timing and carb help

[kevken1959]

I need some advice on timing adjustment on my 72 351HO vert. I'm not very familiar with the dual advance vacuum canister. I usually use a single advance and hook it up directly to the carb vacuum port. With this car, I want it to be the way Ford made it, so I put on all the correct distributor vacuum advance equipment and routed the vacuum lines correctly. Here's my problem:

1. The green emissions decal specific for this car says to set the initial timing at 14 degrees with the vacuum hoses off at the distributor. I did that, then hooked up the hoses, and when I check the timing at idle it goes all the way down to a negative 5 degrees or so (5 degrees retard). The motor didn't feel like it had enough timing advance there, so I bumped the timing up to 8 degrees advance with all the hoses connected at idle. It idles good at that point, seems to have good throttle response (just goosing the carb in the driveway, not driving it around town). When I take the motor up to 4000 rpm the timing maxes out at 40 to 42 degrees total advance (which is better than my other Cleveland's which are bad about kicking the timing up to 48 to 50 degrees total advance when I goose the carb. The motor doesn't ping, I can easily take it up to 5000 rpm in the driveway but don't know if it will perform well on the road. When I kill the car it doesn't pre-ignition. The motor feels like it can even use a little more advance. Opinions?

2. When I open the carb throttle all the way with the engine off the secondaries open up. When I goose the motor all the way up to like 5000 rpm (with the choke all the way open) with the motor running I don't see the secondaries moving at all. Does the motor have to be under load for the secondaries to open? Suggestions?

I'm going to drive the car around to check things out when the weather gets better. Just wanted to get some input from the members who are experts on factory timing and ignition. BTW, I added a 40,000 volt coil and a pertronix set up and trashed the points.



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[midlife]

Engine must be under load for the secondaries to open for non-mechanical secondaries.

When you took off the vacuum lines to set initial timing, did you plug those hoses? You'll need to do that; otherwise you'll have a vacuum leak.

 

[kevken1959]

Engine must be under load for the secondaries to open for non-mechanical secondaries.

When you took off the vacuum lines to set initial timing, did you plug those hoses?  You'll need to do that; otherwise you'll have a vacuum leak.

Hi Midlife. The carb is the factory Motorcraft spreadbore 72 r CODE carb. I thought it had mechanical secondaries?

Yes. I plugged the hoses.I set the timing at 14 but when I hooked the hoses back up, the timing went all the way down to Negative 5. It seems the retard on the dual vacuum canister is much stronger than the advance. That makes since as the vacuum going to the retard is manifold and the vacuum going to the advance is carb. Under load/rapid acceleration the advance should kick in and the retard should go down. It just still seems a negative 5 advance at idle really snuffs the motor.

 

[Bill73Ragtop]

4300D is vacuum secondary - the only way (I can think of) to see them actually open is to run it on a dyno and observe.

Although I've spent most of my life with single diaphragm distributors, the reading you are getting does not seem right. Cleveland's like initial timing at 14 (w/o vacuum hooked up), but I've always seen timing maintain initial settings using ported vacuum and then increase as vacuum kicks in with rise in RPM.

I was always under the impression the secondary retard vacuum was something that kicked in under higher temps to keep emissions 'reduced'.

Would love to have someone who has super tuned a setup like yours chime in.

 

[kevken1959]

4300D is vacuum secondary -  the only way (I can think of) to see them actually open is to run it on a dyno and observe.

Although I've spent most of my life with single diaphragm distributors, the reading you are getting does not seem right.  Cleveland's like initial timing at 14 (w/o vacuum hooked up), but I've always seen timing maintain initial settings using ported vacuum and then increase as vacuum kicks in with rise in RPM.

I was always under the impression the secondary retard vacuum was something that kicked in under higher temps to keep emissions 'reduced'.

Would love to have someone who has super tuned a setup like yours chime in.

Thanks Bill! I've always done exactly as you mentioned with the single diaphragm and 14 initial to the ported vacuum. I spent a LOT of time studying the schematic provided here on this site, and what I found out was that it is VERY complicated! What is kind of cool though, is that I got an opportunity to check which vacuum and where kicked in as the car went from cold start to normal operating temps. I saw everything kicking in, from the carb choke to the actuator on the snorkle, to the "air gulper" on the side of the air cleaner. The main point I can make is that I checked the advance and retard on the canister by sucking on both of them and watching the "arm" move, and what I found was that the retard is more sensitive and moves more with less vacuum. The advance moved, but only with a lot more vacuum. If you follow the schematic, the retard is only supplied by intake manifold which is strong at idle but goes down under load. The advance can be supplied by ported or intake vacuum, depending on what the small blue canister behind the carb or the temp switch on the block allows (when I checked the blue canister, it was only allowing ported vacuum at idle with normal operating temp). The temp switch only kicks in when the motor gets hot. That changes the advance from ported to manifold to kick the idle up and bring the temp down. So if you follow everything I said, it only makes sense that the vacuum advance will actually retard or bring the advance way down at idle. But under heavy load, the total advance would kick up a lot FASTER as intake manifold vacuum goes down (decreasing the retard) and ported vacuum goes up (increasing the advance at the front nipple of the module). I'd appreciate anyone else chiming in who might understand all this better. I'm thinking the heavy retard at idle gives more time for the fuel to burn thereby reducing emissions? But it seems to me it makes more sense for the retard to kick in under heavy acceleration because that's when there is more fuel available that needs to be burned? For now, I set the advance at 8 degrees with everything hooked up. I feel that's an acceptable compromise between a decent idle, and what it seems what Ford wanted for the motor.





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