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willysmjeeps.com :: View topic - Timing an M38 with a vacuum gauge std engine 134 Flathead
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Timing an M38 with a vacuum gauge std engine 134 Flathead

 
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horse
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Location: Yorkshire U.K.

PostPosted: Wed May 20, 2020 6:36 am    Post subject: Timing an M38 with a vacuum gauge std engine 134 Flathead Reply with quote

Hi my M38 has been timed the normal way.

Check point gap with feeler gauge when breaker lever on high point of cam.

Turn engine over and on compression stroke and aline pointer with 5 degree TDC. Checked with Vac gauge and finger even a balloon for good measure.

Turn distributer anticlockwise until points closed then back clockwise until points start to open. Rotor should point to No. 1 position. Yes it does. Tighten clamp.

Set up timing light and adjust distributor until the timing marks line up.

Tighten clamp.

Went for a run, okay but seemed lacking power.

All okay so far I think.

Did a check with the Vac gauge and it reads 17Hg and normal motor.

I moved the distributor clockwise a few degrees and the revs increased, sounded smoother and the gauge went to 20 Hg, I backed it off 1 Hg and went for a run.

Went the best ever ,but on return I put the timing light on and it was miles out,about 13 advanced at 700 rpm.

Not wanting to damage anything I would ask if I am doing anything wrong?

On the Vac gauge instructions it does talk about on old engines it is difficult to get reliable timing from the original guidelines.

As a tool it is very easy to use but how accurate on my timing not sure.

Comments would be appreciated.
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wesk
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PostPosted: Wed May 20, 2020 8:32 am    Post subject: Reply with quote

Vacuum gauge timing is for the old muscle car era where easy starting, and no pinging were not on their priority list. It is a technique used to squeeze all the juice out of your 134 giving great top end performance and ignoring startability and engine longevity. The choice is yours but if you want that performance level that can be very damaging to your 134 why not just get the right engine for the job. A V-6 is the best all around performer with the running gear these jeeps have. The V-8's dictate an upgrade in tranny, transfer and axles since the original jeep equipment was meant to be used with 60 or 72 HP L or F 134's. All the choices are your.
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Wes K
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mdainsd
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PostPosted: Wed May 20, 2020 9:11 am    Post subject: Reply with quote

Listen carefully for any indication of pinging. I time all of my MVs (gas ones at least), with a dwell meter followed by the vacuum gauge. I do it exactly as you do. Ive been doing this since the sixties and I have yet to loose a single MV engine, other than to high miles on the freeway, and that was just a need for a rebuild, not a failure as such.

When I go to meets I just shake my head at the guys who seem to be in a competition for how long they can crank their Jeeps without them starting. They all tell ya, that they are tuned "by the book".

The carb is as important to easy starting and great running as anything else.

All of my MVs (Willys, Ford, Dodge and White) start instantly hot or cold. No cranking, just touch the starter and they are running.
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horse
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PostPosted: Wed May 20, 2020 9:28 am    Post subject: Reply with quote

Thanks for the reply. I like the engine for what it is but just to run as it should.

She starts hot or cold well on both settings.

No pinging.

I have had fast cars but nowadays you just loose your licence.

Just trying to run her at her best.

She came with a Weber 34 ICT carburettor for some reason, been looking for

the correct Carter YS637S but few about and expensive.

May be that would make a difference.

Thanks
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mdainsd
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PostPosted: Wed May 20, 2020 9:56 am    Post subject: Reply with quote

When we used to play with Hot Rods we tuned them using the poor mans dyno.
Get them warmed up and ready to go. Start the engine. Run the idle up high, then pull out ever other plug wire (so the engine is only running on half of its cylinders. Using a tach run the rpms up to where the advance is full in, then adjust the distributor timing for highest RPM's. shut it down and return the idle setting and plug wires to normal. Worked great!
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horse
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PostPosted: Wed May 20, 2020 10:05 am    Post subject: Reply with quote

Wow, many ways back in the day.

Any idea if the correct carb would make a difference?
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mdainsd
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PostPosted: Wed May 20, 2020 10:09 am    Post subject: Reply with quote

Just an opinion, but the Military carb is not a performance part, it had other tasks that it had to do, like run under water. The Weber is probably far more tunable than the stock M38 carb. But even with the stock carb they can be made to purr.
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horse
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PostPosted: Wed May 20, 2020 10:33 am    Post subject: Reply with quote

Thanks, I will still keep half an eye out for one but I would like that purr !
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wesk
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PostPosted: Wed May 20, 2020 10:47 am    Post subject: Reply with quote

The YS637S had another feature important to jeeps. It's ability to operate smoothly irregardless of the jeep's relative angle to the ground.

Notice in my original reply I did not say it was a bad way to time your jeep. I said it can result in some bad things. If you believe you are a super knowledgeable mechanic and it works for you great. If you do not feel comfortable or confident timing that way then do not do it that way. And although not mentioned here a few degrees advance is a good thing with modern 80 plus octane fuels.
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horse
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PostPosted: Wed May 20, 2020 11:12 am    Post subject: Reply with quote

Got it.

I am certainly not super anything, just started with the Jeep last year but like

things to be set up as they should be weather that is fast or slow.

Nice to know about the Carter as we have a lot of hills in my area, good tip on

the octane.

Will keep on learning. Smile
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dpcd67
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PostPosted: Wed May 20, 2020 9:29 pm    Post subject: Reply with quote

That is the only way I time engines; using a vacuum gauge and my ear. Never fails to make them run better than using the timing marks. I do not even own a timing light!
You broke the code on how to do it.
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horse
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PostPosted: Thu May 21, 2020 5:22 am    Post subject: Reply with quote

Another fan of the Vacuum gauge, just need to train my ear for a few years.

I am going to advance the std 5 BTDC to 8 degrees as Wes suggested for modern petrol. Will see how she sounds/runs then as it will be part way between the two systems of timing the motor. May be a happy compromise.
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horse
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PostPosted: Thu May 21, 2020 7:35 am    Post subject: Reply with quote

So she is now set on 8 degrees advanced with the timing light and then set base idle with the Vac gauge(better than my novice ear) best reading 18.5Hg.

Went for a run out and happy with the results, runs well with hopefully no engine explosions.

Thanks for all the input.
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ih8pepl
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PostPosted: Fri May 29, 2020 4:11 pm    Post subject: Reply with quote

dpcd67 wrote:
That is the only way I time engines; using a vacuum gauge and my ear. Never fails to make them run better than using the timing marks. I do not even own a timing light!


Well this explains a lot... I can name 1 Jeep where your method failed.
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