1989 GS500 - high speed fuel starvation

[Nipedley]

Hi guys,

Been chasing this gremlin for a little while now.

What it does: I can accelerate up to 90mph no problem at all (and no doubt would go faster), but if I hold my speed over between 67 - 72 mph depending on how the bike is feeling that day, for more than 15 - 20 seconds, it will start to pull back (that running out of fuel feeling), start to bunny hop a bit, then slowly decelerate while the throttle makes no effect at all - just like running out of fuel. It then refuses to start until I 'PRIME' it for a while, and then we can take off. So, I presume the issue is lack of fuel

What I've done: Cleaned the carbs, twice. New float valves and seats, new fuel lines (not kinked), new fuel filter (and also ran without filter, no change). Cleaned fuel tap. Removed petcock from tank and cleaned (filter not like new but looks like it would flow fine).
I discovered as per a previous post I have large chunks of old fuel tank liner inside my fuel tank that I am unable to remove, but they shouldn't be fouling the petcock filter or flow I would seriously doubt.

So I am left with: Still dirty carbs (unlikely), faulty fuel tap?, or perhaps the large chunks of old fuel tank liner are causing a problem

What do you think, or can you guys suggest anything else?

Ta very muchly

[Watevaman]

 Have you tried switching to PRIME while you're running and having these problems? I know adidas and others can chime in better, but I've heard it's an issue with fuel flow at high speeds like this. Or it may be a clogged vent in your gas tank. For now, though, try running in PRI (but don't leave it on PRI when you hop off!) and see if that alleviates it.

[radodrill]

There's a vent tube on the carbs that's supposed to be routed to the battery box; if this tube is left in an un-sheltered area, then you can have fuel delivery issues at high speeds.

[The Buddha]

Hi guys,

Been chasing this gremlin for a little while now.

What it does: I can accelerate up to 90mph no problem at all (and no doubt would go faster), but if I hold my speed over between 67 - 72 mph depending on how the bike is feeling that day, for more than 15 - 20 seconds, it will start to pull back (that running out of fuel feeling), start to bunny hop a bit, then slowly decelerate while the throttle makes no effect at all - just like running out of fuel. It then refuses to start until I 'PRIME' it for a while, and then we can take off. So, I presume the issue is lack of fuel

What I've done: Cleaned the carbs, twice. New float valves and seats, new fuel lines (not kinked), new fuel filter (and also ran without filter, no change). Cleaned fuel tap. Removed petcock from tank and cleaned (filter not like new but looks like it would flow fine).
I discovered as per a previous post I have large chunks of old fuel tank liner inside my fuel tank that I am unable to remove, but they shouldn't be fouling the petcock filter or flow I would seriously doubt.

So I am left with: Still dirty carbs (unlikely), faulty fuel tap?, or perhaps the large chunks of old fuel tank liner are causing a problem

What do you think, or can you guys suggest anything else?

Ta very muchly

You have a lean surge @ between 1/2 and 3/4 throttle - needle territory.
Then ... why it wont restart is probably a unrelated item.
You can run 90 on open throttle, like you keep accelerating you will keep going ... yea lean @ 1/2-3/4 throttle.

Cool.
Buddha.