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vacuum unit which one?

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skagroovy

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need to replace the vacuum unit on my distributor... it is the stock distributor from a 71' tr6 is this a retard only unit or do i need a advance unit... i am a little confused why there are so many choices i thought you just wanted to advance not retard can some one clarify.... thanks
 
The original setup for 71 would be a combination vacuum module, for both advance and retard.

The two functions come into play at different times, for different reasons. The advance only functions at part throttle, to help make the engine more efficient. So it gives somewhat better gas mileage (1 or 2 mpg), and slightly better mid-range throttle response.

The retard is an emissions thing; it only functions at idle and, at least in theory, reduces unburned hydrocarbons at idle. But it also raises fuel consumption and CO2 output, as well as making the engine more prone to overheat.

Note that the 4 ATDC timing figure is with the retard connected and functioning. If it is disconnected or non-functional, the timing should be more like 10-12 BTDC. However you may have some trouble getting the idle rpm down without it. On my Stag (which has a similar setup), I had to adjust the float bowl vent valves as well as the idle screw.
 
So my distributor only has one unit on it and it is on the firewall side, which one is this retard or advance ? Also is the a way to test them to see if the vacuum unit is working...
Mid throttle to full throttle is seems to really fall off.... My main issue is I can't get the thing to pass emissions... High hydrocarbons at 2500 rpm....
 
Pretty sure that would be retard...you should be able to test it just by taking off the distributor cap and sucking on the hose going into the vacuum unit. If it's working, you'll see stuff move.

Edit: Moss video on testing vacuum unit. They use a vacuum pump, but that isn't necessary.

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I am assuming that if my unit has a retard only that there is a mechanical advance underneath the points, if that's the case are you able to adjust the advance curve
 
skagroovy said:
I am assuming that if my unit has a retard only that there is a mechanical advance underneath the points, if that's the case are you able to adjust the advance curve
Click to expand...
They all have mechanical advance, regardless of which vacuum module is installed. But the mechanical advance responds only to engine rpm, it doesn't know if the engine is working hard (full throttle) or cruising. So the mechanical advance curve has to cover the "worst case" for full throttle, which is less advance than optimum for cruise conditions.

BTW, HF sells a nice little hand vacuum pump, which is very handy for testing vacuum operated things on a car. I haven't really used mine enough to say for sure, but it seems to be much sturdier than the MityVac I've been using.
https://www.harborfreight.com/brake-bleeder-and-vacuum-pump-kit-92474.html

PS, in case anyone is wondering, the vacuum advance was eliminated in order to reduce NOx emissions. Again, it accomplishes that goal, but increases CO2 emission and fuel consumption.
 
thanks for all the great input ,I assume that before top dead center is on the driver side of the pointer, so now I'm just debating whether not this is ignition problem or a jetting problem still , at 2000 rpm the power seems to just fall off
 
I'll let someone that is more familiar with the TR6 field that answer; but it doesn't sound right to me.
 
DamperMarks.jpg

The damper rotates clockwise viewed from the front.
BTDC has the most marks.
 
skagroovy said:
thanks for all the great input ,I assume that before top dead center is on the driver side of the pointer, so now I'm just debating whether not this is ignition problem or a jetting problem still , at 2000 rpm the power seems to just fall off
Click to expand...
I can't say, but if your engine has high miles the damper marks are not reflecting the true timing. The actual timing will be more retarded than than the marks indicate.
 
if the retard unit is work how many degrees should it retard, 5 to 10 degree's?
so if it is working 4 ATDC and not 10-12 BTDC correct...
thanks
 
There's not enough Vacuum when the engine is running at 2000rpms to activate the Vacuum retard..so it's not an issue as far as what you are experiencing. I don't use the timing marks as a reference when setting the timing for the reason stated
I use a Vacuum Gauge:
https://automotivemileposts.com/garage/v2n8.html
 
Ok so I had the air fuel tested and I am right on with herring but the timing and ignition continue to create problems... It idols perfect at 900 rpm but has hesitation until 2000 then is ok and but is ruff all the way to 4000 under heavy acceleration ... Do I need to do a ignition over haul, coil, petronix, new plugs???? FYI hydro carbons were low but the co2 has still too high...
 
CO2 or CO? High CO is usually mixture; low HC would indicate the ignition system was doing its job. CO2 isn't usually tested, since it is pretty much a fixed quantity for the amount of fuel burned.
 
Ok looks like my dampner has moved but timing it via vacuum proved successful however I have a new problem I think I have too much carb... I have 2 42mm hsr mikuni's that I had to jet down to a 120 main jet, (stock is 160 keep in mind I am at 4500 feet in Utah)to get it to run ok however at 3/4 + throttle it just shuts down do i have too much carb
They run 213 cfm each vs the 155 of the strombergs...
Thanks
 
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