Author Topic: Odd adjusting screw on throttle body. Ideas?  (Read 1971 times)

Worldflier

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Odd adjusting screw on throttle body. Ideas?
« on: June 15, 2021, 18:18:07 »
Good day,
While chasing my warm starting issue, I removed the throttle body (throttle plate assembly?) from the intake manifold and noticed a tiny set screw near the back of the assembly.

Does anyone know for what this is used? It connects to a vacuum port in the body, but spraying cleaner into the hole didn’t reveal where it leads.

Btw, this car is a 1967 230sl with the M127 engine.

Thanks for your ideas!
Dre

Worldflier

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Re: Odd adjusting screw on throttle body. Ideas?
« Reply #1 on: June 15, 2021, 18:19:23 »
One more picture.

Pawel66

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Re: Odd adjusting screw on throttle body. Ideas?
« Reply #2 on: June 15, 2021, 21:16:52 »
Is it not a vacuum port? For certain tests.
Pawel

280SL 1970 automatic 180G Silver
W128 220SE
W121 190SL
G-class

Peter

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Re: Odd adjusting screw on throttle body. Ideas?
« Reply #3 on: June 15, 2021, 21:37:40 »
Just what I thought.
See Hayne manual.

Peter

Tyler S

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Re: Odd adjusting screw on throttle body. Ideas?
« Reply #4 on: June 16, 2021, 03:49:55 »
That grub screw is very small, non magnetic, and blends into speckled epoxy flooring. Never did find it.
1968 (67) 250sl. 4 speed manual. DB180 Silver
1955 220 Cabriolet A. White Grey
2019 E450 Wagon. Majestic Blue
1936 Ford PU Flathead V8. Creme on tan interior.
1989 Volkswagen T3 Westfailia Campmobile. Dove Grey (blue)

wwheeler

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Re: Odd adjusting screw on throttle body. Ideas?
« Reply #5 on: June 16, 2021, 03:56:45 »
I have seen that test before and never knew what grub screw they were talking about. Interesting. Anybody ever done that vacuum test? Seems like the split linkage test would have about the same effectiveness and a whole lot easier.
Wallace
Texas
'68 280SE W111 coupe
'60 220SE W128 coupe
'70 Plymouth Roadrunner 440+6

Tyler S

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Re: Odd adjusting screw on throttle body. Ideas?
« Reply #6 on: June 16, 2021, 13:13:40 »
Wallace,
I have done that test before and all it really gets you is a visual representation of the vacuum level at closed throttle. It isn’t much different than the split linkage test.
BTW there is one part of that procedure I do during a split linkage test. I disconnect and apply my own vacuum to the distributor with a hand pump as it can skew your results. On an 051 distributer, The timing advances when you crack the throttle via the vacuum retard setup. Even if the engine is lean it can raise the RPM significantly as advancing timing will allow for a leaner mixture.
« Last Edit: June 17, 2021, 00:37:48 by Tyler S »
1968 (67) 250sl. 4 speed manual. DB180 Silver
1955 220 Cabriolet A. White Grey
2019 E450 Wagon. Majestic Blue
1936 Ford PU Flathead V8. Creme on tan interior.
1989 Volkswagen T3 Westfailia Campmobile. Dove Grey (blue)

wwheeler

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Re: Odd adjusting screw on throttle body. Ideas?
« Reply #7 on: June 16, 2021, 19:50:44 »
Good point and I will try that! Thanks for the tip. Maybe add to the Split linkage tour?
Wallace
Texas
'68 280SE W111 coupe
'60 220SE W128 coupe
'70 Plymouth Roadrunner 440+6

Tyler S

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Re: Odd adjusting screw on throttle body. Ideas?
« Reply #8 on: June 17, 2021, 00:39:43 »
I edited above to include that I use a hand pump to supply my own vacuum to the distributor. Not sure how I forgot that part.
1968 (67) 250sl. 4 speed manual. DB180 Silver
1955 220 Cabriolet A. White Grey
2019 E450 Wagon. Majestic Blue
1936 Ford PU Flathead V8. Creme on tan interior.
1989 Volkswagen T3 Westfailia Campmobile. Dove Grey (blue)

col320ce

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Re: Odd adjusting screw on throttle body. Ideas?
« Reply #9 on: June 17, 2021, 03:06:58 »
I made a plastic connector to measure the vacuum where the screw is... Worked well. Then broke it and tried to make another out of brass but failed.
Col

1964 230SL
1965 250SE coupe
1993 320CE Sportline