No.4

[DavidZ1R]

Well guys, lost on this one, had a fault on slow running, got it down to no.4 cylinder, it does not fire on low revs , remove plug cap a few millimetres and it will pop and fire, put the cap back on, nothing, have swapped the coil, same, plug same, even plug cap just the same, I have a bald spot on my bonce from scratching it, say please any help to save may hair, what's left.

[warren3200gt]

No 4 pilot circuit fueling? Lifting the cap increases the resistance in the ignition line changing the spark which then reacts differently with the fueling issue???? Maybe?
I often had this issue, lifting the cap to get it firing and then replacing the cap sorted it. Thinking about it I've not experienced it since soley using Shell v power with Stabil 360 marine.
Interested to hear what others have to say..

[Hard Road]

what does the spark plug look like ? if its wet/sooty then it could be a float valve leak.

[DavidZ1R]

Not wet but it is sooty

[warren3200gt]

Not wet but it is sooty

That does point to a rich pilot mixture. With lifting the cap it weakens the spark which effectively leans the mixture and only partially burns the cycle load. With the the cap lifted are you getting any firing in the exhaust from unburnt fuel?

[Hard Road]

Not wet but it is sooty

if you have tried adjusting the mixture screw with no fix then time to check the float valve, if one has a small leak it will fill the float bowl up and cause an over rich mixture making the plug black and sooty, if its sooty it will cause a miss fire, but at higher speeds the extra fuel will get used and run on all 4. its the low side when it causes problems.

[warren3200gt]

Choke plunger failure?

[DavidZ1R]

Choke plunger failure?

Rob Meggitt did the plungers

[DavidZ1R]

Not wet but it is sooty

if you have tried adjusting the mixture screw with no fix then time to check the float valve, if one has a small leak it will fill the float bowl up and cause an over rich mixture making the plug black and sooty, if its sooty it will cause a miss fire, but at higher speeds the extra fuel will get used and run on all 4. its the low side when it causes problems.

Yes, at low speed it does run uneven, open it up and runs great, I will check the float level and turn in the fuel mix screw, see what that does

[Hard Road]

Not wet but it is sooty

if you have tried adjusting the mixture screw with no fix then time to check the float valve, if one has a small leak it will fill the float bowl up and cause an over rich mixture making the plug black and sooty, if its sooty it will cause a miss fire, but at higher speeds the extra fuel will get used and run on all 4. its the low side when it causes problems.

Yes, at low speed it does run uneven, open it up and runs great, I will check the float level and turn in the fuel mix screw, see what that does

it dies sound like leaking float valve, or your pilot jet has dropped out !!!!!!

[DavidZ1R]

Well I checked the fuel level, perfect and stable, no rise after 10 minutes, took the fuel screw back to seat, then out 1 1/4 turns , still the same, won't fire unless I pull the cap back a little, can't fathom it out.

[gray]

sounds like a drop the carbs out situation unfortunately, and check the pilot circuit and flush it it the direction of airflow + reverse flush it too from the venturi hole backwards ( bit more tricky)

[Gray17]

Hi thats exactly the same symptoms as my Z900 runs fine and pulls well on main jet, but slow running is terrible and after 30 or so miles soots both 3 and 4 plugs up, no smoke though, alway black sooty. Again like yours i had my chokes plungers done by Rob, but he also set everything up and it ran perfect for about 100 miles or so then started doing this. I can clean the 2 sooty plugs and bike will run reasonable u til they re soot then starts to misfire. Brand new B8ES plugs, tried a grade hotter one too still the same. Compression great and equal on all 4 cylinders.
I'm thinking same that something is causing issues on slow running side, so alas im going to have to remove carbs and as recomended reverse blow them out and re clean them again. My thoughts a small piece of dirt etc blocking the airflow orifice as the adjuster seems to do very little by way of altering it.
I Know Rob set float heights up and no over flowing now either so dont think its that. No settings have changed, ign spot on and advancing as it should too, so again unlikely. The only other possibility i can think of is if cylinders 3 and 4 valve stem seals are leaking and allowing oil in when running, they are new though and as stated no smoke so unlikely?
Be interesting to read your findings and solution too.

[zapo]

Silly but.......If your HT lead is long enough, maybe remove plug cap and cut a quarter inch off the end of HT lead to be sure that the plug cap to HT lead connection is not dodgy?

[Hard Road]

check the small air drillings at the airbox side of the carb, if an air jet is blocked on a carb it will effect the idle circuit and cause rich mixture.