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1974 620 timing degrees


Richie

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hey, 

 

So I rebuilt my L18 engine thanks to you guys for all the help. I am using a weber 32/36. My buddy brought his timing light over so we can set the timing. Some concerns I have. 

 

1. when we were setting the timing he noticed that when i bump the rpms up, the timing doesnt advance. He said i am about 8 degrees off of timing. How do I fix this?

2. I can not get the dizzy to line up with the screw hole enough on the plate to set the timing. I am really close. What steps should I take. 

3. I know i have tune the weber. Should I be messing with the vacuum adjuster screw on it? 

 

For reference, my vacuum advance on the dizzy is facing the radiator, I tried to take it off and turn it 180 degrees like I was told previously but the plate where the screw goes in will not line up at all. Like I said I know i need to tune the weber but the instruction say i need to have the timing correct first. 

 

thank you. 

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If the timing weights are stuck it won't advance or retard back to idle. I would get the centrifugal advance working first and it will likely fix the other problem. 

 

Timing should advance from idle to before 3,000 RPMs about 20 degrees (an approximation) add to this the static idle of about 12 degrees gives you the 32 degrees most L series engines like to run at.

 

 

 

I don't do Webers but...

 

http://www.redlineweber.com/html/Tech/carburetor_set_up_and_lean_best_.htm

 

http://www.redlineweber.com/html/Tech/34_ICT_tunning.htm

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34 minutes ago, datzenmike said:

If the timing weights are stuck it won't advance or retard back to idle. I would get the centrifugal advance working first and it will likely fix the other problem. 

 

Timing should advance from idle to before 3,000 RPMs about 20 degrees (an approximation) add to this the static idle of about 12 degrees gives you the 32 degrees most L series engines like to run at.

 

 

 

I don't do Webers but...

 

http://www.redlineweber.com/html/Tech/carburetor_set_up_and_lean_best_.htm

 

http://www.redlineweber.com/html/Tech/34_ICT_tunning.htm

well when we turn the dizzy counter clockwise it idles better and doesnt die. Clockwise it idles but dies. It sounds better turning counter clockwise. So i would need to reset the timing chain all that again?

Thanks for the weber stuff

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The timing chain has absolutely no connection to the ignition timing

 

 

1 hour ago, Richie said:

 

1. when we were setting the timing he noticed that when i bump the rpms up, the timing doesnt advance. He said i am about 8 degrees off of timing. How do I fix this?

 

When the engine RPMs rise above about 900 the mechanical, or centrifugal advance comes into play. The faster the engine turns the less time there is for the gas and air to burn completely. The answer it to start the burn earlier by advancing the ignition timing. As you can't get out there and do it while driving, a mechanical advance is used to optimize the combustion process automatically for you.

 

If your timing does not advance when revving the engine, then that is a problem. Always fix the obvious problems first. Fixing them often fixes other symptoms. 

 

IF, after fixing or resolving the mechanical advance you still cannot set the timing properly we'll deal with it then.

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3 hours ago, datzenmike said:

The timing chain has absolutely no connection to the ignition timing

 

 

When the engine RPMs rise above about 900 the mechanical, or centrifugal advance comes into play. The faster the engine turns the less time there is for the gas and air to burn completely. The answer it to start the burn earlier by advancing the ignition timing. As you can't get out there and do it while driving, a mechanical advance is used to optimize the combustion process automatically for you.

 

If your timing does not advance when revving the engine, then that is a problem. Always fix the obvious problems first. Fixing them often fixes other symptoms. 

 

IF, after fixing or resolving the mechanical advance you still cannot set the timing properly we'll deal with it then.

Ok this weekend we are going to get at it again. Ill keep you updated, thank you.

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You may have to take the points out and remove the breaker plate they mount to to get at the counter weights. Bet they are rusted. Look something like this...

 

75rTmkH.jpg

 

 

 

 

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Could be the weight springs inside are loose or detached somehow. Better have a look inside the distributor.

 

My soap box - the distributor is one of the most overlooked parts of an engine, and if not working properly, can cause problems ranging from lack of performance to erratic timing to broken piston rings. Distributors are so easy to manipulate to get them to do as you want. The timing curve of a stock Datsun L series distributor is pretty good, but can easily be made better. This is known as re-curving the distributor. You may find a how-to somewhere on the web, but for a first time, I would pay to have someone else do it. For $100-$150 you will get back a rebuilt unit with a proper advance curve.

 

But yeah, back to your problem. Your weights are either stuck or already advanced, so take a peek in there before proceeding to the next potential issue.

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6 hours ago, banzai510(hainz) said:

you sure you have TDC right? when you installed the dist?

wads this running before the rebuild so why would the dist go bad? Vacuum adv,

 

of set right the dist shoul be able to go from zerp to +25 deg BTDC at idle

yea i checked with you guys mulitple times for TDC and I got it matched up with the book.  Yes it was running before the rebuild. 

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1 hour ago, datzenmike said:

It will run with the advance stuck. Maybe stuck all along. Timing light shows no advance when revved up.

I need to post a video to you guys. This is kind of confusing. Saturday ill post a video with what we are doing. 

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yoo, I dont know why but the black bar is the video. If you copy and past it in the url it will work.  The other links are just pictures of the Tac and temp gauage/oil pressure. Play the video with volume and you can hear my buddy hitting the throttle.

 

 

https://imgur.com/cObVYkv

 

 

https://imgur.com/rn2IPxA

 

 

https://imgur.com/wOzzFy5

 

Also I have a question. You know the little plastic piece on the dis that is for the wire whole? Its on the side the wires feed threw it. If it is broken could that be a potential vacuum leak?

Edited by Richie
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1 hour ago, Richie said:

Also I have a question. You know the little plastic piece on the dis that is for the wire whole? Its on the side the wires feed threw it. If it is broken could that be a potential vacuum leak?

Absolutely not. If it's broken there is risk the insulation may rub bare and the wire ground against the case.

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33 minutes ago, datzenmike said:

Absolutely not. If it's broken there is risk the insulation may rub bare and the wire ground against the case.

Did the video url work?

 

Also I am really not trying to buy a new dizzy, is there anyway to fix this vacuum advance problem besides trying to find an OEM dizzy?

 

Edited by Richie
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There are TWO types of ignition advance.

 

One is the vacuum advance from that round thing on the side of the distributor using ported vacuum from the carburetor. It is engine load dependent. Low speed, high vacuum, more advance. Step on the gas, low vacuum, little or no advance.

 

The other is called mechanical advance. It is RPM dependent. It increases with engine speed. You said the timing does not advance when the engine is revved up, but it should. Grab the rotor and try turning it.

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11 hours ago, datzenmike said:

There are TWO types of ignition advance.

 

One is the vacuum advance from that round thing on the side of the distributor using ported vacuum from the carburetor. It is engine load dependent. Low speed, high vacuum, more advance. Step on the gas, low vacuum, little or no advance.

 

The other is called mechanical advance. It is RPM dependent. It increases with engine speed. You said the timing does not advance when the engine is revved up, but it should. Grab the rotor and try turning it.

Ok I have to do this all on monday because NFC wild cards are today. So what should I look for after I try turning the rotor?

 

Also if i have to end up buying anything, can I just buy the vacuum advance itself? https://www.ebay.com/itm/402162647877

Edited by Richie
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Why do you think your diaphragm is bad?

 

Get a cheap hand held vacuum pump to test the diaphragm. With the pump connected to the diaphragm, you pump it and watch the rod move. If it does not move, then the diaphragm is broken.

 

I suppose you could do this with a running engine too. Hook it up to a vacuum source and watch the rod. Disconnect the vacuum and watch it move again.

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Or just suck on the end of the vacuum advance hose. Done this many times and the breaker plate will twist clockwise. Put your tongue over the end and if ther is no leak the plate will stay advanced till you release ti.

 

I think the mechanical and the vacuum advance both turn the breaker plate so if one is seized the other probably won't move either.

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2 hours ago, datzenmike said:

Or just suck on the end of the vacuum advance hose. Done this many times and the breaker plate will twist clockwise. Put your tongue over the end and if ther is no leak the plate will stay advanced till you release ti.

 

I think the mechanical and the vacuum advance both turn the breaker plate so if one is seized the other probably won't move either.

so I actual did this and nothing moved. I didnt actually think it was a way to test it. So when I did it nothing moved. But I did fine someone with a ton of distributors and he is checking if he has a single point distributor for an L18 and let me know. I think i am going to bring a pump with me to check if it is good. Thank you for the help. I am getting close to being able to drive it. All that is left is the brakes, alignment, and this advance problem! Also figuring out how the steering wheel went back on. 

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On 1/17/2022 at 8:08 AM, Stoffregen Motorsports said:

No, the mechanical advance only moves the distributor cam, not the breaker plate.

Well i got the hand pump like you said. And i cant find a new dizzy so is there a way to fix this. I am posting a video, sorry for the gardening noise in the back. 

 

 

https://imgur.com/rbIj2aa

 

 

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You don't actually need a vacuum advance. If you disconnect it, you can add in a couple more degrees of base timing and get a better throttle response. Ideally, the timing on a small motor like an L18 would be about 12-15 at idle and then top out at about 32 degrees at around 3000 rpms.

 

If you're thinking of making some performance mods to the truck, spending the $150 to have the distributor re-curved will be money well spent.

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