DUI advance adjustment ?

[lomusass]

Looking for some help with a DUI.
Rebuilt 2f 145lbs open throttle compression
Was running ok , had ping under load though,
Then all of a sudden when ever i touch the gas it would die, start straight back up again, but if i touch the gas it will just cut out, like turning ignition off., no sputtering, coughing just cut..
Any ideas would be really gratefully received.
Thanks.
Paul.

 

[JohnnyC]

Hay Paul...how are ya....

not good news you may want to check out this thread...he had the same issue...i think the ign mod or coil is bad...

you would need to test the coil and mod...i dont have those tests for ya however...here in the states ....you can bring it to an auto supply store and they can test for free here

https://forum.ih8mud.com/40-55-seri...-carb-dui-dizzy-need-some-insight-please.html

 

[lomusass]

Johnnie,
Im ok thanks, be better if i can find the bloody problem with this Dui..Going to ditch it and throw in a stock to see if we have some joy.
will be in touch.
I searched, and I just read the latest post on that link, I´ll follow it closely to see if we have the same problem.
Paul.

 

[JohnnyC]

i found this on another site about testing the HEI type ign mods and coil hope it helps:
Easy tests for HEI system:



1. Test for power at the pink BAT terminal. You should have battery voltage w/ the key in the start and RUN positions.



2. Connect the ground side of your test lamp to the battery POSITIVE cable. Probe the TACH terminal on the dist. cap while a helper attempts to start the engine. The test lamp should blink repeatedly as the engine cranks. No blink= bad module or pickup coil. Further testing is required to pinpoint the problem. Blink but no spark = bad ignition coil.



3. Remove the cap & rotor. Remove the green & white leads from the module. Connect your ohmmeter to the green & white leads. You should have approx. 800-1500 ohms depending on the ambient temperature. Open circuit (infinite ohms) = bad pickup coil.



Wiggle the green & white leads as you test. Ohm reading should remain constant if the leads are good. If the reading varies as the leads are wiggled, the pickup coil is bad. You'll often find broken pickup coil leads this way.



4. DVOM (meter) still connected to green & white leads. Set your DVOM to AC VOLTS. Have a helper crank the engine as you watch the AC VOLTS reading. A good pickup coil will produce about 3V AC when cranking. Less than approx. 2V AC indicates a bad pickup coil.

 

[numby]

The point of vacuum advance is not to have a bunch of advance at idle, then have it disapear @ WOT.

The point is to have no vacuum advance at idle, then bring in advance imediately on light throttle, then have it disappear at WOT.

I disagree. The point isn't about vacuum at all. The point is a stable, efficient, clean idle as well as consistent power delivery at light throttle. Ported vacuum advance doesn't do any of that as well as port vacuum.

I'm assuming that by I can interchange "port" vacuum with "manifold" vacuum?

I thought that there's no need for large amounts of advance at idle because of the separate idle fuel circuit incorporated in these carburetors. This seems to me to be the source of a good (clean, stable, efficient) idle. The idle is not fed via the normal primary/secondary/etc circuits that require the throttle plate to be opened excessively for unilateral idle setting. In the short time I've been reading here it seems a fairly common mistake when adjusting carbs. The complaint is always something like "my idle mixture screw has no effect" with the solution usually being to lower the idle speed enough to bring the idle mixture screw back into play. Idle timing (if from ported vacuum) usually requires correction as well as the throttle plate is adjusted back below the vacuum advance port.

With ported vacuum advance there is little advance at normal idle speeds where we're not looking for power but efficiency. That's why idle timing could be a little retarded by comparison to burn hotter thus reducing emissions. As soon as you want to accelerate you also need to bring in timing advance with ported vacuum to generate power until engine rpms develop mechanical advance. (I don't know whether stoichiometric ratios are applied to idle or not.) Both ported and manifold vacuum advance characteristics disappear as the throttle plates continue to open. True, it happens a little slower and later with ported vacuum. Hasn't manifold vacuum been traditionally used with a retard mechanism where the retarding disappears with an opening throttle and diminishes manifold vacuum thus advancing timing? I have a feeling I still don't understand this...

Stacking 22 degrees of vacuum advance on top of 5 degrees of base timing isn't going to make a good idle. The amount of vacuum advance must be limited. Engines with low compression ratios should require less vacuum advance than the higher C.R. spec'd V8's that most of these advance cans were made for in the first place. You will most likely have poor results by switching to port vacuum if you are not mindful of the amount of vacuum advance you are feeding the motor.

Pick any motor with computer controlled vacuum advance. Strobe it or use a datalogger to verify timing at idle. You won't find a motor with timing anywhere near 10 degrees, much less 5.

Maybe I'm reading you wrong but if 27° at idle is bad why would lowering it to 10° (much less 5°) be good? Plus these modern vehicles have computerized fuel delivery and timing curves that can not be achieved with our old Toyota technology. Not really apples to apples.

Vacuum advance allows the distributor to adjust the timing appropriately for varying engine loads. Vacuum is an excellent indicator of engine load. Less vacuum=more load=less timing.

Consequently more vacuum=less load=more timing? Isn't that what a ported vacuum advance mechanism allows for?