Hi, ive had problems recently with my vfr400 back firing drastically especially from cold starts, backfiring 10+ times while i ride around 5k revs etc,

my bike has just been DYNO'd today and the mechanic has told me (aswell as replacing my 4 spark plugs :S thanks) that oil has been getting through and oiling up my plugs so its back firing etc etc.

after he's set it up and balanced carbs etc, its power has goen from 56 - 58.8 or something, not much tbh, especially when its got a full Tyga Exhaust system etc,

anyway ive been out on the bike today after i paid up, and it doesnt seem as nippy of the line/lights as before, maybe it has a bit better mid range torque? and it sounds totally different. a bit more deeper?

weve taken off the Snorkel to let more air in ? has this effected the sound? what else can i do ? he has advised i take out the Air FIlters FOAM, just leaving the metal filter, saying this will give me better air flow ?

any ideas people ? im onyl a young 21 year Old NC30 rider, and Love my Bike to pieces

also when i got home, i novticed my fuel tap was set/turned to RES, i think hes DYNO'd my bike on Reserve :S would this effect results etc ? what else would this mean ? or does reserve not matter ?

many thanks adam :)

Can you stick up a post of the graph?

Not entirely convinced by the work tat was done on it...

I would be amazed to find out how you get oil on your plugs... Where was the dyno centre..??

Reserve just allows fuel below the line of the normal level to be used, makes no difference as theres no separate section for this fuel.

DONT take the filter out, anyone suggesting that is a complete retard.

Your mixture is probably off, running rich or lean and causing unburnt fuel to ignite in exhaust. See below
from wiki:
Backfire in an automobile engine typically results from various malfunctions related to the air to fuel ratio. Backfiring can occur in carbureted engines that are running lean where the air-fuel mixture has insufficient fuel and whenever the timing is too advanced. As the engine runs leaner or if there is less time for the fuel to burn in the combustion chamber, there is a tendency for incomplete combustion. The condition that causes this is a misfire. The result of a misfire or incomplete combustion is that unburned fuel or flammable hydrocarbons are delivered to the exhaust manifold where it may ignite unpredictably. Another backfire situation occurs when the engine is running rich (with excess fuel) and there is incomplete combustion during the Otto cycle, with similar results.

The dyno a/f graph should give some insight.Also check the colour of your plugs for an indication, if black its running rich, if white its running lean.

Does it backfire mainly on engine braking?

Check your exhaust headers arent leaking

sorry, his printer wasnt working so i havent got any print outs,, although when he Dyno'd my Aprilia rs125 a few Years ago he gave me print outs,

ive seen them on the Computer, also stood through one of the DYNO tests and he told me my Speedo/clocks were well out, more so when it went over 70 mph, i think he said when my bike was reading 100 on clocks i was only going 75 etc, which isnt good,

if i get the print outs i would love to post them to get somebodys opnion..

Thanks for your opinions, why should i not take out the red foam filter ? (dont worry i wont if you say so) ill listen,
what's your opinion on removing the Snorkel ? any differences ? why does my bike Sound different to before ?

i am really guttered after paying so much money my bike doesnt seem to much better, it just doesnt back fire like before. and when it was it was back firing it would do it for about a Miles Ride maybe running on 3 or 2 Cylinders ? and would do it very bad and get me looks lol,

the Dyno is in Bentley, Doncaster, the place is called TRAX.
He spent along time on my bike, i appreciate the V4 engine isnt the easiest bike to work on, but i was unhappy after i rid my bike, it just sounds a bit deeper/louder and doesnt accelerate liek before.

i think my bike was Running really RICH before he sorted it out, hence my plugs maybe getting oiled up, hopefully it wont start re back firing soon,

oh and btw by oiled getting into the air filter, the inside of the Air filter, black plastics were a little damp with oil from him running the bike on dyno a few times, if that makes sense ???

i really Appreciate your help btw, and im sorry if i dont explain my self properly or good enough

butler

Well, for starters, take it back and tell him it is not right. I appreciate it might be a bit daunting but the bottom line is that you paid some money for a service. The service has not been what it was supposed to be..so he'll have to work on it again, for free, to make sure you get what you originally paid for.

He's made a fuck up on your bike..simple as that.

"He's made a f*ck up on your bike..simple as that. " Hahaha lol :)

i dont think hes f*cked it up too bad, he has stopped my Back firing Problem, and hopefully set up my carbs better ? ? ? ?maybe my bike rid like it did before because it was constantly running Rich for years ? that after a year since replacing the Spark Plugs they have just oiled up, hence it back firing ?

now my bikes running more normal ? maybe im not used to how a V4 HONDA should run ?

i might leave it for a week to see how it runs, and see if i get used to it,. then maybe get back in touch with him? i was looking at buying one of them TYGA carbon air filters that give a better 8% air flow, hoping this might make my bike better ? any thoughts ??

again, much appreciated. butler

The snorkel acts as a venturi, drawing air from the wider opening through a narrowing, this increases its velocity, whether taking it off decreases the efficiency, probably not at low rpm, but taking it off isnt going to give you more noticeable/calculable power.

The foams there to filter, let it filter or you'l draw in crap. Foam is already freer flowing than paper elements.

Like CMSMJ1 said take it back, and at the very least demand a readout of the dyno so you can check the a/f &power. Also check the state of the old plugs if possible, if the electrodes were worn then that prob was behind the back firing. Ask what changes he made to the fuelling. He prob didnt change any jets so the fuellings prob the same.

Did you fit the tyga? carbs would have been richened for it.

Does the bike bog or surge under hard acceleration?

I'd say get yourself a haynes manual and don't let anyone touch your bike from now on...

Now then Butler, Don't take this the wrong way...but you'll not find many dyno operators* that have been sad enough to try out all the various options on an NC30/35 than the collective fettling on this forum.

*there are a few dyno operators/NC tuners on here and they are a rare bunch who I am sur would generally agree with the points I'm about to put to you..

1: A standard NC30 really likes to have all of the airbox equipment left in place - standard filter(Honda), standard snorkel and the rubbber flaps that live on the brace behind the headstock. Without these the bike will not run properly.

2: The carbs like to be clean and setup with no sticky chokes, no random air screw settings and with the jets adn emulsion tubes in the right carbs.

3: You need to tell the Dyno operator you are not happy with the current setup, and if required, tell him you have been onto a specialist forum...and he can come here and hopefully be able to justify whatever he did to yor bike.

4: you NEED the graphs off this guy - on paper, via email or whatever. They are vitally important to see how the bike is behaving. Also, you want to ask him what the jet sizes are in each carb, what the float heights have been set to and also what the air/fuel idle screw was set to. He should know this..it is his job to know it and I would expect if he did some work on the bike that this was written down somewhere. Also, what were the jets, flaots and idle screw settings before he started to fiddle with it?

5: Tell us some more about the bike - how long have you had it? WHat has been done to it? Was it restricted? Have a look about this forum (and welcome in dude) you will see that we don't fuck about...the bikes are awesome pieces of kit, the like of we'll never see built again.

6: If you want to get an opinion on the bike - drop me a note - I work in Wakey and will be dropping down to another forum members gaff in near Donny next week - so am happy to come have a look and see what goes on.

CMSMJ1 wrote: youon the bike - drop me a note - I work in Wakey and will be dropping down to another forum members gaff in ne will see that we don't fuck about...the bikes are awesome pieces of kit, the like of we'll never see built again.

that bought a tear to my eye mark



mark knows his shit butler, take note, another guy that knows his shit with nc30 carbs is cammo, hell be along shortly the day will be break in sunny auz pretty soon, and again hell back what mark has said up.

dyno/tunning is like brain surgery with these bikes, if you dont do things to the tee they dunno run right, yes trial and error is the key but when you paying someone who should know what there doing then really you should be asking to get it done right or you money back

out of curiousity what did you pay him?

thanks for your detailed response CMSMJ1 :)

1. would you recommend i put that Snorkel back in place ? i could understand why he said remove it as it made sense, BUT it was designed like that for a reason, we also discussed hoe the air gets into the air filter, how does it ? as where the Snorkel is threres just the front of the frame in like a little area with no way of air getting there kinda, if that makes sense ? like theres no Air Scoop etc, so how does Air get Directed to the ari filter (btw) i know you wont like this, but my bike has Full "tyga bodykit" on it in movistar replica, obv this has nothing to do with the power, but the 1989 etc fairings will be different, (just to clear that up) so you know where i am..

2, surely Everything is in its right place ? the bike does ride, and doesnt seem to be odd, just seems less powered than before and Sounds different.

4. i will ring him sometime soon and try and get some details out, like jet Sizes etc, would this help you guys ? to knwo more about it ?
could it be possible he's not bothered doing certain stuff and changing stuff and just set the carbs up differently (less Rich),

5. the bike is my 2nd bike , when i was 17 i had a chinese (sukida roma) retro looking scooter that struggled to hit 30 lol then i got an Aprilia Rs125 (51 reg) and then last April i think it was, i bought this VFR400nc30 from Somewhere near Blackburn.(DARWEN to be precise) from a dealer,
the lad who ahd it before me had already speant a lil bit of money on it pimping it up kinda, like Braided Lines (are they standard?) Full Tyga Exhaust System, obv the Full RC212V body kit by TYGA and other bits and bobs nothing to important to brag about, i think it has a WP shock, as theres an Adjustable thing under my seat with WP on it,
thats about it, ive had it for about 8-9 months, ive had it rhough an MOT and have done a Full Service, oill Filter and new oil changed all 4 spark plugs etc, its had new Set of tyres and Chain etc etc.
My uncle Andy who raced bikes years back told me one of the pipes near the Carbs was leaking or something ? a few days ago the DYNo man also said this, but even though he told me he knew aman who had the (o Ring things) he never went through with it and replaced them) instead i think he just said the reason it was back firing was because i was running to RICH and i had oiled up my spark plugs..
i do think he speant a while on the bike.. i gave him my bike at 9.45-10am yesterday morning, then by 4 o'clock when i finally got through to him he told me hed be another hour, so an hour later when it was gettin dark,i asked if itd be ebst i picked it up the next morning, he said hed get in touch about 12ish, didnt so irang about 1, the bike was finished then i went down n got it, So even thought he most likely was doing other things it wasn't a 1 hour jobby

i think i mentioned earlier that the bike is making roughly 58.8 Hp, which isnt to bad, but didnt they run 59 stock ? i know its been 20 years, but with the TYGA race? exhaust and set up etc should it not be more ?? it doesnt seem as nippy of the line as a few weeks ago before my problems ???

thanks again adam