400R NC30

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VtypeV4
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400R NC30

Post by VtypeV4 » Sat Jun 27, 2009 11:40 pm

I need some help..Having been riding my old Yam Fj1200 round for many years (which i still love and would never change), i decided to buy my friends' VFR400R. I thought a toy would do me good for a bit of fun. Its been well cared for and has a number of mods including an ohlins front for setup. It flew its MOT having not really been used for a 18 months or so but i have a fueling issue.

My friend (always wanting modify things which are just fine) decided to up the jets in the carbs and he did something with the needle/diaphragms too. It now pulls very nicely from just above tickover up to 8000rpm then really comes alive through to about 12000 rpm. Above these engine speeds it feels like its stifled; running out of breath. I can push it to the limiter but it really doesn't want to do it. I've a maximum speed of 110 mph out of it and i know it should do much more than that. Bens old NC24 that was falling to bits would push 130...

I have replaced the (frightfully expensive!) plugs and run it exclusively on super/98 ron fuel. The bike has a none-standard air filter, i think it might be an HRC or K&N item and the exhaust is a D&D can using the standard honda header/link/collectors.

Any light in the right direction would be lovely, Thanks, Matt

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mrdidlydingo
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Re: 400R NC30

Post by mrdidlydingo » Sun Jun 28, 2009 12:04 am

Sounds to me like it needs attaching to a dyno meter and sorting properly, any fuelling issues will come to light on there.

The alternative is removing replacing jets yourself but if you cant see where it needs fuel can be a long winded process

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Re: 400R NC30

Post by MexicanGringo » Sun Jun 28, 2009 12:48 am

Iv a suggestion if you want to fine tune the fuelling yourself for less than a two or three hour dyno.. Pickup a generic lamba sensor and attach to a multimeter, then change down the size of those jets (probably down) and also set the idle mix.. Tho you have to drill and weld a nut onto each pipe for each cylinder and its harder to hide on the rear pipes.. Otherwise maybe take the shims on the needles off as a start, thatl lean it out prob right amount.. Was it hesitating after he changed it?

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Re: 400R NC30

Post by VtypeV4 » Sun Jun 28, 2009 2:38 am

Cheers guys!

It used to fuel great before he messed with it. He complained of a flat spot around 7-9 rpm but i never really noticed it when it was his. It pulled cleanly right up to the limiter.. I do have the original jets but not slides etc. He made mention of putting RVF slides in too for better air flow due to the domed cutouts at the top. I understand the VFR ones are straight? I don't know whats in it now. Its gonna have to come apart isn't it?

I need to learn about the model better. I know loads about the FJ, i've done lots to it but this is a new ball game altogether. This site is very helpful.

Thanks again. :Bmods:

VtypeV4
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Re: 400R NC30

Post by VtypeV4 » Sun Jun 28, 2009 2:45 am

It was hesitating a little and only when cold at lower revs < 5000 rpm. When its running even just for a few mins from cold this clears but the lack of top remains. Is there a mixture screw to adjust? If so should i touch them? Or just save myself a load of grief and get all the standard parts and rebuild it that way? I'd like to keep the air filter and the can.. The airbox is standard by the way. Sorry this all a bit vague but don't know what exactly he did to it.

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Re: 400R NC30

Post by CMSMJ1 » Sun Jun 28, 2009 7:53 am

Just to note that RVF and VFR slides are totally incomatible - one is semi flat slide and the other is round.

He'll mean the NC24 slides (previous model VFR400) which have a shape similar to the HRC slides.

I would go back to basics on it - proper filter, no airbox mods and 1 0.5mm shim under the needles. jetting around 118/120 and go from there.

This site is the place that'll get you sorted :up:
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VtypeV4
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Re: 400R NC30

Post by VtypeV4 » Sun Jun 28, 2009 12:42 pm

Looks like a strip then when i have the time. I have to do the head bearings on the FJ first, its starting to feel like like i'm steering in semi melted ice cream then when thats done sort the 400. I really wished he'd never messed with it cuz it used to be really sweet.

Thanks again and to all who replied with wisdom. I'll no doubt need some more help when it decides it'd be fun to do something silly next time!

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Re: 400R NC30

Post by VtypeV4 » Mon Aug 03, 2009 8:06 pm

Ok, so i bit the bullet and took to my local dyno people..

It pulled a paltry 37.6 hp at 10200 rpm and a measly 20.5 lb/ft torque at 8100 rpm. Whilst i am well aware that such figures are way too low, the fueling curve graph denotes no serious deviation from the "ideal" 13:1, leading me to believe that the jets are fine (I've since found they're a 120 front and 122 rear). The air/fuel mix never rises above 14:1 or dips below 12.8:1 from 4000 to 14000 rpm.

The dyno man asked me if it was in anyway restricted to which i said not that i was aware of. Its had the speedo restrictor mod done but even so, i suspect it wouldn't do this. Is it possible my friend put the wrong diaphragm-plunger-needle assembly in it? Some kind of jap restriction to limit them to less than 40 bhp? I've not inspected them yet but i'm running out of ideas with it.

I've also found the air filter is stock and that the D+D can has little more flow than the stock honda item.

Thanks to anyone who has a suggestion. Matt

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Cammo
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Re: 400R NC30

Post by Cammo » Tue Aug 04, 2009 8:42 pm

VtypeV4 wrote: The dyno man asked me if it was in anyway restricted to which i said not that i was aware of. Its had the speedo restrictor mod done but even so, i suspect it wouldn't do this. Is it possible my friend put the wrong diaphragm-plunger-needle assembly in it? Some kind of jap restriction to limit them to less than 40 bhp? I've not inspected them yet but i'm running out of ideas with it.
There aren't many (any?) other diaphrams that will fit easily and cause those problems. Is it possible that has UK restrictors in place (these will be washers in the carb manifolds)?

There are no other forms of restriction.

Best to take a look inside the carbs yourself. There are different needles (and emulsion tubes) for the front & rear carbs, but I doubt having these around the wrong way will lose you 20+hp.


Did you see the jet sizes for yourself or just going off what you were told?
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VtypeV4
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Re: 400R NC30

Post by VtypeV4 » Wed Aug 05, 2009 2:16 am

I'm gonna take it apart tomorrow and have good look. I've not seen the jets myself however, I know the man that fitted them.

I guess it may well just be knackered diaphragms not lifting the plunger out of the way. The plunger part did seem a little stiff on all four carbs whereas they're lovely and smooth on the FJ.

The bike has never been a 33 bhp one, i've known it for 3 years plus. I wished my friend hadn't messed with the carbs when it was his.

Whats the score with NC24 needle-plunger-diaphragm assemblies?

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