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DannDZ

800RPM idle, good accel, timing off by 20 degrees!

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I am attempting to tune my '71 with the old round top SUs. I performed a rudimentary (at best) carb tuning and then turned to the ignition. While tuning the engine I was able to get the it to idle well at 800 RPM and it had strong acceleration up to about 6K RPM and 90 MPH. (On a track only, of course! 😉) But when I look at the ignition timing with a timing light, it shows that it is about 25-degrees BTDC!

The distributor is at its limit of adjustment. Is it possible/recommended that I remove the distributor itself and move it by "one position" to fix the problem and get me back to the right range where I can make timing adjustments just loosening the distributor cap and adjusting?

What is going on and how I can fix it?

Thanks!

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If that's in 4th gear I'd leave it be. Pretty good numbers imo. But you could set it at tdc and remove the distributor and see where the spindle is. Should look like this...

motordistributortiming.jpg.png

 

 My distributor is maxed out too. I'm at 17 btdc and 34 full advance at 3,000 or 3,500? can't remember but at the higher rpm my timing mark is at 0. At idle its 17.

I'm no ignition guy but could you plugs wires be off on the cap?

Edited by siteunseen

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2 hours ago, DannDZ said:

 about 25-degrees BTDC!

is that at idle?  Do you have a vacuum hose connected to the vacuum advance?

Make sure that the rotor is actually pointed at #1 wire when the timing mark is close to zero.  Take the cap off to see.  Many possible causes for what you're seeing.

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Those 3 screws have the dizzy vacuum hose connection on the front one. Closer to the valve cover, pointing more towards the radiator. I can't find a image, sorry.

Edited by siteunseen

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If he has 25 at idle he could have 43 to 47 at full advance, if that's with no vac advance.  I had a couple of 22 degree mechanical advance distributors.

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Check your crank pulley has not slipped first.

Also with a 8mm wrench you can loosen the bolt under the dist and adjust to get more

adjustment when you have run out of range. I run 10 degrees max at idle myself.

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So many great suggestions! Thanks to everyone. I have much to learn. Today I am going to (try to) tune and balance my carbs. Then it is back to setting the ignition timing. Having not actively worked on it for about 20 years, I'd forgotten how interrelated everything is. An how ANALOG! Cars today make all those interdependent adjustments on their own.

Thanks again! 

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12 hours ago, 240260280 said:

Z's love advance while idling so 25 is fine....but it usually pings when under load as the rpms rise.

Starting would be  hard at 25!

I don't here any pings on load, but I can listen more carefully. When warm, haven't tried it cold yet, it starts with no choke and no foot on the accelerator. If I didn't know the timing was off, I'd think everything is fine.

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11 hours ago, 240260280 said:

10 while cranking , 25 at idle, 32-38 max, and higher only  under cruise would be great

How can you tell the timing under all these different conditions? While cranking and idling I can understand, but how can it be measured at cruise? And, can you provide any insight on why everyone suggests that is may be OK when it is so far from what the manual says? Is it just the nature of a warn system that you adjust until it runs right, the book be damned? 

Edited by DannDZ
Added question about why not the book values?

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You need to look and mark your timing marks on the pulley carefully. I almost bet you are sitting at 20 BTDC at idle and not 25. More than likely you have 17 degrees of mechanical advance with that dizzy and that would total you out at 37 WOT.

20 degrees idle advance would start and idle easier without choke because all that advance makes for a strong idle. Does your vacuum advance work? That’s where you might run into issues . You might be adding too much advance at cruise and be causing detonation that you can’t hear . Might suggest getting an Advance type timing light to check full mechanical advance and vacuum advance. 

 

Check your vacuum advance is working properly and not sticking 

I’ve run all my motors with close to 20 degrees at idle ,  with no vacuum advance. I also had cams that ran better that way. Figure out what dizzy you have with the chart below. 

Just 45 miles south of you I noticed!

5BC08466-01A3-403A-BB72-2CD4D74A7B95.jpeg

Edited by madkaw

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50 minutes ago, madkaw said:

Just 45 miles south of you I noticed!

Very close, I live in the Center Grove area.

Thanks for your advice and the table. It will certainly be helpful when I try to figure out what is going on. I may not be as far off as I suspect. What I really don't understand is why this is so far from the "factory specs" in all the manuals.

Regards,
Dann

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3 hours ago, DannDZ said:

What I really don't understand is why this is so far from the "factory specs" in all the manuals.

Could be that your damper pulley has slipped and the marks aren't correct, or that the vacuum hose has somehow been attached to the wrong vacuum port.  Distributors use "ported" vacuum, that is only active when the throttle blade is off-idle.

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