View Full Version : TR5/TR250 TR250 Vacuum Lines

05-01-2012, 07:34 PM
Finally trying to sort out carb tuning (future posting) and I have encountered some questions on the vacume retard lines.

I have the original (or year appropriate) 22D distributor having both advance and retard vacuum units. AND I have the "vacuum assist control valve" attached to the linkage bracket under the carbs. I've replaced all the lines, elbows and other rubber fittings and am now confused with which line goes where.

Page 46 or TRF's TR250 specific parts book (the red one) shows the line from the advance routing to the bottom of the control valve with the retard line connected to the top of the front carb.

For kicks, Page 45 of the TR6 blue book shows the exact opposite routing. It has the retard heading to the control valve on the bottom of the fromt carb with the advance connecting to the top of the front carb.

What gives? I thought the 69 TR6 and the TR250 were identical when it came to carbs, dizzys and such.

Bentley and Haynes manuals offer zippy help on this.

I'm sure someone is going to tell me how to work around that vacuum valve but for originality sake, I'd love to know how it was supposed to be connected as well.

05-01-2012, 07:40 PM

Does Moss help at all or confuse the matter more....


M. Pied Lourd

05-01-2012, 07:47 PM
Hmmmm... that's the same set-up as shows in TRF's blue book. Looks like this might be a poll question! 2-1 so far.


05-01-2012, 08:27 PM
I believe the "blue book" is correct. The control valve was a temporary fix because the rear carb was not drilled and tapped for the timed vacuum retard port. The valve simulates the same thing, by only opening when the throttle is closed (which is the only time the retard should do anything).

The "work around" is to simply cap off the vacuum line and ignore the retard. Set the timing to the "static" value (10 or 12 BTDC, I forget which offhand) and readjust the idle screws to bring the idle down.

05-01-2012, 09:31 PM
Maybe I should back up a bit. Standing on the driver's side of the engine looking down at the dizzy, the advance unit is on the left and retard is on the right side (of the distributor). Correct?

Assuming I've got this right, here is how routing the vacuum lines affect the way the engine runs at idle.

Advance unit connected to vacuum assist valve under front carb:
Timing is noticibly advanced at idle, RPM's increase. Under acceleration, I can see the advance unit physically move outward from the dizzy.

Retard unit connected to top of front carb (with advance connected as above):
Seemingly no affect at idle.

If reversed:

Advance unit to top of front carb:
Seemingly no affect at idle.

Retard unit connected to vacuum assist valve under front carb (with advance connect as above):
Timing is noticibly retarded, RPM's drop to near stall.

Anything sound about right?

05-01-2012, 10:22 PM
The last one is right. Set the timing to 4 ATDC with the retard line connected, advance line disconnected and plugged. Then reconnect the advance line (which won't make any difference at idle, the advance only operates at part throttle) and adjust the idle rpm per the book (or emissions tag if you still have it). (800 - 850 IIRC)

05-02-2012, 11:53 AM
I agree with Randall. That's the way I have my 250 set up. One issue is the poor quality of those vacuum valves. IIRC, BL sourced them from the USA, maybe Ford, since theses were used for domestic applications. The one I have on now is the third one since 1985 and I currently have no spares. I wish some one could locate an all metal replacement. That location is very hot close to the exhaust manifold and fuel/exhaust fume filled environment, so the plastic valves take a real beating and don't last very long

05-03-2012, 08:47 PM
Thanks all. Vacuum lines re-routed and "dynamic" timing set to 4 ATDC as above. Idle at ~800-900.

You're right Frank. I just realized the vacuum valve is indeed plastic and not too far away from the manifold. I'm wondering if I shoudln't consider removing it for daily driving and save it for originality/show purposes... like I'm ever going to get this car to a concours level!

What about the plastic vacuum line from the retard down to the vacuum valve? How did you route it to stay away from contacting all those heat sources? Advance line was easy to clip it to the fuel rail right there next to the dizzy, around front, then you're there.