Stooging the Throttle Plate Balance?

I need to balance the throttle response of the eight throttle plates on the 355. There is a factory tool for this task which I do not have. Has anyone messed with a DIY or simpler way to measure the air through each independent throttle plate?

 

I purchased 4 gauge vacuum readers x2 for this purpose. Getting to the ports on each throttle body is a challenge. The factory tool is a mercury level with all 8 banks showing.

I didn’t fine tune it so hard to know but I was concerned after updating the throttle lever to the later item the throttle linkage would be out. So I tested it using the vacuum gauges.

 

There is also this which I considered as it’s very similar to the factory tool, you’d need two.
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YelCab if you acquire a setup for this lmk.

My stooge method was with the air plenum off to measure the each throttle body at various open positions with a caliper (reverse side from top lip to end to max positions on the throttle body). Then to make sure each throttle body opened at the same time. Took a lot of trial and error until the throttle bodies were all within half a degree. Issue is that it wasn’t done under load.

Tony at modena motors has a 12 cylinder vacuum setup. Doubt he’d let you borrow but might be worth a call since thats the factory tool.


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OK, I am getting this set up.

 

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No that does not work. I have that. You need one that can be attached to a hose and with 8 inputs

 

I didn't see which car you were referring on this post ..stupid answer /post by me ..i was thinking you were on a 308 ..please disregard

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Intake plenum is one part of a 355 I've never dealt with -- I guess because the MAF is upstream, there's no way to run the engine with the plenum off so you can put an STE on each of the intake trumpets. I love the STE, such a great little device for balancing the carbs on my early 911.

 

Here you go Mitch.

 

https://www.amazon.com/dp/B004MSJ7C8/ref=redir_mobile_desktop?_encoding=UTF8&aaxitk=4b10c6deb122b3e635b92a9609ff5dea&hsa_cr_id=5298842560901&pd_rd_plhdr=t&pd_rd_r=adcbb925-f6de-4989-8b1b-d21aac1c4c48&pd_rd_w=QxIEh&pd_rd_wg=wbRj3&ref_=sbx_be_s_sparkle_mcd_asin_1_img

I got these for the 348. They're actually pretty nice.

sjd

 

He has 8 throttle bodies he needs to balance though.

 

There's a 4-up version too. Get two?

Ignore all the graphics except for the vacuum measurement. try all of them on a known source to be sure they are all calibrated the same...good to go!

sjd

 

Hi Mitch I have two sets of gauges with dials from Honda but I have personally seen the motion pro work and two of them would be the cheapest as you have stated

 

I bought two sets of quad gauges and started on checking the balance of the throttle plates. I only measured a few cylinders to see if there are any issues. And right off the bat, at idle Cyl 4 (of bank 1) generates 5 inches of vacuum, while Cyl 5 and 6 (bank 2) generate almost zero vacuum at the measuring ports. I tried to cheat and adjusted the throttle plate screws (indicated by the service manual) and it did not make any difference.

I am in the middle of a smoke test right now to see if any vacuum leak is seen below the throttle plates (where the ports are), and so far none. I don't know what is causing this ... imbalance.

 

Possibly the seals for the throttle plate shaft/s have gone bad, or the gasket/s have/has a leak??? Are the bypass screws open/closed/missing???

 

Did not touch the bypass screws.
The other thing I do not know is how much vacuum is expected on a 355 with its overlapping intake/exhaust valves. It does not generate that much vacuum.

 

I would have a look at the bypass screw/s

 

Did you pull the carbs and blank off the engine or just with it on and plenums removed

 

By "gauges" do you mean that you bought eight individual Bourdon tube type gauges with a mechanical moving needle mechanism that measure vacuum relative to the atmospheric pressure or something like that Motion Pro Sync Pro in post #3 (which is a 4-channel differential pressure manometer)? Can you post a pic of these "quad gauges", or give a link with a description?

(5 inches Hg vacuum at idle (or zero ) seems very low -- even for something with some overlap -- if the vacuum measurement is made relative to the atmospheric pressure. But a differential pressure measurement between cylinders would ideally be 0 inches Hg vacuum so the measured vacuum differences would always be in the relatively smallish range of things even if a cylinder is somewhat misadjusted relative to another.)

 

PS Forgot to mention that if you were going to use that Motion Pro Sync Pro, you wouldn't want to get two, and use a separate one on each bank because that would only ensure that the cylinders in each bank were equal, but the two banks could be different. Using just one Sync Pro, you would:

1. Balance the four cylinders in one bank (call this bank 1), then

2. Balance two cylinders in bank 2 using two cylinders in bank 1 as the reference (i.e., only make adjustments on the two cylinders in bank 2 -- don't touch the adjustments on the two cylinders in bank 1), then

3. Balance the remaining two cylinders in bank 2 to match the two cylinders in bank 2 that were just adjusted in step 2.

That way you end up with all 8 cylinders being the same vacuum at idle.

 

I bought two of these. I ended up using only 2 of the ports, one for bank 1 and one for bank 2. One additional note for the 355 which the service manual does not mention. You have to loosen the measuring port a few turns to get the vacuum to flow, that fact is not mentioned. And of course, number 3 brass port broke right off.

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Half a day spent on this yesterday and this is what I got.

1) Measurement at the ends of tube 19 before it goes to the check valves: Bank 1 has 5 inch of Hg, Bank 2 has about 5 inch of Hg. Similar numbers.

2) Measurements at the end of item 44: Cyl 4 has 5 inch of Hg, while Cyl 5 has close to zero vacuum.

3) a smoke test reveals no major leaks on bank 2 below the throttle plates. There is only a very small wisp of smoke at the throttle shafts where they are all connected for adjustments. But very small wisps.

 

With no official specs, I am guessing that the 355 generates only a small amount of vacuum. It is for this reason that the 355 with the Bosch ABS system requires a cam shaft driven vacuum pump for brake booster leaving the engine vacuum to drive only the bypass valve and the secondary air pump controls. So, I think 5 inch of Hg is likely correct.

I still have to figure out why the bank 2 measuring ports do not have the same numbers ... maybe Ernie's got it right. Gotta check the bypass screws.

 

You've tried all 4 gauges on the port that is reading to make sure they're all reading the same?

sjd