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Discussion Starter #1
Hi Has anyone had any problems with the vacuum advance on there cars. I am trying to sort out a problem, Got the links for the manuals thanks.
It has a missfire when exceleratting. I have checked everything out . replaced all the leads/cap/rotor arm ect and coil. When it drives it drives nice, ticks over very nice, just when you excellerate only. Has anyone had anythying!.
 

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Hello

I don't feel that you have a problem with the advance. If you try and rotate the rotor arm by hand, is there some spring resistance one way, such that you can turn it a little way then when you release it, it rotates back. If this is so, the mechanical advance is doing something.
As for the vacuum advance, if you can suck on the pipe with your mouth, and you can create and keep the vacuum you form within the advance capsule, then that is probably OK too. You may even be able to see the advance capsule moving the points base plate as you suck (with the distributor cap off).

Have you checked that there is oil in the carburettor dashpots to the correct level?. Also are you sure the carbs are not set too lean?. Have you checked the fuel pump is working properly?

Cheers... Rob.
 

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Discussion Starter #3
Thanks

Hi Rob thanks for your reply. Ok so far i found that the vacuum pipe from the manifold left had inlet manifold was blocked, so i tea'd off from the front of the manifold and now have vacuum working, and a big improvment. Ok so now i will try and look at the carbs. They have been messed about about a bit by a diy'er and i think now maybe the dach pots have been swoped about or something. I am going through everything. I am a Mechanic by trade but this is old for me so i want to look at the basics first. I have been told it has a new fuel pump, but really need to check that out. do you knoe what it should pump out per second! . I will paly with the carb's on saturday as the car is in Italy.
Thanks
Gino
 

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Hello Gino

Sorry, I don't know what the flow rate of the fuel pump should be, but I'm sure it will tell you in the manual.
Also
What do you mean, you have taken the vacuum from a T on the manifold?
The vacuum connection is usually on the carburettor, very near or at the butterfly valve. It is located so that the vacuum is more accurately varied as the throttle demand changes. The venturi effect at the edge of the butterfly at this point means that at light load, you get full advance, but at idle, you get nothing. If you take the vacuum straight off the manifold, even at idle you will draw sufficient vacuum to give you full vacuum advance, which is not correct.

Cheers... Rob.
 

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Discussion Starter #5
Vacuum

H Rob, yes you are correct but the hole must be blocked. I took t from another source only for test. Now i have to look at the carbs i will make good the problem blockage. Nothhing comes out , you cant even blow through the pipe.
Gino
 

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Hello Gino

Just a thought before you do anything rash.
Check that you can blow through it with the throttle open, or better still, see if you get any vacuum at that point with the engine running and the throttle open a little (fast idle).

The vacuum may be valved off somehow by the carb (maybe by the dashpot piston?) when the throttle is fully closed/engine stopped. It might just be a Rolls Royce trick.

If the above proves not to be the case, I feel you will need to take a carb off for inspection before just poking something down the pipe stub.

Gently gently as they say.

Cheers... Rob.
 
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