@Kleinbaai Also, since that #1 carburetor is so close, put a drain line onto the nipple on the bottom of the bowl. Then open the drain screw. Fuel should readily flow out of the carburetor and eliminate the air in the line. Close the drain once the fuel is flowing steadily.

 

Item #6 on this page is the air vent for the upper half of the float bowls. It needs to be open and not capped off. I know this link is for 1988, but the US didn't get the 1000F in 1989.
https://www.ronayers.com/oemparts/a/...arburetor-assy

 

Cheers again for the input. Yep, the air vents are free, checked those before putting the carbs back on after the rebuild. The tanks are full and the hydrostatic pressure of the fuel should be more than enough to flow freely. Like I have said. When the carbs are connected to my 1 litre slave tank, this issue does not happen, everything works as it should (although, thinking on it, that does sit a bit higher than my tanks as it hangs next to the bike). I have tried squeezing the lines to push the air back into the tank, does not seem to make any difference. Will be checking my fuel pump today to make sure it works. Also have a few more ideas to try as well.

 

So, trying to drain fuel out via the float bowl didn't work?

 

Not done the drain yet as when I went into the garage yesterday morning, lo and behold, the fuel line was half full (even though I had turned the tap off). Turned the tap on and gave a the line a few squeezes, kinda like a motorboats fuel primer bulb, and the whole lot filled up rapidly. More squeezes and wiggles on the line and a few large air bubbles came from the carb side of the line. After that, seemed to have no issue with feed. Warmed the bike up, and again let her run up through the rev range. There is a flat spot about half throttle, but then picks up again. Do have a plan to put it on a rolling road once the feed issue is fully resolved, so not too worried about that.

 

This morning, did drain the nearest float bowl as suggested. Drained and then stopped flow. Was not continuous even though the fuel tap was open. Closed it off and re primed the line. Just been out for a shakedown run. Warmed up well, set off. No issues in lower rev range, bike did ok,. As speed increased, seemed to have a big flat spot around 50mph, but could power through it and then seemed to accelerate well after that. Did feel as if struggling for fuel in the flat spot, so not sure if due to poor fuel delivery or just jetting. Pulled over to check, idle seemed a bit ragged at first, but then settled. Checked fuel line, no air bubbles in it at all after the initial blat about, so taking that as meaning the bowls are full and fuel is flowing OK now. Set off back, gave it berries on pull away and hit 70mph short shifting through the gears, did not hit a flat spot. Only appeared again when staying in one gear and opening the throttle fully. May still go with the fuel pump to be sure, but also definitely getting it on a rolling road in the near future as think jetting/needle heights may need a looking at.

 

Tried it with the fuel filler cap open? That'll eliminate the breather hole in the cap.
Taken the fuel tap apart to check for blockages/duff reassembly by a PO?

 

How long does it take for the engine to die when connected to the tank? If you leave the gas cap open, does it still die?

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Thank you for your time and consideration.
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Have you tried removing your existing lines/filter setup and using a single piece of clear tubing from the tank to the carbs as a quick and easy check?
This would indicate if the gasoline filter is the source of the problem, with the crabs' suction inadequate to suck the fuel through the filter.