Low vacuum with no leaks, correct TDC, and ignition timing

[sundaydriver]

1983 VH 202 3.3L straight-6 with the Varajet II.

I am getting ~15 inches/mercury vacuum. Which puts it in the 'late ignition timing' zone on the vacuum gauge.

The effect of this a jerky acceleration at low speed @ initial take off. Occasionally a hesitation when taking off hard at very low speed or stationary start.
I image there are other peripheral side-effects (maybe loss of power, and fuel efficiency?) but the acceleration issue id my main concern.

1. I have correct ignition timing (~6-8 as suggested by workshop manuals) and that's based of correct TDC (timing mark on balancer is at 0 when cylinder #1 is at TDC, and the rotor and dizzy mark line up)
2. I have checked for vacuum leaks, and can't find any - done the spray test, smoker, and propane test. All reveal no leaks
3. The head gasket is fine
4. I have replaced valve stem seals
5. have cleaned all the lifters
6. Pressure tests (wet/dry) all tight and normal - ~150-155PSI
7. New ignition system (module, leads, rotor, dizzy cap, wiring, and plugs)
8. Carby has been rebuilt (all jets are clean/new, new needle/seat/float, gaskets) and idle mix and bypass are good. Idle stop has not been altered

Basically, I am getting 15 inch/mercury when everything is dialled in based on factory/workshop manuals.

I can only get the right vacuum (~18 steady) when I advance the timing to roughly 25-30 (guesstimating, because the timing marks on the block only go up to 12). Unfortunately, this puts the RPM up to 1300. I can bring it down to 1100, but that seats the idle bypass screw. Doing it the other way round (correct timing, but raising the idle RPM with the bypass screw) gives a similar, but no where near as smooth, result - i.e. very shaky, 1000 RPM, and a wobbly ~16-7 vacuum.
So it's either correct vacuum with stupid-high RPM, or correct timing with the acceleration issues, and a slightly shaky idle.

 

[Immortality]

I thought you had this problem sorted in your other thread?

 

[strgas]

might be a silly question but have you tried another vacum gauage to check how accrute your first gauage is ??
I havent used a vacum gauage in years to fine tune a car .
Varajet can be tricky to set up balancing between air bypass and idle speed settings to mixture screw settings changing one can and will affect another ....

 

[sundaydriver]

I thought you had this problem sorted in your other thread?

Sort of! That thread what for this specific problem, yes. Went down the rabbit hole and sis all that other guff (seals, ignition etc.) and found a faulty solenoid, which helped - but that was only a improvement, didn't fix it. Vacuum got a bit better, and the acceleration got a bit smoother, but it's still there.

 

[sundaydriver]

might be a silly question but have you tried another vacum gauage to check how accrute your first gauage is ??
I havent used a vacum gauage in years to fine tune a car .
Varajet can be tricky to set up balancing between air bypass and idle speed settings to mixture screw settings changing one can and will affect another ....

Yep - had the same thought. Got 3 gauges - 4 if you include the dash - all say the same.
Yeah, they're tricky, but apparently if you set the timing first, then the get the RPM in range, the mixture screw is last and can be fine-tuned with a vac gauge too. there's a couple vids on the web if you're interested.

 

[Immortality]

Have you tried temporarily bypassing all that hocus pocus anti-pollution crap to see how it runs?

I had a 3.3 VK and all that crap was disconnected and it ran sweet

 

[greenacc]

Were these issues there before you started working on the car?

 

[sundaydriver]

Have you tried temporarily bypassing all that hocus pocus anti-pollution crap to see how it runs?

I had a 3.3 VK and all that crap was disconnected and it ran sweet

Bypassed the EFE because that snapped off. And the faulty solenoid between the caby and vac-advance. The EFE is still there though - think that could be causing it?

 

[sundaydriver]

Were these issues there before you started working on the car?

Yep - that's what got me started.

 

[greenacc]

When you checked for vacuum leaks did you check the inlet manifold gasket ?