Vacuum Fluctuates Wildly at Idle

[65Cobra]

Have a 99 Busa with a modified Mr Turbo setup. Bike sat unused for most it's life due to medical problems... has less than 8,000 miles.

Summer 2008... worked on motor... no issues... just to make more durable. All APE products... valve springs & retainers, head studs, main bearing studs, Cometic gaskets (including .030 MLS Head Gasket), high volume oil pump gear, minor clutch mods. Still have original pistons, rings and bearings as less than 500 miles since turbo was installed.

Summer 2009... worked on turbo system... realized what garbage Mr Turbo sold. Made new plenum... installed new Tial wastegate & BOV... and literally replaced every component from his kit with the exception of the header and Rajay turbo which have been fine.

Summer 2010... figured I only needed to setup the map. The bike would start and idle fine... ran good when I open it up... but surged from richness while cruising. Had some issues with BEGI working properly but they have since been resolved and I seemed to be making headway.

This week... latest LM-2 recording while in garage shows air/fuel stays level until about 2,100 rpm at which point it begins to rapidly fluctuate between 10 and 14... causing the bike to surge.

Today... even though I have an Auto Meter Vacuum/Boost Gauge mounted on my dash, I decided to connect a standard automotive vacuum tester to TB#1. The needle was highly erratic during idle... bounced rapidly between 5-21 psi... same result when connected to TB#4. I didn't expect this but the Auto Meter gauge has a built in restrictor which might explain why it doesn't show any erratic readings.

Not sure what this means or where to go from here. Tried searching the internet and one site mentioned my erratic reading was an indication of a blown head gasket... but I don't want to go there unless I'm sure. I'd really appreciate some help. Thanks

Cobra

 

[2wicked]

Have a 99 Busa with a modified Mr Turbo setup. Bike sat unused for most it's life due to medical problems... has less than 8,000 miles.

Summer 2008... worked on motor... no issues... just to make more durable. All APE products... valve springs & retainers, head studs, main bearing studs, Cometic gaskets (including .030 MLS Head Gasket), high volume oil pump gear, minor clutch mods. Still have original pistons, rings and bearings as less than 500 miles since turbo was installed.

Summer 2009... worked on turbo system... realized what garbage Mr Turbo sold. Made new plenum... installed new Tial wastegate & BOV... and literally replaced every component from his kit with the exception of the header and Rajay turbo which have been fine.

Summer 2010... figured I only needed to setup the map. The bike would start and idle fine... ran good when I open it up... but surged from richness while cruising. Had some issues with BEGI working properly but they have since been resolved and I seemed to be making headway.

This week... latest LM-2 recording while in garage shows air/fuel stays level until about 2,100 rpm at which point it begins to rapidly fluctuate between 10 and 14... causing the bike to surge.

Today... even though I have an Auto Meter Vacuum/Boost Gauge mounted on my dash, I decided to connect a standard automotive vacuum tester to TB#1. The needle was highly erratic during idle... bounced rapidly between 5-21 psi... same result when connected to TB#4. I didn't expect this but the Auto Meter gauge has a built in restrictor which might explain why it doesn't show any erratic readings.

Not sure what this means or where to go from here. Tried searching the internet and one site mentioned my erratic reading was an indication of a blown head gasket... but I don't want to go there unless I'm sure. I'd really appreciate some help. Thanks

Cobra

Surges because it is reading the vacuum at each intake stroke, it is normal, if you want it to show a smoother or steadier vacuum you need a dampener inline to the guage. Even a set of syncronizing gauges have dampener on them, if you do not use them the needles swing wildly.

Richard

 

[ogre]

you have to hook it to all 4 cylinders to get an idea of the general condition of the motor. i'd think one cylinder would bounce around a little bit, as it'll suck air in, then stop, then suck air in, then stop...

 

[ogre]

lol, beat me to it

 

[65Cobra]

Thanks... I'll try again using a signal from all four throttle bodies. In the meantime, what would someone use as a dampener?

Cobra

 

[POWERHOUSE]

Are you running a one-way check valve in your signal hose to the BEGI? This is necessary if you are using a hose from the throttle bodies, i.e., one that sees vacuum. It is not necessary if you run your signal from the plenum itself to the BEGI.

If you are using a vacuum line to the BEGI without a check valve, it would explain your A/F going crazy at partial throttle . . .

 

[65Cobra]

Are you running a one-way check valve in your signal hose to the BEGI? This is necessary if you are using a hose from the throttle bodies, i.e., one that sees vacuum. It is not necessary if you run your signal from the plenum itself to the BEGI.

Amazing, I just happen to post another topic at the same time you made that comment... and it answered the other question. I'm impressed

I am using a check valve, but since I can take the BEGI signal from the plenum (I have an unused connection on the plenum) I would rather do that and eliminate the check valve. Also, freeing up that one TB connection will let me make better use of my vacuum connections. Thanks.

Cobra

 

[65Cobra]

The original Mr Turbo kit had me remove a number of items from the bike... pair valve, air box, etc., which also included the VCSV, VTV and Vacuum Damper. The manual states "The vacuum damper is also provided in the vacuum line for the purpose of suppressing and stabilizing vacuum fluctuation." Should I put the Vacuum Damper back into the system?

 

[POWERHOUSE]

The original Mr Turbo kit had me remove a number of items from the bike... pair valve, air box, etc., which also included the VCSV, VTV and Vacuum Damper. The manual states "The vacuum damper is also provided in the vacuum line for the purpose of suppressing and stabilizing vacuum fluctuation." Should I put the Vacuum Damper back into the system?

The VCSV, VTV, and vacuum damper should be placed gently in the garbage!

That whole setup is for the stock Gen 1 airbox "flapper" system . . .

 

[scrappy]

lol

"gently in the garbage"

 

[65Cobra]

I finally had a chance to connect the vacuum tester while tied in to all four throttle bodies and you were right... the difference in fluctuations was dramatic. Thanks for the help.