Losing 1 cylinder at idle...

Just fired up my bike from a little over 8 years of storage. Pulled the carbs and cleaned inside before attempting first start.

Bike seems to be losing at least 1 cylinder at idle. If I use the choke, the cylinder(s) comes back... Am I correct in thinking I'm not getting fuel to that one cylinder at idle? If so, what fixes that? Need to remove and re-clean carbs or will I be able to ride with Sea Foam and get it to auto clean? Are float level or clogged pilot jet possible causes?

Can't tell if the cylinder comes back with choke because of fuel, or because the engine rpm's increase. Just off idle, all cylinders fire pretty consistently.

Would a weak coil cause similar issue with reduced voltage at idle vs. when engine is running faster? I appreciate this would kill 2 cylinders, not one. Not sure how many I'm losing, definitely big difference when they kick back in.

Assuming this problem is present after the engine warms up; check to ensure your carb holders aren't leaking. If they are, the air/fuel mixture at idle speed will be wrong (lean) and the cylinder(s) with the leaky carb holder(s) will fire erratically or not at all. Let us know if you need instructions on how to test carb holders (it's easy). Ed

650ed wrote: Assuming this problem is present after the engine warms up; check to ensure your carb holders aren't leaking. If they are, the air/fuel mixture at idle speed will be wrong (lean) and the cylinder(s) with the leaky carb holder(s) will fire erratically or not at all. Let us know if you need instructions on how to test carb holders (it's easy). Ed

Carb holders the boots between engine and carbs? Problem does seem better after warm up, but still there some.

LukeMacPU wrote:

650ed wrote: Assuming this problem is present after the engine warms up; check to ensure your carb holders aren't leaking. If they are, the air/fuel mixture at idle speed will be wrong (lean) and the cylinder(s) with the leaky carb holder(s) will fire erratically or not at all. Let us know if you need instructions on how to test carb holders (it's easy). Ed

Carb holders the boots between engine and carbs? Problem does seem better after warm up, but still there some.

Yes; those are the carb holders. You can test them by letting the engine warm up, then turn the idle knob down as far as it will go without killing the engine (you want the idle real low for the test), then spray carb cleaner around the joint where each carb holder attached to the cylinder head. If the carb holders are leaking (letting the engine suck air between the holder and head) some of the carb cleaner will be drawn into the engine. If this happens, you will notice an immediate change in the idle speed . When mine were leaking and I performed this test the engine stopped immediately. If you find they are leaking the best bet is to replace them. Also, make sure the clamps are tight where the carbs enter the holders.

If the problem you describe only happens when the engine is cold, and if as the engine warms up all cylinders fire smoothly without the choke, you may simply be noticing the cold blooded nature of these bikes. Mine has always needed the choke on to start it when the engine is cold, then the choke reduced as the engine warms up, then the choke shut off after the engine is warm (it takes a couple minutes depending on the outside temperature). Ed

Thanks. I'll be checking valve clearances and removing the broken piece of my tach drive. If clearances are ok, I'll try the carb holder leak test. If not, I'll have a wait a bit so I can get correct shims.

May be that I just haven't let it warm up enough. I'll post back once I've had a chance to get things checked out.

Thanks again,
Luke

Take a multimeter and check the sparkplug caps, they unscrew from the sparkplug wires. 5000 ohms is what they should test at. www.z1enterprises.com sells new ones & most motorcycle shops carry them too.

Thanks, I'll check that too.

When you "cleaned" the carbs, did you squirt carb cleaner thru the pilot jet passage in the carb, and visually confirm its flow by watching it fire into the carb bore?

Sounds to me like you have a clogged pilot passage in a the carb itself.

If everthing worked fine put away, its something thats been added to the equation - like fuel grunge plugged up in that shit.

Good luck!

Pull pilot jet. Squirt cleaner up there. Watch it come out all small holes in carb bore. Done.

LukeMacPU wrote: Just fired up my bike from a little over 8 years of storage. Pulled the carbs and cleaned inside before attempting first start.

Bike seems to be losing at least 1 cylinder at idle. If I use the choke, the cylinder(s) comes back... Am I correct in thinking I'm not getting fuel to that one cylinder at idle? If so, what fixes that? Need to remove and re-clean carbs or will I be able to ride with Sea Foam and get it to auto clean? Are float level or clogged pilot jet possible causes?

Can't tell if the cylinder comes back with choke because of fuel, or because the engine rpm's increase. Just off idle, all cylinders fire pretty consistently.

Would a weak coil cause similar issue with reduced voltage at idle vs. when engine is running faster? I appreciate this would kill 2 cylinders, not one. Not sure how many I'm losing, definitely big difference when they kick back in.

What model/cc size bike do you have?

1975 Z1
www.kzrider.com/forum/10-new-members/496984-new-in-indiana
www.kzrider.com/forum/11-projects/498857...n-the-road-hopefully

Including information about bike year and model is helpful to viewers and usually elicits better responses.
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Good Fortune!

Maybe I missed it (getting old) but I didn't see any mentioning of carb sync... Possibly this one carb is so out of sync that it requires the choke to even register....

Just a thought

Here, pretty much for all KZ OEM carbs...

KZ Carb files complete

VM Carb rebuild & tuning

BS Carb rebuild & tuning

Carb Identification & Jetting

Old Man Rock wrote: Maybe I missed it (getting old) but I didn't see any mentioning of carb sync... Possibly this one carb is so out of sync that it requires the choke to even register....

Just a thought

Here, pretty much for all KZ OEM carbs...

KZ Carb files complete

VM Carb rebuild & tuning

BS Carb rebuild & tuning

Carb Identification & Jetting

AH YES -good info, but remember!

Check compression first! - A bike with cylinders too far off compression like 15% or more, can actually run poorer off idle with a vacuum sync, than with a really accurate bench sync!

Cheers.