Z650 running on 3 cylinders - could this be anything other than carbs ?

Hi, hopefully someone more knowledgeable than I am can help with this one !

Z650B1, running on 3 cylinders but not number 2. Dyna coils & ignition (the ignition unit very recently replaced), S&B air filters (fit to outside of back of each carb, not those awful push-ons that can block airways !)

Compression test is within spec and virtually identical on all 4 cylinders.

I've changed all 4 spark plugs for new ones, and done a bit of swapping around on the off-chance that one is bad. Number 2's new spark plug looks clean and unused compared to the others (which I guess tells me it's either not firing, or fuel isn't getting through).

I've rebuilt the carbs several times over the last year or so; we seem to have a real issue with the quality of fuel here in the UK (I'm using E5 with a fuel stabiliser, to stop it going off after about 2 weeks).  It usually seems to be cylinder number 2 that gives me problems !

So my first question is; am I right in thinking that if I had an electrical problem with the ignition or a timing issue, it would affect numbers 2 & 3 equally ? Is it even possible to not fire on number 2 but still fire on 3 ? 

Assuming that is correct, is there anything else anyone can think it could be other than either a vacuum leak in the inlet rubber or a carb problem ? What else could I be missing ?

Thanks !

i bought a KZ1000A model a number of years ago.  The bike ran on three cylinders and I fiddled with all those things you mentioned.  Ultimately, I pulled the head and discovered that I had a galled (stuck) exhaust valve on the cold cylinder.  The likely culprit is usually simpler than what I went through, though.

Something I would suggest is to move the spark plug leads on #2 and #3 and see if the issue follows the lead that had been on #2. If it does then the issue is not with the carb, but with the coils/leads.

The other thing I would ask is just which carb set you have. Some were pilot screw only, some were air screw only and some had both types of screws. 

Agree swop plug leads 2 & 3 over if it follows the lead then it's not carbs.
If it does follow the leads then check connections both ends of the ht lead. Cap to lead, lead to coil. 
Both sides of a coil use the same windings but the circuit does split to provide power to both leads. I have only once found a break after the split which meant one lead was live whilst the other was dead. So yes it is possible but its unlikely. 
My guess would poorly connected plug cap or knackered plug cap or knackered plug. 

Thanks for the replies !

Good idea about swapping the leads over - I'll give that a try when it's daylight tomorrow. They're the dyna leads with the integral cap rather than separate screw-on NGK type caps, which hopefully makes things easier.

The plugs are brand new, but #2 didn't work with both old and new plugs (even the old ones were very new), so hopefully the odds of getting two bad plugs that just happened to end up in the same cylinder are pretty low !

I thought it was time to come back with an update.....

After trying the suggestions and finding it didn't make a difference, almost by accident I spotted a completely unexpected problem. The reason it was running poorly and header pipe #2 was cold was because it wasn't connected to the engine ! One of the studs had snapped off halfway down and the header had shifted slightly so there was no backpressure into the cylinder. 

I really didn't want to have to take the top end of the engine apart and strip the head in order to remove a thread which has been nicely welding itself in for around 45 years, so I did a bodge. I took a spare collar and filed enough of a slot in it that what remained of the stud would take a nut and washer. Yeah, I know it's not ideal, but it worked !

With all four cylinders working, I was able to get it running reasonably smoothly and synch the carbs successfully.

Sadly, when I came to do the airscrews today, #3 stopped working, and fuel poured out of the overflow pipe. When I drained the float bowl, the fuel included a few tiny black specks, so I'm guessing these jammed the float needle and/or float. So it's time to take the carbs off, clean them yet again and try to work out what's going on.

This has been a constant issue over the last year or two. I've got a fuel filter on (which is pretty new, transparent and looks very clean) so I am starting to think that even with fuel stabiliser the ethanol in modern fuel is breaking down floats, fuel lines and anything else rubber in the carbs. Does anyone have any good solutions to this ? I'm guessing I'll have to replace every single rubber component yet again (mostly they are viton, but I really don't think it makes a difference), and maybe the floats as well.

Are there any bikes with carbs which would swap straight on that are modern enough to be resistant to ethanol ? I'm starting to think that persisting with the original Mikunis is just a road to endless trouble !


 

Any engine/cylinder will run with less or no back pressure or header/air filter box.

Sean I feel your pain! Not fun constantly removing carb sets. This said I have a 650b1 and a z1 but don't get the trouble you are having. This said I always run on the 5% (means up to 5% of course), ethanol, (best you can hope for in the u.k. unless your very lucky in where you live). I do however always drain tanks and carbs for storage but day to day in summer have no issues. Occasionally I am forced to use the 10%, when in Wales for instance, the z1 runs fine on it but does prefer the 5% stuff. I would suggest yes use a filter if your tank is not the best, I don't bother with them, check fuel heights using the Kawasaki fuel line to base of carb tool to get the levels spot on. Using a ruler I find is very hit and miss. Once fuel level has settled leave it for 15 min and see if you get any creep due to float valve needles not sealing properly. These can be lapped in with solvol if required, providing they are not rubber tipped. Check the springs on the plungers Non genuine carb parts can be an absolute pain, use genuine even if used. You can get viton bowl gaskets, I have them on the z1, use quality fuel line and replace if it shows signs of hardening, easy to do. You can easily get the O rings for the carb feed tees in viton. Also worth replacing the 'choke' plunger seals at the base of the plungers, this is often ignored, they harden and don't seal effectively even with non ethanol fuel and can cause no end of mystery problems! My biggest worry is not the rubbers but the brass parts and the carb bodies themselves, ethanol which when it attracts water will have a real go at these parts over time due to galvanic corrosion which is why I drain them down if not in use for extended periods. Good luck! 

Hi Dave,

Thanks for that ! I've done a lot of these things already, but I like the tip about letting the fuel level settle for 15 minutes to see if there's creep. I've even bought two of the fuel height plug & pipes so I could check the fuel height in pairs !

Choke plunger seals are on my "to do" list, but appeared in reasonable condition last time I stripped the carbs, but just in case, they were among the bits I didn't put in the ultrasonic cleaner !

I drain the float bowls each time I put the bike away - I'm starting to think about trying to rig up a rail under the carbs to link up all the drain plugs with a single tap ! The tank was recently fully refurbished and lined with an ethanol-proof liner, and I've used solvol lightly on the float valves and needles. I may use solvol on the float pins to see if that helps reduce sticking.
I am starting to wonder if the floats themselves are what is breaking down due to the ethanol, but replacements appear to be either cheap & nasty copies or made of expensive unobtanium.

But yeah, it's starting to get frustrating ! It definitely feels like I'm chasing my tail on this in a big way, I keep thinking I've solved the problem and then it happens again, but not always on the same cylinder. It even does it with a spare set of carbs I've got, pretty much the same symptoms, so I'm starting to look at real edge-case causes but I've got to the limit of my knowledge and getting nowhere ! The fact that it'll run well for a little while after each carb strip-down is what tells me it's the fuel system rather than electrical or ignition (both of which I've gone through with a fine toothcomb).





 

I see that you're in the UK and ethanol free fuel is probably not available. However you may be able to get some av gas UL 91 at your local small airport. Maybe a couple tankfulls could answer some questions ?  Here's a link on it , from France I believe. Good luck.
   aviation.totalenergies.com/en/fuels-and-...ion-fuels/avgas-ul91

Thank you ! Yeah, the best we can get at the petrol station is 5% ethanol (regular is 10%).

I'm not sure if local airfields will sell fuel to people passing through (we've got some pretty strict rules here), but I've heard from a tree surgeon friend that there are one or two garden trade suppliers that still sell good old-fashioned leaded petrol for chainsaws and other garden equipment that can't run on ethanol fuel.

Im in the uk also. In some parts ethanol free fuel was available until earlier this year. Both Shell and Esso premium fuels were ethanol free. There are now no source for automotive ethanol free fuel.
Your choices are either Avgas, horticultural fuel, or an ethanol treatment. 
Avgas, if you can get it, will be ethanol free but will be expensive and won't be beneficial in any way other than being ethanol free.  It'll likely be detrimental to the higher octane unless you have a tuned motor. 
Horticultural fuel (aspen) is available from any horticultural wholesaler but at about £5 per litre. 
The most cost effective solution is E5 fuel plus a fuel stabiliser to isolate the ethanol molecules preventing them from clogging and attacking rubber components. Normal stabiliser for road vehicles will keep fuel good for about 12 months. The marine varient will keep fuel fresh for about 2 years. 
Lastly, the storage varient will work for about 3 years. 
I use Stabil 360 marine in all my bike and never have any ethanol related issues.