Timing, SVDA and Advance Curves.

Post by **Sluggo** » Thu Jun 07, 2007 2:37 pm

My timing advances too much. I have the Aircooled.net SVDA. From what I understand it should be timed at 28* max advance with the vac hose off and plugged. Mine does go to 28* max centrifugal advance and settles nicely at 7.5* BTDC at idle. But once I hook up the vac hose the timing advances to 34* Max advance! This is too high right? How do I adjust the dizzy springs/weights to make so that I only have 28* advance.

I was reading this thread at Shoptalk http://www.shoptalkforums.com/viewtopic ... ry&start=0

Now I'm a little more confused.

spiffy · Post by **spiffy** » Thu Jun 07, 2007 3:53 pm

I don't think that is too high, that sounds normal to me.

bottomend · Post by **bottomend** » Thu Jun 07, 2007 4:53 pm

Well, the problem is that you cant adjust you're upper limit without affecting your lower setting. Start saving for the Malllory!

It tripped me out to read that old thread. ... Ah, the good ol' daze!

chitwnvw · Post by **chitwnvw** » Thu Jun 07, 2007 5:31 pm

IIRC Colin told me that it should blip up to 40 or so when you goose the gas.

fido · Post by **fido** » Fri Jun 08, 2007 2:37 am

yep - the vacuum can add as much as 10 degrees extra when the engine is not under load. THis is a GOOD THING :) 28 without the hose is perfect.

spiffy · Post by **spiffy** » Fri Jun 08, 2007 7:30 am

When I got my SVDA I was reading alot about timing to max advance and the like and it became apparent to me that I was giving myself a mind f***.

I decided to slap myself back to the stock frame of mind and go for those tuning specs....

Post by **Sluggo** » Fri Jun 08, 2007 9:26 am

Thanks guys. I was thinking it should go up and then return to 28*. Then return to 7.5* BTDC at idle. I won't worry about it. Bus is running better and stronger than ever.

Post by **Amskeptic** » Sat Jun 09, 2007 6:25 pm

Sluggo wrote:Thanks guys. I was thinking it should go up and then return to 28*. Then return to 7.5* BTDC at idle. I won't worry about it. Bus is running better and stronger than ever.

Vacuum advance should hit 40*BTDC when you mildly blip throttle up to 3,000 rpm or so. On the road, when you floor the accelerator, the vacuum drops under full load, then the centrifugal advance is your primary advance. The Type 4 engines are pretty happy up to 30-32* BTDC on centrifugal only. Check at 3,200 rpm with advance hose off, duh course. When you are done, make sure centrifugal advance does NOT exceed your adjusted value when you rev to 4,000 rpm briefly.
Colin

Gypsie · Post by **Gypsie** » Tue May 11, 2010 12:53 pm

Amskeptic wrote: The Type 4 engines are pretty happy up to 30-32* BTDC on centrifugal only. Check at 3,200 rpm with advance hose off, duh course. When you are done, make sure centrifugal advance does NOT exceed your adjusted value when you rev to 4,000 rpm briefly.
Colin

What if it does advance beyond the adjusted value?

Would that mean that it is not fully advanced at 3200rpm?

If so should the high rpm advanced setting get made with a higher rpm to attain max centrifugal advance for the setting?

Curiouser and curiouser...

Post by **Amskeptic** » Tue May 11, 2010 2:33 pm

Gypsie wrote:
Amskeptic wrote: The Type 4 engines are pretty happy up to 30-32* BTDC on centrifugal only. Check at 3,200 rpm with advance hose off, duh course. When you are done, make sure centrifugal advance does NOT exceed your adjusted value when you rev to 4,000 rpm briefly.
Colin
What if it does advance beyond the adjusted value?
Would that mean that it is not fully advanced at 3200rpm?
If so should the high rpm advanced setting get made with a higher rpm to attain max centrifugal advance for the setting?

If it does advance beyond the specification, then the second question is answered by the first. You would want to clean the centrifugal weights and pivots and springs. You need to be dialed-in advance-is-in, at 3,200 rpm. Your immediate concern is to make sure that the timing never exceeds 28-30* at any rpm, and if you need to retard the timing, do it, even if the idle timing is now closer to "0". Idle is not half so critical.
Colin

tvargs · Post by **tvargs** » Sun Jun 19, 2011 4:42 pm

I just had a new (rebuilt) engine from Adrian @ Headflow Masters put into my '77 FI Type 2, stock most everything. There's a long story about it, featuring the amazing, truly exemplary, and unbelievable effort and service of Adrian Audirac and Kenny from Headflow Masters, but I will save that for another thread. Suffice it to say: those guys are worth EVERY PENNY and have gone ABOVE AND BEYOND what a reasonable person would ever expect - I can't thank them enough. =D>

So when we got the engine running, Adrian noticed that the timing went to 40* at 3000RPM, and pronounced that way too high. Without the hose, it stays below 30*. One thing we noticed when we took a look at the distributor is it's a fair bit dirty - my first thought was perhaps a good cleaning will help.

Reading the above post, though, suggests that the high advance shouldn't be too much of a concern. Without the hose, the advance stays below 30*, with the hose attached, it gets way up there. Any thoughts?

Randy in Maine · Post by **Randy in Maine** » Sun Jun 19, 2011 7:15 pm

From Ratwell....

tvargs · Post by **tvargs** » Mon Jun 20, 2011 1:40 pm

Ok, so that graph tells me that the timing goes far too high at 3000 RPM, and I have a problem? And that problem is likely the distributor? (It was suggested that my dizzy may be missing a spring - will have to take it apart to see. Seems like an odd thing, to have a missing spring, but you could fill entire libraries with what I think is odd and don't have the experience to know...)

chitwnvw · Post by **chitwnvw** » Mon Jun 20, 2011 10:50 pm

IIRC, it is 28 degrees without vacuum max advance. With vac if you blip the rpms you can see 40 + degrees of advance briefly, picture you need a bit of acceleration to pass a car on the highway, so you lay on the gas pedal...

But it should pretty quickly settle back to the 30 degree territory...

RSorak 71Westy · Post by **RSorak 71Westy** » Tue Jun 21, 2011 9:09 am

With vac if you blip the rpms you can see 40 + degrees of advance briefly.

This is flat out wrong. When you get on the throttle the engine vacuum goes down not up. So the timing would not advance under these conditions.

If you were missing a spring the timing would come in sooner i.e. lower RPM but it would not go any higher than it otherwise could.

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Timing, SVDA and Advance Curves.

Timing, SVDA and Advance Curves.

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Re: Timing, SVDA and Advance Curves.

Re: Timing, SVDA and Advance Curves.

Re: Timing, SVDA and Advance Curves.

Re: Timing, SVDA and Advance Curves.