chevy small block and IMPCO 425: timing question

[kikkegek]

A wider spark-gap gives a stronger spark.
It makes the ignition work harder to let the spark jump the gap so therefore it is stronger.

But with a low cr and non-performance engine I doubt you will feel much difference between sparkgaps, also since you have an MSD-system already.
I did however feel a difference in low-range power when I went from the stock electronic coil-ignition to the Jacobs Ignition in my daily.

just Jacobcs coil or complete ignition?

[BigBlockMopar]

The coil and ignition-module are incorporated into one box.
Gives out a stronger/longer spark than a MSD-box.

[Steptoe]

checked the lever in my converter today. Was hoping to find a lever that was set wrong, to maybe solve my mistery of the AFR20 for idle at cold engine to AFR14 with warm engine...I have no clue why it richens so much.

well, convert was set perfectly at .7mm to about 1/32" factory setting.

What converter do u have and what height... ?
As Iwcg says above wider gap hotter spark... so long as the system can handlethe volts and current...
And its not just the gap, but compression at the piont of fire, the mixture all contrubute to the resistance across the spark plug gap....and what is also critical when opening up, is not the spark plug gap but the total gap....between rotor and cap pins +plug gap....so corroded pins or a rotor thats been filled down on the end...or sharp edges removed also makes significant difference.
On std HEI I run 32/ 35 thou....I have found this works well in alsorts of mixtures and state of cap wear etc.

A pionts ign works well on a street engine, but must be in V good condition... dizzy, HT leads, the lot.
HEI ...even better...
rem HEI where introduced simply for more consistant firing with post EGR lean cruise mixtures, that require a more high engery spark... lean mixtures are harder to fire.

[kikkegek]

model E converter

and I measured the height by putting a ruler on the casing and measuring the amount of space between the top of the pin of the lever and the bottom of the ruler



sorry, image to big, but its on the right hand page:
http://smg.photobucket.com/albums/v704/ ... ent=E6.jpg

[Frank]

checked the lever in my converter today. Was hoping to find a lever that was set wrong, to maybe solve my mistery of the AFR20 for idle at cold engine to AFR14 with warm engine...I have no clue why it richens so much.

the engine had all the smog stuff on there and I took all of that off...

There may be something else going on in your engine that is causing your fuel mixture to become richer with a warm engine. If you disconnected the Early Fuel-Evaporation (EFE) system (vacuum-actuated heat-riser valve) but left the vacuum switch uncapped, it could cause a cold-only vacuum leak.

[kikkegek]

There may be something else going on in your engine that is causing your fuel mixture to become richer with a warm engine. If you disconnected the Early Fuel-Evaporation (EFE) system (vacuum-actuated heat-riser valve) but left the vacuum switch uncapped, it could cause a cold-only vacuum leak.

he thanks Frank. Yes that would make sense. But I have only a few things connected to vacuum:
- vacuumswitch for transmission
- brakebooster
- vacuum advance ignition
- PCV
- heater-controls
- cruise control

all other eco-smog-junk has been removed. There is one temp-vacuum-switch still in the front of the intakemanifold near the thermostat-housing, but no vacuum is supplied to it:
you can see it here on the right of the picture:

[Frank]

For the fuel mixture to become richer, the fuel must become denser and/or the air must become lighter so that there are relatively more fuel molecules to mix with the air molecules.

In the converter, increasing water temperature should increase the fuel temperature, which should in turn decrease the fuel's density. I would not expect that temperature would have any effect on the pressure being supplied to the engine.

I read that you've got a duct on your air cleaner which draws air from the grill so there should be no difference in air supply density as the engines warms up. The photos show the engine with the Model 300 which was ducted near the grill but still drew air from inside the engine compartment. Does the duct for the Model 425 draw air from in front of the radiator?

If you have a data logger with your O2 sensor that has the ability to track temperature, it would be useful to see if the rich mixture correlates with converter temperature.

Bear in mind that there are factors that affect sensor accuracy and the measured AFR may be richer or leaner than the actual AFR coming out of the engine. You might be trying to fix an AFR problem that doesn't actually exist in reality.
Tech Edge Wideband Oxygen Sensor Installation Guide

[kikkegek]

For the fuel mixture to become richer, the fuel must become denser and/or the air must become lighter so that there are relatively more fuel molecules to mix with the air molecules.

In the converter, increasing water temperature should increase the fuel temperature, which should in turn decrease the fuel's density. I would not expect that temperature would have any effect on the pressure being supplied to the engine.

I read that you've got a duct on your air cleaner which draws air from the grill so there should be no difference in air supply density as the engines warms up. The photos show the engine with the Model 300 which was ducted near the grill but still drew air from inside the engine compartment. Does the duct for the Model 425 draw air from in front of the radiator?

I currently have a IMPCO425 with an original airfilter house fitted on top and air intake from behind the grill. So always cool air. I have taken out the Thermac valve that uses warm air from around the exhaust for cold engine start, as LPG does not need this.

If you have a data logger with your O2 sensor that has the ability to track temperature, it would be useful to see if the rich mixture correlates with converter temperature.

the MTX-L has two analog inputs. I'd have to check how to use them with a temp-sensor...

Bear in mind that there are factors that affect sensor accuracy and the measured AFR may be richer or leaner than the actual AFR coming out of the engine. You might be trying to fix an AFR problem that doesn't actually exist in reality.
Tech Edge Wideband Oxygen Sensor Installation Guide

yes, that is why I have been trying to solve every vacuum leak or other possible source that influences the accuracy of the AFR readings. I might switch the temp-sensor to the other side of the car and see if I get the same readings on the other side.


I did notice today that cold engine start is still 20-21AFR (first start of the day) and then richens to about 15.5 sometimes even lower as AFR14.5.
Also noticed that from about 16.5 the engine runs smooth at idle. any higher will make it run rough...

[kikkegek]

cool!

seem to have found the cause of my extreme lean cold engine starts.

The idle mixture adjustment screws in my Quadrajet throttle base were 12 and 6 quarter turns out. I took them out. Took the springs of. cleaned them. put some locktite on them, turned them fully back in. started the cold engine and its below 10C 2nite over here and car has been sitting for over a day.

AFR of low 16s...I was pretty happy to see that...

some pictures (some found in another topic over here on a IMPCO425-2 mixer)

[kikkegek]

started car this morning...AFR was back to over 20...

think, think, think,......forgot I had pushed the primer once yesterday to check if the gasvalve moved....thus richer cold engine start

so, idle screws didnt change a thing...the search continues

[slow67]

To find those hard to find vacuum leak:

Park in a well lit garage, with zero wind.
Get some small hose, some tape, and a friend who smokes.
Snake the hose down below the throttle plate. Tape up the carb, so smoke doesn't escape the top.
Have your smoker friend blow smoke into the hose, and look for smoke.

I've found vacuum leaks this way that I would have never fount otherwise
(things such as barely cracked thermostatic switches on a motor with tons of emissions).

[Steptoe]

Small pen lpg torch unlit works very well.
And so does a mechanics stethoscope.

[kikkegek]

Small pen lpg torch unlit works very well.
And so does a mechanics stethoscope.

hi Steptoe, can you elaborate on that?

@slow67: thanks, might look into that later...

thing that catches me of my feet right now is that when the engine warms up, the mixture usually gets leaner:
- warmer lpg gas, is less dense, thus leaner mixture
- vacuum leaks would also result in leaner mixtures

the only thing I can think of that causes richer mixtures is warmer air supply. I get my air from behind the grill, so should always be same.
I dont know if the air might heat up so much under the hood, to cause mixtures to get so rich.
I do notice that at a traffic light the mixture will get about .3 - .5 richer...I guess I could squeze a temperature probe into my air filter house and check that against the AFR.

[Steptoe]

Small unlit lpg torch..the lpg gets sucked in the engine speeds up.
A refillable pen torch, doesnt spray heaps of lpg everywhere, easy to get close, turn on and off.
Mechanics stethoscope hears everything, including air being sucked in the thinest of gaps.

Variations in ambant air temps doesnt change mixtures all that much... if that was the case we would all be having major issues regardless of fuel type....sea level to up in snow lines yes denisty does have an effect under these extreme Altitudes...and the colder air has no opposing effect to prevent.
The temp of coolant thru the convertor be it 140 or 180 again doesnt have any significant effect as u have.

Are u 100% sure that your 02 sensor is working correctly... have u had it tested?...is the heater working correctly? is it before any cats.? mounted on the high side so doesnt get effected with water and contaminants?

[kikkegek]

okay, I got one of those pen torches:



might use that in my search and check the rpm's using the timinglight. Then I'll see the smallest change.

friend of mine has a mechanics stethoscope. I'll look into that, but dont know where to start looking.


as for the sensor: I calibrated it in fresh air before installing it into the car. I have disconnected the batteries a couple of times, but never disconnected the sensor from the unit, so should be still calibrated. If I turn on the igniton on the morning and dont start right away. the sensor will heat up and eventualy show 23.9 which is max value and should be proof for good funtionining.

placed it like this, not to close and not to far from the engine: