vacuum nil ??

bones · Post by **bones** » Sun Apr 26, 2009 3:58 pm

ok here goes, edelbrock 500 carb, rover 3.9, edelbrock inlet, 800 rpm idle tickover, vacuum reading from carb zero.??. According to the vacuum gauge it should be between 17 and 20 at idle, what should it be reading??

rich

Post by **katanaman** » Sun Apr 26, 2009 4:27 pm

do you mean vacuum reading from the carb ports? If so your probably on the wrong one, there is one bellow the throttle valve and one above on the edi. Only the one below will show a vac at closed throttle.

bones · Post by **bones** » Sun Apr 26, 2009 5:54 pm

i take it that port only shows when the engine is reved up, if this is the case what reading should it be and what rpm.Or aslong as it shows something when reved its ok.?

rich

mgbv8 · Post by **mgbv8** » Sun Apr 26, 2009 6:59 pm

Rich!!
If you look at the vac ports on the front of the carb you will see that one is lower than the other. On the weber 500 the lower port to the right of the idle mixture screws is the one which will give you max vac at idle. This is for the dissy vac module. The one to the left of the mixture screws will give you more vacuum as you open the throttle. This is the port I use for the kickdown vacuum modulator on my chevy gearbox.

What is it you are trying to do??

The actual amount of vacuum you see will depend somewhat on the state of the engine.

Perry

bones · Post by **bones** » Sun Apr 26, 2009 8:05 pm

Hi Perry, as you look from the front of the carb, ive use the port on the left for the dizzy as that is what the info said with the carb and the right port is for an auto box if it needs a vacuum, I just going through some stuff and checking things as i dont think the timing is right yet

rich Ok another edit, just watched a film on the edelbrock ,they use the right port for the dizzy on old muscle cars and only use the left port if the co2 is to high, and the other film shows it the oppisite way around. Is it any wonder i get confused

rich

bones · Post by **bones** » Tue Apr 28, 2009 10:22 am

only happens to me, got a edelbrock fuel pump set at 6.5 psi and that is what both gauges showed ,know there showing 9 psi, ive tried adjusting the regs but they wont go below 7 psi. The gauges are oil filled mallory ones, so they cant be sticking. Any ideas welcome

rich

mgbv8 · Post by **mgbv8** » Tue Apr 28, 2009 7:17 pm

Rich!!
The Edelbrock info is wrong for your application.

Just stick a vac gauge on the ports. You will see the right hand port shows max vac at idle. This is the one for the dissy mate.

I'm using a Carter marine pump for my carb, and a Holley red top for the nos fuel supply. Both run via Real Steel fuel regulators to a dead head. I have no problems with this setup. 5psi on the carb and 6psi on the nitrous side.

bones · Post by **bones** » Wed Apr 29, 2009 10:24 am

i put the gauge on the carb and it showed late ignition timing, somewhere between 16 and 18 in,hg. what ever that means, is 19 to 22 ok as that is what it shows on the gauge to be normal, The gauges and pressure have been spot on but at the weekend they showed 10 psi, im using holley fuel regulators

rich

CastleMGBV8 · Post by **CastleMGBV8** » Wed Apr 29, 2009 10:52 am

Rich,

Perry is correct it is the full time vacuum port you need to connect to and this is definitely the right hand one looking from the the front as indicated on page 33 of the handbook item 51.

You will only get full vacuum at idle approx 800 RPM

Not sure what you mean by late ignition timing, can you clarify.

kevin

bones · Post by **bones** » Wed Apr 29, 2009 11:20 am

Hi, the gauge i got from real steel and on it its got a section that says late ignition timing ,and this is where the needle went round to when i connected it to the carb righthand port,but when i advanced the dizzy the needle went to 19 and in the so called normal section, but i dont know what the reading should be. If that helps im gobsmacked as im more confused

rich

mgbv8 · Post by **mgbv8** » Wed Apr 29, 2009 4:51 pm

Rich
What have you set the timing at??
ie, Dissy disconnected, vac line plugged off and at around 900-1000 rpm?

I cant remember the spec of your engine but 8-10 degree's of advance at idle is a good starting point.

Once you have this set, you can reconnect the vac line to see how much further it advances while watching with the strobe lamp.
This will give you an idea of how the vac module is working too.
You can then reset the idle speed to normal with the vacuum connected. This should give you a reasonable running condition to work from.

Can you check total advance, ie, do you have timing tape on the crank pulley or just the normal rover markings?
My strobe lamp has the function to measure this even if the timing mark goes way off the scale on the pulley.
This is important if you intend to use nitrous on the engine.

I've got some time free over the weekend if you want me to pop over for a couple of hours to cast a fresh eye over the engine and bring my timing light.
PM me to discuss

Perry

bones · Post by **bones** » Thu Apr 30, 2009 6:36 am

ive got a timing tape on it, static is at 10 btdc, i had lost my timing light so ordered another one ( sealey digital tach/dwell/advance/volts plus,) and know my old one has turned up, but i cant do anything till weekend as some water leaks have appeared,

rich