Fuel type

[larryd]

As I have already said I am new to this model.
Can some one advise me if I need to to use a lead additive in the petrol and also can I use regular 95 octane.
My engine number ends in 8 which the book says should be ok for 95 however the car seems to run better on the premium
Larry D

[stuarthardy]

Hi Larry

Unleaded petrol without any additives should be fine in your car. I use 95 octane in my 420 without any problems. I agree it runs better on 97 RON. My car is 9:1 compression ratio, it appears yours is 8:1.

All that might change of course when standard pump petrol becomes 10% bioethanol.

Regards
Stuart

[J44EAG]

What will be the effects of bio ethol?

Hotter cylinder head temperatures? Valve burn?

Predisposition to destructive detonation in "without anti knock sensors" in older engines? Or indeed problems with newer engines even if fitted with knock sensors?

All change to super unleaded?

Need for upper cylinder additives again to help reduce detonation, especially in older engines?

Have to say the suggestion has me a bit worried. They will soon have us all running on the equivalent of that old abominable old pool petrol! Give me octane and plenty of it. Detonation control equals long lifed power units.

The only person left unaffected would be Jenner because he lives near the end of the world and he has already detonated!

Anyone know their stuff on the subject?

Mike

[stuarthardy]

I just know what I've read recently in the classic car press from the Federation of Historic doodahs.

The main worry is centred on corrosion in the fuel system of older (classic) cars because ethanol is much more hydroscopic than petroleum. This is especially the case when cars are laid up for long periods. There is a suggestion that nylon fuel lines and washers etc. are vulnerable to the ethanol effects. The Federation are carrying out some tests of (yet more) additives to try to neutralise these effects but I personally resent the idea of having to squirt an extra £7 into my tank every time I fill up.

We currently buy 5% bioethanol and in 2013 (I think) it will be increased to 10%. Funny but there's no suggestion that we'll pay less for the fuel due to decreased petroleum content.

I don't know how bioethanol compares to petroleum in terms of volatility so can't comment on performance related matters.

Regards

[J44EAG]

Interesting Stuart.

We need to find out more about bio fuel and calorific values then.

I use fuel drier in diesel powered boats. As you say, the costs are not insignificant. Boats are notorious for getting "wet" fuel. Leaking deck cap seals (horizontal), fuel fills when it rains, condensation in tanks, etc. I check drain a fuel sample from the tanks every time I go to sea. I can`t and won`t tolerate "wet" fuel. I need it to sparkle in a beer glass under gun fire! I have enough mechanical problems to contend with without dodgy fuel quality.

Water erodes injector nozzles and causes huge carbon problems where diesel heater units are concerned. Also as you say, corrosion issues.

I wonder how prevalent this problem is for petrol power plants?

Mike

[larryd]

Hi Larry

Unleaded petrol without any additives should be fine in your car. I use 95 octane in my 420 without any problems. I agree it runs better on 97 RON. My car is 9:1 compression ratio, it appears yours is 8:1.

All that might change of course when standard pump petrol becomes 10% bioethanol.

Regards
Stuart

Many thanks to you all now I am worried I will stick with 95 and bubg some lead replacelment do da in.
Now one more qestion for you all.
I am thinking of changeing the ignition to electronic there are a lot of kits out there any Ideas or experience?.
I have had the carbs and timeing set up but she is still a bit lumpey.
As i have a three speed auto box the tick over reves are set at 700 which is ok but when i stand in gersr they can drop to 500 and at times cut out. Any feed back welcome.
Larry

[Car-Nut]

As far as Im aware 500 /550 rpm is correct for a manual box

But 600 / 700 on an auto box...

HTH

[piman]

Hello CN,

I think you have those back to front, the lower tickover is for the automatic, helps prevent that thump when engaging drive.

With regard to 10% ethanol it attacks lots of metals that are used in older cars, copper based, zinc for example both used in fuel systems. Also cork and other seals. The Federation of British Historic Vehicle Clubs is looking into this and also the feasability of an additive, much as they did when leaded fuel was being phased out.

Larry, if your distributor is in reasonable condition then I doubt you'l see any gain with an electronic module instead of points. Do check that the advance (mechanical and vacuum) is working, check the valve clearances and set the carburettors accurately. You say you had some of this done, but how well? The Jaguar engine is a smooth unit normally.

Alec

[Car-Nut]

Alec,

I stand corrected

Haynes Quote:

"The engine of the 3.8 and those with automatic Transmission idling is 500rpm.
4.2 litres with manual should idle at 700rpm"

So what about 4.2 litres with auto box as most of them are

[larryd]

Many thanks to you all I may not have been clear on the issue so I will list the actions to date.
1) Fuel I use both 95 and 97 it does do better on 97 however 95 does not seem a real problem I also put in some lead additive.
2) Carbs and timeing I am lucky that I found an old jag man who set up the timeing and the carbs he did say that the veniar adjustment was rusted up so he could not set the advance and retard exactley he did the final adjustment with the dist body. He set up the carbs using his vac gauge and colourtune and he set them at approx 650 revs. He also set up the the center carb for auto starting when cold and thats fine it starts well and he has diconected the electronic switch someone had screwed into the wood dashboard.
So cold start fine runs at about 1000 reves till she warms up then drops to 650.
Now its not happy or consistent and the engine is a bit jumpy at these revs
I have increased the tickover to 750 and its still not consistant but better and of course when warm I do get a thump when engageing gear.
She runs ok and drives fine but I normaley slip the gear into N when I have to stop as I cannot seem to achive a smooth tickover.

I have carb refurb kits but have been told they are not required as the carbs are fine.
So I thought maybe the electronic ig may help?
Would it? and if so whats the best to get and fit I have heard some of them do not take into account the advance and retard?
Maybe I can find a tuneing specialist in the north if anyone knows one please let me know I am in the Newcastle area.

Once again any help welcome .
Regards
Larry

[piman]

Hello larry,

do you know if he balanced the carburettor air flow, and whether he dismantled the dashpots to clean the pistons? (I also assume the plugs were checked?)

I think I would check the valve clerances and then do a compression check to have a sound basis on which to work. If the vernier has seized I wonder how the rest of the distributor is, if you remove the distributor cap and twist the rotor arm against the direction of rotation it should move and return when released? Also does the vacuum advance work? How does the car run otherwise, does it seem to have plenty of power and accelerate smoothly?

Personally I would not fit electronic modules to replace the points.

Alec

[stuarthardy]

Hi Chaps

Service manual quotes 500 rpm idle when warm for a 4.2 litre car with an automatic gearbox when in P or N. This will drop slightly when D1 or D2 is engaged.

Before tuning carbs you should, as Alec said, check cylinder compressions, valve clearances, spark plug gaps, contact breaker points gap and adjust as necessary. Also check the operation of centrifugal and vacuum advance mechanisms and set the ignition timing to specification.

All this before you even consider tuning the carbs. Also, check that the butterflies are properly synchonised with each other such that they are fully open and fully closed simultaneously.

Hope this helps.

Regards

[stuarthardy]

Also, electronic ignition units will exaggerate some problems. I don't have anything against them but I don't think fitting one will help unless the problem lies with the points or condenser.

Regards

[larryd]

Hi Chaps

Service manual quotes 500 rpm idle when warm for a 4.2 litre car with an automatic gearbox when in P or N. This will drop slightly when D1 or D2 is engaged.

Before tuning carbs you should, as Alec said, check cylinder compressions, valve clearances, spark plug gaps, contact breaker points gap and adjust as necessary. Also check the operation of centrifugal and vacuum advance mechanisms and set the ignition timing to specification.

All this before you even consider tuning the carbs. Also, check that the butterflies are properly synchonised with each other such that they are fully open and fully closed simultaneously.

Hope this helps.

Regards

If I set the tickover to 500 when in p or n it will cut out.
Plugs are new disp cap and rotor arm are new . New copper tubeing and rubber elbow fitted to advance and retard. (They where leaking). I have not checked tappets. Time I found tuneing specalist?
Regards

Larry