Choke trouble

[TommyTheGun]

Hi,

I have beem having trouble getting the choke to work properly on my nc30. It sounds like it is flooding the bike it just dies. It has been an ongoing problem since i got the bike back in October. I have recently taken the carbs off and given them a good clean with carb cleaner, checked float heights and installed new seals in the pilot screws. Emulsion tubes and needles are in the correct carbs. I have the hole in the slider driled to 2.25. I am running 115f and 118r and pilot screw out 2 turns. I checked the choke is opening and closing properly but still having the same problem.
The bike will start with out the choke as long as i blip the throttle a bit, but when the bike is warm if i apply choke then the choke will work and the bike will sit at 3500 rpm.
Also when warm the revs seem to hang a bit and dont go down as quick as they should.
I dont know what else to try any help appreciated.

[CMSMJ1]

Sounds too rich - basically. SO, hows about smaller main jets? Or a clean and OEM air filter?

[TommyTheGun]

I put a new filter in it in december. Did used to have 118f and 120r with screw turned out 2.25 to suit an after market can but i was getting black speckles all over the number plate and back lights and bike would start no problem without choke of even blipping it. This has stopped with the smaller jets and screw in a bit. I had heard tho that the size of the main jets only effect wide open throttle.

[Malc]

Does the hanging revs not usually indicate an induction air leak? Are the carbs properly mounted in their rubbers?

[TommyTheGun]

I will check that tomorrow, bike runs fine when on the move apart from that and idles ok when up to temp.

[Neosophist]

Does the hanging revs not usually indicate an induction air leak? Are the carbs properly mounted in their rubbers?

either air leak or lean.

given the bike id say air leak is most likely.

[TommyTheGun]

I checked the carbs tonight and they ar definitely down as far as they can go on the rubbers. Looks like i'll be needing so e new screws soon for the clamps that go round the rubbers as the heads are getting rounded quite bad but they are all tightened up. I have wound the pilot screws out to 2.25 turns. If that fails then maybe i'll be needing new rubbers for the carbs.
I had replaced the seals in the tank fuel tap during the winter, usually when i take the tank off i have the tap turned off and get a small dribble of petrol when i take off the hose which stops eventually. Tonight i forgot to turn off the tap and the fuel was gushing out unrestricted. I took the tap apart and worked out i had installed the larger diaphram backwards so put it back together the right way and it now works as it should, only tried it off the bike hopefully it works on bike too.
Would the fuel tap problem have been causing the choke problem?

[TommyTheGun]

Started the bike today no change, choke will only work a bit once the bike is warmed not at all when cold. When warm sits at 3500rpm for a few moments then rpm drops down until bike cuts out. Only way it will sit at 3500rpm is if i roll the throttle a bit up to that point then let go then the choke will work for a bit.
Would the sliders being drilled to 2.25 affect it at all?
Or could they make the rpm drop slower?

[Malc]

When the engine is fully warmed up to normal working temperature, what is your tickover set at?

When warmed up, pulling the chock will increase the revs, then it will die cos its being flooded with extra fuel. This, if nothing else, proves your choke circuit is working.

Drilling the slides improves throttle response, so discount that as an issue.

Are the carbs clean, insides properly clean? Has the bike been sat a good while unused? I would think its a good idea to take them and get the ultrasonically cleaned as it sounds like some of the very small air and/or fuel channels in them may be blocked/restricted.

[TommyTheGun]

Malc i gave the carbs a good clean with carb cleaner but havent had them ultrasonically cleaned. I found out yesterday that the back left cylinder is not firing at low rpm but bike goes ok at higher rpm. Confirmed when starting the bike the exhaust pipe from that cylinder not getting as hot as the others alough the spark is sparking and have also tried another coil to be sure. Plug not showing any signs of flooding.