2 annoying niggles, CBR400 NC23

[Billing]

Hi all, my CBR has 2 small problems which don't seem to be particularly damaging, but are annoying all the same.

1- When starting from cold (i.e left overnight) the bike fires up fine, but will die if you don't hold the throttle open a little. This happens no matter what the position of the choke, I know the choke is working because I had to use it a week or so ago. This problem goes away after literally 5 or so seconds, and the bike will idle happily after this point, it also doesn't happen if the bike is slightly warm (i.e left for 15 minutes) What could cause this, and what can I do to fix it please?

2- After I changed my exhaust system last monday (mild steel was changed for stainless) I have noticed that there is a metallic rattling coming from the bike. This happens at 5k to 6k, in any gear or neutral, with the throttle on or off. I have been told that stainless systems can sometimes do this, and not to worry too much, is this true? If not then what should I be looking for? I have been all over the bike making sure things are tight, and so far I haven't found anything loose
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'84 TS50X, '91 TZR125, '89 CBR400RR, '91 VFR400R NC30, '98 R1
"Hey copernicus! Why don't you navigate yourself to the back of the line with your feet and stand there with your shit."
BCF Eastern members map here ---> g.co/maps/2tm8b PM me to be added to it!

[DrDonnyBrago]

[Billing]

nothing is loose or touching, so a bit confused as to what it could be. 100% not possible it could be the CCT, it doesn't have or need one!

cam gears ftw
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'84 TS50X, '91 TZR125, '89 CBR400RR, '91 VFR400R NC30, '98 R1
"Hey copernicus! Why don't you navigate yourself to the back of the line with your feet and stand there with your shit."
BCF Eastern members map here ---> g.co/maps/2tm8b PM me to be added to it!

[temeluchus]

Carburettors could probably do with attention. If the bike is more than ten years old they will have wear and perished seals.

If anything is worn in the choke circuit it simply wont work as well.

As for rattling, you'll simply have to check everything that you may have moved whilst fitting the pipe. Sure everything is done up nice and tight? Was anything resting against the stock pipe or one of its brackets that isnt supported now?
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Some shite cruiser. Now with guns and FREEDOM!

[Phoenix]

I would suggest your poor idle issue might be down to slightly blocked pilot jets, if the bike has been sat for any length of time, it's quite common in older 400's with gunged up carbs. You'd have to take the float bowls off to remove and check them (make sure the passageway through them is clear) but its' worth doing as you can check the main jets and the floats and float valves at the same time, all of which can suffer on a 20 year old bike.

Your exhaust rattle may be a loose baffle inside, if you look down the end of the exhaust with a torch you may be able to see some of the mesh type metal lining has come loose (while the engine is off obviously), or you can just poke a cane or something down there and have a gentle tap to see if the baffle rattles when you tap it. If it is that then a welder may be able to do something temporary but ideally you want a new exhaust or to cut it open and fix it properly.

[Grimnir]

Billing - I can't really offer much advice in this case, but could you clarify something? You present two problems - did they occur at the same time? i.e. did your choke problem start when you fitted the new exhaust or did you have this problem before? I'm thinking along the lines of back pressure / breathing etc. Although you didn't mention which system you went from / to. Still wouldn't mean a whole lot to me but it might mean something to other BCFers.

[Freaky_1]

As for the rattling, I've SOMETIMES had luck getting the bike warm, loosening the exhaust and retorquing them.

[Phoenix]

Actually, some bikes are supposed to have copper crush gaskets on the exhaust headers, are you sure they didn't come out with the old exhaust? You'd be able to isolate the noise to where the headers bolt on though if that's the cause as it's fairly obvious.