Hello there,

I'm writing to request some help from this huge knowledge database that is this forum.

I'm facing quite an intriguing technical challenge with my 1981 3.5l Carbs V8. Symptoms are lack of power and torque and a (difficult to describe) change of engine noise.

So far I've checked and replaced fuel filter, spark plugs, ignition test (making sure ignition gets to every spark plug) and done a compressions test with the following results:

Values are for dry/wet (PSI) test respectively:
Left bank
Cyl 1 110 / 120
Cyl 3 112 / 124
Cyl 5 108 / 126
Cyl 7 106 / 125
Right bank
Cyl 2 102 / 122
Cyl 4 118 / 120
Cyl 6 100 / 117
Cyl 8 101 / 116

The manufacturer's reference gives a pre ignition cylinder pressure of 135 PSI. The missing pressure I attribute it to the high k's (280k) but overall it doesn't seem to have a serious ring, valve or head gasket failure from what I reckon.

The spark plugs that were replaced had no apparent issue apart from a dry sooty aspect (too rich mixture?) on four of them, not from the same cylinder bank.

Additionally there are no coolant leaks, no traces of water in the engine oil and the engine has never overheated (if I believe the temperature gauge). Also, I've done nearly 3000 k's since the first symptoms appeared so I've excluded things such as a bad fuel batch, etc.

I'm no expert in analysing this data but it all seems reasonable on the inside.

Any experts out there have faced similar issue?
Any other tips on what I should start to investigate next.

Cheers in advance,

Carbs. Blimey. Long time since I thought about those... Strombergs I think they were.

Poorly adjusted or blocked carbs could cause this. I'd suggest you check the carb, jets, needle valve (prone to sticking esp if its worn), floats and (if adjustable) mixture; I assume it's a twin carb, you might find one bank is good and the other out of whack. Stripping, cleaning and reassembling them isn't difficult. Haynes manual helps or I'm sure there's an online resource. Graham

____
Gone: 10MY L320 RR Sport HSE, Ipanema Sand
Gone: 20MY Jaguar iPace HSE, Silicon Silver
Gone: 17MY RR Evoque SE Tech, Loire Blue
Gone: 08MY Discovery 3 XS, Stornoway Grey
Gone: 07MY FFRR TDV8 Vogue, Stornoway Grey

You should balance the carbs with a carb balancer gunsons make one but any one will do atleast you will know that they are sucking together onto no6 Range Rover

Everyone needs a hobby

Carbed V8 ... my favourite! luv em.

the compressions look *reasonably* even across the banks ... i.e. there isn't one thats massively down on the others.

You comment on the spark plugs some darker than others ... each carb does not feed the 4 cylinders on a single side. Each carb will feed 2 cylinders on each bank ... if you look at the casting of the inlet manifold you'll be able to see the how it splits the air ... the 2 carbs dont combine the air they let into the manifold.

I think you need to describe you're symptoms a bit more ... i.e.

Does it idle smoothly?
Does it rev smoothly from idle at standstill?
Does it pull evenly when accelerating when driving?
If you driving along does it suddenly lose power?
etc etc
describe the issue and how it appears.

What springs to mind is the mileage of the engine you mentioned. Has it had any sort of rebuild in its life?

For older rover blocks, 80k miles and beyond = wearing of the components ... Camshaft , lifters and timing chains being some of the first to go. Have they ever been done? If not, then my first port of call would be the camshaft and lifters are worn, thus not pushing open the valves fully and not letting the air in or out well enough.

If your gut is saying its the carbs, then a couple of very quick rough and ready tests you can do to check them are:

Mixture:
- Engine off.
- Take the filter and elbow pipes off so you can see the inlet of the carbs.
- You should be able to see the diaphram piston that lifts up, and if you lift that upwards, you would see the throttle butterfly.
- If you gently put a flat bladed screw driver to the bottom edge of the piston, you should be able to liftly lift the piston upwards without much resistance.
- Now, with the engine running at idle
- Gently lift the piston upwards ... I'm talking fractions here ( like less than a millimetre ) just enough to move it.
- If the engine drops its revs *ever so slightly* then the mixture is pretty good.
- If the engine revs notable increase ... its too rich.
- If the revs drop notably, its too lean.
- Adjust mixture as required. ( Strombergs have a funky wee tool to do that , not expensive )
Now check the idle / balance...

Idle:
A quick method to check whether the carbs are balanced is to get a flexible tube that you put one end into your ear and the other just at the inlet of the carb. ( place the tube at the bottom most part of the inlet )
You'll be able to clearly hear the draw of air into the carb inlet.
Stick the tube into the other carb at the same place ( bottom of the inlet )
Does it sound the same?
Higher pitch = higher drawer of air.
Get the idles adjusted to make em sound the same - carbs then balanced

Now check the mixture...

And go through that a couple of times and its normally enough to get you going without the need for mega tuning equipment.



Lastly, sorry its a long post:

I'd personally lift the rocker covers off and run the engine and watch the rockers moving ... they have clear pulse movements of pushing open the valves.... if they barely move, then its worn camshaft type stuff.

My old one ran seemed to run fine but would smoke alot, took the covers off and saw that #8 cylinder outlet valve was barely moving ... so fuel wasn't getting burnt and ended up smoking down the exhaust. V8 or else ...

Wow, great post. An expert, unlike me. Graham

____
Gone: 10MY L320 RR Sport HSE, Ipanema Sand
Gone: 20MY Jaguar iPace HSE, Silicon Silver
Gone: 17MY RR Evoque SE Tech, Loire Blue
Gone: 08MY Discovery 3 XS, Stornoway Grey
Gone: 07MY FFRR TDV8 Vogue, Stornoway Grey

Hi there -

Had similar probs with my '72 RRC. Do you have Stromberg carbs ? - If so, have you replaced the diaphragms ? I seem to remember them developing tears that were barely visible . . . . .

 Where do you go after one of these . . . ?

Oh yes, I had that on my Triumph Herald... dim memories come flooding back of roadside repairs and AA Relay... Graham

____
Gone: 10MY L320 RR Sport HSE, Ipanema Sand
Gone: 20MY Jaguar iPace HSE, Silicon Silver
Gone: 17MY RR Evoque SE Tech, Loire Blue
Gone: 08MY Discovery 3 XS, Stornoway Grey
Gone: 07MY FFRR TDV8 Vogue, Stornoway Grey

fisha wrote:

Carbed V8 ... my favourite! luv em.

the compressions look *reasonably* even across the banks ... i.e. there isn't one thats massively down on the others.

see this additional overview how the carbs are working

Last bit of saddo knowledge ... The beaty burble of the rover block comes from having the firing order such that there are 2 times where the cylinders on the same bank fire one after the other rather than on alternate banks. This creates a double pulse of exhaust gasses down the exhaust manifolds whic by the time it reaches the end creates the 'beat' of the rover v8

Another chance to post my old rebuild of my 86 rrc ...

 V8 or else ...

Thank you very much for all your answers.
Amazing knowledge on this forum!

My lack of expertise even made me think each carb fed a complete bank of cylinders... Now things like the sooty spark plugs not from the same bank start to make sense.

Here's a bit more information:
The engine does not idle as smoothly as it used to bit, the lack of power is noticeable throughout all the rpm range and it's not sudden. The engine doesn't seem to work and sound as it should (rough sound not a regular proper V and I'm even afraid to accelerate more so can't really tell what happens at full throttle.

Don't really know much of what has been done in the past so camshaft, lifters, etc may be in need of replacing. What made me think more it's on the carbs side is the fact that it happened after I did a little less than 400 km on the sand on an island so some dirt/sand might have gotten somewhere.

And they are indeed the Zenith (Stromberg?) ones.

With all Fisha's tips I have some work to do on the carbs and will try to take them apart. Will also remove the covers to see if there's any visible discrepancy in terms of valve lift.

The picture of your engine is awesome, it looked amazing!

Thanks again,

if you check the carbs have a look to the diaphragms, no need of special tools and easy to change

and by chance a pic of my V8 (LR 101)

Click image to enlarge

Guys,

I would just like to say WOW. I, as long term RR owner of 25 years, joined the forum a couple of weeks ago and as the forum is dedicated to FFRR had, mistakenly, thought that it would be exclusively for that. Reading this post has brought back memories of carb V8's and the 'fun' we had. But more importantly shows what really great members there are on the forum. People who take the time to post detailed replies with drawings and helpful suggestions for those in need. I hope I too can assist in the future, if my failing memory will allow.

Some awesome pictures too.

Nick 2019 D5 HSE Lux SDV6 Indus
55 D3 SE
98 MX5 1.8 RS
gone 17 older variants of FFRR

I second what Nick Ground has previously said.

Couldn't find such valuable and detailed technical advice even on the so called specialist forums.

I also hope that I will be able to contribute although my RR experience is somehow limited compared to the other members. But I'm keen to learn as once you get the RR bug I believe you never abandon it!

Going by your sand escapades, the a clean of the carbs sounds a good idea.

A long time ago, I had a. Very very detailed manual on the strombergs and su carbs in a PDF file. I will try and find it for you and post it. no guarantees tho.

Nice 101 by the way... I'm very jealous ... Always wanted a 101 but I don't think I'll ever be allowed. V8 or else ...

Ok ... prepare to have yer mind blown ...

Here is a link some better descriptions of tuning the carbs:

http://www.gerull.nl/mg/technics/carb/carb_tuning.html

And here is a link to the haynes carb manual ... its a 61mb download from rapidshare and its 354 pages long ... ( you'll need to copy and paste the whole line, the forum doesn't seem to want to make it a link even with the URL tags either side of it )

https://rs106dt.rapidshare.com/#!download|106tl|122895021|Weber_Carburator_Manual.pdf|64750|R~0|0|0 V8 or else ...