VFR400R bogs down with full throttle.

[PeteLyons]

I have an '86 vfr400r, 13000kms. The bike runs fine in the city, but when i take it out on the highway, where i have to give it more throttle, the engine sometime bogs down, it even stalled on me a couple times.

Basically, at high speed, when i give it more that 1/2 throttle, there's practically no power, the engine tone deepens quite a bit, and sometime stalls. But if i keep the throttle no more than 1/4, it seems to run fine. I've pulled the plugs, and 3 of them were blackened quite a bit, so I'm guessing its running too rich, but i'm not sure how to fix it.


Any help would be much appreciated.

Pete from Canada.

[lostinflyz]

hey pete.

i have the same bike that had the same problem. too be honest i did a number of things and i dont remember which one actually worked. When my power cut (bike bogged) it was really random and didn't do it always.

Having had a play with a few of these v4's now my best suggestion is to check the fuel tap particularly the internals as well as the vacuum line that opens the diaphram. make sure that hose is good.

Another problem i had was a aftermarket filter (should i say an aftermarket sponge) being fitted. I sourced a new one and it worked well. Additionally make sure the jet arent blocked at all.

Off the top of my head im pretty sure my problem was in the vacuum line. I think at certain orientations it had a hole in it that was either slightly pressed shut or wide open causing the random bogging down.

Pretty much work your way down. fuel tank, airbox then carbies. Don't screw with the carbs if u can help yourself, unless you are 101% sure theres a prob. There a bastard.

Additionally check the electrics cause i have heard they can be pretty dogdy sometimes on these

[monkey99]

Ahh I had this happen to me on an NC21 VFR400.. After much jiggery pokery it was discovered as bad packing in the exhaust can..

All the other parts as refer to "lostinflyz" were checked and it solved the problems only below 70km/h

So it was good to check thru the electrics and the diaphragms were a bit ordinary with a bit of tired rubber.. well it turned out after accelerating hard on the throttle that a peice of packing in the end can would block the exhaust and essentially it was suffocating the engine..

So check the packing & exhaust flow also

[BMW_RACER]

If its random, could be an electrical problem. Check your coil packs and wiring.

[moT]

I have an '86 vfr400r, 13000kms. The bike runs fine in the city, but when i take it out on the highway, where i have to give it more throttle, the engine sometime bogs down, it even stalled on me a couple times.

Basically, at high speed, when i give it more that 1/2 throttle, there's practically no power, the engine tone deepens quite a bit, and sometime stalls. But if i keep the throttle no more than 1/4, it seems to run fine. I've pulled the plugs, and 3 of them were blackened quite a bit, so I'm guessing its running too rich, but i'm not sure how to fix it.


Any help would be much appreciated.

Pete from Canada.

is you speedo connected? or the wires dammaged to your speedo?

[FJRider]

Check vaccum lines are connected correctly at both ends and not kinked. If your fuel tap has a "prime" setting, try it doing the same type of riding. Reserve sometimes does the same thing... Let fuel through without vaccum. Maybe just blocked fuel TAP (the latter MY bet) If it is blocked, get it cleaned out properly and get it relined. Won't happen again then.

[koba]

Pretty much work your way down. fuel tank, airbox then carbies. Don't screw with the carbs if u can help yourself, unless you are 101% sure theres a prob. There a bastard.

Best bet, I've had problems with the fuel tap.

It has a Vacuum regulator on it and the diapgham (SP?) on mine was poked casing it to not move correctly to regulate the fuel flow.

[koba]

Also a bike that age with such low KMs is likley to have spent alot of its life sitting around, possibly without fuel in the carbs.
It is a good idea to check (or have a shop or mate or whatever do it) the fuel and Vacuum lines.
Mine was old and split and I ended up riding 20kays with my hand undwer the tank, touching the hot engine while holding the makeshift fuel line from pincing shut because it was an old volkswagen engine breather line.
Not fun,
Not Recommended!

[koba]

I have an '86 vfr400r, 13000kms. The bike runs fine in the city, but when i take it out on the highway, where i have to give it more throttle, the engine sometime bogs down, it even stalled on me a couple times.

Basically, at high speed, when i give it more that 1/2 throttle, there's practically no power, the engine tone deepens quite a bit, and sometime stalls. But if i keep the throttle no more than 1/4, it seems to run fine. I've pulled the plugs, and 3 of them were blackened quite a bit, so I'm guessing its running too rich, but i'm not sure how to fix it.


Any help would be much appreciated.

Pete from Canada.

Any luck??

[chaozhoi]

hi, i'm facing the same problem and i'm riding a RVF400. Only thing i can try now is to take out my exhaust to do a check. May I know what I should look out for in the exhaust? If a problem was to be found in the exhaust, how can i rectify it? Thanks.

[lostinflyz]

hi, i'm facing the same problem and i'm riding a RVF400. Only thing i can try now is to take out my exhaust to do a check. May I know what I should look out for in the exhaust? If a problem was to be found in the exhaust, how can i rectify it? Thanks.

have you checked all the bits prior to the exhaust??

If its the exhuast re: bad packing then you can just repack the exhaust can. Should be a rather simple job depending what can is on it. these vfr/rvf's are very picky and it can be many things but almost all are simple fixes.