Basket case 98 needs some help

Hi everyone! I’m a new member, I just got a VFR800 with 26k miles.

It starts and idles ok - will rev no problem.

When I take it out and put under load it bogs and doesn’t want to keep going above 5k..seems like it might not be getting enough fuel or spark.

There are a couple vacuums not connected and random things that don’t seem right..I have yet to get a manual for this bike so I was just throwing it out there.

Are these bikes prone for weak spark or anything I should look at directly?

TIA!!


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You can download a pdf manual from vfrdiscussion.com in the browse->downloads section. Its also annotated and searchable which helps. I'd start with the easy stuff: plugging those vacuum lines, checking/replacing the spark plugs, and putting fresh gas in the tank.

 

So today I did stuff.

Replaced the fuel pump (aftermarket - but looks and fit identical)
Removed the fuel filter (for testing purposes)
Replaced the spark plugs with OEM ngks
Found the choke mechanism was not closing..

Nothing I’ve done today has made a difference.

Mid throttle up to 5k and falls flat - if I throttle through it, it will pick up again and keep going kinda

It’s either an injector or coil / wire problem I’m assuming at this point.

Of course it’s raining and making this more complicated than it needs to be


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Make sure you check for restrictions in the airbox and the exhaust system. Bikes that sit get critters in them.

 

Yea I’ve seen that. At this point I have no air filter and I have confirmed the exhaust is free flowing.
At a stand still the bikes idles and revs ok..it will hesitate if I do a throttle chop which I believe is the same problem I’m having while riding.

Once under acceleration it wants to flatten out around 4500-5k rpms. Then if I roll off and slowly accelerate thru it will clean up and continue to rev..
I know once I figure it out it will be something very stupid.


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Are you getting any FI fault codes?

You chould check that you have vacuum hoses connected to the manifold air pressure sensor (back of the airbox) and also to the fuel pressure regulator. You should also have the flapper valve opening above 5500 rpm on the airbox, from memory that should default to open if there is no vacuum however.

I had a problem with weak sparks on a bike that had been stored outside for 10 years due to some connector corrosion on the main power feed going to the ECU. That gave bad misfiring whenever I tried to rev that one above 4000rpm, but ran perfectly below that.

 

On of the biggest problems with bike that have sat for a long time, indoors or out, is corrosion on the connectors. Corrosion causes a resistance and a drop in voltage that can play hell with ignitions systems computers. Also make sure, as Terry suggested, that you have all the vacuum lines ether hooked up or plugged.

 

I am so glad someone else pointed this out, not only does corrosion cause a voltage drop, resistance creates heat!

 

In my case it was the big red connector that feeds power up and back to the right switchblock and ignition switch.

 

I will start pulling connectors when I get home. Thanks guys for the help!


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