VFR400 NC24 runs for 3 minutes then .....

[Pirates Cove]

Hi

The VFR has a problem. I went to Tesco and back and just as I was getting to my pace it stalled and then started running very rough and would not rev above about 2000 rpm.

Now if we leave it for a while it will run ok for 3 minutes and then goes back to this weird mode.

We have.
- disconected the REG/REC in and out .... still does it
- fresh fuel
- check fuel bowls and fuel flow ... ok
- battery ok 13.65 volts
- lines and fuses look ok
- new plugs
- coils seem ok and have power even when bike is running bad.
- not over heating
- cdi , coils and wiring not getting hot (or even warm)

Any ideas ?

Mark

[Jon]

Hi.
Welcome to the forum.
It sounds like a fuel restriction, or tank vent blocked, getting partial flow but not quite enough to keep up.

Does it run any better/longer on reserve?
Does it run longer at an idle rather than riding it?

regards
jon

[Pirates Cove]

Hi.

Have taken the tank apart and it is clean and looks like it is flowing ok.

RES and on flow the same. The vac is disabled.

Thanks

Mark

[Cammo]

When it has problems try opening the fuel tank filler, if you hear a whoosh of air then it's fuel breather problems.

Also check that the fuel lines aren't getting pinched by the tank etc when warm.

[Pirates Cove]

Hi all.

What seems to be happening is that the spark plugs are getting carboned up then getting wet then not/mis - firing and after some time the fuel dries and it runs.

The carbs look ok and the float levels are 6.8mm ....

don't know what size the jets are perhaps have to get them out.

The carbs are VD keihin's but have no pilot screws at all.



Mark

[Cammo]

The carbs are VD keihin's but have no pilot screws at all.

They do have pilot screws, they're underneath. There are only 2 screws underneath, 1 is the float bowl drain the other is the pilot screw.

Good chance these are out of adjustment and causing it to run rich!

[wullvfr]

The carbs look ok and the float levels are 6.8mm ....

that is spot on,
is the bike back firing at all?


william

[Pirates Cove]

Hi.

No the carbs do not have any screws on the passage where the pilot screws go into.

There is no back firing but at idle the exhaust has a little black smoke.

Mark

[Cammo]

No the carbs do not have any screws on the passage where the pilot screws go into.

So you're missing the pilot screws??

Perhaps that's your problem!!! The bike will run like a bag of sh!t at low revs without them.

They should be set at 2.5 turns out.

[Pirates Cove]

Yeah its very difficult to check 2 as they are right up against the frame. The book shows the two carbs diagonally opposite have pilot screws and these definately do not.

The carbs are coming off for a check and to verify that the pilot screws are not there.

Thanks for all the advice.

Mark