VFR400 NC24 | Starting Issues

[Gregmeister]

Hi All,

Trust everyone is well,

I've recently rebuilt my NC24 and installed new pistons and rings, including most gaskets and other bits and pieces.
After battling incorrect cam timing, I've managed to get it correct and all is in working orders,

I also bought a pair of 2nd hand carbs from someone which was stripping their bike - The bike was running no problems, clean rev'ing etc etc. My carbs were giving me flat spots, leaking air and not playing ball, so decided to swap them out, expecting them to a "plug n play" type situation, but surprisingly not.

My old set of carbs didn't have a working choke, whilst the "new" carbs do - But I am unable to get it to start - Here is what I've done thus far in terms of troubleshooting and corrections:
- Fresh spark plugs - including checking for spark after a few failed starting attempts - Great strong spark present,
- Idle adjustment on Carbs reset back to factory - 2 full turns out from closed.
- Carbs cleaned, blown passages out with compressed air - checked and reset float levels - confirmed they were filling up by opening the bowl drain once they were filled with fuel,
- double checked the wiring to ensure i didn't wire any coils backwards,
- Purchased new intake rubbers - installed them without to much of an issue,
- Purchased a new air filter - installed as normal,

My starting process is as follows - full choke, no throttle, start - I get a few splutters and a low start, but once i stop pressing the start button it does - I have also closed the idle adjustment on the throttle linkage to increase fuel and decrease air - also opened the throttle slightly thinking it was over fueling.

Last but not least - i poured a small amount of petrol directly into the carbs, no choke, no throttle - Still nothing.
After all the above mentioned processes - I checked spark, and still getting great spark.
Plugs were slightly wet, but I would have thought they would have been drenched by the use of the choke and no throttle.

Can anyone suggest anything else? Jets are still standard - no aftermarket exhaust, no mods what-so-ever.

[Neosophist]

Hi All,

- Idle adjustment on Carbs reset back to factory - 2 full turns out from closed.

I have also closed the idle adjustment on the throttle linkage to increase fuel and decrease air - also opened the throttle slightly thinking it was over fueling.
.

you mean the pilot mixture with the first mention right.

secondly the idle speed ajustment is the one you can turn by hand, not sure what you mean by "closed" screw it in so the screw pushes on the cam more to open the carbs to give a higher idle.

with so many factors at play here its going to be very difficult to diagnose anything accuratly over the net without having somebody there.

new pistons? oversize or stock, why would you change the pistons?

did it ever run?

are the cams in the correct places (they are different), have you verified valve clearanaces and cam timing?

could even be something daft like your fuel vaccum pipe not connected so you have poor fuel flow to the cabrs (dummy tank will eliminate this)

compression tested it?

having done so much its a bit like a needle in a haystack.

youll need to really double check everything, somethings obviously not right..

starting seems ok, full choke no throttle, dont crank the throttle though, a few spluutters is a good sign, make sure your idle is turned up first and your fuel supply is ok...

[Gregmeister]

Thanks for the feedback Neosophist - I've managed to get it running and found the issues,

The 2 front cylinder coils were problematic - They didn't spark consistently - highly intermittent - I replaced those, replaced the plugs again, checked their gaps, also re-set the floats, found that 1 carb bowl wasn't filling completely due to a sticky float needle - lucky i had a spare close by.

Also - Noob mistake on my part - I forgot to close the vaccuum pipe which normally connects to the fuel tap, as I was running the bike without the tank on and had a little "make-shift" fuel bottle hanging above the bike. So the mixture was completely out.

Now that the bike is running, its idles around 2K - which is a struggle - doesn't sound healthy - almost wants to die - is their anyway I can combat this? any adjustments i can make?

Also - I am unable to get the bike above 10K RPM - the bike sorda goes into limp mode. A friend suggested my Cam timing is out? or my spark leads are leaking spark - How can i test for these suspicions? Although the rev is real clean from 3K to 10K.
Would adjusting the idle mixture screw to about 2.25 solve this issue of idling so rough?

Has anyone got any ideas as to how I can fix the leak I'm having from my Petrol tap? just as the toggle comes out of the tap and into the side of the tank for me to select, on/res/off - It leaks just there - is there a O-ring i can replace? I really dont want to pull it apart with a full tank unless I know what I'm in for,

Thanks in advance.

[Gregmeister]

Okay - So just a quick update -

Yesterday, I decided to take a closer look at things and try figure out what could be causing the high idle and inability to rev over 10K,

I had my ballast for my HID kit placed around the intake for the airbox area, which I thought could be causing a starvation of air, as well as moved any wires or obstructions from the air intake area,

I also - Checked and cleaned all plugs, they look great, a light brown colour - I referenced my NGK spark plug chart which confirmed a healthy running condition,

I at the same time, had issues with my fuel tap, which i dismantled and used a bit of gasket maker to stop it from leaking, as well as replaced the vacuum pipe - thinking it could be collapsed or leaking.

I also - checked my intake rubbers, 1 was a little cracked, so to be safe, I used a small amount of gasket maker to seal them 100% - Great difference - so i suspect their was a air leak.

I also upped my idle mixture screen to 2.25 - which has helped with cold starts, but not to much towards my idling,

My next suspicion is that the cam time is out on the front bank - I did put them back in a bit of a hurry due to outdoor lighting - I will check that tonight.

Could my CDI cause this issue?
I double checked all my earth points, but considering adding 1 or 2 more to make uber sure.

Can anyone think of anything else which I can check? I really am running out of things to check? Also - some things are hard to check - like if my spark is arcing somewhere it shouldn't...

Thanks in advance.

[Neosophist]

spark leak is easy to check for, start the bike up somehwere dark with no panels on and look all around the plug leads from coil to plug.