Timing Marks

[Rafe Hollister]

Questions:
1) So the two vacuum choices are called 'ported' & 'unported'? Which one is drivers side? Which one gets full vacuum at idle? Why doesn't the other one get vacuum as soon?
2) Do you think I will get a benefit by changing the primary boosters to 500 stuff? More responsive throttle? Better gas mileage?

[Bud]

If I remember correctly, the vacuum port on the drivers side is ported vacuum but it is easy enough to check. With the engine at idle, put your finger over each port. The one with no vacuum is the one you want. I don't know if you would get a substantial benefit from doing a parts swap. My earlier Carter 9500 series AFB's have the smaller boosters in the primary venturi's and after leaning the fuel mixture a bit, I'm happy with their performance. When Carter was still producing the AFB's, the cfm rating was changed in the secondaries and the primaries were left alone except for the 400 cfm AFB's which were produced early on in the 9500 series AFB's. I've seen 23 mpg out of my 62 Hawk with a four speed, 3.31 rear end and a 9625 Carter AFB so I would say to leave the carburetor alone except for getting a jet kit and leaning out the mixture a bit as the AFB's generally are jetted rich from the factory for performance. Bud

[Jeffry Cassel]

I initially hooked the vac advance to the wrong one too. I think I was following the instructions (should know better,right?) Makes a BIG difference. Lots of talk about just setting timing by ear. That can be done but it takes an ear that is well trained and experienced. If you set it where it is nice and smooth at idle, you'll have way too much advance. Just use the light inside with the lights off and set it 4 deg BTDC to 6 degrees. at 550rpm with vac advance disconnected -- and plugged. Edelbrock sells electric choke for about $50. You must be able to buy better gas in AZ that here in the not-so-great white north SO, does anyone know what "IN OP" means???

[NCDave51]

I initially hooked the vac advance to the wrong one too. I think I was following the instructions (should know better,right?) Makes a BIG difference. Lots of talk about just setting timing by ear. That can be done but it takes an ear that is well trained and experienced. If you set it where it is nice and smooth at idle, you'll have way too much advance. Just use the light inside with the lights off and set it 4 deg BTDC to 6 degrees. at 550rpm with vac advance disconnected -- and plugged. Edelbrock sells electric choke for about $50. You must be able to buy better gas in AZ that here in the not-so-great white north SO, does anyone know what "IN OP" means???

Vote #1: Intake Opens

[Jeffry Cassel]

Dave; Think about it. #1 is at TDC . The spark plug just zapped the air-fuel mixture 4 deg. previously. Would that be the time to open the intake valve??

[NCDave51]

Dave; Think about it. #1 is at TDC . The spark plug just zapped the air-fuel mixture 4 deg. previously. Would that be the time to open the intake valve??

Gosh, you’re right. Answered too quickly.

No other responses to your questions from 30-days ago. Let’s see what others think.

[JoeHall]

Vote #1: Intake Opens

Agree, but it is on the stroke between power strokes. In other words, #1 intake opens roughly 360 degrees (one complete rotation) after ignition, same as the other 7 cylinders. IMHO, anyone who thinks the intake opens on same stroke as ignition is confused between 2 and 4 cycle motors. Agree with you

[doofus]

If you read the book In Op 1 is used for checking valve timing like when a cam gear loses teeth. it's a reference point not to be confused with timing marks. Luck Doofus

[JoeHall]

If you read the book In Op 1 is used for checking valve timing like when a cam gear loses teeth. it's a reference point not to be confused with timing marks. Luck Doofus

There is ignition, and there is valve timing. Valve timing is via the cam and crank timing gears' relative positioning. Ignition timing, is then via distributor cam and valve cam relative positioning. The valve timing marks on the damper are for valve timing, and the ignition timing marks on the same damper are for ignition timing. You must establish correct valve timing first, which is done during assembly of the motor. Really not complicated.

[Jeffry Cassel]

It totally makes no sense whatsoever to have valve timing set up with camshaft and crankshaft marks aligned , but then to have to set up ign timing on #6 or rotate the engine 360 deg to set dist on #1. You're right, Joe--it ain't that difficult once you figure it out. My little Corvair is the same way--But other cars are logical. There is no reason for valve timing and ign timing to be divorced from one another when they are totally dependant one upon the other!

[doofus]

Convenience Gentlemen, Sheer Convenience. Luck Doofus

[JoeHall]

Agree, the valve timing mark on the damper is for convenience: can be used to double check that the timing between crank and cam is correct, without having to pull the timing cover. Can also be used to double check cam profile, if in question.