vfr200 Posted April 6, 2020 Share Posted April 6, 2020 Hi all, first post here. I've been lurking since I bought my VFR 18 months ago but this is the first problem I've had which I can't find a clear, well-written fix for. Whenever I play around above 7,000 rpm for any period of time and then release the throttle, as the rev needle passes through about 6,000 rpm I hear an almighty bang. This only happens under engine braking - if I pull in the clutch at the end of a blast at the top of the rev range the revs drop below 6k without incident. I'm 99% confident that my exhaust isn't leaking anywhere. Separately, during the course of testing this to try and single out the exact conditions which give rise to the backfire I've discovered that my clutch slips above 6,000 rpm in higher gears under heavy throttle. This is fairly well-documented here and the solution seems to be to clean/rebuild the hydraulic side first and then if that doesn't work to refresh the actual clutch itself. My question is whether the fairly specific backfire I'm experiencing is related to the clutch slip, or should I be looking somewhere else? Given that it happens reliably at very specific revs, is that when the PAIR valve opens perhaps and the fresh air is cooking off unburned fuel from the overrun? I've replaced all the numpty-serviceable parts (plugs, oil, filters) and the issue is unaffected. Link to comment Share on other sites More sharing options...
Member Contributer Dutchy Posted April 6, 2020 Member Contributer Share Posted April 6, 2020 If you are confident the exhaust is 100% tight then yes have look at the pair crap. AFAIK the PAIR kicks in at low revs. I'd start by unplugging the hose (near the airbox I assume) and block it. Large bolt or put a marble in, secure with a bit of tape. Go for your run,. Not owing a vted, I'd not know if/how that could affect things Link to comment Share on other sites More sharing options...
Member Contributer Dutchy Posted April 6, 2020 Member Contributer Share Posted April 6, 2020 But euh...... 1st post without a picture? How do we now know you exist and are not merely a www mirage? Link to comment Share on other sites More sharing options...
Member Contributer FJ12Ryder Posted April 6, 2020 Member Contributer Share Posted April 6, 2020 Any kind of aftermarket tuner, like a Power Commander? How many miles on it? After market air filter, like a K&N? Link to comment Share on other sites More sharing options...
vfr200 Posted April 6, 2020 Author Share Posted April 6, 2020 3 hours ago, FJ12Ryder said: Any kind of aftermarket tuner, like a Power Commander? How many miles on it? After market air filter, like a K&N? Just nudging 40,000 miles. All stock bar a Wingrack, the Givi touring screen and a set of proper handlebars from Hurricane. Air filter is OEM and was replaced in December. Two previous owners, both of whom had it serviced properly. Bloke I bought it off was fairly big (in case he's reading this I mean well-built, not fat) and I think he had his wife on the back most of the time which presumably wouldn't do the clutch any favours. 7 hours ago, Dutchy said: But euh...... 1st post without a picture? How do we now know you exist and are not merely a www mirage? Sorry. Re the PAIR stuff, do you know whether it shuts off somewhere around 6k? Link to comment Share on other sites More sharing options...
Member Contributer BusyLittleShop Posted April 6, 2020 Member Contributer Share Posted April 6, 2020 POP Technically speaking backfiring on deceleration is generally the result of a lean condition in the fuel system... What occurs in a lean mixture is it fails to ignite consistently... The result is unburnt fuel migrates into the exhaust pipes... As next engine cycle does fire... those unburnt gasses are ignited down wind in the exhaust pipes... pop you hear the sound of backfire. Normal fix is to eliminate the possibility of a intake or exhaust leak. Check torque all the intake clamps and exhaust bolts... Some people check the intake system by starting the motor and spray a little carb cleaner around the intake manifold. If the RPM's increase then you found a leak... CLUTCH If you wish high mileage clutch life then you have to invest is some good old sweat equity... because at the first sign of slip it doesn't automatically mean your clutch is tired and worn out or that your clutch plates are wore too thin because you can Mic them to determine serviceability and within the factory specifications... Under scrutiny you'll find that your slip was due to normal glazing and contaminates... Deglazing clutch plates ain't nothing new... no sir... back in the 70s it use to be part of every savvy rider's maintenance plan... and for some reason that all change during the 90s... why fix what you can buy new is the what you hear now a days... but if your interested in making your clutch bite good as new then roll up your sleeves and read on... i Inspect the friction plates for glazing... make sure you have plenty of material to work with... your shop manual states clutch thickness in thousands of an inch or mm... First removed the contaminants with Acetone... pick a hard surface to lay over a 600 grit black dry emery paper... rotate the clutch plate in a circle... you're just busting the glaze... don't get carried away remove too much material... You should end up with a friction plate looks dull like a new one as opposed to a shinny glazed one... recheck thickness... Next check the pressure plates for bluing caused by localized heat... make sure they are not warped... consult the manual for a thickness range... now removed the contaminants with Acetone and wire wheeled them to erased the blue and also to generally scuff up the surface... you should end up with a dull surface free of Blue marks... Bike on its side is a simple way to shift the oil level to an angle in order to remove the clutch cover without spillage... Have a new gasket standing by... Link to comment Share on other sites More sharing options...
Member Contributer BusyLittleShop Posted April 6, 2020 Member Contributer Share Posted April 6, 2020 6 hours ago, FJ12Ryder said: After market air filter, like a K&N? VFR K&N filters are designed to pass the same amount of air as the stock filter so the owner will not have to re map... whereas orange BMC filters are designed to pass more air than stock so remapping is necessary to cure a lean mixture... Link to comment Share on other sites More sharing options...
RVFR Posted April 6, 2020 Share Posted April 6, 2020 Gee, which air filter to use from K-N Actually the newer style does flow more air over the original version shown on the left. The trick is in making sure which one you will get as they use the same part number. Link to comment Share on other sites More sharing options...
Member Contributer FJ12Ryder Posted April 7, 2020 Member Contributer Share Posted April 7, 2020 Well, not to be too contrary, but an engine is only going to flow so much air. A bigger filter doesn't automatically mean it will flow more air, it just means that there is a larger opening that could let in more air if the engine could take advantage of that. Bigger isn't necessarily better, sometimes bigger is just bigger. Link to comment Share on other sites More sharing options...
Member Contributer Grum Posted April 7, 2020 Member Contributer Share Posted April 7, 2020 5 hours ago, BusyLittleShop said: VFR K&N filters are designed to pass the same amount of air as the stock filter so the owner will not have to re map... whereas orange BMC filters are designed to pass more air than stock so remapping is necessary to cure a lean mixture... Hi BLS. Curious to understand why "re-mapping" would be necessary with a greater flow air filter. Wouldn't the MAP sensor and the O2 sensor inputs to the ECM go a long way to compensating AF ratio for a given intake airflow? After all, intake airflow will vary normally with dirt/crap contamination during an air filter's service life, would imagine the ECM and its inputs would allow for that! Just a thought! Cheers. Link to comment Share on other sites More sharing options...
Member Contributer boOZZIE Posted April 7, 2020 Member Contributer Share Posted April 7, 2020 Faulty o2 sensor? Link to comment Share on other sites More sharing options...
Member Contributer BusyLittleShop Posted April 7, 2020 Member Contributer Share Posted April 7, 2020 1 hour ago, Grum said: Hi BLS. Curious to understand why "re-mapping" would be necessary with a greater flow air filter. Wouldn't the MAP sensor and the O2 sensor inputs to the ECM go a long way to compensating AF ratio for a given intake airflow? After all, intake airflow will vary normally with dirt/crap contamination during an air filter's service life, would imagine the ECM and its inputs would allow for that! Just a thought! Cheers. Hiya Grum... Dyno tuners are in agreement... Remaping optimizes fuel air ratio beyond what the system maybe able to compensate when faced with a less restrictive filter... Link to comment Share on other sites More sharing options...
Member Contributer Grum Posted April 7, 2020 Member Contributer Share Posted April 7, 2020 2 minutes ago, BusyLittleShop said: Hiya Grum... Dyno tuners are in agreement... Remaping optimizes fuel air ratio beyond what the system maybe able to compensate when faced with a less restrictive filter... Thanks BLS. Understood in order to gain maximum benefit. But by just fitting an air filter with better flow does it absolutely mean you have to have it remapped? I am surprised that simply having a greater flow capability through the filter means the ECM can't cope and needs remapping! Interesting stuff. Cheers. Link to comment Share on other sites More sharing options...
Member Contributer Grum Posted April 7, 2020 Member Contributer Share Posted April 7, 2020 11 hours ago, vfr200 said: Sorry. Re the PAIR stuff, do you know whether it shuts off somewhere around 6k? The PAIR Control Valve, is a Normally Open device, meaning that until the ECM energises it to close, its allowing air to the exhaust ports. The ECM looks at Engine Coolant Temp, Intake Air Temp, Throttle Position, Manifilod Pressure and RPM in its decision making regards the Control Valve. It appears that normal operation when you throttle off (Valve Open), would imply some amount of backfire as this most certainly is when the air is injected to burn off the unburnt fuel. An aftermarket pipe (if you have one) will exaggerate this effect. As to when the ECM decides to shut the valve, I've no idea, apparently, it's generally open for the low to mid range throttle operation, and throttle off situations. You may be right in suggesting a shut off around the 6k rpm.! Link to comment Share on other sites More sharing options...
Member Contributer MBrane Posted April 7, 2020 Member Contributer Share Posted April 7, 2020 Both my bikes are de-PAIR'd, and there is no more burbling/popping on decel. The air box is much easier to deal with now too. Unless you have overfilled the oil you should be able remove the clutch cover without spilling any with the bike on the side stand. Link to comment Share on other sites More sharing options...
Member Contributer Dutchy Posted April 7, 2020 Member Contributer Share Posted April 7, 2020 @vfr200 That is a fine looking banana VFR! I was told once by a tuner that the pair solenoid switches at/near idle rpm and that the valves itself will clog up over time/use anyway. My SP2 (with aftermarket BOS mufflers) never popped on decel. Still wanted a Power Commander (had some money to burn) and asked him about de-pairing. He said he would do it if I insisted, but he felt since they clog up, i'd waste money. But if I insisted, he would. YMMV Link to comment Share on other sites More sharing options...
vfr200 Posted April 7, 2020 Author Share Posted April 7, 2020 1 hour ago, MBrane said: Both my bikes are de-PAIR'd, and there is no more burbling/popping on decel. The air box is much easier to deal with now too. Unless you have overfilled the oil you should be able remove the clutch cover without spilling any with the bike on the side stand. But your avatar says you have three VFRs, not two... If it was only popping/burbling I'd just live with it, but this really does sound like a rifle going off as the rev needle drops through 6k. Do you have a picture of the hose I need to block off to disable the PAIR system temporarily? Would there be any downside to just unplugging the PAIR solenoid to leave it in "always on" mode to test whether it is causing my backfire? Link to comment Share on other sites More sharing options...
Member Contributer MBrane Posted April 7, 2020 Member Contributer Share Posted April 7, 2020 One of my 5th gens is basically a rolling parts donor these days. I suspect it has a cracked head. It's been at 245° on several occasions. There are 2 hoses that go to the PAIR valve (one from each cylinder head). I bought a pair (no pun) of block-off plates from a member here (don't remember who I've slept a lot since then), and removed all the parts/plumbing. I guess you could just unplug the valve from the wiring harness to test if that's what's causing your backfire. Link to comment Share on other sites More sharing options...
Member Contributer Grum Posted April 7, 2020 Member Contributer Share Posted April 7, 2020 36 minutes ago, MBrane said: One of my 5th gens is basically a rolling parts donor these days. I suspect it has a cracked head. It's been at 245° on several occasions. There are 2 hoses that go to the PAIR valve (one from each cylinder head). I bought a pair (no pun) of block-off plates from a member here (don't remember who I've slept a lot since then), and removed all the parts/plumbing. I guess you could just unplug the valve from the wiring harness to test if that's what's causing your backfire. Woops!, 3 hoses go to PAIR Valve, one is the air input from the air box (A), the other two (B) go to the front and rear cylinders. Best to just pull the air box hose and block that hose. Link to comment Share on other sites More sharing options...
Member Contributer MBrane Posted April 7, 2020 Member Contributer Share Posted April 7, 2020 Thanks for the correction dude! Like I said I've slept a lot since then. Link to comment Share on other sites More sharing options...
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