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Old June 19th, 2019, 08:19 PM
randall555 randall555 is offline
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Default timing a stock m715 engine ???

does any one know if there is any thing special to do when timing a stock m715 engine . and also what is the timing for it ??? where is the timing mark on the front of the engine . I need to know because my truck will idle just fine but when I give it fuel it dies or misses really bad . i put a new carb on it not rebuilt and its the correct one . and new plugs and wires and points . also a new fuel filter does anyone have any ideals why it wont take fuel ?? does anyone know of a good aftermarket plug not the oem kind but regular plug type that would be a good choice ???
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Old June 19th, 2019, 09:12 PM
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brute4c brute4c is offline
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Timing with the stock wires requires an adapter to hook a timing light to OR a modified spark plug wire to hold a standard style spark plug and then allow a standard timing light to connect to it...

I did it this way:
Get a length of standard plug wire...strip down to the inner wire on the NON spark plug end...take off the #1 shielded wire (thats the stock military wire) and put this wire you made above in its place with the stripped part shoved down the hole of the cap first...the bottom of the hole and only a little of the side is where contact needs to be made...use a boot like the coils used in the 60's and 70's to hold the wire down in the hole.

Use a conventional Autolite #275 spark plug and time with a normal timing light.

To see the timing mark location, scroll down the tuneup section from the manuals to Figure C-10 on this page:

Timimg spec is listed as 5 degrees before TDC.

Make sure your points are properly gapped OR use a dwell/tach for, in my opinion, an easier and more precise setting. The instructions are on that same page linked above.

If the fuel filter wont fill up with fuel, you may have a restriction in the fuel system. Sometimes there is crud in the tank that needs cleaned out or in the lines. There is also a "sock" type prefilter in the tank that is known to deteriorate with modern gas and can plug the line. In such cases, members have taken off the fuel line and blown compressed air back down the line into the tank to blow the "sock" off the line and stop that restriction. You could also have a weak fuel pump.
Can you verify that the pump is pushing fuel to the motor?
Do you have an electric fuel pump you could put in the line to see if it pumps fuel when the stock one doesnt?
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Old June 19th, 2019, 09:30 PM
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brute4c brute4c is offline
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Also check the float setting...the M715 uses a different float setting that civvy units with the same carb and these are often set for the civvy purposes.
Scroll the following page to Figure 4-11 and it has the dry float setting there:

Another thing to check is the accelerator pump arm...the stock one is plastic and tends to break, which means the truck will stumble when one tries to accelerate from idle, here is an image that shows the part:

Look at the line for the #5 item in the image, follow it up to the arrow at the end. Now go a little left and down and you will see 3 small circles in an arc...this is one end of the accelerator pump arm...the rest of the arm runs from there to the left and has a metal "J" shaped rod through the hole in the left end.
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Old June 19th, 2019, 11:13 PM
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jeepdan jeepdan is offline
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All great info above^^^^

Also check to make sure that the accelerator pump is actually squirting fuel out of it's jet, by looking down into the carb while opening the throttle.
The rubber diaphragm can go bad, especially with todays methanol laced fuel.

What kind of a new carb? An old New Old Stock carb?
If so, you will need to overhaul it with a new kit that is methanol compatible.

The harmonic damper is known to have the outer ring slip on the rubber part shifting the timing marks out of place.

My truck must be that way. If I time it by using a timing light, it doesn't run well.

I have to time it by ear

Last edited by jeepdan; June 19th, 2019 at 11:22 PM.
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Old June 20th, 2019, 10:56 AM
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kwai kwai is offline

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You misspelled ethanol. Gasoline has ethanol in it.

You can also set the timing using a vacuum gauge.

If you have an old military spark plug wire, you can remove the shielding to create a spot for the timing light to get a signal.

Your symptom sounds most like an incorrect float setting. Follow the TM procedures to set the proper float level. And check all the other areas mentioned as well.
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Old June 20th, 2019, 01:25 PM
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Barrman Barrman is offline
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There is a military kit out there for timing and rpm gathering. Here is a shot of the adaptor to get a tach signal and the manufactured lead splice to do as Jon described to get the timing light signal:

RRRR.... I thought I remembered the new way to post pictures here. If you want to look, click on my user name and go to my albums. Picture post is the album that has these to parts. Sorry.
Remember if you didn't build it you can't call it yours.

6.2 powered M715, 5 M1009's, M416, 2 M101's, 2 M105's, 3 M35's, M1007 6.5 turbo Suburban project called Cowdog.
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