vacuum gauge timing

1941 - 1945, MB, GPW Technical questions and discussions, regarding anything related to the WWII jeep.
dpcd67
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Re: vacuum gauge timing

Post by dpcd67 » Wed May 16, 2018 7:29 am

That is how M38s work as they have a sealed system; with a notch in the pulley and either a pointer or the TC and 5 degree marks on the front cover. I still don't use them. This is not a hot rod engine and it is easy to tell when they are running right. And easy to tell when they are wrong, without a light.
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Re: vacuum gauge timing

Post by 101son » Wed May 16, 2018 8:03 pm

I put the vacuum gauge on it today and it runs pretty good, but, it is advanced quite a bit. More than the OI mark on the flywheel. If I set it by the timing light to half distance between the OI and the IGN it runs like a dog fart. It is around 13.5 on the vac gauge so adjusting for altitude that would be like 19.5 at sea level correct?
To get the best vacuum out of the mixture adjustment, it is about 3 turns out. Do you think this is because of altitude?(6500 ft)
How do I know if it is too lean/rich?
I don't hear any ping, although it is hard to hear with the wind blowing around me. Maybe if I close the doors I could hear better :D Anyhow I will wait to hear from you on the adjustments.

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Re: vacuum gauge timing

Post by artificer » Thu May 17, 2018 1:39 am

Mixture screw should only be out 1.5-2 turns max.

Sounds like the 'Carter' metering rod needs adjustment to get correct fuel @ idle then you can fine tune with the mixture screw.

There is an order to doing these things otherwise you'll be chasing your tail, as seems to be happening now.

The vacuum gauge reading @ your altitude [all being right] will be about 17" of mercury no more.

The gauge is currently telling you something is wrong & you need to establish & rectify what that is.
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Understand how system parts interact with one another. GOOD parts can then be established & the NOT GOOD problem/s part/s isolated for repair or replacement.

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Re: vacuum gauge timing

Post by Ben Dover » Thu May 17, 2018 3:59 am

Too much guess work, this is going all over the place, there is not one active ingredient to this situation. At least the timing light will be most effective as it is not guess work.
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Re: vacuum gauge timing

Post by 101son » Thu May 17, 2018 5:48 am

The vacuum gauge reading @ your altitude [all being right] will be about 17" of mercury no more
I read that 1"per thousand so figured 13.5 would put me in the ok zone. I guess I miscalculated.
Should the advance not be working [seized shaft] the engine will be running retarded not advanced so no physical damage like to pistons bearings etc. could or would be taking place. Just gutless & perhaps running hot.
How do I check for this? And how to fix if it is a problem?
Last edited by 101son on Thu May 17, 2018 6:09 am, edited 1 time in total.


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Re: vacuum gauge timing

Post by Wolfman » Thu May 17, 2018 5:59 am

Take the distributor cap off and manually turn the rotor in the advanced direction. It should move forward a little, not a quarter way around, and return to it's original position when released. If it does not move at all, it is stuck.
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Re: vacuum gauge timing

Post by 101son » Thu May 17, 2018 6:10 am

will do-

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Re: vacuum gauge timing

Post by 101son » Thu May 17, 2018 7:59 pm

It snaps back to position and is only a little movement like you mentioned. Is there anything else to check to see if it is functioning correctly? Maybe that is why when I set the timing at about 7.5 degrees advanced it still was a dog and still running a little hotter than it should.?

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Re: vacuum gauge timing

Post by artificer » Fri May 18, 2018 1:21 am

A vacuum gauge tells one how the engine is breathing.
Not close to being right mechanically [like worn for example] next including fuel air mixture [in particular] & timing will be indicated with vacuum or general running indicates one needs to find what the vacuum reading indicates & fix it/them. Then read again or experiment.
John GIBBINS Member Institute of Automotive Mechanical Engineers [Ret], ASE Master Medium/Heavy Truck & Auto Technician USA -2002 Licensed Motor Mech NSW MVIC 49593 Current 2015
TO DIAGNOSE, TROUBLESHOOT OR FAULT FIND ANY AUTO SYSTEM....
Understand how system parts interact with one another. GOOD parts can then be established & the NOT GOOD problem/s part/s isolated for repair or replacement.

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Re: vacuum gauge timing

Post by Wolfman » Fri May 18, 2018 5:42 am

Sounds like the advance is not stuck. It moves.
To check the function, you need a timing light or a distributor machine that checks the distributor function off the engine.
With a timing light installed, set the idle timing and then watch the timing marks as the engine rpm is increased. You can watch the timing advance in action and see how much. On a jeep this isn't easy. Marks on the front pulley and timing chain or gear over is much easier when trying this.
Insufficient timing advance will cause loss of power and over heating.
Some engines set timing to maximum advance at a higher rpm instead of doing it at idle. That way you are sure the engine timing is advanced to the proper point at higher speed and under a load. Talking some Ag. and Industrial engines. Not jeep.Timing advance still needs to be functional.
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