Lack of Free Reving beyond 2500RPM 1972 V8 3500S Manual.

[harveyp6]

Re: Lack of Free Reving beyond 3500RPM 1972 V8 3500S Manual. Nee

I think you need to start from the basics in a logical way.

Very sensible advice there.

 

[Lovel]

Re: Lack of Free Reving beyond 3500RPM 1972 V8 3500S Manual. Nee

I have been following this saga without putting my oar in as I thought you were getting somewhere with the problem. However having got to this stage, putting myself in your shoes I would be tearing my hair out (not that there is much left anyway !)

Seems there is a lot that is not quite as it should be from the throttle butterflies not opening properly to the EFI cam. I have rebuilt my 10.5 CR engine twice in the last 40 years with my car, prior to the last rebuild in 2008 I did contemplate fitting a hotter cam (fast road spec) but was advised against it by a friend of a friend who prepared Buick V8 engines for racing – I quote from his e.mail “ unless you are going to go the whole hog and race spec the engine and obviously upgrade everything else, brakes etc, stay with the standard “S” cam which – if in good unworn condition, will give you all the breathing you want for spirited road use” . This advice was 4 years ago and better information may be forthcoming now, but my engine has always reved to the red line (down the Silverstone straight when I got a bit carried away on the Classic in 2010)

I would not have changed so many things at the same time as you have done, doing so fogs the positive and an advantage, and whats a negative, sorry not to be more constructive but I think you need to start from the basics in a logical way.

Yes I agree too, back to basics it should be, but you know how it is, I had the engine out on the bench and plenty time to rebuild it so you start to think how to improve things. Yep I'm nearly at the point where I am contemplating taking the EFI cam out and replacing with original.

I have just rebuilt the fuel pump, but no change there unfortunately and if I get my Wins delivery of carb goodies tomorrow and get the carbs fully rebuilt, I'll be one step closer to finding the culprit. Actually the carb components look to be in good shape tbh, but at least I can eliminate them if this is the case.

After the carbs I am going to recheck my valve timing (I have good vacuum pressures already but hey ho....)and check tappet preload, failing that an original new cam profile is going back in, possibly with original tin head gaskets in place of the composite gasket.

 

[chrisyork]

Re: Lack of Free Reving beyond 3500RPM 1972 V8 3500S Manual. Nee

With respect, that isn't an awfully logical approach.

By all means check you have the cam timing right. But no point swapping cams everywhere - cams and tappets live together, and swapping things around will lead to premature and imminent cam failure.

But then it's back to basics.

I suggest you tackle and eliminate the ignition sytem first.

1 Change the plugs for the correct for your engine new ones (do you have P6 or SD1 heads? they use different plugs)

2 if you are on points, change the condensor for a known good old Lucas one

3 Change the coil for a new one. If you are using the standard wiring, that will need to be a ballasted type. If you are using a feed direct from 12v then a standard coil.

4 Set the timing static at, say, 4 degrees beefore. Don't get the strobe out!

5 Check that the centrifugal advance retard is working. Do this by checking that you can twist the rotor arm and that it springs back afterwards.

6 Check the vacuum advance retard. Do this by sucking on the pipe from the inlet manifold to the distributor. The plate on which the points are mounted should rotate and spring back.

7 Check for vacuum leaks. If in any doubt whatsoever, renew the pipe between inlet manifold and distributor and also the pipe between inlet manifold and servo.

8 renew the rotor arm, distributor cap and plug leads. The latter with Magnecors - they're the only leads proven to allow clean revving on the V8 without cross firing. If we knew of anything cheaper that worked we'd all be using them!

Then come back and we can talk about how to repair and set up the fuel system (starting with draining the tank of any fuel of a dubious age and refilling with fresh!)

Chris

 

[Lovel]

Re: Lack of Free Reving beyond 3500RPM 1972 V8 3500S Manual. Nee

Chris,


I have tried to explain the main parts replaced and or work that I have carried out on the engine without going ito detail too much, I didn't want to scare folk away from the post by being to techy and detailed tbh, however I can appreciate that without this information it can be difficult for posters to give solutions.

With regards to your points I have the following to add.

Change the plugs for the correct for your engine new ones (do you have P6 or SD1 heads? they use different plugs)

P6 heads with new plugs fitted

if you are on points, change the condensor for a known good old Lucas one

Switched to electronic ignition a complete new disttributor and with a module mounted externally

Change the coil for a new one. If you are using the standard wiring, that will need to be a ballasted type. If you are using a feed direct from 12v then a standard coil.

New high energy lucas coil to suit ignition running from balast resistor supply as recommended by supplier. I also have the old distributor which has been completeley overhauled with new vacuum unit included and have swapped back and forth between them to try and eliminate.

Set the timing static at, say, 4 degrees beefore. Don't get the strobe out!

Set up with dial gauge indicator on piston 1 during engine assembly.

Check that the centrifugal advance retard is working. Do this by checking that you can twist the rotor arm and that it springs back afterwards.

Done this and working fully throught range. also marked out 30deg BTDC on pulley to check for full advance and tried to time engine from this point backwards if you know what I mean

Check the vacuum advance retard. Do this by sucking on the pipe from the inlet manifold to the distributor. The plate on which the points are mounted should rotate and spring back.

Have a checked with proper vacumm gauge and all good here have actual readings when everything moves.

Check for vacuum leaks. If in any doubt whatsoever, renew the pipe between inlet manifold and distributor and also the pipe between inlet manifold and servo.

Gauge indicates holding vacuum for long time

renew the rotor arm, distributor cap and plug leads. The latter with Magnecors - they're the only leads proven to allow clean revving on the V8 without cross firing. If we knew of anything cheaper that worked we'd all be using them!

Havent done this, but are you saying that all P6 and SD1 had to have magencor leads fiited, surely not? My leads are brand new but not the brand you reccomend, in fact the OLD leads I removed were almost brand new too and there is no change.

Then come back and we can talk about how to repair and set up the fuel system (starting with draining the tank of any fuel of a dubious age and refilling with fresh!)

Iv'e had about four full tanks of fresh fuel with castrol valvemaster plus through the system since the rebuild and checked the fuel filter which is spotless. I'm quite happy setting the carbs up initially, but getting the needles right to suit engine profile seems to me to be a bit more tricky.

 

[rockdemon]

Re: Lack of Free Reving beyond 3500RPM 1972 V8 3500S Manual. Nee

post your full engine spec, including exhaust, carb tybe, air filter setup, compression ratio and i'll run it through my carb program for you on monday. All RV8s in p6s and sd1s seem to be specified as very weak...

 

[chrisyork]

Re: Lack of Free Reving beyond 3500RPM 1972 V8 3500S Manual. Nee

Good, I'm much re-assured.

All Rover V8's with distributor ignition are extremely sensitive to cross firing. That is, the spark escaping from where it was meant to be going and finishing up somewhere else! Spotless and nearly new distributor caps are essential. Rotor arms have been known to upset things but less often. The real secret is in the leads. High rpm misfires - say above 3000 rpm - are quite difficult to identify from inside the car until they get really bad. These are invariably down to crossfiring between leads. Magnecor are the only leads that definitively eliminate it. We've had a number of proposals for alternative makes, but none has so far come back with a clean report. They really do make a difference you can feel, even when you haven't identified a specific misfire and even over brand new ordinary leads. Why the Rover V8 should be so sensitive to this is not obvious - but it definitely is!

I mentioned petrol because even a very small residue of stale petrol has been known to cause significant problems. Modern unleaded appears to deteriorate with age in a surprisingly disruptive manner. I wouldn't have thought 4 tanks would have been enough to clear this effect unless taken right down to run out each time.

Best leave you to get on with the carb rebuild at this stage then.

When you put them back on, check that the throttle pedal movement gives you full throttle. There are a number of rubber bushes in the system that go missing, leaving you only able to obtain part throttle. The favourite is the one on the bulkhead that the accelerator shaft launches from on its way across to the engine, but there are others too.

Let us know how you adjusted the inter carb linkage - for full throttle together or balanced idle together. We have conflicting views on how this should be done. Otherwise the only advice out of norm is to use at least two colourtunes when setting up the mixture.

Don't worry about things getting techy. If they don't we won't any of us learn anything!

Chris

 

[Lovel]

Re: Lack of Free Reving beyond 3500RPM 1972 V8 3500S Manual. Nee

post your full engine spec, including exhaust, carb tybe, air filter setup, compression ratio and i'll run it through my carb program for you on monday. All RV8s in p6s and sd1s seem to be specified as very weak...

Ooh er that sounds interesting

Standard bore & stroke
CR was 10.5:1 originally but has composite head gasket so maybe 10:1 ish? (head has not been skimmed, checked against dimensions of new)
3.5 EFI cam
P6 heads
Electronic distributor assy 35DLM with Lucas coil from Powerspark
JRW stainless exhaust and manifolds for S models
GSP531 Unipart plugs with .025" gaps (have tried with .035" too) , plugs to me seem to be nice tan colour
Standard air filter box withBritpart star shaped air filters
HIF6 carbs with BBG needles
Castrol valvemaster plus added to unleaded fuel 95?

 

[rockdemon]

Re: Lack of Free Reving beyond 3500RPM 1972 V8 3500S Manual. Nee

BBG is weaker than BAK which is specified for standard p6 engines. With the modifications it'll want to be richer not weaker.

I'll find you some ballpark needles to play with on monday. Obviously these cant be as good as a rolling road setup but should give you a starting point.

Still dont think they would prevent revving though?

Rich

 

[Lovel]

Re: Lack of Free Reving beyond 3500RPM 1972 V8 3500S Manual. Nee

All Rover V8's with distributor ignition are extremely sensitive to cross firing. That is, the spark escaping from where it was meant to be going and finishing up somewhere else! Spotless and nearly new distributor caps are essential. Rotor arms have been known to upset things but less often. The real secret is in the leads. High rpm misfires - say above 3000 rpm - are quite difficult to identify from inside the car until they get really bad. These are invariably down to crossfiring between leads. Magnecor are the only leads that definitively eliminate it. We've had a number of proposals for alternative makes, but none has so far come back with a clean report. They really do make a difference you can feel, even when you haven't identified a specific misfire and even over brand new ordinary leads. Why the Rover V8 should be so sensitive to this is not obvious - but it definitely isChris

The new leads I fitted are branded Lucas, but I would think that they maybe Chinese clones TBH so the quality is questionable. I was led to believe that especially the leads on cylinders 5 & 7 are the ones to ensure that they are kept apart as these had the biggest chance of crossfiring. However the spare Bosch leads and champion plugs I have give me basically the same results.

When you put them back on, check that the throttle pedal movement gives you full throttle. There are a number of rubber bushes in the system that go missing, leaving you only able to obtain part throttle. The favourite is the one on the bulkhead that the accelerator shaft launches from on its way across to the engine, but there are others too.

Have replaced the complete throttle system rubber bushes, spider coupling including the 2 brass bushes on the inlet manifold. I found that I wasn't getting full travel, maybe 7/8 open, I adjusted all the throttle rods precisely to the handbook settings, but to get full travel I removed a small triangular stop plate which was mounted into one of the brass bushes of the manifold, once removed full travel was obtained I noted that the throttle levers now strike the carb body at the same time, indicating fully open and at the same time. a quick look into the venturi confirms this.

Let us know how you adjusted the inter carb linkage - for full throttle together or balanced idle together. We have conflicting views on how this should be done. Otherwise the only advice out of norm is to use at least two colourtunes when setting up the mixture.

The inter carb link was adjusted at idle only, however at full throttle both stops hit the carb body at almost the same time, there maybe a few thou in it but its' certainly close. I think I will look at this again though just to confirm.

 

[Lovel]

Re: Lack of Free Reving beyond 3500RPM 1972 V8 3500S Manual. Nee

BBG is weaker than BAK which is specified for standard p6 engines. With the modifications it'll want to be richer not weaker.

I'll find you some ballpark needles to play with on monday. Obviously these cant be as good as a rolling road setup but should give you a starting point.

Still dont think they would prevent revving though?

Rich

Its revving eventually just not as willing as I think it should. If you floor the pedal in top it seem to get to 2500rpm and just get bogged down, but if I change down a gear then we eventually we get back some higher revs, but even then she is none too happy. It used to misfire too but I have sorted that bit of it I think. I have tried pulling the choke on when this occurs, but really no change. Maybe my imagination but its better on light throttle openings.

I noticed that the spec for the 1972 3500S was BBG needle too? I think my car has not been tampered with as most things seem to be original hence I have BBG's still fitted. I have a new pair of BBG coming hopefully tomorrow, so maybe I have made the wrong choice here :roll: . However I could possibly take my old BBG's and turn then down a wee bit to maybe replicate BAK needles dimensions?

 

[Lovel]

A Welcome Growl Returns

We now have a free reving tiger, thank goodness at long last

I rebuilt the carbs today with new BBG needles, main jets, throttle seals, spindles, viton needle valve and seat .

Revs fully now and with some urgency too. Thank you for all your support and contributions to the thread.

 

[rockdemon]

glad it's working Out of interest why BBG? These were never standard for the P6 from what i've found on the sucarb website?

 

[Lovel]

glad it's working Out of interest why BBG? These were never standard for the P6 from what i've found on the sucarb website?

I had ordered the needles a couple of day ago based on info in Rover workshop manual which mentions BBG for the 3500S. Maybe I have interpreted incorrectly.

My carbs have the alloy name tab AUD521 on them (maybe these are incorrect for the 3500S ? The SU site lists AUD623 for the 3500S

 

[rockdemon]

I'll check and follow up on monday when i have the needle selection program at my fingertips from memory they were fitted to the SD1 and not the P6. They're actually weaker accross the range than BAK which look weak accross the rev range any way - especially with larger throttle openings....

Rich.

 

[Lovel]

I'll check and follow up on monday when i have the needle selection program at my fingertips from memory they were fitted to the SD1 and not the P6. They're actually weaker accross the range than BAK which look weak accross the rev range any way - especially with larger throttle openings....

Rich.

Thanks, if there is something I can optimse on even more then all the better, I would be keen to try this out.

 

[chrisyork]

Splendid! HIF series carbs do seem to produce some odd effects when the needle and the jet assembly are worn. Harvey likes the HIF's for their precision, I like the HS's for the reason you have found!

It is well worth following through on this needle selection business. The programme Rich has, seems to compensate for the change in the characteristics of fuel since Rover did their selections. Plus it is focussed on optimising engine performance, not on achieving emissions figures or perhaps best fuel consumption at a stedy 70 (or 55?). The change in urgency can be quite dramatic!

Chris

 

[DaveHerns]

I'm glad this problem is now solved .I was going to suggest there may be a blockage in the exhaust - ie baffles collapsed

 

[MJP6B]

My carbs have the alloy name tab AUD521 on them (maybe these are incorrect for the 3500S ? The SU site lists AUD623 for the 3500S[/quote]

I have HIF AUD 521L & R carbs fitted from new on my “S” and I would agree with Harvey about their precision , and they do keep their tune for a reasonable period – except when something fundamental fails as happened to me some time ago when the jet bimetallic heat compensator on one carb played up (it is mentioned on this forum somewhere) which took some finding. It is at times like that when I align with Chrisyork and wish I had HS carb fitted !!!!

Lovel – so glad the problem you had seems to be cured, but as Chrisyork so correctly inferred, with all due respect, it pays to change one thing at a time and see what the result is before changing anything else. Great result, now you have full revs please dont go and blow the engine up !

 

[Lovel]

I have HIF AUD 521L & R carbs fitted from new on my “S” and I would agree with Harvey about their precision , and they do keep their tune for a reasonable period – except when something fundamental fails as happened to me some time ago when the jet bimetallic heat compensator on one carb played up (it is mentioned on this forum somewhere) which took some finding. It is at times like that when I align with Chrisyork and wish I had HS carb fitted !!!!

At least we can confirm that AUD 521 carbs are fitted to the 3500S. Could you confirm the needles that you had fitted or are using now?

now you have full revs please dont go and blow the engine up !

No I hopefully wont be doing that, most of my driving will be tootling about, tbh. I just have to have the things working fully and efficiently as the manufacturer intended or I cannot live with it.

 

[rockdemon]

try http://www.richardfaulkner.me.uk/WinSU Report1.odt