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different vacuum timing thread.

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T

Tinster

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Don't wish to steal someone else's similar thread.

Poolboy/Paul:

I downloaded the vacuum article thanks.

Data:
My valves are set at a not-tight .010", timing is 12* advance,
points at .015", carbs are close but not finally dialed in.
Warm idle was 1100 to 1200 rpm when I took the last vac. test.

I get a very constant, non-twitchy 21 in-Hg at this idle.
Punch the throttle shaft and I get a fast drop to zero
followed by and equally fast surge to 25 in-Hg and then back
to a constant, non-twitchy 21 in-Hg.

<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<,
Today: 1/2 Hr drive to warm engine. Car ran very well. While hot,
adjusted carbs to a nice 900 rpm. Timing was at 10* advance,
vacuum at 21 in-hg w/ steady needle. Vacuum maxed out at
22 in-Hg.

With dizzy and vac pipes plugged; I was able to get vacuum
down to 19 in-Hg before engine stalled. At 20 in-Hg the engine
was somewhat smooth running but my timing was deep into
negative-below zero on my gun and my idle rpm were bouncing
around 400 to 500. My timing wheel is not original. It has
one slot full across and one 1/2 slot across the width.

So, wuz up with my engine?

Thanks as always,

dale

PS: If I time by ear and then test- I end up with 10-12* advance, 1000 rpm idle and 21 in-Hg.
 
I don't know, Dale, and I apoligize but I just don't feel comfortable speculating.
 
poolboy said:
I don't know, Dale, and I apoligize but I just don't feel comfortable speculating.
Click to expand...


Jeff S. rebuilt the dizzy 10 months ago.
Jeff P. rebuilt the carbs 24 months ago.

Should I have them rebuilt again possibly to lower the
manifold vacuum?

How dangerous is it to drive a TR6 with 21 in-Hg?
It seems to run fine and my spark plugs are a light
toasty brown. No indications of detonation. No pings
or knocks. I run 93 octane with a bottle of octane booster
per fillup.

thanks,

dale(Tinster)
 
No offense, Dale, but I see where this is going. Before you know it you'll have half the engine apart again and I really don't want to be part of that. Sorry.
 
The range of vacuum that an engine potentially could pull is based on allot of different things beyond just the timing. The design of the cam shaft is equally important.
Set the timing at whatever Jeff told you when he rebuild the dizzy and take Wendy out to for a long ride to the bikers club.
 
If I'm reading your post correctly, you were trying to get the manifold vacuum as *low* possible at idle? Yea, you'll have the timing way retarded to get that. You went the wrong direction. You don't want minimal manifold vacuum, you want peak manifold vacuum. But do beware that's "optimal" for an unloaded idling engine. It doesn't mean it's optimal for driving that engine, or at other rpms or engine loads.

Comments were made about the surging at ridiculously low rpms, and erratic ignition timing under those conditions. Yep, that sure would happen. Trying to idle at 400-500 rpms has the engine just barely able to keep on ticking over. It's going to be rough and surgy because you're at nearly half the correct idle speed. Ignition timing will be very erratic as the camshaft (which drives the distributor) is popping back and forth against the timing chain slack because of the valve spring loads (camshafts don't rotate smoothly against the cam lobes).
 
Dale,

I was working late yesterday and missed the previous post on this. Sorry about that. If I were you, I would set the timing at the 10 or 12BTDC that you had it where it ran well and set the idle at a comfortable 850-900 RPMs and just drive it. These cars are all different and what is optimal as a vacuum setting for one may not be for another. Plug color sounds good, so adjust the timing and idle and head for the mountains.
 
:iagree:

Too much information is often worse than not enough!

(Think ingredients in some of those wonderful dishes you and Wendy introduced us to.) :wink:

Enjoy!

Mickey
 
Brosky said:
Dale,

I was working late yesterday and missed the previous post on this. Sorry about that. If I were you, I would set the timing at the 10 or 12BTDC that you had it where it ran well and set the idle at a comfortable 850-900 RPMs and just drive it. These cars are all different and what is optimal as a vacuum setting for one may not be for another. Plug color sounds good, so adjust the timing and idle and head for the mountains.
Click to expand...

<span style="color: #990000">Just a quirk I notice this afternoon. Took off
the air filters, cold engine, full choke, turn key, engine
starts instantly (10* advance). Vacuum gauge is reading
18 in-Hg.

Engine warms up, choke off, engine now pulling 21 in-Hg
Carbs exactly balance at 900 rpm. Plugs all toasty, light
brown.

I wonder why full choke draws less air?

Thanks all for the input.

dale(Tinster)</span>
 
I really couldn't answer that with being there and trying several different things and even then I probably wouldn't get the answer right.

But if I were in warm weather like you are and had the engine conditions that you just described, the air cleaners would be back on and Wendy would be in the car with me headed for the mountains.

With the video cam......
 
Thanks Paul/Mickey!
I've doing internet research on intake manifold vacuum reading.

Other than the 21 In-Hg, steady at 900 RPM, the car runs really
well at 10* advance.

I read two things that might contribute to the 21 In-Hg.
1. I have aftermarket exhaust headers (6 into 1 )
2. I live and drive at sea level.

Altitude?

If looking at the absolute readings, it’s important that you remember that the vacuum readings will decrease as your altitude increases. So if you live on top of a mountain, remember to drop 1 inch of vacuum for each 1000 feet you are above sea level.

So, if I drove my car up onto a 3,000 ft height mountain- I would test
at 18 In-Hg. I might try that sometime just for data input.

I think, I'll final adjust the valves today.

best regards,

dale
 
Vacuum is not absolute Dale.
Close but not Absolute.
Drive and enjoy
 
Well, I tried one more thing. The car still had DPO Pedro's
rubber vacuum hose from manifold to brake servo. It had a crink in it. ( a restriction? )

I had a custom made braided SS vacuum line made , with 90*
fittings and that lowered the vacuum by 1 In-Hg. The car
still idles at 900 RPM but now sucks 20 In-Hg instead of 21. Still at 10* dizzy advance. ( I can feel the car wants 12*,
the engine really smooths nice out at 12* )

thanks all,

dale
 
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