'78 FI 2.0 too much advance... Why??

[honeybus]

Colin, you saw this '78 in Springfield VA this past spring.

The '78 has decent advance WITH VACUUM DISCONNECTED.

7.5 BTDC at idle (850-900 RPM - engine warm)
28 BTDC at 2500 RPM.

The '78 has dangerous advance WITH VACUUM CONNECTED.

7.5 BTDC at idle (850-900 RPM - engine warm)
36 BTDC at 1700 RPM.

The VW was rebuilt by a California outfit, has GD case with hydraulic lifters.

It did have dual carbs. Now it has normal fuel injection

Colin saw this condition when he was here and we (he) set the timing to compensate for the wild advance. It was set about 0-5 ATDC retard.

Thinking it might be a bogus distributor, I replaced the unit with a different (stock 205 S) distributor, but I get the SAME dangerous advance that Colin recognized.

It M I G H T have had a 009 distributor from California, I can't remember.


Question: Is there possibly something in the setup of a dual carb - 009 - hydraulic lifters - unknown cam that would cause such a severe advance with the throttle vacuum connected to the 205 S distributor?


Background: I have only driven this '78 about 1500 miles since rebuilt with the fuel injection, and ZERO mile before that. The PO was happily running the VW in California, and drove it cross country to Virginia without mishap.

An engine fire around the right carb cause it to come into my hands. I would have kept the P&C except that the engine laid fallow for about 2 years, and when I tore it apart, the pair of P&C on the right (fire side) were unrepairable (water and chemicals from the fire) However, there was no indications of pre-ignition damage.

I took the block, a new set of P&C and a pair of rebuilt heads to my local legend. He split the case in front of me, and we considered the main bearings to be fine (it did have a recent rebuild in California). So we saw the guts of the beast, and were pleased.

I did not pay attention to the thing-a-ma-bob cam that is slightly different for solid vs hydraulic, so I don't know if it was a hydraulic cam that was used by the rebuilder (it is a GD case, and I should have been more observant)

So, eliminating the distributor as the culprit, what could the issue be??

Thanks
Barry Burneskis
Springfield VA



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[honeybus]

Ok. I disconnected and closed the vacuum to the distributor (SVDA) and I am running this:

7.5 BTDC at idle (850-900 RPM - engine warm)
28 BTDC at 2500 RPM
32 BTDC at 3500 RPM.

On a test drive, I seem to reach the 3500 RPM point during normal acceleration when driving, so I guess I have to be careful.

I don't know my vacuum or compression yet.

I plan a trip to New River Bridge opening his coming weekend, so wish me luck.

Barry

[Bleyseng]

Should be ok with that, vac advance is should be only from 1200 to 1800 rpms for a boost in accel. Now if someone buggers the dizzy then all bets are off.

[honeybus]

Should be ok with that, vac advance is should be only from 1200 to 1800 rpms for a boost in accel.

Bleyseng, I was seeing 36 degrees of advance @ 1700 RPM with vacuum connected. Do you think my vacuum would DROP to 28 degrees [from 36 degree] if I continued [from 1700 RPM] to 2500 RPM?

Now if someone buggers the dizzy then all bets are off.

But this is a SECOND dizzy, with apparently near identical result. Granted, unknown dizzys, but what's the odds???

Also, Colin thought the VW ran weak, missing power. I was then thinking possibly a loss of manifold vacuum or low compression. Maybe it is this 'advance' mystery.



Barry

[Randy in Maine]

From Ratwell and Old Volks home....





205P = 205S

It does seem to come on a bit early (but we don't know what kind of vacuum you are seeing) to make that call. Could you T in a vacuum gauge to determine that? Where are you pulling vacuum from for the distributor anyway?

At around 1700 with the vacuum hose disconnected you should be seeing about 18º of centrifical advance + the 7.5º of initial timing ~ 26º.

Pretend you are driving down the highway at about 65 mph and are headed down a dcent hill (high RPM and high vacuum) what kind of total advance are you seeing? I would expect to see about 42-44º.

[DjEep]

36 sounds about normal for a vac advance. Don't forget that when you are under heavy load at high RPM, where too much advance would kill it, the throttle plate is wide open and not much vacuum is pulling on it. It's hard to replicate that in a non-moving test because the with no load, the slightest throttle will send the engine racing.

[honeybus]

It does seem to come on a bit early (but we don't know what kind of vacuum you are seeing) to make that call. Could you T in a vacuum gauge to determine that? Where are you pulling vacuum from for the distributor anyway?

Yes, I will 'T' in a vacuum gauge tomorrow. (I just coated the driveway and the VW is outside, waiting for the diveway to dry)

I am getting the vacuum from the throttle (air intake, going to the air mixture box - fuel injection).

At around 1700 with the vacuum hose disconnected you should be seeing about 18º of centrifical advance + the 7.5º of initial timing ~ 26º.

I will check advance at 1700 RPM, sans vacuum. I get the 28 degrees mechanical advance at 2500 RPM, I don't know mechanical advance at 1700 RPM.

Pretend you are driving down the highway at about 65 mph and are headed down a decent hill (high RPM and high vacuum) what kind of total advance are you seeing? I would expect to see about 42-44º.

How would I see the advance while driving?? I have a vacuum line going to the front. for the driver to view, but that is the 'manifold' advance, from the air mixture box. And 42-44 is beyond the range of my timing scale; 40 is max.

Tomorrow. Thanks all. Barry

[honeybus]

36 sounds about normal for a vac advance.

When I saw 36 degrees advance at 1700 RPM, I freaked out. All I could think was that I would 'blow' the engine if I didn't immediately back off!!

Do I need the throttle vacuum when I am climbing a hill? It seems to run fine, but I have minimal expectations for performance.

Barry

[Randy in Maine]

As soon as you put your foot in it to climb the hill, the vacuum advance will go away.

When you go to time it with the vacuum hose off, wind up the engine until there is no more centrifical advance to be had and make that point to be 28º BTDC. You will be pretty wound up to about 3500 RPMs or a little more. We want to make sure there there is no more centrifical advance to be had no matter how fast the engine is throttled up.

No need to run a vacuum gauge all the way to the front of the bus. Just do it in your driveway. There really is no load on the engine just playing with the throttle there. Just confirm that you are pretty close. Then take it for a ride and see how it does.

Make sure you are pulling the ported vacuum this way...it sounds like you are hooked up correctly.

[Amskeptic]

The '78 has decent advance WITH VACUUM DISCONNECTED.
28 BTDC at 2500 RPM.

The '78 has dangerous advance WITH VACUUM CONNECTED.
36 BTDC at 1700 RPM.

Barry? This is normal. SET the timing with no hose to 28* MAX at 3,400 RPM.

With hose on, the advance should reach anywhere between 36- 40* got that? FORTY. Vacuum advance is smart. It knows to drop out as you apply a load.
Colin