Vacuum unit on dizzy.

classicalgreen

classicalgreen

Active Member
Found out mine was not working as perforated. Suck test or blow just has air passing and no movement.
Bought a replacement from distributor doctor. Can't seem to notice and advance occurring? Checked vacuum at idle from vacuum tube and it sucks on finger though not a great deal. Checked tube into inlet seems perfectly clear.
Tried to operate it by sucking on tube to vac unit but no movement.
Is this right?
If I can't get it fixed? Is there an all electronic unit that can be fitted thus replacing vacuum unit altogether ?
 
checked that. was OK. also checked movement with unit off distributor. still no movement when trying to apply a vacuum by sucking. have e mailed supplier ..waiting response.
 
vac unit returned. note saying perfect. apparently gives 6 degrees advance.. impossible to check by sucking. managed to check engine vacuum on inlet at idle. approx 21mm hg.
strobe check..no noticeable effect when vacuum unit connected .disconnected on timing advance.. still disappointing acceleration for such a big engine. my wives fiesta can out run it from lights! will check it again in couple of weeks time when removed off dizzy but with vacuum from engine applied. quick rev ought to see movement ?
 
classicalgreen wrote,...
quick rev ought to see movement ?
Click to expand...

No, you won't see any as it runs ported and not manifold vacuum. There is a major difference between the two, with the Lucas distributor as fitted to the Rover V8 engine designed to accept the former.

The only time the module will deliver advance is when driving at a constant speed with minimal use of the throttle. The take off point for the vacuum is before the butterfly, so the more it is opened, the less advance the module will deliver.

Vacuum advance has no bearing on acceleration, so if your engine is not running as you would like, then the problem can be found elsewhere.

Ron.
 
not fully up to speed on rover as not had it 2years yet and most of time its been off road or laid up due to tax .
checked vacuum line to dizzy. it runs from nipple on nearside carb just behind throttle plate so responds to vacuum as plate is opened. having checked line is clear and using a sun vacuum unit i get 20" hg when revving . it dips as expected as plate opens fully. at idle is not registering anything as I would expect.
tried the replacement vac unit but cannot see any discernible movement when revved. swapped for another vac unit from a different car ( unknown model/make) it stays static at idle but opens easily ( moves ) when revs applied. ( which was what I thought ought to occur to new vac unit ) as angle or plate movement is lot more than I would expect ..have limited it by mechanical block to small amount. currently now using wrong vacuum unit as test basis to see performance etc over next few trips... will start saving to buy a vacuum unit that i can apply a set vacuum to anything so can test any vac unit in future for movement.
car still can't out perform my wives fiesta but suppose after 40 years a 3500cc engine can't match power output of a 1600cc. plus rover is a tad heavy car though a p5 i note driving locally as plenty of oomph. if i get chance to speak to driver will try and see if its actually got a standard 3500 unit .
my understanding of a 'ported' vacuum would be a vacuum switched in/out by a device such as valve/actuator.
 
classicalgreen said:
car still can't out perform my wives fiesta but suppose after 40 years a 3500cc engine can't match power output of a 1600cc.
Click to expand...

Yes this was always my complaint, though I likened the scenario to that of being easily last with any drag from the lights with a mini 850 ( I tried and confirmed many times :( ).
My solution was the Weber 500, now my 3500 is far more powerful and later moderns cant compete with me.


classicalgreen said:
plus rover is a tad heavy car
.
Click to expand...

Very simply put, NO.

1300 KG is a light to mid weight family saloon size now more so than ever with many comparable moderns creeping up in the weight scales to the 1700 or 1800 kg class.

It is likely that there is some thing going on with your cars tuning as a P5 definitely weighs more than a P6, maybe worn cam lobes? just a thought.
Many here will tell you that the SU's are great once fully and properly tuned, I never found this to be the case and now having experienced the Weber 500 would never entertain the thought of reverting to the SU setup.


Graeme
 
Yes this was always my complaint, though I likened the scenario to that of being easily last with any drag from the lights with a mini 850 ( I tried and confirmed many times ).
My solution was the Weber 500, now my 3500 is far more powerful and later moderns cant compete with me.


classicalgreen wrote:
Tried full throttle stuff on quite straight bit of road. Look like it's getting performance of a 1300cc unit as when I get in my wife's fiesta afterwards to go to tesco,,it felt like a racing car by comparison.
Sadly funds don't allow a carb and manifold change as spent entire savings buying the damn thing ( silly me)
Just tried colour tune on both sides . Nice Bunsen blue frame .. Still crap power. Going to recheck base timing next week see if it's far out? He said hopefully.
Otherwise have to consider it a car just for slow cruising around in. Eg 40 mph can be traced in around 15 seconds.. Don't ask how quickly fiesta gets there but if I recall correctly it's 0-60 in 10 seconds. Gives an idea how embarrassing driving it can be. Must buy a lottery ticket next week... See if I can win enough to get decent carb fitted but nice to know no only one finding it too slow for it's size. Oh will carry out compression test in next few weeks too. As under 34,000 from new .. Ought to be ok but it's ossicle valve s and seat have corroded in storage giving too low a compression value and hence power loss.
 
With under 34,000 Miles from new, your engine should push your Rover like a train. There is nothing wrong with the Rover manifold and SU carburettors in terms of acceleration, provided everything is set and working as it should be. If your engine's breathing system is not functioning efficiently, that will impact negatively on performance, as will retarded ignition timing.

When did you last replace the air filters?

Ron.
 
SydneyRoverP6B said:
With under 34,000 Miles from new, your engine should push your Rover like a train. There is nothing wrong with the Rover manifold and SU carburettors in terms of acceleration, provided everything is set and working as it should be. If your engine's breathing system is not functioning efficiently, that will impact negatively on performance, as will retarded ignition timing.

When did you last replace the air filters?

Ron.
Click to expand...
new filters fitted few months ago. just before overhauling carbs. colour tuned etc. still pulls slower than a milk float but not carried out compression checks yet.
air inlet etc checked for leaks. new vacuum pipe fitted etc. also suffers well known? lack of power after stopping with shot engine. suspect fuel evaporation due to engine heat. electric pump didn't work so refitted a serviced mechanical. will fit heat shielding later under carbs see if any changes.
 
Hi, try taking off the rocker covers off, turning over by hand and checking valve lift. Just
because it's 34k doesn't mean the cam can't be worn, maybe lots of short journeys.

Colin
 
vacuum unit checked for air leaks=none. for operation ..unable to move as engine only gets up to 21"hg . so dizzy relies on mechanical advance it seems. so swapped for different unit from another vehicle ( non rover) this advances easily when revving. so vacuum unit I am assuming is rubbish! ( waste of lots of cash there then) .carried out a cold dry compression test. one cylinder was partly low at 140psi. rest averaged around 160psi . will do a wet test later in week . currently waiting new servo so no road testing etc.
will check out base timing for number one max tdc of piston versus crank timing mark. will assume this is likely correct but worth checking .think I can get it using a probe in cylinder as piston rises on compression stroke to get within plus or minus a degree or so. will then set timing advance based on that.
so hopefully will start to get a car that can out accelerate an old mini or morris minor.
still not sure about it cutting out after a 'hot' engine stop but suspect its fuel vaporisation so will be looking later in year to fit some sort of heat sheilding to carbs.
 
1 from what your saying---I bet cam lobes on pistons 7 and 8 are ground down to 0 lift ==rings and valves fubar possibly
2-Vacuum unit wont work if cams not right due to less hg
3 su carbs were fitted to v8 due to Rochester wouldn't sell rights to 4 barrel and Rover had legal commitment to SU and that is fact ==spoken to people who were there-1 was a test driver of a C reg with a v8 put in it and he said it kept flooding up--nobody knew how to set up a rochester carb
4 rover p6 is not heavy--mine is --due to iron block but a 3500 probably same as 2000 or near 1300kg
 
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