Weak fuel pump and lackof power?

[des@helium-labs.com]

Hi Y'all.

I have a 75 with 34 k miles. Second owner. Almost completely original. Bike is sweet (after I deveterrized it) and after the usual fettling needed for a bike that sat for a few years (fluids, brake rebuilds, fork seals etc.) mostly runs great. The only issue is it is gutless at higher speeds (struggling to crack the ton). I have had the carbs professionally cleaned and balanced (although that's no promise it was done correctly). I checked tank, fuel cock, petrol filters and fuel lines. All seem good. Bike has the electronic ignition upgrade so assuming it's not a timing issue. No smoke. Starts right up. Runs smooth with no discernible missing or hesitation. Just runs out of oomph.

I recently made the following observation. When the bike is on the flat it idles fine. But when I had it pointing uphill on a steep slope it started to idle poorly. Back on the flat again and no problem. Wondering if my fuel pump is a bit sad? Has anyone seen something similar? Or is this pointing to a dodgy float or carb? Any advice on how to test the fuel pump much appreciated.

- Des (Austin TX)
75 Goldwing
56 Squarial
70 Guzzi (project)
72 CB750
89 Honda GB500
2000 BMW R1100RT (strictly for longhauls)
2007 Suzuki SV650 (naked)
72 Suzuki GT380 (project)
It's an addiction - and I don't care

[cfairweather]

I believe there is a testing procedure in the manual. Just hook up a discharge hose to the outlet of the pump and see if it squirts out a reasonable amount of fuel. If so, I would then look at the carbs. Take a close look at the plastic buttons on the caps. It could be they are leaking and the slides cannot fully raise due to a lack of vacuum. Also, verify the float levels using the clear tube method.

[Whiskerfish]

viewtopic.php?t=43633#p453019

[redglbx]

I would check that the vent hole in the gas cap is clear & functioning as the very first thing, they seem to rust and critter like to invade that space, this will usually cause the bike to stall after a period of time and then restart once the vacuum created in the tank is relieved, but a partially blocked cap vent may appear to be a bad or weak pump. I consider them to be a bit weak even when new but it is hard to argue with something that lasts and works as long, anyway check that the gap is venting, it’s simple and most importantly free.

[cfairweather]

Good suggestion Steve.