normal vacume reading for carbs?

[unity1]

Does anyone know the normal vacume reading for the carbs of an 89 Turbo. I checked mine tonight (first time) for sync and found one way out (400mm). Whats more interesting is that the mm measurement for the other three was only around 220. Is this normal as on a bike I would expect to see around 500mm.

I had to turn the bleed valve 2.5 turns to level it up. I'm not a professional but does this sound like and air or valve leak to you. Will do a compression test Saturday and hope for the best.

[lotusguy]

unity1 said:

Does anyone know the normal vacume reading for the carbs of an 89 Turbo. I checked mine tonight (first time) for sync and found one way out (400mm). Whats more interesting is that the mm measurement for the other three was only around 220. Is this normal as on a bike I would expect to see around 500mm. I had to turn the bleed valve 2.5 turns to level it up. I'm not a professional but does this sound like and air or valve leak to you. Will do a compression test Saturday and hope for the best.

Hi,

Ok, first off, it is not a contest, the numbers mean absolutely nothing! More is not better! In fact, you need to detune the stronger of the two barrels/carb as well as the stronger of the two carbs to match the weaker one. This is because you cannot strengthen the weaker one. It is simply a matter of balance.

Further, it's very difficult to make the appropriate adjustments measuring one barrel at a time. You need a 4-tube mechanical manometer, such as the CarbTuneII made by Morgan and sold through Eurocarb Ltd. (www.dellorto.com), or a true Hg 4-tube manometer (much less desireable) to achieve an acceptable result.

Comb through the archives to find the step by step procedure I wrote some months back. Happy Motoring!... Jim'85TE

[unity1]

Thank Jim I suspected you would have the answer. I do have and used a four gauge meter so am sure of the difference. Even changed the connecting hose to verify it was not a faulty gauge. I did managed to balance all the cabs to the lower level and adjust the tick over but was just concerned that the level was much lower than what I get from a bike for 3 of them while 1 was almost the same. It just lead me to think that the others are not creating as much a vacume due to an air leak. Especially as she was in the body shop for some time last year and I cannot be sure that pressure was not applied to the top of the engine (your other post about the O rings)

As a example to get barrel 2 the same the bleed screw is now almost at the top. I also had to decrease the mixture of the others to get the revs at the highest point (while decreasing tick over to compensate). Once achieved I turned them all back 0.25 a turn. I could be doing this wrong but the car runs a lot better and does not pop and bang any where near as much as it did. I now only get judder when pulling from 1000 rpm in top where as before it would have been more like 1500.

Would you guess I do have leak and if so would it be a problem?

*edit to correct spelling

>> Edited by unity1 on Thursday 29th April 16:13

[lotusguy]

unity1 said:

Thank Jim I suspected you would have the answer. I do have and used a four guage meter so am sure of the difference. Even changed the connecting hose to verify it was not a faulty guage. I did managed to balance all the cabs to the lower level and adjust the tock over but was just concerned that the level was much lower than what I get with a bike for 3 of them whike 1 way almost the same. It just lead me to think that the others are not creating as much a vacume due to an air leak. Especially as she was in the body shop for some time last year and I cannot be sure that pressure was not applied to the top of the engine (your other post about the O rings) As a example to get barrel 2 the same the bleed screw is now almost at the top. I also had to decrease the mixture of the others to get the revs at the highest point (while dereasing tick over to compensate). Once achieved I turned them all back 0.25 a turn. I could be doing this wrong but the car runs a lot better and does not pop and bang any where near as much as it did. I now only get judder when pulling from 1000 rpm in top where as before it would have been more like 1500. Would you guess I do have leak and if so would it be a problem?

Hi,

The carb insulators may well be leaking, not only due to the possibility that they were leaned on, but merely because, if original, they are 15+ years old.

The purpose of these rubber 'O' rings is to allow the carbs to 'float' on the intake manifold so that engine vibration does not 'foam' up the fuel in the float bowls. They are not to be drawn up tight, rather a 4mm gap between the carbs, spacers and intake runners should be maintained. This can be easily accomplished by using a 3/16ths drill bit to gauge the gap.

A couple ways to check them is to either drip some ordinary tap water onto them while the car is idling. This will temporarily seal them and the engine idle will change. Similarly, running an open, but not ignited propane torch around them will also affect the engine idle by adding more 'fuel' through the leaks.

It is a two-fold problem not to have these sealing properly. First, you can have fuel foaming in the float bowls, second, you can create a lean condition as any air bypassing the faulty seal(s) negatively alters the A/F ratio. This can expose the pistons and valves to excess heat and cause internal engine damage. On a turbo car, you want to actually run a little rich at idle to insure you do not go lean once on boost. Your plugs should be a dark brown to slightly black in color. With a car of this age, if in doubt about these carb insulators, change them. Happy Motoring! ...Jim'85TE

PS Make certain that you have only one air adjustment screw open per carb. This is the only adjustment you make to affect the balance of a carb barrel with it's mate.

>> Edited by lotusguy on Thursday 29th April 14:43