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> CHT seems high - oil normal?
rfinegan
post Aug 24 2023, 08:44 AM
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Plug your fuel pressure gage into the Cold start injector. It is not in use in the warm weather and no T fittings needed.
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FlacaProductions
post Aug 24 2023, 09:14 AM
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Yup. Did just that @rfinegan - right on 30psi.
A bit more than stock sooooo - leave it?
Bumping timing next.
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rfinegan
post Aug 24 2023, 09:31 AM
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Lots of people run at 30 psi...leave it there for now
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FlacaProductions
post Aug 24 2023, 01:03 PM
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Bumped the timing from 28 to 30 and it seems to like it.
Noticeably lower temps - feels snappier but I think there's more room for improvement. I'll bump to 31 or 32 and see what it says but I have to call it progress.
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914_teener
post Aug 24 2023, 01:48 PM
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QUOTE(brant @ Aug 23 2023, 06:02 PM) *

QUOTE(emerygt350 @ Aug 23 2023, 01:59 PM) *

Do you have an AFR? I would suspect lean mix at cruise is probably not helping. Does your 74 have a vacuum advance? Some do, some don't.



Bingo!
I’ll read the rest of the thread
But even a stock MPS is too lean with todays fuels.
Richen the fuel. Verify with AFR
And I bet your head temps drop



I agree with Brant as well. Do that stuff first.
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914_teener
post Aug 24 2023, 02:01 PM
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QUOTE(FlacaProductions @ Aug 24 2023, 12:03 PM) *

Bumped the timing from 28 to 30 and it seems to like it.
Noticeably lower temps - feels snappier but I think there's more room for improvement. I'll bump to 31 or 32 and see what it says but I have to call it progress.



Get that vacuum gauge and test the vacuum cans for leakage on your dizzy and report back.
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FlacaProductions
post Aug 24 2023, 02:01 PM
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@914_teener and @brant - I follow.
Going to be a longer-term (probably winter) project in order to have the window to get the AFR installed as well as a bung welded in.

And then "richen the fuel" - this means via MPS tuning with the AFR - correct? No other way to mess with mixture.

Vacuum gauge - on it next for both dizzy cans and MPS
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914_teener
post Aug 24 2023, 02:06 PM
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QUOTE(FlacaProductions @ Aug 24 2023, 01:01 PM) *

@914_teener and @brant - I follow.
Going to be a longer-term (probably winter) project in order to have the window to get the AFR installed as well as a bung welded in.

And then "richen the fuel" - this means via MPS tuning with the AFR - correct? No other way to mess with mixture.

Vacuum gauge - on it next for both dizzy cans and MPS



Test the vaccum cans first. I've got a gauge if you need to borrow it.

30 psi with djet should be plenty for that displacement. Think that cam has some overlap but no a lot.

Don't touch the MPS until you've done that. Do what Brant suggests first and if you need a vacuum gauge I've got one.
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FlacaProductions
post Aug 24 2023, 02:18 PM
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@914_teener - I appreciate the offer but I'm with the 914 in SE Indiana.
Getting the Mityvac later today.
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emerygt350
post Aug 24 2023, 04:02 PM
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Yeah, only touch the mps once you are sure about what is going on.
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FlacaProductions
post Aug 24 2023, 04:25 PM
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QUOTE(emerygt350 @ Aug 24 2023, 03:02 PM) *

Yeah, only touch the mps once you are sure about what is going on.


If that's the bar....it'll NEVER happen!
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emerygt350
post Aug 24 2023, 04:32 PM
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Yeah, true.
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FlacaProductions
post Aug 24 2023, 04:37 PM
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A couple of pics of my distributer advance can and associated hoses.

TOP of can - this one has always been open/without a hose:
Attached Image

Firewall side of can - this is the one I disconnect and plug when setting timing:
Attached Image

TB/Plenum - this red plug has always been present:
Attached Image
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emerygt350
post Aug 24 2023, 05:50 PM
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Where is that vacuum hose headed? Does it go to the tb or the plenum? I can see from the picture your car does not have advance, only retard on the timing.

Pretty sure the inside can is the retard. That hose coming off of it should go to the back side of the TB.
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emerygt350
post Aug 24 2023, 05:52 PM
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And just FYI, from the factory they would dangle a hose off the unused advance can. No idea why.
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emerygt350
post Aug 24 2023, 05:56 PM
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I believe on a 74 that little plugged nozel would head to the decel valve. They really switched those things up between 73 and 74. Same with the PCV.Attached Image
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emerygt350
post Aug 24 2023, 06:04 PM
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Here is the 73 version. The place where your plugged nozel is located is a large diameter version heading to a t which goes to the pcv valve and a small hose that heads to the decel.

On the TB you can see the plugged advance on the right (123 dizzy and I don't use it) and the plugged retard port on the left (same there, I don't use it).
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914_teener
post Aug 24 2023, 06:08 PM
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Ok...couple of things I see:

1. Looks like you have a dual diaphragm on your dizzy.

2. The advance hose is plugged to somewhere....probably and hopefully ported vacuum on the throttle body. Ported vacuum is on the atmosphere side and not the plenum side of the TB. Check Jeff's diagram on his website.

3. In one of the pictures...it shows a plug on the plenum which probably at one time went to the other side of the can...hopefully the retard side. If not needed...don't plug the nipple on the can, so in this case leave it.

The dual "nippled" or dual diaphragm can...if it doesn't leak always has to have vacuum for the dizzy to provide the correct amount of timing advance. Technically you don't need it (advance/retard)....being that when at low rpm...where manifold vacuum is high...provides a little less time for combustion sake...so hence the rumor it is not needed since we live in a different time( pun intended). HOWEVER this will change the dynamic curve somewhat and that MIGHT be your problem since that is how it's engineered since it is a dual acting vacuum cell..but check the vacuum cell first..if one side leaks..the whole cell is bad.


If it leaks...on static timing to spec....it will idle too high and most people just adjust the air bleed or idle mixture to take care of it. Ask me now I know...wait...don't ask me I'm telling you it will. So while you think statically it's timed right at idle and idles perf at 800 rpm...that won't be the case through the RPM and different loads conditions...like cruising. So check that first.
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FlacaProductions
post Aug 24 2023, 08:17 PM
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Next up:
-picture/confirmation as to where the advance hose is routed on the other end.
-checking vacuum on MPS.
-checking the vacuum cans on the dizzy - how?
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emerygt350
post Aug 25 2023, 05:01 AM
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Just pop the vacuum pump on there and see if they hold 15 or so. It does appear your decel valve is gone, not a big deal, just hard on the mps. If it is there it may not be hooked up correctly.

I suggest pulling the distributor cap and watching the rotor move while you do it. Watch to see how easily it returns after you release the vacuum. The mechanism often gets gummy and starts to stick over the years. Retard would send the heat to the oil rather than the head though.

A issue that can happen with gummy weights is you pull the retard vacuum line (and plug it of course), and the rotor does not return, you set your timing and you have now set it more advanced than you thought when the weights finally spring back.
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