effect. 

On the diagram below, I made sure the pilot jets (#2) were clear, and when I squirted carb cleaner in the orifices it came out of the pilot air jets (#5).  Does the pilot screw (#1) affect anything other than idle?  That's the one part of the carbs I didn't touch. 
 

The pilot circuit should have been cleaned. If they are blocked, the engine can be made to idle ok by raising  the slides a tiny bit with the idle adjustment screw. However, when the throttle is opened farther, the mixture will go very lean because main circuit is set up on the assumption that fuel is coming through the pilot jet. The pilot jet never stops flowing fuel, but it becomes less influential because it provides an ever smaller percentage of the fuel as more flows through the main.
With all of that, I am not sure clogged pilots by themselves would cause the engine to die, but in combination with another problem might do so.

Just brainstorming

Are all 4 plugs fouled equally?
If so, it's a global issue affecting all cylinders equally.
How's your air supply, charging voltage, fuel quality?

F64 wrote:

Just brainstorming

Are all 4 plugs fouled equally?
If so, it's a global issue affecting all cylinders equally.
How's your air supply, charging voltage, fuel quality?
 

I appreciate any brainstorming!  The middle two plugs are fouled. It's a pain to check the outer two just because I have a bunch of defenses set up to prevent crackheads from stealing them (I live in SF, stealing spark plugs is an annoying thing here). 
Air filter is clean and it's new fuel.  Haven't thought to check charging voltage, will take a look. 

Just looking at your signature.
Are you running pods and K&N's with your CV carbs?
Was it ever running ok if you are using pods?
Also, check your ignition timing at different rpms with a timing light as you may be still using the adjustable ignition module.
 

Success!!
I went back in and cleaned the carbs again like my life depended on it, paying particular attention to the pilot circuit.  To be honest, everything was already clean, but I did notice the o-ring on the idle screw of carb #1 had disintegrated.  Buttoned everything back up, started the bike and...wahwaaaa, the problem was still there as bad as ever. 
At least I knew the problem had to be elsewhere.  I ran the bike for a while and sprayed the exhaust headers with water. Turns out cylinder #1 was not firing.  
Last weekend I had pulled the middle two spark plugs and noticed they were fouled with oil.  I hadn't checked the outer spark plugs on cylinder #1 and #4 just because i have them super locked down to avoid crackheads stealing them SF.  But I took the time to dismantle my spark plug defenses on cylinder #1 and sure enough it was heavily fouled with oil.  Cleaned it up, put it back in and, voila!  She's running perfect now.  Unbelievable. 
I'm thinking this or something like this was the likely series of events: I overfilled the oil, excess oil made it's way up the crankcase vent into the airbox and into the carbs and both fouled the cylinders and spark plugs and potentially clogged a pilot jet or two. 
In any event, all's well that ends well, I'll be more careful about oil levels going forward. 
 

F64 wrote:

Just looking at your signature.
Are you running pods and K&N's with your CV carbs?
Was it ever running ok if you are using pods?
Also, check your ignition timing at different rpms with a timing light as you may be still using the adjustable ignition module.

No, I'm running the stock airbox (with a K&N filter). 
Thanks for the tip on ignition, was in the back of my mind when I decided to check for spark on all the cylinders. 

Good job!
Yeah, overfilling the crankcase can cause some fun things.
 

Well I guess I spoke too early.  The issue came back and I think at this point it's pretty clear there's something going on internal to the engine, most likely a blown head gasket or other seal (I do see oil weeping out the sides of the engine).  Maybe that shouldn't be surprising given the bike has almost 80K miles on it and I thrash it thoroughly and gleefully almost every weekend. I do wonder if overfilling the oil was the last straw. The good news is that this is an excellent excuse to overbore the engine during a rebuild and install some 615cc Wiseco pistons.  I've already started ordering parts. Will likely start another thread for the engine rebuild. 

Zaddict, 80k+ miles is a good innings!

If you're set on re-boring anyway, fine, do that!
However, a hone and a fresh set of rings could save you a packet, and future usable life of the cylinders...

My 1100 exhibited the same oily "symptoms" and upon inspection, the bores were good, the rings not so much! 
All I did was hone and fit new rings, and gaskets, and valve-stem seals while I was in there!

H.