Howdy fellas, I'm completely new to the vfr400 world and I have just picked up an ex race bike here (rc30 version) in Oz to race in our local post classic race series. I Usually run 2T GP bikes, Yam TZ250 4DP and a Honda RS125 NF4 and my knowledge is mainly in that area
I've started to do all the inspections and checks on the VFR and everything is going ok at the moment but I do have a question about running no airbox and filter. Everything I've read on the forum so far seems to indicate to use the airbox with an air filter fitted.
This bike has 150 mains fitted with no airbox and a home made wire mesh cover for a filter. The previous owner said it use to have some type of foam filter fitted but was missing as he use to remove it between riding/starting the bike in the shed due to the petrol breaking down the foam. He never gave any indication about any jetting issues when he rode it.
I've cleaned the carbs in an ultrasonic bath to get rid of the varnish and general crud. Gaskets need replacement and the air bleed screws were all set differently. Except for race exhaust fitted, the bike engine looks standard to me so far. Valves have been checked with some of them outside of spec but not by much.
Can these engines run ok with no air box and no filter?

Thxs for any advice
Cheers Steve

Yep, the HRC kit requires the airbox and filter to be removed. The kit is more than just jetting though, you will also require the short velocity stacks, needles and a carb tray. People have argued though that the tray is more to shield the carbs from heat than direct air.

I'm currently running the HRC open carb setup and my mains are a little larger than yours (155 from memory) but I also have reground longer duration/higher lift cams. Needles wise, the best option found was actually the OEM NC24 needles that I got with the slides rather than any of the HRC spec'd needles which were all too rich.

Cheers
Luke

Cheers for the info Luke. I was given a fibreglass tray with the bike so that makes a bit more sense about what it for, but the construction of it looks like a home made fibreglass copy of a decent one. Hard to know when to stop inspecting and replacing things on this bike if I want to be ready for next year. At this stage just want it to be safe and run smooth before chasing any potential power from the engine. I do have a new shock on the way from Nitron and have to inspect the forks to see what's inside before deciding what to do. Brakes are getting a full overhaul as the pistons seals are showing signs of breaking down and one of the lines was leaking from the banjo crimp.

Thxs again
Cheers
Steve

Yeah - I have never seen a genuine one. Mine is a fibreglass copy as well. I have all the stuff I need to build a mould and then I can start making my own versions as mine is in really crappy condition + I feel like I can produce a higher quality item.

Getting power from these engines isn't easy unless you cheat and go big bore. I think I have done about as much as I can with mine without spending some serious coin or going big bore. Last dyno run puts mine around 70-72hp which I'm happy with