Annoying idle problem

[Banditmax]

Right so i come home for easter and think ill take the bandit out for a spin. All is going well although everytime i come to a redlight or junction and let the bike idle for any extended period it sits nicely at about 1800rpm then just gets slower and slower and cuts out. So i get home after many uses of choke thinking its been stood for a while so i'll have the carbs off and ultrasonically clean them. Did that and set the float heights etc. Its had new o rings, float needles, needle jets and a factory pro ti carb kit so thats the carbs really well ruled sorted i think. Put them back on the bike fire it up and take it up the road still the same problem. So then i think maybe it's electrical so i get a set of new coils and a new reg/rec oh and a horn but that came free with the reg/rec. So i fit the coils and reg rec and go through the whole bike cleaning up the electrical connections and making sure there tight. And then again take the bike up the road and still the same thing when i let the bike idle for a while. So now im getting really baffled but i remembered my cam chain maybe getting a little bit worn so i order a new one with rivet link fitted that yesterday timed the cams spot on and set all the valve clearances so its all good there. Whilst the carbs where off again i gave them another quick clean just to make sure they are really clean. And then i take it up the road again. Its improved now but still if left for a minute or so the revs drop back and it stalls needing choke to fire it up again. Having done all this im starting to think ill play with the fuel screws but no matter what i seem to do with these it still cuts out when left to idle for a short period. Has anyone got any ideas on what else i can try doing? This one really is confusing me.

[PitterB4]

Wow!  That's a lot of work in one week!

It sounds to me like it's starving for fuel...  When it's at idle it's not sucking enough vacuum to fee the carbs.  Partially blocked vent?  Next time it does it, open the tank and see if you get a suction sound.  Could be a kinked fuel line or partially blocked-up in-line filter?  Anyway, my bet is on not enough fuel getting to the carbs.  The other way you could check is next time it stalls out, see if you have any fuel left in the bowls.  I'll bet they're dry or close to it.  From your description of needing the choke to restart, I'm guessing it is difficult to start.  I'll bet that's because you're priming the carbs from being dry.  Good luck!

[Banditmax]

Ahh it might be the vent. Inline filter is clean though checked that already. I tried running it on prime all the time to make sure the tap was working properly but that made no difference. Unlikley to be the vent though as it pulled 120 up a slight hill this morning

[mademiriam]

wrong thread...i don't think i should get up on sundays 

[txbanditrydr]

lets face is the majority of people on his show can't afford to pay him and are probably there for the catered food trays backstage 

 

[magicGoose]

Sounds like you checked everything.
Although you replaced the reg/rect maybe try measuring the voltage at idle?

[Banditmax]

Checked voltage at idle too to make sure. Only reason i got a new reg/rec was i saw a gsxr6000 2006 model one on ebay with bracket and horn for £10 and i thought well thats a bargain worth having. Fits on fine and works like a dream. The coils i fitted where from an 06 650 bandit which only had 1000miles on the clock but also have the same primary and secondary as the 400 was meant to have and they where only £25.

[pmackie]

So...if I understand you correctly, the bike seems to run fine during normal operation, but once left to idle, for more than a minute or so, it looses rpm, then stalls, and needs the choke to restart?

I would have said float height, but you have already checked/set the float height.

A couple of other things to check:

1. A slight vaccum leak around the carb manifold to head connections, and/or the manifold to carb connections. Usually this would cause surging at idle as well.

2. Air screw adjustment. I would richen them up somewhat. Not sure which way that is on the 400 carb screws.

3. Sync the carbs. Maybe they are not all set correctly. This shows up most at idle and small throttle openings. This along with air screws can make a noticable difference.

4. How's the compression? Low compression on one or more cylinders might be causing less vaccum.

[Thief400]

A couple of things that I can think of are as has been said before a small air leak somewhere. Also check the pedcock and makesure it's working. 1800 rpm is a little high in the idle department. never set mine over 1450

[Banditmax]

Yeah when it was set lower than 1800 it was stalling even quicker checked the petcock and all around for air leaks with contact cleaner. And no difference then wound the fuel screws out 1/2 a turn to 2.25 as most people with the same ish parts as me use and decided id go for a long 200 mile ride. And miraculously when i return home i think this is idling a bit fast so wind it to about 1400 and let it set and it's idling away fine for a good 5 minutes so whether it was the fuel screws or just the long run that did it i dont know but all seems to be ok now hopefully. Cheers for the ideas guys.

[Thief400]

It wasn't the ride, you were really lean, if you where just a little lean the idle would hang up high like say 2500 if you revved it up and slowly come down . If it's a lot lean then it just stalls out. Glad you got it sorted out