Nc30 misfiring, help

[nc30chris]

Guys, getting towards the end of my restoration project nc30, but I have a fairly major issue. When the bike is cold it misfires like a bitch, will start easily enough but when you attempt to pull the throttle it tries to die, once it's warmed up for a few mins, it will then rev right up to max but you can still hear it misfiring. It's got new plugs and I did the carbs a while back following the guide on here. There isn't much fuel in it,but I run it on the reserve setting, it doesn't seem to make any difference if I remove either of the rear ht leads from the plugs, sounds exactly the same! Seems better when warm but still not right, anyone have any ideas?? Haven't tried pulling the front leads, next thing to try I guess, any help would be appreciated.

[nc30chris]

Quick update, tried removing the front leads also and still sounds the same, now she's warmed up a bit it seems loads better, the idle is all over the place, so I'm guessing I need to balance the carbs, but would out of balance carbs cause really poor running from cold?? Bit lost where to go next and ideally don't wanna chuck money at stuff that might not fix it, but now it's warm it runs ok, just idles crap.

[bikemonkey]

Balancing the carbs is a good idea.

Have you changed/checked any of the settings in the carbs?

[nc30chris]

well when i got the bike it was in a really bad state, been stood outside for a few years, i got it running before i stripped it, and it misfired and ran really rough. i stripped and cleaned the carbs, and did the few small mods in cammo's giude, after that it seemed to run better but still a bit rough, i then barely touched it for 5 months and didnt start it, next time i tried it wouldnt go just turned over and over, put new plugs in and it fired up, ran rough as hell for a few mins then after that seemed to run sweet, left it running a while, then re started it again later and seemed fine, again left it running till it came up to temp.. but been away for a week, started it when i got home and again, ran really rough, started on choke, no throttle as always, it did however start on the button, but as soon as i tried to blip the revs,it tried to die, after a few mins of sounding rough it would then rev, again not sounding brilliant. switched it off. went back a while ago to see if the front leads would make a difference, and it started on the button and ran lovely, idle is quite up and down, but seems loads better when warm. im toying with the idea of getting rick oliver to babance the carbs and do the valve clearances, just really wondered if anyone had suffered similar symptoms.. sorry to run on but i wanted to put as much detail in as i could.

[bikemonkey]

Put some paragraphs in there, hard to read.

Do you know what jets are in the carbs?

Did you set the float heights?

It's also possible that in the 5 months you left it that the carbs will need cleaning again. I'd advise ultrasonic cleaning as it's the only way to get them completely clean.

[trevor1]

I had the same issues recently with my bike but much worse.It wouldn't rev when cold or even when it warmed up.

I cleaned the carbs,changed coils,ht leads and new plugs.Still had a problem.

then i stripped carbs again and checked float heights and 2 of them where only 3mm instead of 6.8mm.

I was also running the bike without the airbox or filter fitted.some one advised me to put everything back together,which i did.

Bike is running sweet now.Hope this helps.

[CMSMJ1]

Is it complete? Speedo, air box and has it ever worked?

[Neosophist]

check all 4 pipes are warm first (spray some water on them dont toch them)

if one is slower to steam than the others you have a non running cylinder.

as above really though, airbox needs to be complete and filter in, no vaccum leaks, carbs all adjusted and set properly.

the Japaense bike will misfire after 5500 rpm if you dont have the speedo plugged in (or a speed limit remover installed)

[nc30chris]

thanks for the advice guys, it was almost a year ago that i did the carbs on the bike following cammo's guide, looking back on it i dont think i did anything with the float heights, as this wasnt listed on there and at the time i was new to bike carbs! so i guess thats a good place to start, is there a guide on here that states how to do it? as i dont know where to start. also thinking about replacing the float valves at the same as they seem to cause problems.

[bikemonkey]

The haynes manual has how to set the float heights, do a search on here too for a float height setting tool you can make out of an old credit card.