Author Topic: Low vacuum  (Read 668 times)

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Offline nk140

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Low vacuum
« on: October 10, 2018, 02:38:19 PM »
Been meaning to ask this question for a bit.  My bike runs great and has good compression (150 psi), but I am having a hard time getting the bike to idle properly.  It will die sometimes when coming to a stoplight.  Bike is a kick start only right now until I can fix the starter clutch this winter.  It takes a lot of kicks to get it started the first time but once started it will run and start great all day.  I noticed when syncing the carbs lately that the bike has very low vacuum.  In fact we can pull the hose off the vacuum port and the engine doesn't miss a beat.  The bike seems to have only between 5-8 psi of vacuum.  The plugs are looking perfectly brown.  We can't find any vacuum leaks anywhere.  Any advice on where to look?
« Last Edit: October 10, 2018, 02:40:23 PM by nk140 »

Offline dailydose1

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Re: Low vacuum
« Reply #1 on: October 10, 2018, 03:25:01 PM »
Have you tightened the headbolts? tightened the two bolts on the right side of the engine? sprayed carb cleaner at the carb joints and looked for increased rev at idle? valves adjusted to spec?

Offline nk140

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Re: Low vacuum
« Reply #2 on: October 10, 2018, 05:28:47 PM »
Have you tightened the headbolts? tightened the two bolts on the right side of the engine? sprayed carb cleaner at the carb joints and looked for increased rev at idle? valves adjusted to spec?

I have torqued the head bolts.  What two bolts are you referring to on the right side of the engine?  I have sprayed  around the carb joints and no idle change.  Valves were checked and put to the loose end of spec but will check again.

Offline nk140

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Re: Low vacuum
« Reply #3 on: October 11, 2018, 02:39:40 PM »
what kind of vacuum do these bikes normally have?  I can't find a spec.

Online guylr

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Re: Low vacuum
« Reply #4 on: October 12, 2018, 01:06:45 PM »
There is no vacuum spec that I know of. If compression is in spec then vacuum should be sufficient.

Guy
Now Retired Yamaha guy. Cut me and I bleed "Cinquasia Red"

Offline nk140

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Re: Low vacuum
« Reply #5 on: October 12, 2018, 05:57:14 PM »
There is no vacuum spec that I know of. If compression is in spec then vacuum should be sufficient.

Guy

Both cylinders are 150+ psi.  Just weird that the engine didn't run rough when pulling the vacuum line.  Like I said the bike runs great other than idling conditions and rpms are slow to return to idle after letting off the throttle.