Gsx400f - Revs falling - engine dies

[Guest]

I have 1982 GSX 400 F.

It starts with a light touch on the starter button and idles nicely.
However, when I am riding along, I sometimes experience that the revs are falling, and I am loosing speed and eventually the engine dies out.
Then I cannot start the bike unless I apply the choke. Then it starts easily and I disengage the choke right away and everything is fine.

If I engage the clutch when the revs are dropping, it revs up with no fuss, but as soon as I let the lever go, the revs drop and the engines dies out.
Right before the the revs drop, I get a bumpy sensation in the bike, as if there were "lumps" in the petrol. I have checked the fuel lines and the fuel tap, and the petrol runs perfectly.

I am not a 100% certain when the problem occurs, but it mostly happens when I am giving it the beans in a straight line. Sometimes it happens when the bike is right out the garage and sometimes when I have been riding for a while.
I never experience it, when I am doing a lot of curves and changing the gears a lot.

Hopefully there is a genius out there who can help me out.

[pete]

Two things I can think of... when it happens, try opening the fuel cap and see if it starts straight away. The tank needs to be able to take air in to replace the fuel as the level goes down, and if the breather is blocked it will cause a vacuum which will stop fuel flow.

The other... do you have an inline fuel filter between the fuel tap and carb's? If so, they can be too restrictive and starve the carb's of fuel.

There are other possibilities as well actually... carb float height too low for example...

[1979nicolaus]

Two things I can think of... when it happens, try opening the fuel cap and see if it starts straight away. The tank needs to be able to take air in to replace the fuel as the level goes down, and if the breather is blocked it will cause a vacuum which will stop fuel flow.
I have tried that, but it doesn't seem to help.

The other... do you have an inline fuel filter between the fuel tap and carb's? If so, they can be too restrictive and starve the carb's of fuel.
There is a filter. I will try and bypass it and see if I get the same problem.

There are other possibilities as well actually... carb float height too low for example...

I have never fiddled with the carbs, so I am not entirely sure about what it means.

Thanks for the help.

[pete]

No worries, let us know how you go!