550 wont rev

[Anonymous]

Hi all,I have a 78 GS550 which has just returned to the road after 4 years.Last time on the road it ran fine,it had Yam Virago silencers and a homemade airbox stuffed with foam--------!. OK you can stop laughing now,STOP I say.I changed them for pods and "universal" silencers.Problem is,it wont rev past 5000,also,when you blip the throttle hard from idle it die's and stalls.
I have cleaned & synched the carbs,set floats and mixtures (plugs light brown) replaced the points, set the timing and checked the valves. Its not a petcock problem as its fitted with a different tank (dont ask!).The main jets are 92.5 (orig,80) done by PO.
Nothing seems to help,it feels like its being starved of fuel above 5000. Just read about the vent pipe issue so will try that today. Pleeeaase dont make put the Virago pipes back on !

[IanFrancisco]

Well, you say the jets are oversize and the PO had foam in a homemade airbox. Certain pods (K&N) are more restrictive than others. I would guess that the jets may be too large for the pods you're using and momentarily flood the engine when you blip throttle. That wouldn't neccessarily show up in a full-thottle/cut-motor plug test. Other people have mentioned using WD40 sprayed around the intake boots to check for leaks (w/ engine running) and also the o-rings that go under them.

[Anonymous]

Thanks Ian, got some standard jets off a mate today, same thing happens.Tried spraying the inlet rubbers but they seem ok,I think an air leak problem would have shown up when I had the vaccum gauges on to synch the carbs.Going to try a different set of silencers,maybe the ones I have are too open ?

[gspaul]

Try lifting the carby needle's one notch,and readjust your idle mix,and sync your carb's again to be certain.