walt03

Can someone give me the specifications to set up my engine's timing?
I've got a 1979 Trans Am with 403CI and automatic with highway gears as stock. also,
I've got a dial back timing light to read all settings at 0 because you can't read them with a regular timing light.

Can you use the highest vacuum setting with vac hose plugged and then back down 1 degree to set timing?

Do you use straight vacuum or ported to the dist vac canister?
Degrees of initial timing ? at what RPM in neutral, Drive ??

this engine is advertised at 7.7-1 compression so I started off with 18 degrees of advance with the vacuum line plugged.

To set the carburetor, I think I need to connect the vacuum line and then set the idle rpm

Any comments are appreciated.
Walt

Morley

It is 20* BTDC @ 1100 RPM with the hose to the vacuum advance removed and plugged. Idle is 600 rpm in D and 800 in N.

walt03

Thanks Morley

there isn't any stickers on the front support with diagrams so could you tell me if the vacuum to the distributor is the ported vacuum from the drivers side of the carb (also shared by the EGR) or does it go straight to full vacuum ( left side of carb which is shared by the trans modulator)?
I really appreciate your advice.
Walt

Morley

Not sure on the routing of the vacuum...I'll look in my Clymer's manual and see if it says. I still have the manual from when I owned my T/A back in 85.

Morley

Well, Clymer's didn't have the hose routings BUT according to several people, it should be a timed port. Is there a port up at the front of the carb?.

walt03

Morley,looking at the engine from the front there is a vacuum port at the top left of the carburetor that is full vacuum and goes to the vacuum modulator on the transmission and there is a second takeoff that I thought was for the distributor vacuum canister. Right now I'm routing it to the distributor vacuum canister and it gives an additional 15-16 degrees in neutral, I set the idle speed with it connected.......On then lower right of the carburetor, right by the idle mixture screws there is a port that is connected to the EGR valve. This port has the opening above the throttle blades so it is "ported' and not full vacuum. ALSO, I noticed a plastic piece( like a fishing bobber) that is not connected to anything, just laying underneath the alternator that probably should be connected to something.


I took the car out this morning with the setup above and timing at 20 degrees at 1100 rpm and I have a BOG that comes on slowly as I'm give it the gas up a hill. I don't know what's causing this but I'll check the setting of the carburetor secondaries to see if the spring is tightened at least 1/2 turn in when the secondaries close but we''ll save that for later. Now I want to get the hoses connected correctly and save the BOG for later.

Morley, thank you once again for your persistence in helping me sort through this problem.
Walt

Morley

One palce says the distributor should be hooked to a timed port, above the throttle blades, and Moroso says full vacuum, below the blades. So, your guess is as good as any of theirs. You could try hooking it to one, then the other. The timed port sounds more logical since you don't want full vacuum on it at idle, but then again I seem to remember there was vacuum at the hose on mine at idle. A timed port shouldn't have vacuum on it at idle.

Do you have the casting numbers from the carb or the model number for it?

walt03

The carb casting number is 17059253.

Morley

Well, I got bored and did some surfing. This stuff should help. You have an M4MC carb and should be one of these casting numbers 17059250, 17059251, 17059253, 17059259.
Check these links http://peterpam.customer.netspace.net.au/quad.htm http://www.geocities.com/gtopercy/Pi...rajetTech.html http://www.gmcws.org/Tech/quadrajet/...iles/frame.htm http://www.tocmp.com/manuals/Carbs/Rochester/QJet/
This is a link to the Delco Q-jet manual http://www.bdub.net/manuals/Quadraje...anual_1981.pdf
http://www.78ta.com/HTMLobj-16215/W72TECH06.pdf

That stuff ought to keep you busy for a while.

walt03

Hey Morley,
Some good stuff here.
Hopefully there'll be some hose diagrams.
Thanks,
Walt