[Formula jg]

I have another thread going in the Street section that started as a carb issue but may now potentially be a distributor problem.

When I stab the throttle at light cruise I get a bad stutter and when I stab throttle enough to open secondaries the engine will literally cut out if I keep the throttle in the stabbed position.

Coil is an old Accel (1990) with red/white leads. Using Ohm meter I touch both these wires and get a reading of 0.5 ohms and when I connect 1 meter lead to either the red or white and other lead to underside of coil it reads 8950 ohms.

Looks like coil maybe ok unless there is something else going on that can't be tested with ohm meter, let's not forget the coil is almost 30 yrs old. Anything else I can do to test this igintion coil?

Now for the pickup coil it reads 830 ohms but when I wiggle the green/white wires the meter numbers fluctuate a bit. I have 4 other new and used pickup coils in my tool box that I tested and they all act the same when moving the 2 wires around, is this normal?

Thanks for any direction you guys can provide.

[Geoff]

Provided your meter is making a solid connection with the p/up wires, you should see NO change in the ohms reading. Changing/flickering reading indicates a bad/broken connection.

["QUICK-SILVER"]

Originally Posted by Geoff

Provided your meter is making a solid connection with the p/up wires, you should see NO change in the ohms reading. Changing/flickering reading indicates a bad/broken connection.

I'd retest and move the wires slow and see what happens. The green and white wires usually fray and break right where they go in the pickup. If reading goes way high or open the wires are definately coming apart inside the insulation.

Clay

[jonmachota78]

Just a thought if you suspect pickup wires are the cause. Assuming you are using vacuum advance, when you stab the throttle, you're loosing vacuum, causing the vacuum can to pull timing out flexing those pickup wires. Maybe disconnect the vacuum can and take it for a drive and see if the problem still exists.

[george kujanski]

Sure sounds like the pickup coil.......if confirmed, change it when it's in the garage...not easy on the road...need to take the dist apart. It's not xpensive, just some time.

George

[Formula jg]

jonmachota78, why can't I ever come up with these simple and logical tests, I'm always looking to complicate my life and have less money in my pocket...need to hang out with you guys a little more.

I bought a new AC ignition coil earlier this week because I wanted one as a backup to the 30 yr old thats in there now. Retested all my spare pickup coils and each one has the same issue when wiggling the wires the ohms jump around, so I ordered a new one and it better have solid wire connections.

I will update once further testing is done this weekend.

[David Ray]

"Please explain how a vacuum operated load compensator would ADD timing at acceleration? "

Welllllll, as we all know, full manifold vacuum REDUCES upon engine acceleration, because engine vacuum reduces as throttle position is increased, during engine acceleration. So, there would be no additional timing, no second acceleration curve as this occurs.

PORTED vacuum is moot at low to no load, and high engine vacuum levels, such as no to light load cruise, and when the engine is accelerated, vacuum is created at the ported port, bringing into operation, the 'load compensator', forcing it to work completely opposite of how it should, adding vacuum advance degrees upon engine acceleration, CREATING A SECOND ACCELERATION ADVANCE CURVE ADDED TO THE MECHANICAL CURVE, MAKING TWO DISTINCT ACCELERATION CURVES.

That's how.

[Kenth]

"Welllllll, as we all know, full manifold vacuum REDUCES upon engine acceleration, because engine vacuum reduces as throttle position is increased, during engine acceleration. So, there would be no additional timing, no second acceleration curve as this occurs."

Since manifold vacuum is reduced at the same rate, ported or full manifold source to the load compensator the result would be, and what i have found, the same, reduced timing advance at acceleration.
Test driving with a vacuum-meter teed to the load compensator hose will show no "second acceleration curve".
The needle may hick-up when the throttle blade passes the ported source slot in the bore creeping away slowly with the car, but i would not call that hick-up "second acceleration curve".
Maybe this can be accomplished with some sort of delay valve for the load compensator?

[70gtojosh]

When you get your new pick up coil pay attention to the metal piece the coil sets in. If it is not stamped or machined to the correct thickness/height it may be difficult to reassemble the distributor. I've been down that road. Had to reuse that bottom metal piece in my experience. Just because the part is new does not make it good! Good luck.

[Geoff]

The most important part of replacing the p/up coil is to ensure it is centered, such that none of the reluctor tips make contact with the pole piece tips. There must be an airgap.

[Formula jg]

70gtojosh, I’m trying to determine exactly which part of the pickup coil your referring to.?

Geoff, thank you for the air gap tip.

[70gtojosh]

It would be the part that has the little "arm" that the vacuum advance can attaches to. Hope that helps.

[David Ray]

WRONG.

Since ported vacuum is taken further up the throttle bore, well within the smallest diameter of the venturi, vacuum is created there, to pull a vacuum advance diaphragm into adding timing during acceleration, or, make a second acceleration timing curve..

The vacuum signal at the base of the carb at WOT is extremely low, to completely NIL, so, no vacuum pull, no vacuum advance timing on full manifold vacuum sourcing at full throttle, NO secondary acceleration timing curve..

VAST difference with vacuum levels between full manifold and WOT ported sourcing.

Try driving around with TWO vacuum gauges connected, one to each type port, as I have, many, many times.

[Formula jg]

I’m not qualified to debate this either way and I’m not picking sides here but can confirm after countless testing of both ported and direct manifold setups my combo idles and runs better and cooler on a direct manifold setup to the load compensator.

On another note I scored a couple of advance springs today, they feel stiff enough to slow down this curve but won’t know for sure until the weekend.

Also, someone suggested I check fuel pressure when stabbing the throttle under load as the mech. fuel pump may be acting up and causing the stutter/stumble and excessive lean spike condition that we have been chasing, another test for the weekend.

[Kenth]

Ok, are you suggesting that venturi vacuum is activating the load compensator at the ported vacuum source at acceleration with low intake manifold vacuum?
That sounds odd since the ported source is below the throttle blade exposed to intake manifold vacuum, or lack of vacuum, at acceleration.
My observations differs from yours, i have found vacuum drops at the same rate at acceleration, ported or full manifold source..

[Kenth]

Originally Posted by David Ray

WRONG.

Since ported vacuum is taken further up the throttle bore, well within the smallest diameter of the venturi, vacuum is created there, to pull a vacuum advance diaphragm into adding timing during acceleration, or, make a second acceleration timing curve..

The vacuum signal at the base of the carb at WOT is extremely low, to completely NIL, so, no vacuum pull, no vacuum advance timing on full manifold vacuum sourcing at full throttle, NO secondary acceleration timing curve..

VAST difference with vacuum levels between full manifold and WOT ported sourcing.

Try driving around with TWO vacuum gauges connected, one to each type port, as I have, many, many times.

I can assure you i know the difference between the ported or the full manifold source for the ignition vacuum advance, and why either is used.

Wouldn´t it be easier for you to just give an example on any carb or engine that uses a ported source to add a second advance curve from the ignition vacuum advance, instead of twisting and turning my words against me and make up fantasy statements?

Thanks.

[Formula jg]

Update.
The new pickup coil has not arrived yet but I wanted to eliminate other possible culprets in the meantime.

First thing I noticed was the ignition coil screw holes in the distributor cap were stripped and the coil was not held firmly in place so I replaced the cap. Retested the pickup coil with ohm meter and the numbers definitely jump around when wiggling the wires.

Put it all back, road test with vac. adv. distconnect as suggested by 70gtojosh and there's no stumble or stutter, awesome.
Reconnect vac. adv. and still no stutter or stumble when stabbing the throttle. The only thing that was changed was the dist. cap so I guess some wierd movement with the lose ignition coil was occurring when stabbing the throttle.

I went ahead and replaced the 30yr old Accel ignition coil with the new ACDelco coil just to see if there was any difference. First noticed the new coil needs longer cranking to start the engine, the Accel would fire it up instantly. Short road test is inconclusive at this time, need to review the data logger to see if anything jumps out at me.

I'll test the new pickup coil when I recieve it and if the ohms are steady when moving the wires around then I'll install it and report back.

[Formula jg]

I rec'd the new pickup coil and sure enough the ohms reading jumps around when wiggling the green and white wires, now I have 5 of these things all acting the same.

Can someone reconfirm that there should not be any change in ohms reading at all when moving the wires or is a little fluctuation in numbers acceptable?

thx all.

[Bill Hanlon]

Given that all 5 do it, I'm willing to bet that an analog meter's needle would be fairly steady to not moving at all under the same test. Reading a slight change is hard to do with a digital meter.

[David Ray]

Hilarious, very entertaining.

So, NO other carb creates ported vacuum above the throttle plates. That is just plain false.

It seems in your world, other carb manufacturers simply cannot drill any vacuum passages other than straight into the side of the base plate, no passages upwards and sideways into the top of the venturii, as I have seen for decades.

And, well, I do have to confess, I do have extensive carburetor experience, as when I worked for Duntov at Skunk Works, I did engine design development, helped develop the coil in cap HEI, AND, worked extensively on carburetor development.

I also worked at Holley for a few years, I band sawed Dominator's in half for Pro-Stock racing, creating "Split-Dual" carbs for drag racing, and working directly for the racers.

By what you say as to ported vacuum production in non-Holley carbs, the same could be said from you, that there cannot be any oiling of an engine past the point of crankshaft feed galleries, because there are never any oiling passages drilled in engine blocks upwards to deliver oil pressure and oil above the crank center lines, and no water above the water pump insanity as well, nor can you drink any liquid from a cup that is half full even with a straw and suction applied, nor blow bubbles from that straw downward into the liquid, either. I am sure you will use those erroneous examples to prove your incorrect point as well, next.

PLEASE, "stop all this no ported vacuum above the wide open throttle plates" BS, we know better. Give it a rest.