Flat spot around 1500 rpm

[Garry Kent]

Flat spot occurres round the 1500 rpm mark and stalls the bike if you let it .
Done fuel filter aircleaner and plugs .
Any ideas would be welcome
Regards
Garry
1993 aspencade

[virgilmobile]

My first suspect is 26 year old vacuum lines need replacing.Those rubber hoses just don't last forever.

[Garry Kent]

Thanks mate , let you know how it goes.
Cheers

[virgilmobile]

Don't forget.Theres one under the black thermal mat that sets between the carbs and engine.

[Straydogg]

[Garry Kent]

Cured 90% of the flat spot by replacung red hose from filler cap and adjusted idle speed to 800rpm . Flat spot is now in the 2000rpm range .Really appreciate your help as i am trying to negotiate this prob wih out the assistance of a mechanic .
Kind Regards
Gazza

[CRAFFS]

Flat spot at 1500 - 2000 rpm points at blocked primary jets. Unfortunately the carbs needs to be removed for cleaning....(
I recently started inspecting my 1993 GL1500's fuel system after the bike had been standing for 2 years. So far I found the following: -
1) Fuel pump has "died", new pump ordered (workshop manual describes how to test the pump).
2) I will replace the 26 year old fuel filter after finding rust in the tank.
3) Checked the diaphragm in the AUTO FUEL VALVE ("petcock"). The diaphragm tested fine but I might replace it in anyway (26 years old)
4) Did a vacuum test on the AUTO FUEL VALVE. No vacuum - the vacuum line between the engine intake manifold and auto fuel valve for sure leaking (see photo from "Straydogg" & Virgilmobile's comments). Once I have the carbs out I will check all rubber hoses and replace where needed. (Workshop manual shows to do a vacuum test.
5) Did an "initial" test of the carbs by "gravity feed" fuel to the carbs (I connected the rubber hose from the gravity feed bottle to the rubber fuel hose at the outlet side of the auto fuel valve). The engine started immediately but A) had a flat spot when revving and B) petrol streamed from the carb float chamber overflow hose. So, I have blocked primary jets plus stuck float(s) in the float chamber(s).

Think I will take a break before attacking the carb removal...

[Garry Kent]

Thanks for the info , carbie removal and cleaning is beyond my skill set even with the aid of you wonderfull guys and a manual .
I just have to find a workshop capable and willing to undertake the task.
Cheers
Gazza