GSX 400f dies after 1/2 an hour ride.

[johnmc]

G'day all
My GSX 400 f has an issue that I can not figure out . The bike starts up straight away with no issues at all . 30 minutes into a ride it slowly loses power and dies .
. After about 1 hour I kick it over and starts up straight away . I thought it may be the coils as the bike would kick over freely but not run. So I replaced them and to day I was lucky to make it home as the issue is still there . Any thoughts on what could be causing it .
Regards
John
Sydney Australia

[tom203]

Check petcock for fuel flow....might be restricting fuel delivery to carbs, so they starve after a bit of running

[zuluwiz]

Check for air leaks in the intake. my old GS1000 did exactly the same thing because of cracks in the intake boots.

[steve murdoch]

Don't know if your gas tank has one but many have a vent in the gas cap.
They can become clogged and pressure can build up and choke the gas flow.
On an old Honda i could open the cap while riding and it would alleviate the pressure.

[Nessism]

Agree about checking the petcock and tank venting. I'm not sure about access on that model bike but you may be able to check for fuel in the float bowls when it craps out by removing one of the float bowl drain screws.

Tight valves can hang open when the engine is hot causing compression loss. The engine would have to be in dire condition for this to cause the situation mentioned though. Also, be sure to check your charging system. Hard to imaging it causing the issue but it never hurts to check all the common issues.

[Redman]

.
...................................... 30 minutes into a ride it slowly loses power and dies .
.
.

Next occasion when it starts to loose power, switch the petcock to PRIme for a while (dont leave it there), if that doesnt releave the symptoms, then try opening the cas cap, see if that clears the symptoms.

[GregT]

This time of the year in Oz, if it isn't fuel supply, it's heat related.

I'd check the valve clearances first. Correct spark plug grade ?

[LAB3]

Next occasion when it starts to loose power, switch the petcock to PRIme for a while (dont leave it there), if that doesnt releave the symptoms, then try opening the cas cap, see if that clears the symptoms.

Good advice although I'd try one (the gas cap) first than the other (switch to RES) to isolate the issue. My bet is gas cap venting, it makes the most sense if the problem is consistent, same thing happened on my 'Wing just after getting it on the road.

[johnmc]

Thanks everyone for the advice. I've removed the vent from the petrol cap and see How it goes from there.

[LeT]

Hopefully, the tank breather will be the cure. However, I had this exact same problem with a Hinckley Triumph 900. It would start and run perfectly from cold, then after about 30 mins would die refusing to start until cool again. The cause was the ignition pickup coil breaking down with heat. Replacing that was s complete cure. Maybe it could be the same thing for your bike? Can't swear the electrics on these old GSX bikes are the same but I think they also rely on Hall effect pulses.
I did have valve problems with my GSX400FX: burned out two exhaust valves on cylinder 4. However, it still ran on the other cylinders to get me home. Good luck with diagnosing.