Haywired

Hello everyone,
I have a few questions about Timing, quick backround first 67 Coupe 289 4v c-4 just rebuilt with the addition of a 204/214 .480 cam and Comp roller tip rockers. cam is set on the timing marks on the gears, timing set at 12 BTDC.

Question 1 is if I tune with a vacuum gauge and get into spec with the gauge 20 inches of vacuum and check the marks with a timing light it is now at about 40 degrees.is this o.k?

also in neutral I have to keep my idle at at 1100rpm to get 750 when in gear anything less and it just will not idle

Comments Suggestions

Sorry about my 1 st post being a novel but I wanted to give as much info as possible

Thanks
Rob



1967 Coupe 289 4-V C-4

boogerschnot

Sounds like you have your vac advance line hooked up wrong. When you time the motor with the gun be sure that you pull the advance line and plug it so that you are not timing with the advance active.. Also the line going into the distributor should not have much vaccum on it at all when you are at idle.. If you have a strong vac there then you must be hooked up to the wrong port on your carb.. Your car should have an advance port that will only start sucking when the rpms come up.. And if you have to idle that high, make sure you are timing it when the car is in gear and rpms are down around 750.. I think 40 deg is about 5 deg too high.. I may be wrong though,, you should only come up to about 35 at total advance..

Another thing,, you dont just want to get your carb into spec at 20 inches,, you should get it timed right (probably around 12* btdc) and then make sure you have no vac leaks and tune it to the highest possible vac while adjustingyouridle to stay around 750 if it will.. that camshould..

Im supprised that no one has chimed in on this yet..Im dissapointed..this guy needs some help..

urban_cowboy

40 is pretty high timing if you are not running racing gas. I would bet you are going to have dentation issues at that level.

Haywired

No vacuum advance hooked up, line pluged so no vacuum leaks.I checked the timing this morning and it 36 BTDC at idle.
I am wondering if the centrifigul advance weights are stuck or broken . I am going to check that out

also no pinging all the way up to 4800 so that also has me wondering about the advance

boogerschnot

It usually wouldnt ping unless you had a load on the motor,, not just free reving.. You may want to check out your advance pot.. It may be stuck..

67t5ponycoupe

Some camshafts require some crazy initial advance. I would just test drive it and see if it pings with a load. If it doesn't I would go with it.

Haywired

Update:

Mechanical weights under the breaker plate only had one spring the other is long gone!
I have a 18L and 13L weight so I ha31 degrees of mechanical advance from idle on up.
I wil report back after i get a set of weights and springs.

Starfury

That would do it. Idle should be about 12*, ramping up to 28-32* all in by 2800rpm (with the vacuum advance disconnected).

boogerschnot

YAYY!!!! Should be purring like a kitten petty soon...

67mustang302

Yeah, idle timing should be around 10-16 and total around 30-36. Give or take, it's going to depend on fuel availability and how the engine/car is set up. Different engines have different requirements. As far as 20" vacuum at idle, good luck on that. The 20" rule was from back in the day when carburetion technology sucked, so you needed a lot of intake vacuum to get enough velocity through the carb to meter. They used small everything to get the intake vacuum and you could get a 20" idle, but that was when carbs would need like a minimum of 5" to meter, modern carbs will meter on 0.5" or less. Chances are you won't see an idle over 17" unless you have a tiny cam. One problem with setting idle/timing so you have the highest vacuum, is that may put the butterfly in a position where the transfer slot is uncovered at idle, so you're off idle throttle response will suck(it depends on the engine setup). Generally you're better off setting idle timing/speed for a certain rpm.