NC30 plug fouling, poor running, full choke won't rev past7K

Rutts · Post by **Rutts** » Tue Feb 16, 2010 8:42 am

Hi, sorry about the title but it may help someone in the future when searching for a similar problem.

I bought a 1992 VFR400 NC30 track bike early this year and have been struggling to get it running properly.

Current symptoms are:
with clean plugs starts on the button with full choke no throttle
the bike sits at around 4K revs and will rev to 7k then it drops down and struggles to even run (too much fuel? ) after doing this it eventually conks out and I have to remove the plugs and clean them again to get it to start.

I've stripped the carbs and cleaned them following the excellent instructions on this site. I need to do it again as I didn't check the needle bore size or the that everything was in the correct place as I missed the part that said the front carbs are different to the back. I just cleaned them.

The fact that the plugs are getting covered in crap highlights, to me, that its over fueling but this could just be because I have to use the choke all the time. Would this suggest I have a problem with airflow? Its all bog standard though the airfilter is the one that was with the bike when I bought it. A new one will be ordered as they are pretty cheap anyway.

Does the NC30 run OK without the air intake assemble on it? As that will be what I try next to fault find the issue.

Also would poor valve clearances cause this kind of problem?

This forum has been a wealth of information so far my thanks to all

Post by **Cammo** » Tue Feb 16, 2010 9:17 am

Rutts wrote: Does the NC30 run OK without the air intake assemble on it? As that will be what I try next to fault find the issue.

Welcome to the site, stick around and the bike will be sorted easily!

It definitely won't run well or at all without the airbox/filter, best to try and sort it with everything in place. It should still run and rev well even the valve clearances are out. Whatever the cause is it will be a fairly simple fix and nothing major.

Some more info should help get it sorted:

When started from cold, how long do you let it idle for before revving it and finding this problem? When started from cold with full choke, if you don't rev it will it idle for as long as you like?

I think you're on the money when you say that the plugs will be covered in crap after starting it with choke all the time, this is pretty normal.

If it was mine I would be making sure all carb settings were correct (front and rear), and then putting new plugs in making sure to start it full choke no throttle (your start technique is correct), don't rev it until the rads get hot. Do this until you get familiar with starting it.

You may have killed the plugs beyond the point of no return by starting it on choke constantly.

New plugs are the key here I think, the little buggers can easily die from constant overfuelling, an expensive lesson to learn but you only make this mistake once!!

Rutts · Post by **Rutts** » Tue Feb 16, 2010 9:42 am

Thanks for the reply,

When the plugs foul up I remove them, soak them in carb cleaner then burn off any deposits using the gas flame on my cooker. With this done it fires up on the button. It appears to sit at idle on full choke if I don't rev it. Perhaps I've been too keen to get it going :) On previous bikes it would start on choke idle at low revs then the revs would increase which would be a sign to turn the choke down. At full choke is 4K about right? If I get a chance tonight I will fire her up and leave her running on idle until the water gets hot to see how she does. I will be doing the carbs again this weekend.

If it doesn't run well without the airbox on it how do you go about balancing the carbs (another job on the list) I'd have thought you'd need all the airbox parts off to access the carb.

I have a growing list of parts that I'll order in one go. I don't want to order spark plugs then destroy them so hoping I can find as many issues now before getting all the new parts.

Cheers

Post by **Drunkn Munky** » Tue Feb 16, 2010 10:27 am

Are you letting her get warm before revving it? NC's are funny buggers and like to be started certain ways as dataracer said, plugs can die just from looking at them the wrong way so be carefull, what plugs you using? ER9's are standard and ER10's are recomended for racing, higher heat range or something and ive always found it harder to start a bike with ER10's in. Killed a brand new set due to being a dumbass and floading them, easily done tho when you havent got the knack of starting NC's.

I only use choke from cold for a short time, as soon as it can idle without choke i let it tick over till warm, never rev it as high as 7k till its properly warmed up, ever!

Does sound like your plugs are shot tho, does it backfire when your trying to keep it running?

Rutts · Post by **Rutts** » Tue Feb 16, 2010 10:52 am

I think the key here is that I'm not letting her warm up.

I'm not sure what the plugs are apart from that they are NGK ones. I'm taking Friday off so I can spend 3 days of spannering to get the little beast fighting fit. I'll fire her up and see how she runs on the choke alone. I'll let her get warm then see if I can roll of the choke and let it idle as normal. Normally any attempt to roll the choke off leads to it stalling but again, impatience on my part may be largely to blame.

New plugs are on order

Cheers,

Rutts · Post by **Rutts** » Fri Feb 19, 2010 3:28 pm

Well I took the carbs off and gave everything a once over. Its running 115f/118r standard for a jap import.

I flushed the old fuel out the tank and replaced it with new stuff. Bolted he back together, full choke, button press and she was alive. I let her run, rolling off the choke bit by by till it was running normally. When it got to temp I reved her up and she will rev up to the red line.

Do I need to re-jet it to 120f/122r or will it be fine as it is?

Cheers

Post by **CMSMJ1** » Fri Feb 19, 2010 3:57 pm

I'd leave it as it is now - 120/122 will be far too rich unless you have heavily modded induction and exhaust

woodward1248 · Post by **woodward1248** » Sun Mar 07, 2010 9:43 pm

i put my plugs in the oven over 10 min at 150 till they were dry from any fuel then wire brushed then spryed carb cleaner down the tops put together full choke no throttle and boom she started but after 30 sec i reved her she revered fine but turned her off to put radiater bact on seening you got to take it off to get to the plugs shocking. try starting her back up but wont having it. not happy.
mine has the same problem. iv orded some coils after reading this i wish i hunted the site more. im gonna try this exact thang tomoz. leave til shes warm. carnt wait.

updates tomoz.

carl nc30 · Post by **carl nc30** » Sun Mar 14, 2010 8:57 pm

this must be a common thing cos mine is doing exactly the same,did the hrc thing with the fuel tap,put new fuel in and pumped it through,fired it up,left it for abit and took choke off,then when i revved it it was spluttering and farting till the revs dropped right down to finaly dying then would'nt go again,its driving me mad

NC30 plug fouling, poor running, full choke won't rev past7K

NC30 plug fouling, poor running, full choke won't rev past7K

Re: NC30 plug fouling, poor running, full choke won't rev past7K

Re: NC30 plug fouling, poor running, full choke won't rev past7K

Re: NC30 plug fouling, poor running, full choke won't rev past7K

Re: NC30 plug fouling, poor running, full choke won't rev past7K

Re: NC30 plug fouling, poor running, full choke won't rev past7K

Re: NC30 plug fouling, poor running, full choke won't rev past7K

Re: NC30 plug fouling, poor running, full choke won't rev past7K

Re: NC30 plug fouling, poor running, full choke won't rev past7K