Hi guys. Me again.

I have another weird issue.

HA HA..
At least I have you guys to throw it at.
Besides when we get a tough issue and figure it out we all learn.
There are very few individuals who know anything about these old engines.

He goes......


If I pull the vacuum line to the adjustable Vacuum advance unit, (ported vacuum) and romp on it there is no ping at all. It just hauls A$$

So...
I hook up the vacuum back up to the unit.
No vacuum at idle. (its ported remember?)

I take him out and apply medium throttle at cruising speed and it pings like mad.

I turn the adjustable vacuum counter clockwise and try again.
Still pings.

I turn the unit counterclockwise until it bottoms out at the stop.
Still pings.

Ideas?


Bill

 

Sounds like your base timing is high. What is it at?

 

^^^ This. disconnect and plug vacuum advance and run it up with a light. What is the total mechanical advance at 2, 3, and 4k RPM?

You may have to back off on the initial, if you don't limit the internal distributor timing. Once the initial + mechanical is sussed out, then re-connect vac advance and tune as the final step.

 

That is odd actually. Did this start all of a sudden, or was there some work done to the truck before hand? New to you truck? Maybe the mechanism inside the can is broken. I would take the can off and see if the arm is physically being limited when you back out the adjusting screw just by working it in and out manually.

 

It does not ping at WOT with the vacuum advance unit (VAU) disconnected and plugged. This engine LOVES the timing. It freeking roars.

It has 20 degrees mechanical with 11 degrees Initial timing which makes it 31.

I have the vacuum advance unit cranked down as far as it goes.

I'm figuring that the VAU even with it cranked down all the way is STILL allowing too much advance at mid throttle.

I really like vacuum advance because it makes the engine more responsive in the mid range during acceleration. The word here is PEPPY, Chrisp response that without vacuum advance leaves partial throttle opening lacking.

Tedster... I simply refuse to restrict the base timing to this monster. All I want is a few more for cruising. At WOT the vacuum unit is seeing almost zero vacuum and retarding the timing would make WOT even less powerful.

Classic..."Maybe the mechanism inside the can is broken. I would take the can off and see if the arm is physically being limited when you back out the adjusting screw just by working it in and out manually."
I need to find out a way to get this think down further in advancing.

RESEARCH
Thank goodness for the internet. It's not just for pictures of pretty girls. LOL


That's what I'm thinking.
__________________


Thanks.

Until I figure this out the vacuum advance unit stays unplugged.

 

Run it up with a light on the damper and see what it's doing connected, disconnected, full CW, full CCW, etc.

 

NEWS !!!

Without vacuum. Distributor vacuum line disconnected. Vacuum line plugged.

Wide open throttle? No ping

1/4 throttle at cruise I easy heavily into the throttle... PING

I even retarded the initial advance.... Still ping.
But no ping when I romp on it full throttle.

WHAT?

Now i'm confused.

Is there possibly something broken in the distributor?
Has anyone heard of such a thing?

The ping during acceleration from cruise speed IS NOT the vacuum advance unit.

HELP! I'm lost now

More research

 

Sure, why not? The mechanical advance has to be freely moving. Distributors get worn, sticky, erratic, springs broken, missing etc..

Run it up with a light and look for smooth advance AND return, excessive "scatter" on the marks under the light etc.

 

What are you running for a carb? Maybe it's going lean at mid throttle?
An AFR meter can be a good investment.

 

2X. Sounds like you need to dig into that distributor and check springs and weights. Check breaker plate for smooth operation, check the vacuum advance arm that attaches to the breaker plate for movement and travel distance. I wouldn't even waste time putting a light on it if you're having that many issues. Good luck

Dan

 

I'm running a Holly 4150. Its 4 bbl,780 cfm, dual inlet , vacuum secondary.

I had it rebuilt about 2 years ago by one of the NHRA's finest Carb shops

I hadn't thought of that.

Thanks all..keep em coming..

 

Bad or cheap(re) gas will send mine for a loop.

 

Best fuel in Iowa. 91 octane.
But Iowa fuel is junk

 

Six, what is an AFR meter?

 

Look for straight gasolene in your area here: http://www.pure-gas.org

Dyno's Sinclair has 87 without any corn squeezins, looks like