Problem synchronising throttle body vacuum

[dooby]

Hi folks,

I have been following the service manual for my 2011 250R (UK edition, fuel-injected) for the 15,000 mile service.

I have reached the part where I should check and sync the throttle body vacuums (no carb's on my model). I warmed the engine and found my idle was high, so I fixed that and then fixed the throttle play as per the instructions. I they tried to get a reading off cylinder 1 side's throttle body by disconnecting the vacuum hose that leads from the throttle body up to the inlet air pressure sensor on my model.

I found that my vacuum gauge showed nothing useful - the needle was swinging rapidly and wildly from pressure to vacuum. According to the manual I am looking for 180mmHg +/- 10mmHg but there's no way I can make any sensible reading with it pulsing so much. I can even feel the pulsing on my finger when I use it to cap the hose, so I don't think the gauge is faulty - it's showing what's happening but how do I take a meaningful reading?

On cylinder 2 I have removed the vacuum take-off blanking plug that was fitted as stock and attached my vacuum-operated Scottoiler there and that appears to be working as expected so I was fairly certain that was the right take-off point on the throttle body. Anyone know any different?

If it matters, I have removed the UK equivalent of the KLEEN air system, but the service manual seems to indicate to remove the hose and block both ends for this task anyway which I believe is the same as having removed it entirely and blocked it at the cylinder head and air-box as I have...

Anyone got any advice? Is my method wrong? Is there perhaps another take-off point I can't see?

Thanks, Pete

[micoulisninja]

Originally Posted by dooby

Hi folks,

I have been following the service manual for my 2011 250R (UK edition, fuel-injected) for the 15,000 mile service.

I have reached the part where I should check and sync the throttle body vacuums (no carb's on my model). I warmed the engine and found my idle was high, so I fixed that and then fixed the throttle play as per the instructions. I they tried to get a reading off cylinder 1 side's throttle body by disconnecting the vacuum hose that leads from the throttle body up to the inlet air pressure sensor on my model.

I found that my vacuum gauge showed nothing useful - the needle was swinging rapidly and wildly from pressure to vacuum. According to the manual I am looking for 180mmHg +/- 10mmHg but there's no way I can make any sensible reading with it pulsing so much. I can even feel the pulsing on my finger when I use it to cap the hose, so I don't think the gauge is faulty - it's showing what's happening but how do I take a meaningful reading?

On cylinder 2 I have removed the vacuum take-off blanking plug that was fitted as stock and attached my vacuum-operated Scottoiler there and that appears to be working as expected so I was fairly certain that was the right take-off point on the throttle body. Anyone know any different?

If it matters, I have removed the UK equivalent of the KLEEN air system, but the service manual seems to indicate to remove the hose and block both ends for this task anyway which I believe is the same as having removed it entirely and blocked it at the cylinder head and air-box a I have...

Anyone got any advice? Is my method wrong? Is there perhaps another take-off point I can't see?

Thanks, Pete

Hi Pete...
a few question i have to ask first
is your idle steady or not ?
have you removed secondary butterflies ?
as part of your service have you done other work to the engine that could interfere with throttle body vacuum ? for example is it possible that a collar going to the head is loose or sth like that ? have you double checked that ?


if none of the above is affecting the bodies, then -from personal experience- i would recommend to screw the adjusting screw all the way IN, regardless the readings and see how it works... if it gets better, try unscrewing it little by little till it gets ok... if it gets worse, stick with the screw fully positioned in and try messing with the cyl 2 screw... if you see any improvements, find the best working point of them having equal readings even if not within optimum range...
if you don't, then there are two cases IMHO... one... you really need to triple check if there is a loose collar or if the kleen stuff is definetely airtight...
two...compression is being lost somewhere close to the head... either exhaust fitting on the head is not completely airtight (slight chance but possible, check for black exhaust marks on the headers) or some valve for that cylinder is not sealling properly and needs lapping (really hope not because it would be far too early for 15000 miles...)

please let us know of your progress... hope you find and solve your issue... I believe it is sth minor that you probably have missed...
cheers...

[dooby]

Hi Nick,

thanks for your thoughts. The idle is pretty steady - the manual says 1300rpm +/- 50rpm and it's now 1300rpm +/- 15rpm with the engine fully warm according to my inductive clamp-on mechanics tachometer.

I have not removed my secondary butterflies.

I have done the valve re-shim already a couple of weekends ago, from memory all exhaust-side shims were out of spec so I swapped them, all the inlet-side were within spec. No other engine work this time (aside from the oil/filter/spark plug change of course).

Breathing-wise the mods so far are a Pipercross air filter (freshly washed and re-oiled this service) in the stock air box, and a Scorpion full exhaust system including header pipes and cat delete. The ECU is piggy-backed with a Dynojet Power Commander V.

The bike is generally running well, I'm only really checking the vacuum because the service manual suggests it - I have no reason to believe anything is amiss.

I will head out and check for air/exhaust leaks as best I can, though I didn't knowingly disturb the throttle bodies or collars during the valve shim as far as I know.

I will also attempt a vacuum reading on cylinder two which should help rule in or out a cylinder-specific issue like a valve not sealing.

Cheers, Pete

[dooby]

OK I think I've learnt a few things today - perhaps they will help others.

So I checked, and couldn't find any evidence of inlet or exhaust leaks. I looked more closely at the throttle bodies, and whilst trying a reading from cylinder 2 I noticed something I'd missed before.

On UK models at least, the cylinder 1 and cylinder 2 sides of the throttle body are not identical. On cylinder 1 side there are in fact two brass (?) "nipples" that go into the throttle body. On cylinder 2 side there is only one brass nipple.

As stock on cylinder 1, the right-most nipple has a grey/red vacuum hose leading to the inlet air pressure sensor. There is a second nipple on the left-most side which has a black rubber blanking plug. Interestingly the nipples are not identical, the right-most one leading to the sensor has a much wider internal bore, maybe 1.5mm diameter or so. The left one is maybe 0.5mm internal diameter.

On the cylinder 2 side there is only one "nipple" which is situated on the left side and as stock also has a black rubber blanking cap (or in my case a take-off to my Scottoiler). It is the smaller 0.5mm internal diameter.

I think the mistake I made was failing to spot the second nipple and re-purposing the 1.5mm internal diameter nipple to take my vacuum reading. I suspect the wider bore allowed more ebb and flow of the "signal". Also, it meant the inlet air pressure sensor was open to atmosphere which lit up the FI fault code indicator so may have been affecting the smooth running anyway.

On each side (cylinder 1, cylinder 2) of the throttle body I believe you should use the left-most "nipple". This has the smaller internal diameter of 0.5mm or so. This also means you can use this one whilst leaving the sensor attached to cylinder 1 in place.

Having found this second "nipple" on the cylinder 1 side I found some 3mm ID silicone vacuum hose and attached 50cm or so to each throttle body. I only had one vacuum gauge so I attached one hose to that and temporarily blocked the other hose.

This gave me a much more stable vacuum reading although it still swung between 20cmHg and 25cmHg or so. I could have estimated the centre point but also discovered that very slowly squeezing the silicone hose closed would hold the vacuum on the gauge at the mid-point of the range giving a clear enough reading to be useful.

In the end this gave me 20cmHg for cylinder 1 and 21cmHg for cylinder 2. I raised the tank enough to get access to the screws and attempted to get 18cmHg +/- 1cmHg on either side but couldn't, as Nick hinted might happen.

In the end I followed the service manual instructions and Nick's advice and turned each screw in fully, read which was higher and tried to sync that one down to read the same as the lower one. I believe I ended up with 195mmHg on each side which is as close as I could get.

I am now happier that I have at least checked and synchronised the vacuums even if I couldn't quite get them into the service manual's recommended range.

Logically I suppose if I have created a freer flowing system by fitting a higher flow filter and freer flowing exhaust then I might expect the idle vacuum to be a touch stronger.

Anyway, hope someone finds those observations useful.

Thanks, Pete

[micoulisninja]

Originally Posted by dooby

OK I think I've learnt a few things today - perhaps they will help others.

So I checked, and couldn't find any evidence of inlet or exhaust leaks. I looked more closely at the throttle bodies, and whilst trying a reading from cylinder 2 I noticed something I'd missed before.

On UK models at least, the cylinder 1 and cylinder 2 sides of the throttle body are not identical. On cylinder 1 side there are in fact two brass (?) "nipples" that go into the throttle body. On cylinder 2 side there is only one brass nipple.

As stock on cylinder 1, the right-most nipple has a grey/red vacuum hose leading to the inlet air pressure sensor. There is a second nipple on the left-most side which has a black rubber blanking plug. Interestingly the nipples are not identical, the right-most one leading to the sensor has a much wider internal bore, maybe 1.5mm diameter or so. The left one is maybe 0.5mm internal diameter.

On the cylinder 2 side there is only one "nipple" which is situated on the left side and as stock also has a black rubber blanking cap (or in my case a take-off to my Scottoiler). It is the smaller 0.5mm internal diameter.

I think the mistake I made was failing to spot the second nipple and re-purposing the 1.5mm internal diameter nipple to take my vacuum reading. I suspect the wider bore allowed more ebb and flow of the "signal". Also, it meant the inlet air pressure sensor was open to atmosphere which lit up the FI fault code indicator so may have been affecting the smooth running anyway.

On each side (cylinder 1, cylinder 2) of the throttle body I believe you should use the left-most "nipple". This has the smaller internal diameter of 0.5mm or so. This also means you can use this one whilst leaving the sensor attached to cylinder 1 in place.

Having found this second "nipple" on the cylinder 1 side I found some 3mm ID silicone vacuum hose and attached 50cm or so to each throttle body. I only had one vacuum gauge so I attached one hose to that and temporarily blocked the other hose.

This gave me a much more stable vacuum reading although it still swung between 20cmHg and 25cmHg or so. I could have estimated the centre point but also discovered that very slowly squeezing the silicone hose closed would hold the vacuum on the gauge at the mid-point of the range giving a clear enough reading to be useful.

In the end this gave me 20cmHg for cylinder 1 and 21cmHg for cylinder 2. I raised the tank enough to get access to the screws and attempted to get 18cmHg +/- 1cmHg on either side but couldn't, as Nick hinted might happen.

In the end I followed the service manual instructions and Nick's advice and turned each screw in fully, read which was higher and tried to sync that one down to read the same as the lower one. I believe I ended up with 195mmHg on each side which is as close as I could get.

I am now happier that I have at least checked and synchronised the vacuums even if I couldn't quite get them into the service manual's recommended range.

Logically I suppose if I have created a freer flowing system by fitting a higher flow filter and freer flowing exhaust then I might expect the idle vacuum to be a touch stronger.

Anyway, hope someone finds those observations useful.

Thanks, Pete

damn !! I forgot to mention about the second pressure outlet...
good you found out yourself after all...
when I wrote about compression loss, I had in mind the chance of having fitted a whole aftermarket system recently... most of the times sealing gaskets on the head take up the heat and bolts there need a bit tighening to get them sealing properly again...
anyway... it is absolutely normal having readings above or below specs, not only because of intake and exhaust mods but also highly affected by weather conditions and altitude....
I am glad if I have helped in any way and that you managed to figure it out and share with us Pete
have you thought about removing secondary butterflies ? makes engine a lot "punchier" in the low-mid range without any loss in the high end...makes nicer sound too !!