god damn shunt is killing me
Discussion
Slight thread revival (5 years? Seen worse 
)
I’m seriously considering this adjustment to the vacuum source. One question though @Belle427 - what is the inner diameter of the hose you used to the vac advance module?
I’m going to look to take off the spare outlet that’s tucked slightly behind the PAS reservoir, and will take the current bung bolt to a brilliant hose specialist in High Wycombe to hopefully get a threaded hose tail that fits in one go.
Obviously the current pipe from the ported vac is tiny, but in you photo it looks like it could be 6mm or even 8mm.
I’m also changing sparks to BPR6ES and potentially new leads, so will be measuring the advance that comes with that set up in case it alters from the current B7ECS.
Hoping for better low range pick up, my 400 definitely picks up with more gusto from 3500 to 5500rpm…
)I’m seriously considering this adjustment to the vacuum source. One question though @Belle427 - what is the inner diameter of the hose you used to the vac advance module?
I’m going to look to take off the spare outlet that’s tucked slightly behind the PAS reservoir, and will take the current bung bolt to a brilliant hose specialist in High Wycombe to hopefully get a threaded hose tail that fits in one go.
Obviously the current pipe from the ported vac is tiny, but in you photo it looks like it could be 6mm or even 8mm.
I’m also changing sparks to BPR6ES and potentially new leads, so will be measuring the advance that comes with that set up in case it alters from the current B7ECS.
Hoping for better low range pick up, my 400 definitely picks up with more gusto from 3500 to 5500rpm…
Belle427 said:
It’s best left to someone handy with the spanner’s as you need to mess around with hose sizes etc and find a source of full manifold vacuum.
This is the hose you will relocate
You blank it and relocate to full manifold vacuum.
My source of full manifold vacuum but I have removed the charcoal canister system which used this port.
Not difficult but you would probably need to tee into the charcoal canister hose if you still have it fitted.
Hose to distributor
This is the hose you will relocate
You blank it and relocate to full manifold vacuum.
My source of full manifold vacuum but I have removed the charcoal canister system which used this port.
Not difficult but you would probably need to tee into the charcoal canister hose if you still have it fitted.
Hose to distributor
I've recently made the change to manifold vacuum and generally speaking I'm loving the results. I do have a couple of questions/comments though..
Is taking a vacuum feed from the fuel regulator ok or is better to take it directly from the plenum or charcoal canister vacuum pipe?
At times the car will hold the revs up slightly when coming to a stop and conversly will sometimes die. Any suggestions how to prevent this?
I haven't measured fuel consumption yet but it does feel like it's running quite rich, something my local garage commented on.
Thanks in advance.
Is taking a vacuum feed from the fuel regulator ok or is better to take it directly from the plenum or charcoal canister vacuum pipe?
At times the car will hold the revs up slightly when coming to a stop and conversly will sometimes die. Any suggestions how to prevent this?
I haven't measured fuel consumption yet but it does feel like it's running quite rich, something my local garage commented on.
Thanks in advance.
I dont think it matters where the vacuum source comes from so you could T into the regulator line but i chose not to do it just in case of issues with the dizzy vac canister.
I dont suppose it matters really.
For the idle issues id clean the stepper motor first but did this problem occur after the full vacuum switch because if it did id reverse it and see what happens.
I dont suppose it matters really.
For the idle issues id clean the stepper motor first but did this problem occur after the full vacuum switch because if it did id reverse it and see what happens.
Belle427 said:
I dont think it matters where the vacuum source comes from so you could T into the regulator line but i chose not to do it just in case of issues with the dizzy vac canister.
I dont suppose it matters really.
For the idle issues id clean the stepper motor first but did this problem occur after the full vacuum switch because if it did id reverse it and see what happens.
Thanks for the response. Had already given the stepper motor a clean but decided to do it again. Took the car for a run today and seemed better. I'll see how it goes. I dont suppose it matters really.
For the idle issues id clean the stepper motor first but did this problem occur after the full vacuum switch because if it did id reverse it and see what happens.
Good point regarding the distributor vac canister. I might change the vacuum pickup. I might T into the charcoal canister instead.
That’s exactly what I’m exploring doing.
I’m hoping to get a replacement plug from an old school fastener shop in Slough, so I can preserve the original if it turns out to be a mistake.
I’m also quite close to a brilliant shop for hoses and fittings in High Wycombe, so I’m hoping I don’t need to modify anything just buy adaptor parts.
I found a tap and die kit in my dad’s garage, so I’ve got that option as back up.
I’ll report back.
Don’t forget to check your timing figures.
Mine doesn’t shunt, I’m keen to see if it pulls a bit better through the low revs, though it’s now exactly slow as is. Interestingly, I’ve got a note in it’s documented history that the fuel mapping was looked at, but I have no idea what was done.
Rover gauge needed too!
I’m hoping to get a replacement plug from an old school fastener shop in Slough, so I can preserve the original if it turns out to be a mistake.
I’m also quite close to a brilliant shop for hoses and fittings in High Wycombe, so I’m hoping I don’t need to modify anything just buy adaptor parts.
I found a tap and die kit in my dad’s garage, so I’ve got that option as back up.
I’ll report back.
Don’t forget to check your timing figures.
Mine doesn’t shunt, I’m keen to see if it pulls a bit better through the low revs, though it’s now exactly slow as is. Interestingly, I’ve got a note in it’s documented history that the fuel mapping was looked at, but I have no idea what was done.
Rover gauge needed too!
I finally got round to swapping the vacuum signal to full manifold.
I bought a few bits, and settled on a few parts - an adaptor from the original plug thread to accommodate a 4mm barbed hose tail, then a 4mm ID vacuum hose with some hose clips for security.
So the bits look like this
Then the overall fitting looks like this
And I put a stopper on the ported vacuum barb
If anyone wants the details of the bits I used, please just ask.
So, to the results.
My timing light is a piece of 1970s nonsense, so I can't report accurately except to say that it has added approximately 8-10 degrees, because the blur has moved to be more advanced, on top of an approximate 8-10 degrees advance. New light and accurate information pending.
I can say that the engine sounds great, no obvious unhappy noises.
It also pulls in a notably more lively fashion through the low revs, and feels great.
I should point out that I have fully serviced the car, and have replaced the dizzy cap and rotor arm, upgraded the leads, removed the reputedly notorious extenders, and changed the spark plugs from B7ECS to BP6ES under the theory that they will burn slightly hotter and more readily (since 7-rated plugs are aimed at hot engine racing conditions in our RV8s).
I will add that my car didn't really shunt, having gone through an engine rebuild, including new cam and timing gear, amidst a full-on mechanical body-off rebuild, but it definitely feels smoother through those troublesome 1500-1800ish revs trundling through traffic, and picks up without hesitation from there.
The unexpected bit is that it didn't raise the idle.
I ran it with RoverGauge before swapping the vacuum signal, and it faffed around until it was warm, as per normal, then settled around its target 950rpm.
After making the vacuum signal change, it still targets and achieves 950ish once it's warmed.
It leaves me wondering if the loosely documented (no detail) tuning from a fair few years ago has made a lasting difference, or whether vacuum advance module is doing knack-all. But as mentioned, there is a definite shift to more advanced shown by the crappy timing light.
I love the concept behind this tweak, it's cheap and easy to do, and easy to adjust to accomodate.
I'll report again once I've got the timing measurements in.
Semi-useful update I suppose...
I bought a few bits, and settled on a few parts - an adaptor from the original plug thread to accommodate a 4mm barbed hose tail, then a 4mm ID vacuum hose with some hose clips for security.
So the bits look like this
Then the overall fitting looks like this
And I put a stopper on the ported vacuum barb
If anyone wants the details of the bits I used, please just ask.
So, to the results.
My timing light is a piece of 1970s nonsense, so I can't report accurately except to say that it has added approximately 8-10 degrees, because the blur has moved to be more advanced, on top of an approximate 8-10 degrees advance. New light and accurate information pending.
I can say that the engine sounds great, no obvious unhappy noises.
It also pulls in a notably more lively fashion through the low revs, and feels great.
I should point out that I have fully serviced the car, and have replaced the dizzy cap and rotor arm, upgraded the leads, removed the reputedly notorious extenders, and changed the spark plugs from B7ECS to BP6ES under the theory that they will burn slightly hotter and more readily (since 7-rated plugs are aimed at hot engine racing conditions in our RV8s).
I will add that my car didn't really shunt, having gone through an engine rebuild, including new cam and timing gear, amidst a full-on mechanical body-off rebuild, but it definitely feels smoother through those troublesome 1500-1800ish revs trundling through traffic, and picks up without hesitation from there.
The unexpected bit is that it didn't raise the idle.
I ran it with RoverGauge before swapping the vacuum signal, and it faffed around until it was warm, as per normal, then settled around its target 950rpm.
After making the vacuum signal change, it still targets and achieves 950ish once it's warmed.
It leaves me wondering if the loosely documented (no detail) tuning from a fair few years ago has made a lasting difference, or whether vacuum advance module is doing knack-all. But as mentioned, there is a definite shift to more advanced shown by the crappy timing light.
I love the concept behind this tweak, it's cheap and easy to do, and easy to adjust to accomodate.
I'll report again once I've got the timing measurements in.
Semi-useful update I suppose...
On my side, I've installed the part recommended by ChimpOnGas, a vacuum delay valve. And this is also doing the job quite well.
I was using the clutch a lot when slowing down, like on speed bumps or some slow intersections. And now, the car is able to manage sub 1500 rpm and I can release the accelerator and press it again without shunt at low revs.
I've very happy with this very cheap solution even if this is more a workaround than a real fix.
I was using the clutch a lot when slowing down, like on speed bumps or some slow intersections. And now, the car is able to manage sub 1500 rpm and I can release the accelerator and press it again without shunt at low revs.
I've very happy with this very cheap solution even if this is more a workaround than a real fix.
Interesting, as I tried to achieve that with a one way on the breather hose arrangement, but it was awful, and caused a howl sound. Took me a day to reverse it.
The vacuum signal change cost me under £15, notwithstanding the price of a timing light, and gave the engine a much smoother input to the advance, and smoothness, and livelier pull through that exact rev range.
Felt like a more affirmative adjustment than the valve thing on he breather system.
The vacuum signal change cost me under £15, notwithstanding the price of a timing light, and gave the engine a much smoother input to the advance, and smoothness, and livelier pull through that exact rev range.
Felt like a more affirmative adjustment than the valve thing on he breather system.
PabloGee said:
Interesting, as I tried to achieve that with a one way on the breather hose arrangement, but it was awful, and caused a howl sound. Took me a day to reverse it.
The vacuum signal change cost me under £15, notwithstanding the price of a timing light, and gave the engine a much smoother input to the advance, and smoothness, and livelier pull through that exact rev range.
Felt like a more affirmative adjustment than the valve thing on he breather system.
The delay valve in question goes in the vacuum advance line to the distributor.The vacuum signal change cost me under £15, notwithstanding the price of a timing light, and gave the engine a much smoother input to the advance, and smoothness, and livelier pull through that exact rev range.
Felt like a more affirmative adjustment than the valve thing on he breather system.
Just drill a hole in the plenum side and glue a bit of brake pipe into it with JB weld. This way you can swap between the two take offs easily come MOT time and a bit of heat shrink to block off the one you are not using. It will fail emissions test if you don't go back to factory but you don't need to touch the timing between the two set ups.
andrewbr said:
PaboGee, where did you source those parts from for the vacuum takeoff? What size are the fittings?
Thanks
I got the fitting parts from Spectrum Hose in High Wycombe. Thanks
I don’t have invoice with me, but I can take a photo when I get home in a couple of days.
The hose was eBay (around £4).
I see what Blitz is saying, I just wanted to preserve the original plug bolt rather than drill it.
I need to check the timing (which I will do next time I take it out), as a helpful chap checked my Rovergauge log to find the stepper went to zero to compensate what is potentially a little too much advance.
I’ll report back
Edited by PabloGee on Tuesday 10th October 01:00
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