Honda VFR400 nc30 problem....Help please!

[Danzio]

Ok so i took my vfr for a ride today and its been great weather so i thourght id open it up in the country side abit...

was fine around town through the gears up to 50-60mph but as soon as i took it to about 7 1/2 - 8 thousand rpm it starts to make a really growly noise from the engine, the power which normally helped me hurtle forward feels much more reduces and there is a distinct vibration.

the bike itself is in good working order, fine up till those rpm and it will go to them, all the way to 14500rpm, but its feels like its lost alot of power...

its only just started but need some advice on what to do here, sounds smooth to 8000rpm when it usually picks up but then afterwards dosnt deliver the power ive known it to, sounds more like a v-twin than a four!


anyways heres a good description,

get to 8000rpm, wind it on and its feels like it loses power, sounds like a vtwin, little more vibration and a different exhaust note...

as if i was running out of petrol, but im not, ive checked that!

is it still restricted somewhere? this would be my first guess, either that or a fuelling problem as it wont go past 110mph 180kph.....

im sure it wont be valves, or the carbs as they've just all been serviced and were in good nick anyway.

the bikes done 17300 miles..


HELP!!

[Wafer_Thin_Ham]

Sounds like it drops a cylinder or two when you hit that RPM.

I would suspect a spark issue, so coils, HT leads, to start.
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[Frost]

Might also be fuel/air related.
If you mechanically minded take the carbs off and apart to make sure theirs no shit in them. Check the fuel filter if one is fitted. Make sure you do a good job of fitting the carbs and airbox to make sure theirs no leaks, the filter isn't clogged and give it a fresh batch of fuel. Spray some WD40 around the carbs when its running and see if the rev's pick up. If they do, youve got an air leak!

All free / cheap things to check before you go testing & replacing electrical components. On that note the reg/rec might also be worth a look. These allways fail and can sometimes produce weird electrical issues.

[Phoenix]

As usual, check battery charge and condition, weak battery will often mean your charging circuit can't handle charging the knackered battery and supplying power to the spark plugs and everything else, usually manifests as becoming groggy and unresponsive at high rpm (more power needed for increased HT pulses). Charge battery or try another and try again.

If this is the cause which it sounds like then further investigation is needed and will probably lead you to the regulator, check the charging voltage from it for starters, it's usually about 14.8v no higher and not a lot less.

[chris-red]

Don't these bikes have 180km restricton, do the clocks still read in KM? if so get a MPH convertor or a set of UK clocks.
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[binge]

Dont quote me on this, But I think with the NC29 (CBR 400) if you unplugged the speedo, The bike would run up to 8 or 9k RPM, And then it would cut the power to 2 of the cylinders and only run on two.

Could be the same scenario with the NC30.






Ben

[Danzio]

thanks guys ill check these all today and let you know how it goes,

binge ive never had the speedo off, ever, and i know the restrictors are off as ive had it off the clock many a time.

never been an issue till now but ill have a look at the carbs and the regulator rectifier see what the crack is there, i think the sparkies and ht leads will get a check too.

ill let you know how it goes.

cheers lads

[BenBray]

I had a similar problem yesterday. I'd get to 5.5K revs and it'd just keep spluttering and didnt want to get much higher. It's done it before.

Then on the way back from work, it was revving perfectly clean and fine to the redline. Sometimes happens to NC30's I hear.

It's sometimes about the way you start them. Never use any throttle when you start it, I hear it can play about with the fuel/air mix and make it do similar things. It works trust me.

Was your choke on a tiny tiny bit? That can cause what you're describing.

Apart from that, try plugs. They're expensive, cost me 14 quid each for new plugs. If you can get away with it just clean them and adjust the gaps. Then check air filter and carbs and fuel filter as described above.

If no luck, I've no idea. If your bulbs get brighter [considerably] then maybe the charging system.
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[chris-red]

[chris-red]

[binge]

Just a thought.
Before you go pulling the thing apart. I didnt click at first. But I had an on going problem with my NC29 for months. it wouldn't rev out past about 5k rpm.

Check to see if it will rev out in neutral.


If it will, Then its possible that its your Side stand switch. When the RPM gets higher, The vibrations pick up, And cause the side stand switch to loose contact and cut the engine out, Until the revs drop down again.


Sounds mental, I didnt work it out for months.


Worth a try




Ben

[Phoenix]

Chris_red, NC30 plugs are £12 each on gear4bikes, usually £14 or £15 in shops, ER9EH, expensive, you can get a set of 4 off ebay for about £30 though.

The 180km/h restriction does work by cutting the spark I believe, but as he mentioned this is a new problem and he's had it past 180 before so that's not it. Still betting on battery/regulator personally, no point doing the rest before checking those as they're easiest. A new NC30 SH633-12 regulator with heatsink is £30 from china anyway, cheap as, just bought one myself for Blade.

[chris-red]

[Danzio]

update lads, had a tinker on today checking fuel lines, ht leads spark plugs and other cabling. all fine. checked battery, fine, reg/rec is also fine and is already an aftermarket unit.

vfr 400's dont have side stand engine cut outs, or so my haynes manual suggests so i doubt it would be that either.

just really dont know what it could be. maybe one of you guys could come up and have a look if your near newcastle at all? just a suggestion but it really has to be seen to be understood.

my thourghts now are on restriction and if it was done properly? need to find out how its been undone and make sure nothings been damaged there.

any more ideas get back to me.

cheers.

[Danzio]

been thinking more about the problem and im pretty sure it could be fuelling as its like a flat spot when it needs more fuel, this could suggest a clogged jet and or clogged fuel line/filter.

im going to clean them tonight if i get time, anyone have any advice on the cleaning of carbs? im sure on the vfr4 their CV carbs, no?

any of you lads fancy walking me through this dont be afraid to shout up!

cheers lads, help is always appreciated.

[binge]

The NC30 does have a side stand cut out.

I had 2 of them.






Ben

[prawny1]

might be worth popping the tops of your carbs and giving the needle slide diaphragms a good goin over for splits.

[Danzio]

ok so i took the bike to the garage last night (fuel station) and filled her with vpower and a little redex.

didnt do much good at first but gave it a hand full this morning and instead of the gurgle i got a full powered flig to 14500 rpm! =D

im suspecting fueling problem to be honest. gonna have to clean her out over this weekend

oh and yes they do have a cut out, only found out yday, i left the side stand down and put it into first. engine clicked off as it should have, so no probs there, appologies ben

[Danzio]

right so ive worked out that i can accelerate on the bike nearly cleanly when using little throttle. as soon as i use more than say a quater twist it bogs down. in all gears.

a better explination is to compare it with a cold two stroke when raking it from start when you get that spluttering with the throttle fully back.

has anyone ever had this problem with their nc?

it does rev to 14500 in the lower gears, but has an initial bog down at about 7000rpm and just vibrates alot until 14500, fine on rpm before that.

really need to get the bike back on the road boys, any help appreciated...i mean is their a diagnostic tool i can buy/use to check all the electrics? and would a mechanic (if i paid him an hours labour) look through the bike to diagnose the problem?

[MarJay]

Is the problem that it won't go over 110mph?
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[Phoenix]

What prawny said, check diaphragms for splits, when on full throttle they stretch out (don't actually stretch) as the vacuum increases so the hole becomes bigger and stops it working properly, may explain it.

[Danzio]

marjay: yeah it will from time to time but when it aint working properly i dont want to stress it to much, and its not restricted as ive checked all that and previously had it maxed out at 15000 in 6th, on a private road ofcourse

do i check the diaphrams by just lifting the carb tops off or what?

or are they, like everything else on the nc30, hidden away so only jap hands can reach em?

racism, my forte'! only joking now!

[prawny1]

Ive never worked on an nc30 but should imagine its just a case of poping the tank and airbox off to get to the carb tops, once you gain access just unscrew the tops but be carfull because you have a spring in there which will try to send the top cover flying if your not carefull,
once the spring has been put some where safe you can slide the diaphragm out the top of the carb for inspection.

[Phoenix]

Also be careful when you remove the covers as the diaphragm is usually stuck slightly to the carb or the cover and if it wasn't damaged to start with you might damage it if you're not careful when seperating them. Also make sure you use a good fit screwdriver and push firmly when you unscrew them because the screws are like cheese.

Without going and looking I can't be certain but I think you can remove the tank and airbox and have enough room to remove the covers, the VFR carbs have an annoying plate thing on the top though which gets in the way.

[Danzio]

hi guys, bikes sorted.

just like to say thanks for all the help. it was indeed the carbs but more the fact that the jets were gunked up, nothing else. my dada helped me strip them down and clean them all, which took ages!

i also got some new diaphragm tops for a motorcycle dealer and replaced tham just incase.

so again guys thanks for the help.

it always greatly appreciated.