vfr800fi running badly

Hi, new to this forum stuff so please excuse me if i'm posting wrong place etc,
I purchased a 1998 model and on my first ride out the bike is very flat on acceleration and seemed like it's missing a cylinder,progressively got worse on my ride and i just couldn't wind the throttle back without jerking and spluttering and eventually it cut out,kept restarting nut i had no power to pull across the road safely,eventually rode the clutch and made it home. I removed air filter and where number 3 is on the air filter base was a little wet and down the carb was a little wet,removed the rear spark plugs and number 3 was black.
Question is would a simple duff plug cause this problem or could this be getting too much fuel from pressure regulator making it flood ? Any thoughts welcomed please, thankyou

 

Dodgy plugs would be the easiest thing to swap out. You could also have a poor ignition lead or plug cap connection leading to a lack of sparks. Another possibility would be a fuel injector blockage. All the injectors share the same fuel supply so the regulator won't affect just one plug. The regulator needs to have a decent vacuum connection to the intake port, maybe you have a crack in the hose, that would give overall excess fuel pressure.

 

Thanks for your input,i think i will definately change the plugs and see what happens,the guy i got it from didn't do many miles on it, he took for mot and said it rode perfectly fine,transported it home in a van and then i took it for a ride and this is result, he was an older guy and seemed very genuine so either he lied or something just went by coincidence.

 

Did you get gas right before it started acting up?

 

No M8, it had fuel in it,I did wonder about bad fuel, it rides like fuel starvation and starts running like when you are about to run out of fuel, then when you get to junction it stalls,fires up straight away but throttle response is flat and engine doesn't sound like it's firing on all cylinders

 

Gotcha. Start with plugs as Terry states and go from there. Also, how does the air filter look?

Does it run ok again after sitting for a while and then go to shit again?

 

Air filter looked ok,it just doesn't sound as I'd expect and throttle response is poor, as soon as you give it a rev to maybe 3 or 4 k it sort of splutters,like I say the only way I can describe is the running out of fuel scenario

 

maybe youd get some clues after inspecting the sparkplugs

 

Good advice already.
- Is your Battery Healthy, and have you checked your charging voltage?
- Have a good look at the Fuel Pressure Regulator. A ruputred diaphragm will dump excess fuel into cylinders 3 and 4 and cause terrible running. Check for fuel weeping from the FPR vacuum hose fitting or wet looking vacuum hose
- If replacing plugs suggest fitting Platinum Iridium replacements. NGK CR9EHIX-9.
- Closely inspect Main Fuse B 30amp located next to the Starter Relay it and its wiring can suffer badly from burnt high resistance connections causiing EFI issues. Its a high failure rate item.
- Lastly there is an orange colored common Earth Block located in the wire harness just above your chain guard. This device causese multiple issues due to bad connections within this earth block. Check it for burnt looking connections. Multiple devices have their earh wire comming into the earth block then two genuine earth wires go to Ground.

Good Luck. Hope you get it sorted. A well running 5gen is a Great bike.

 

Thanks for all the replies, I am definitely getting some plugs,and I will check around fpr, I looked at that orange block the other day and seemed fine,I looked at white block connection from the rectifier at the same time as I just replaced all this on my srad, the block sort of looked ok but wonder if worth chopping out and soldering wires. Can someone tell me why there is also a black connection block on the rectifier that doesn't connect to anything? I will keep updated on here with my findings, just really want to get on and ride to experience the bike how it should be. Many thanks, pic of plug 3

 

Can anyone tell me what this thing does and if this could cause any of my problems, the pipe that attatches to the bottom doesn't stay on too good so could possibly have been off.

 

That is the one-way valve that operates the flapper via a solenoid valve. If the ends are uncapped you will have a vacuum leak into an inlet port and that is a Bad Thing. You will have no running issues if you cap off or plug any hoses connected to this device except (if it is still fitted) the flapper valve in the air intake will be permanently open (which will give a bit more intake noise at lower revs but otherwise won't affect operation). All of the vacuum hoses that connect to the throttle body need to be leak-free, and the two that connect to the fuel pressure regulator and the MAP sensor are critical for proper running.

 

Many thanks for that, I've just ordered second hand throttle bodies with injectors and everything so hopefully I can get this sorted out, reckon I need to get a workshop manual too

 

The service manual can be downloaded here: https://www.vfrdiscussion.com/index...onda-vfr-service-manual-optimized-bookmarked/

 

Thanks for that M8,

 

Just to clarify,ref the picture of the one way valve i posted, are you saying that i can remove that valve fully as long as i plug the 3 lines that go to it ? thankyou

 

The purpose of the one-way valve is to use intake vacuum to charge the vacuum chamber on the front of the airbox, and then the ECM opens and closes a solenoid to use that vacuum to close the flapper valve below 5500rpm. The default position for the flapper is sprung open; it needs vacuum to close. If you don't connect to the inlet vacuum, the flapper stays open; no effect on running, just a bit more intake noise.

Your engine needs to have a good seal between the throttle butterflies and the inlet valves; any unexpected leaks will affect the fuelling to the affected cylinder and probably also cause a high idle. Any of the vacuum hoses that plug into the side of the inlet tract need to seal up to something; e.g. the blank stubs on the airbox, the MAP sensor, the fuel pressure regulator, and the one-way valve (and associated bits). If you remove the one-way valve, you must cap off the vacuum hose leading back to the inlet, a golf tee jammed in to the tube end will work well, or you can fit a vacuum cap to the stub on the inlet. You don't need to worry about capping off the flapper diaphragm, the solenoid or the vacuum chamber if these are still present.

If you disconnect the flapper solenoid electrically, the ECM may throw up the FI fault light, so better to leave that plugged in.

Vacuum tubing is dirt cheap and easy to replace; I would not rule out just replacing all the tubing if you are trying to resolve a problem. Cracks can be very hard to spot.

 

Thanks for the explanation, i have picked up a spare set of throttle bodies complete with injectors, my spark plugs should come tomorrow so im going to change them and probably put back together, i was actually tempted to replace all the pipes but i was unsure if i wanted to remove my throttle bodies if i didn't have to, i could clean the second hand ones i have and replace all the pipes on them in case i was going to swap over the whole thing. I will do the plugs and then update. cheers

 

I also have some fuel injection issues, that I hope to solve with fresh vacuum tubes.
I found it a bit hard to find a source of suitable vacuum tube, but Honda has a 3.5mm bulk package of 1M: 950053500120M
Which I think is the correct type...
I have just ordered 3M here:
https://www.cmsnl.com/products/bulk-tube-tb-35x1_950053500120m/