Z1100 Shaftie idling on two cylinders

Hi all, My Z1100 shaftie is only idling on two cylinders, Nos. 1 and 2. If I remove the plug caps from No. 3 or 4 cylinders the idle does not change, if i remove No. 1 or 2 plug cap, the engine stops dead!
The leads for Nos 3 and 4 are sparking fine when I use a spare plug held to the cylinder head, so I am ruling out the ignition side of things.
I find it impossible to balance the carbs, if I get them near to balanced, the idle RPM are sky high even with the idle adjuster backed right off. I can only adjust the idle back down with the centre balance screw, but then of course the balance is right off song again.
So, when the engine has cooled, I am removing the carbs to see if i have a blocked jet or split diaphragm.
At the end of last year I checked the valve clearances and all were fine. The compressions across 1 -4 are 135,135,130,135 on a COLD engine,all well balanced and I would expect them to be higher on a hot engine.
Suggestions please.

Ride safe Doebag

You have multiple problems I think. The idle issue is due to air leaking into the pilot system somewhere BUT I would address the non-firing on 3 & 4 cylinder FIRST. The fact that 3 and 4 are not firing point to either plug wires or caps OR carburetor issues. First thing is to swap the 1 plug wire for the 4 plug wire and the 2 for the 3. See if the non-firing MOVES to the 1 & 2 cylinders. This will help eliminate electrical problems if the problem doesn't move. I know you think this is likely carb related but PLEASE eliminate the electrical first as no amount of tuning can fix bad wires or caps. Make sure that if the whole lot is resistor type, keep all of it resistor type (plugs, caps and wires) and if it isn't, keep it all non-resistor.

OK, If it is NOT electrical related as verified by the wire swapping, then you are not firing at idle. Since you have compression, you might want to remove the 3 and 4 plugs and place them next to the engine case and double check for spark. Then consider what could be keeping 3 & 4 from firing at idle. Remove the carbs and then bowls and pull out the black rubber plugs over the pilot jets. Remove the pilot jets and ensure that fuel flows through them by checking them carefully and/or spraying carb cleaner through them to ensure there is no blockage. Spray carb cleaner into the pilot jet hole and make sure it comes out inside the venturi via the small hole where the pilot mixture atomizes. Spray carb cleaner into the hole on the edge of the carb venturi linked to the pilot jet and make sure it comes out the pilot jet hole. I would also remove the FOUR needle seats and blow compressed air into the air inlet and make sure it came out equally in all four holes where the needle seats had previously been installed.

I can't think of much else to try at this point but I would definitely isolate the problem as I noted in my first paragraph before tackling potential carb blockage issues. I would also make sure that the petcock screen inside the tank was unobstructed as well as making sure a new fuel filter is installed. A low fuel flow when the bike is on side stand will cause the 3 & 4 cylinders to starve some as they are higher I guess.

Doebag UK wrote:

The leads for Nos 3 and 4 are sparking fine when I use a spare plug held to the cylinder head, so I am ruling out the ignition side of things.

Thanks for the quick reply, I will try to see if the problem moves to the other cylinders, but as you can see, I THINK the spark on 3 and 4 is OK.

Also the fuel tank is off the bike, I am running from a secondary tank with an in-line filter while I investigate.

Post edited by: Doebag UK, at: 2006/02/17 11:52

I wouldn't totally rule out ignition until you see the plugs installed in 3-4 sparking. I wouldn't use spare plugs to test the spark... Just my 2 cents.

Right, had the carbs off last night. I cleared all the jets , airways etc wth compressed air. Float heights are Ok, BUT I did find that the O-rings on Nos 3 and 4 Idle mixture screws were split. Could this be it. I have replaced them, and will refit the carbs this afternoon. Also one of the the rubber carb mounts was slightly loose on the cylinder head, not good either, so hopefully it will be OK now.
Is it a bad idea to use some sort of sealer on the carb mount to cylinder head join, it does not mention any in the shop manual, so guessing that a dry joint is the way to do it.

Since you didn't take the initial steps I suggested for your problem and went off in another direction, I will let someone else jump in here and help you. Good luck.

wiredgeorge wrote:

Since you didn't take the initial steps I suggested for your problem and went off in another direction, I will let someone else jump in here and help you. Good luck.

??????????

Anyway, I had already eliminated the coils ,plugs and leads by substitution, if that was not clear from my first post,:huh:
So the bike is running fine now, O-rings and No 3 carb mount to blame. Now just have to cure a slight oil leak from the front of the cam cover:angry:

Nope, not clear at all from your first post, all you said was that you had tried different plugs held against the cylinder, and that don't really tell you much. It takes a lot more power to create a spark in a cylinder under compression than it does in free air, so it's entirely possible (and common) for an ignition system to be bad and still get a spark when tested in free air. That's why the manual calls for resistance measurements at every step. And ~80% of carb problems are actually ignition problems, hence the advise to check the ignition first.

Disagree with Steve's assessment that 80 percent of carb problems are ignition related. If the customer has mucked around with the carburetors, the liklihood that the carbs are the problem is about 99 percent but if they have not mucked around with the carburetors, the ignition is probably the problem, coming in at about 99 percent bwhahahaha

When folks contact me for carb work, I like to explore problems they are having because if I rebuild the carburetors and they perform perfectly on my test bikes, and they STILL have the problems they had before, my business/services do not end up meeting their expectations and that is bad business! I have suggested doing the WG coil powering upgrade to MANY potential customers and never hearing from them again not to mention suggesting doing a tune up... carbs come at the end of the problem resolution chain... basic tune up and electrical first.