Bigpower

After sorting engine probs I am now looking to check the carb set up. I am basing this on a standard Opel Manta 2.0 GTE Exclusive although as think I have a 2.1 rebore please bear this in mind. I don't want to set it so it is not up to the job if it is a 2.1.

Anyone know what the recommended Emulsion tubes, idle jet, main jet and air correctors would be for these.

It is currently running 35mm venturis is this correct?

Also what is a pump jet and aux vent which ones (sizes?) are recommended?

Sorry if this is obvious but so far have only learnt about engine and you could still write my knowledge of carbs on a postage stamp a big one but still a postage stamp!!! :-D

Thanks again

Suzy

engine all ok now then??

Yup dismantled and reassembled the lifters and this seems to have sorted all the compression issues as now have compression of 150 psi on all four, in fact everything sealing so well now we had to open the throttle to let the air in to get compression reading :-D
Looks like could now be down to the carbs balancing and jetting, also need the timing set up as don't have a strobe.
Just trying to find what recommended jetting etc would be to see if what I have is right and if not if it will work or need replacing.

Suz

you have the mixture screws on them, might be worth setting them up first

gary@apt wrote:you have the mixture screws on them, might be worth setting them up first

Would that be worth doing if the carbs are out of balance?

yes each carb has a mixture screw,if these are wrong they will affect idle to cruise

gary@apt wrote:yes each carb has a mixture screw,if these are wrong they will affect idle to cruise

Looks like job for tomorrow night. This is what I have found so far, does this sound about right?

When you are sure that the carbs are drawing the same volume of air, visit each idle mixture screw, turn the screw counter clockwise (richening) in small increments (quarter of a turn), allowing a good 5 - 10 seconds for the engine to settle after each adjustment. Note whether engine speed increases or decreases, if it increases continue turning in that direction and checking for engine speed, then the moment that engine speed starts to fall, back off a quarter of a turn. If the engine speed goes well over 1000RPM, then trim it down using the idle speed screw, and re-adjust the idle mixture screw. If engine speed decreases then turn the mixture screw clockwise (weakening) in small increments, again if engine speed continues to rise, continue in that direction, then the moment it starts to fall, back off a quarter a turn. The mixture is correct when a quarter of a turn in either direction causes the engine speed to fall. If that barrel is spitting back then the mixture is too weak, so start turning in an anti-clockwise direction to richen. During this procedure, the idle speed may become unacceptably high, so re-adjust it and repeat the procedure for each carb barrel.

After all the mixture screws have been set, the idle should be fairly even with no discernible 'rocking' of the engine, if the engine is pulsing, spitting or hunting then the mixture screws will need further adjustment. If the engine is rocking or shaking then the balance is out, so revisit with the airflow meter/ carb synchroniser. No amount of adjustment will give a good idle if the throttle spindles are bent or leaking air or the linkages are loose on the spindles!

Suz wrote: in fact everything sealing so well now we had to open the throttle to let the air in to get compression reading :-D
Suz

Compression testing should be done with all the plugs out and throttle wide open.

Gerry H wrote:

Suz wrote: in fact everything sealing so well now we had to open the throttle to let the air in to get compression reading :-D
Suz

Compression testing should be done with all the plugs out and throttle wide open.

Knew plugs had to be out didn't know bout the throttle though, Thanks

Suz wrote:

gary@apt wrote:yes each carb has a mixture screw,if these are wrong they will affect idle to cruise

Looks like job for tomorrow night. This is what I have found so far, does this sound about right?

When you are sure that the carbs are drawing the same volume of air, visit each idle mixture screw, turn the screw counter clockwise (richening) in small increments (quarter of a turn), allowing a good 5 - 10 seconds for the engine to settle after each adjustment. Note whether engine speed increases or decreases, if it increases continue turning in that direction and checking for engine speed, then the moment that engine speed starts to fall, back off a quarter of a turn. If the engine speed goes well over 1000RPM, then trim it down using the idle speed screw, and re-adjust the idle mixture screw. If engine speed decreases then turn the mixture screw clockwise (weakening) in small increments, again if engine speed continues to rise, continue in that direction, then the moment it starts to fall, back off a quarter a turn. The mixture is correct when a quarter of a turn in either direction causes the engine speed to fall. If that barrel is spitting back then the mixture is too weak, so start turning in an anti-clockwise direction to richen. During this procedure, the idle speed may become unacceptably high, so re-adjust it and repeat the procedure for each carb barrel.

After all the mixture screws have been set, the idle should be fairly even with no discernible 'rocking' of the engine, if the engine is pulsing, spitting or hunting then the mixture screws will need further adjustment. If the engine is rocking or shaking then the balance is out, so revisit with the airflow meter/ carb synchroniser. No amount of adjustment will give a good idle if the throttle spindles are bent or leaking air or the linkages are loose on the spindles!

As a start point, turn each screw until it gently bottoms and turn back 1 and a half turns. It's a needle valve and is easily damaged by turning too hard onto it's seat. This causes a ridge in the needle so loosing the fine adjustment.

To get the air flows balanced, use a length of small bore rubber tube, say 6mm bore, or less. Stick one end in your ear and the other into the choke tube, in front of the butterfly. You're listening to the 'hiss' of the air being drawn in and after a short while, of quickly swapping from one to another, you'll hear any slight change. Adjust so they all have the same intensity.

The idea, as your text states is to get the fastest, even idle speed but as the idle increases, adjust the idle screw to the recommended speed and start again, adjusting the speed down as you go. Hope that makes sense.

Distributor adjustment is similar, i.e. set to fastest idle. Start by ensuring the points gap is correct. Determine the direction of rotation of the rotor then, the initial setting is by using a 12v light bulb with fly leads and crocodile clips. One side to earth, the other to the sprung contact. Set the crank pulley to the prescribed number of degrees BTDC. Slacken the pinch bolt so the distributor is free to turn then, if the light is on, rotate the distributor the opposite way to the direction the rotor goes until the light just goes off. If the light was off, rotate the distributor i the same direction as the rotor until the light comes on, then rotate back to put it out. It may take a couple of goes but that will be the static timing. Strobe would be good for dynamic timing and if you're pushed I have a strobe you can borrow. I also have a Colourtune somewhere.

Exhaust should be a nice steady beat, any missed beat indicates rich or weak mixture. A regular miss is slightly rich and irregular is weak iirc but it's been a while. Plug colouring will confirm.


Iirc the pump jet is the little tube that looks into the venturi. It adds a squirt of petrol when you plant your foot which has the effect of losing vacuum so, no fuel being drawn in, hence the need for a neat squirt to keep things going

HTH