Throttle Body Vacuum Ports

I need some assistance. A while back when doing a TBS I was having some problems with #1 cylinder and ended up having to completely close the air screw while having #3 open roughly 1 full turn. This also caused some issues with too high an idle speed that I could not adjust with the idle adjustment screw.

I aquired a Vacuummate on the advise of the National Service Manager for Yamaha Canada who also happening to be a fellow club member and when going over the vacuum readings I was getting some very strange readings from #1 cylinder that I didn't really understand. The Vacuummate uses pressure transducers that have a very quick response time and the instrument also has a dynamic mode that allows comparison of the vacuum pulses between the cyinders. The vacuum pulse on #1 cylinder appeared to have less vacuum being developed but also less vacuum being lost which gave a shorter pulse duration that the other three cylinders.

It was looking like I was going to have to pull the throttle body assembly off but before I went too far I tried some throttle body cleaner after having a discussion with Ray over what could be a root cause thinking that there may be a blockage in the air screw circuit. When I went to put the straw down into the vaccum ports I was able to insert the straw into the ports on three of the cylinders but found what appears to be an installed restictor on #1 cylinder....





Here is a photo showing both #1 and #2 Vacuum port....



What I am trying to determine at this point is the restriction in the #1 Vac port normal? I was able with some effort to remove it and then the Vacuummate showed a reading in agreement with the other cylinders and I was able to get some adjustment with the #1 air screw to achieve a TBS and lower my idle speed with the idle adjustment screw.

What I would like is the next time any Gen II owner has the tank off their FJR could you please have a look and see if there appears to be a restrictor in the #1 Vacuum port. I have a McCruise Cruise Control System and I double checked the instructions thinking the restriction was part of that installation but that is not the case and I can't think of any other valid reason for the restrictor to be there. There are enough differences in the throttle bodies between Gen I & II that a comparison with the Gen I Vac ports on the throttle bodies may not be definitive. It would be best if this was done by a Gen II owner.

The instrumentation shows that this restriction was definitely attenuating the vacuum signal so my interest is peaked to see what is the stock arrangement on another Gen II.

Thanks.

I have an 07 (almost identical to your bike) and my No. 1 did not have a restrictor in it that I can remember.

Looks like someone left a piece of a vacuum tool behind on a previous TBS

I have a spare set of gen 1 throttle bodies and there are NO restrictors in the vacuum ports.

It almost looks like a check valve although I have no idea why it would be there (or a restrictor, for that matter). In normal operating mode, it wouldn't have any effect anyway since there is a rubber cap over it. It would, however, severely screw up an attempted TBS. Have you had problems with TBS adjustments in the past? I haven't looked that closely but certainly don't recall anything that looks like that on my bike.

Did mine this past weekend and no restrictor in mine...2010

I've had all 3 Gens...no restrictors on any ports. Must be a part from a previous TBS procedure or some shade tree mechanic screw up.

That looks exactly like a restrictor from a Motion Pro sync tool.

From your description of the symptoms, it sounds like it is doing just the job it was designed to do

Twigg said:

That looks exactly like a restrictor from a Motion Pro sync tool.
From your description of the symptoms, it sounds like it is doing just the job it was designed to do

Click to expand...

+1

I still have one of those useless POS kicking around somewhere. I think the little brass restrictors are MIA, but they looked exactly like the one in the pic. (And they aren't stuck to the vac ports)

I now use the vastly superior Morgan Carbtune Pro. Just did my annual TBS a couple of days ago, in fact.

silver spirit said:

+1
I still have one of those useless POS kicking around somewhere. I think the little brass restrictors are MIA, but they looked exactly like the one in the pic. (And they aren't stuck to the vac ports)

I now use the vastly superior Morgan Carbtune Pro. Just did my annual TBS a couple of days ago, in fact.

Click to expand...

Not to open an "oil debate" type threadjack here, but my Motion Pro really works rather well The accuracy is decent, although for throttle bodies, like for CV carburetors, we obsess about accuracy way too muc. As long as they are all close, you won't feel the difference.

That said, I would have bought the Morgan Carbtune if I could afford it, and I would always recommend it over most of the others.

It is British, after all ... We have to stick together

I don't have a pic and haven't done a sync in several months, but I'm going against the flow here and say #2 looks too big. My recollection of the vacuum ports is they all are considerably smaller then the regular vacuum ports (like used for the manifold pressure sensor).

Looks like the answer(s) are definitive..

Twigg said:

Not to open an "oil debate" type threadjack here, but my Motion Pro really works rather well

The accuracy is decent, although for throttle bodies, like for CV carburetors, we obsess about accuracy way too muc. As long as they are all close, you won't feel the difference.
That said, I would have bought the Morgan Carbtune if I could afford it, and I would always recommend it over most of the others.

It is British, after all ... We have to stick together

Click to expand...

LOL! I must have gotten a Motion Pro made on a Friday! The thing just didn't function correctly -- the liquid failed to stick together! I was lucky to get a Carbtune at a discount a couple of years ago

Denver_FJR said:

I don't have a pic and haven't done a sync in several months, but I'm going against the flow here and say #2 looks too big. My recollection of the vacuum ports is they all are considerably smaller then the regular vacuum ports (like used for the manifold pressure sensor).

Click to expand...

That pic is deceptive. Use the size of the screw heads as a reference. The #1 port does have a Motion Pro, (or similar), brass restrictor stuck on the end. #2 is the right size. At least, it looks identical to the ones on my feej.

Ha! Who was drinking last time they put those hoses on? It looks like the hoses for the #1 cylinder are crossed; you're using a manifold port for the throttle sync. See pics in this post.

Particularly this one.

This is going to get embarrassing for someone (possibly me) ... I think he has the correct ports although it is possible a couple of manifold hoses are crossed ... I'm not sure that is relevant here

Denver_FJR said:

Ha! Who was drinking last time they put those hoses on? It looks like the hoses for the #1 cylinder are crossed; you're using a manifold port for the throttle sync. See pics in this post.

Click to expand...

Unfortunately the photo that Denver_FJR linked to was badly out of focus unless he wanted to show us the footpeg. I am hoping he was not referring to the port going back into the airbox that the air injuction system uses (the black plastic fitting in the photo). It is pretty hard to screw up the hoses since the vacuum ports used for a TBS are the only ones that are capped or in my case the vac lines for the cruise control (my system uses #1 and #4 vac ports).

I think most of the folks here are correct that it was an errant restrictor that got left behind. With it removed all seems back to normal though a test ride scheduled for tomorrow will tell the complete tale. I have a group bicycle ride and then taking the dirt bike out later to do some trail work today.

Thanks for the help.

Denver is right. The #1 vacuum connections are crossed, maybe they've been that way from the factory.

The one on the right of each TB should be the syncing port. The left one connects to the hose network going to the intake pressure sensor (MAP sensor). The left ports include a small orifice -- there's very little air flow in the MAP sensor network.

Go to Yamaha's part diagrams for your model. Look at the "Intake 2" section.

https://www.yamahamotorsports.com/partviewer/default.aspx?ls=sport

Was Carver supervising this TBS??? :rofl:

Best shot I could find of the (capped) vac/synch ports. #1 is hidden behind the electrical connector. Note the ports are all in line and equidistant from one another: