Won't run

The fact that it runs for a few moments suggests a fuel issue. If you disconnect the fuel line from the carbs does fuel flow freely into a vessel? If not the fuel tank filter on the tap may be blocked. Similarly, when you reconnect the fuel pipe, turn the tap on and open up one of the carb drain screws does fuel run out freely? If not it could be stuck floats or float needle. You do not mention the choke. My 400NC won't start without choke and won't idle until the choke has been on for a few minutes. Of course all bikes are different. If it is not a fuel issue my bike would not rev and it was a faulty CDI unit.
Dennis

daft question, are the choke butterflies stuck?

so mixture/pilot screws 2 out (I'm assuming 250?) its the black plugs that are throwing me a bit. did you fit new pilot screws with spring, washer and oring? are they in the correct order? did you carefully fish out all remnants of the old orings.

if all is good there I'd be suspecting the ignition system, test the stator first (rex's speedshop have good figures for that) if thats ok its worth trying a new coil, its obvious I know but make sure its got a really good earth, after that your looking at the cdi. easiest way to check the cdi is to fit a known good one, otherwise its send the whole kit and caboodle to a shop like rex's for testing. hope this helps

Hi thanks for getting back to me, all the parts in the carbs have been replaced and all set to the manual, the carbs were thoroughly cleaned sonic cleaned twice. Today i have had the stator checked out by a friend of mine who is an auto electrician and he said it is working fine,he also checked the coil and that's fine to, so tomorrow I shall pull the silencers of just out of curiosity thanks once again.

Don't know much about testing them myself, but you can check the advance is working with an ordinary strobe light and the Honda manual (download in 'Manuals' section) has a schematic which might help checking connections etc. Don't think anyone on here has posted a problem with the 250 CDI, unlike the 400 which quite a few have had to replace, including both my 400s, which now have Rex CDIs while my 250 is still running round on the original. Conversely, 250 carbs seem to give lots of trouble but I've not had any trouble from my 400's carbs  . Might be worth a look at the 'a new carb guide' up in the sticky threads at the top of this section

Have to confess, I didn't strobe test either of my 400s when they had running problems due to faulty CDIs. On my 400NA the fault was intermittent at first, started off ok then couldn't do more than 30mph for a few miles, then went ok again, but after doing this a couple of times, one day it wouldn't start - no spark. Pinching parts from my 250, I swapped the coil - still no spark, then the CDI - ran fine, Rex CDI no.1. When the 400 one went, it felt like empty fuel was running out, but I just stuck the 250 CDI in & it never did did it again, so Rec n.2. I used the strobe light many years before when my 400NA wasn't running right, no power & wouldn't rev and I had to limp home from work. Felt like carbs, so stripped & cleaned them along with new gaskets etc. No improvement, so bought a cheap strobe light from ebay & the advance looked ok, SI didn't think it could be the CDI. After trying each of these things & others I would take it for a short test ride - no improvement, until on one test I heard the engine knocking - big end had gone! Engine rebuild no.1. Didn't touch the carbs, coil or CDI during the engine rebuild, but once it was back together it ran fine. That was 15 years ago & I still don't understand what caused the poor running. Never touched the carbs since then & it many years later the CDI finally packed up.