VFR 400

[Andy levitt]

Hey

I recently purchased my second bike. I wanted somthing that i could ride to work on in bad weather and to use to keep me putting stupid amount of miles on the blade. But i wanted sothing to keep me grinning.

So i bought a VFR 400. I love it. i cant wait to finish work and ride her home. Felt slow at first due to me being used to more powerful bikes but i love it .

Your probably wondering why this is in the workshop section. well

When pulling away or at low rpm in other gears. When you open her up to accerate it feels lumpy with small surges of power. Then at about 6,000+rpm its fine again. Im thinking carbs need cleaning. But im no bike mechanic so any help is much appreciated.

Thank you
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Speedfight 50 -> Honda NSR 125 -> Y reg YAMAHA YZF R6 -> 08 YAMAHA YZF R6 -> Honda CBR1000RR
Theory test Done 4/6/07
Practical test Done 21/12/07

[DrDonnyBrago]

Aftermarket downpipes and airfilters can feck up the fuelling giving it flat spots.


Does it have a non original exhaust or a high flow air filter like a K+N on it?


May well have other issues too but flat spots are quite common when replacing these parts.

[Andy levitt]

It has an aftermarket exhaust. Or right. just seems essesive to be from that alone.
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Speedfight 50 -> Honda NSR 125 -> Y reg YAMAHA YZF R6 -> 08 YAMAHA YZF R6 -> Honda CBR1000RR
Theory test Done 4/6/07
Practical test Done 21/12/07

[DrDonnyBrago]

[Andy levitt]

Downpipes look standard to me. Just the end can which is a viper.
I think ill have it checked at a dealer, Carbs balanced. Valve clearances checked.
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Speedfight 50 -> Honda NSR 125 -> Y reg YAMAHA YZF R6 -> 08 YAMAHA YZF R6 -> Honda CBR1000RR
Theory test Done 4/6/07
Practical test Done 21/12/07

[Tim..]

The Nc30's can be very notorious for running badly when fecked about with. Any change to the airbox or exhaust system normally warrents a jet change or dyno session
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Project builds: My VFR400 nc30 build thread + Honda Britain Rep VFR + What? Another VFR +Project 'cos I want one' + V8 coffee table
www.marshallracing.co.uk
OCD - Helping to bring the standard of my bikes up and make me slowly go mad since 1999

[Andy levitt]

Ive checked the carbs. The needles in the slides were loose. I sorted them out.

I followed a guide on anther forum. It states 120 jets in the front and 122 in the rear carbs should be used for a nc30 with aftermarket end can and a airfilter. But mine had 124s in a front and rear. I could only check two of the carbs one front and one rear as the other screws on the float bowls are worn and i dont want to make them worse. Ive ordered the smaller jets.

Thing is the bike doesnt smoke at all. and the plugs aint fouled up from too much fuel. The engine sounds healthy while idling.

Since ive put it back tother too its got worse. Flat spots still there and above 6,000 the bike just seems to be very slow like its bogging down. But it still revs. Its deffianly got to be the fueling.

Any suggestions ? When the jets come im considering taking it to a garage. As im in need of it fixing.


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Speedfight 50 -> Honda NSR 125 -> Y reg YAMAHA YZF R6 -> 08 YAMAHA YZF R6 -> Honda CBR1000RR
Theory test Done 4/6/07
Practical test Done 21/12/07

[shereen]

I agree with Tim.

It needs some time on the dyno, mine was the same as yours when I changed the cans untill it was jetted and spent a couple on hours with PDQ in Slough (highly recommended!!)

Made a massive difference.

BUT the nc30 can feel a bit lumpy until you get to 6000rpm +, the power is higher up the rev range.
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"The Internet is the first thing that humanity has built that humanity doesn't understand, the largest experiment in anarchy that we have ever had"

[Andy levitt]

I had my R6 dynoed and mapped with jordan bikes, there the only place i know near me with a dyno and tuning centre. Cost me £100. Wont it be much harder for them... or costly for me for this VFR as they will need to strip the carbs everytime to shanged jetting to Trial. Am i right here.

How much you reckon?

I took the bike out this morning its so lumpy and runs bad.
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Speedfight 50 -> Honda NSR 125 -> Y reg YAMAHA YZF R6 -> 08 YAMAHA YZF R6 -> Honda CBR1000RR
Theory test Done 4/6/07
Practical test Done 21/12/07

[shereen]

Im not sure to be honest, my bike spent 4 hours on the dyno which cost me £200.

Have you checked the inlet manifolds? If they are fecked that could be a lot of the problem. All mine were replaced which cost £34 for the 4 of them plus PDQ managed to sorce me secondhand carb parts off a race bike for £50 which saved me a few pennies.

I have spent a lot of money getting mine from a dog to a pedigree but it is worth it IMO.
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"The Internet is the first thing that humanity has built that humanity doesn't understand, the largest experiment in anarchy that we have ever had"

[Andy levitt]

To me the intake manifolds dont look too bad. They seem alittle old but still seem to seal. I sprayed them while idling to see if the revs increased, and nothing happened.

Ill just have to have a ride down and ask them about everything. I found david silver spares sells the inlets for £6.25 so if there is a problem with them while jetting ill just buy them.
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Speedfight 50 -> Honda NSR 125 -> Y reg YAMAHA YZF R6 -> 08 YAMAHA YZF R6 -> Honda CBR1000RR
Theory test Done 4/6/07
Practical test Done 21/12/07