timing problem?

[William S.]

I just tuned up my 1969 350/300. Dwell is at 30 and the timing is 4 degrees BTDC. I disconnected vacuum advance before setting timing. The car accelerates fine through the gears but seems to hesitate slightly from a stop. It backfired slightly a couple of times when pulling away from a stop. it idles fine and doesn't seem to show any tendency to run hot. Do I need to advance the timing slightly ahead of what the manual calls for? It ran fine before I tuned it. I haven't done anything with the carburetor.

[Leif A.]

Re: timing problem?

William,
The simple answer is yes. Try bumping a few degrees and see how it idles, drives and temp. There's much more to this process (as I'm sure you know) but this will give you an idea if the timing is too low.

[Michael W.]

Re: timing problem?

Did you reconnect the vacuum line for the advance canister? The stumble you mention sounds like a lean mixture and not timing.

[William S.]

Re: timing problem?

I did, but I think that may be the problem. Someone put a braided vacuum advance line on it at some point and it appears to be very loose. I'm wondering if pulling it on and off and plugging it may have caused a leak. It is very hard to start now, especially once it has cooled down. I advanced timing to six degrees but no difference. I am going to buy a new vacuum advance line and see if that helps. Am going out of town today so it will have to wait until I get back.

[Jim T.]

Re: timing problem?

William do you have the vacuum line you are going to replace hooked up directly to "full time" vacuum from the carb to the distributor advance unit? At idle with the new vacuum line installed and the 350/300 at idle when you connect the vacuum line to the distributor advance unit you should get a idle increase. I have owned my 1970 350/300 since it was new and always set my timing at 10 degrees and when after a month of owning my new 1970 I bypassed the unit on the intake with a new full time vacuum advance line. Gas mileage in city increased and engine temperature was better in city driving.

[William S.]

Re: timing problem?

The vacuum line runs from the advance into the carburetor. That's where it's been since I've had the car. If the line leaks enough would it have the symptoms I'm seeing, hard to start and hesitation when starting from a standstill?

[Timothy B.]

Re: timing problem?

William,

If the vacuum line leaks from a egg shaped/loose fitting there will be a vacuum leak causing the hesitation you describe. start there and make sure the hose connection is good plus adjust your curb idle emulsion screws when the motor is hot.

[Mark B.]

Re: timing problem?

Hard to start sounds like too MUCH advance.
I'm curious, what did your "tune up" consist of in parts changed and work performed?

[William S.]

Re: timing problem?

Points, condenser and rotor. Set dwell to 30 and timing to 4 BTDC. Didn't get to anything else before I noticed the problem.

[Jeffrey S.]

Re: timing problem?

William,
You should read the timing paper by Duke Williams. Long before I read this paper (which confirmed what I did as correct) I attached the vacuum advance to a full time source on my '69 350-300. The idle increased and was smoother. I dialed down the idle to specs with advance attached. I was able to dial in 36 degrees of total advance (initial and mechanical). The initial is now about 10* although that is not really relevant as long as the total is at 36* or so with no ping. I use 93 octane pump (10% ethanol). Starts up immediately, runs smooth and never gets above 190* temp. It is very simple to modify the Quadrajet carb to have full time advance at the original vacuum advance port which I also did. I'm really no expert but this has worked well for me for many years. I hope this helps.
Jeff

[Mark B.]

Re: timing problem?

William,
(I don't know your skill level when it comes to mechanics, so if I'm asking dumb questions please don't take it personally)
Unless your timing light is not functioning correctly or you don't know how to set timing or read the timing marks, (which we then can eliminate from the problem) then more than likely your problem is your dwell setting. Have you set points by dwell before? Sounds like you have too much dwell set in.

Did you set the dwell first or adjust timing first? (Dwell should be set first)
Dwell should be set with vacuum disconnected AND plugged off to the carb side to prevent a vacuum leak.
Have you rechecked dwell since you first set it?

Double check your dwell by checking point gap with a feeler gauge. disconnect your coil high tension cable, set the park brake, put in neutral or park if auto, and have someone bump the starter till the points are resting on the peak of a lobe.

Dwell gauges sometimes are hard to read and the scale for 8 cyl is 2x4 cyl usually.

Dwell is a suggested range from 28 to 30 degrees. The lower end of the setting usually helps lower speed operation and the higher end higher rpm.

[William S.]

Re: timing problem?

Jeff,

Right now my vacuum line is attached to the carburetor. I am a little confused about whether this is ported or manifold vacuum. My understanding is that if it's in the carburetor the way mine is, it is ported and the vacuum advance doesn't work at idle. If this is the case though, why does the manual say to disconnect the vacuum advance when setting the timing at idle?

Is the timing paper the presentation he did at San Diego in 2012? I have a copy of that but it's pretty advanced for me. Is there another one? This sounds like a modification that would be simple and worth making.

Thanks for the help.

[William S.]

Re: timing problem?

Mark,

No offense taken. I've set dwell many times. I set the points with a feeler gauge then set the dwell after starting it. I've checked it a couple of times with a couple of different dwell meters and get 30 every time. I set the dwell before the timing. I don't believe dwell is the issue.

When I get back in town I'm going to try the new vacuum line. The one on there seemed loose when i started and with all the taking it on and off and plugging it I think it needs to be changed anyway. We'll see what that does.

[Jeffrey S.]

Re: timing problem?

Jeff,

Right now my vacuum line is attached to the carburetor. I am a little confused about whether this is ported or manifold vacuum. My understanding is that if it's in the carburetor the way mine is, it is ported and the vacuum advance doesn't work at idle. If this is the case though, why does the manual say to disconnect the vacuum advance when setting the timing at idle?

Is the timing paper the presentation he did at San Diego in 2012? I have a copy of that but it's pretty advanced for me. Is there another one? This sounds like a modification that would be simple and worth making.

Thanks for the help.

William,
If your car has the original carb for the 350-300 car, you can use the AIR port to temporarily get full time advance. Just remove the AIR hose or unplug the pipe if it has been already disconnected and attach a new hose to it and to the advance can. The AIR tube comes out of the carb on the passenger side out to the right just behind the choke pull off. Attached is a picture. If the AIR pump is attached, you can tee off this and have both working. That is the paper I was referring to.
Jeff

[Steven B.]

Re: timing problem?

Dwell is a suggested range from 28 to 30 degrees. The lower end of the setting usually helps lower speed operation and the higher end higher rpm.

This is a new one for me. Since dwell angle is simply coil saturation time, how would there be a difference in helping operation rpm at any speed unless the dwell is changed after initial timing? I also thought that the range was 28 to 32.

Steve