Too much timing?

[TJ's GMC]

Here ya go Clarke. Mine actually has 3! lol!

[Clarke]

Originally Posted by TJ's GMC

Here ya go Clarke. Mine actually has 3! lol!

Yes, that is interesting. Looks like the carb portion is the same, but your lower attaching plate has two additional ports.

Thanks for sharing.

[TJ's GMC]

Originally Posted by Clarke

Yes, that is interesting. Looks like the carb portion is the same, but your lower attaching plate has two additional ports.

Thanks for sharing.

Might also be cause mine was in a larger series truck. Not sure. But the carb should be the same, just a different base.

[bobdylan]

I have a 305 e Stromberg, they have one port, runs to the distributor.

[TJ's GMC]

Wish I didn't get rid of that old dizzy. lol Might have been able to help shed some light on this subject.

[TJ's GMC]

Was driving the ol truck around today. V6 Really seems to be happiest with 10 initial and ported vacuum advance. Everything else I tried just Doesn't seem to be as nice. So I'm sticking with this setup. By the way....I had the ol thing up to 70 MPH for a Short time. LOL Bout 3300 RPM or something like that....super scary though...ain't doing that again. I like that motor and want it to last for awhile. 2500 seems to be it's cruising limit so I don't push past that....Most of the time I'm at a Peak of 2400 which is around 50. Get a bunch of tailgaters, but I don't care...it's My truck and I'm not gonna push it past it's limit cause some idiot is in a hurry on a weekend. lol Cold starting has been more involved, but then it suddenly comes to life. The advanced timing has also helped make warm up times shorter. Used to have to let it idle for like 5 minutes, but now I let it high idle on choke for about 3 and just go easy on it until I get to the high way. Doesn't stumble or back fire when it's cold anymore. She's been a good runner for sure. Confidence keeps going up.

[Clarke]

I left my timing at 16, which is what I set it up a year or so ago. I plugged the vacuum port on the back of the carb and connected a rubber vacuum hose from the intake manifold to the distributor. The truck idles smooter when I hook the full vacuum up to the distributor, as the timing is further advanced.

Once I get above 800-1000 rpm, it seems to be the same as before.

I consistently run mine at 3K rpm and shift around 3,400 rpm when hauling a load. I still might install a gear splitter one of these days. Shifting from 3rd to 4th it drops 900-1000 rpm and when you're hauling a load, it struggles to maintain.

[George Bongert]

Greetings Clarke!

16 degrees BTDC (Before Top Dead Center) initial ignition timing is a bit too much in my opinion. I would set the timing to factory spec, and run the vacuum advance with full intake manifold vacuum. That will be where you will get your best performance. You will lose power with ignition timing that is too far ahead as well as with timing that is too late. It will interest you to note that ignition timing that is too late (retarded) will contribute to engine overheating problems. That is why the people who designed the engine designated that the initial ignition timing be just so many degrees (factory spec) BTDC.

[TJ's GMC]

X2 with everything George said. When I bumped the timing up to 10 degrees and then hooked the advance pump to Manifold timing...the engine idled Super smooth...as seen in the video I posted....But, it had some hesitation coming off idle and under wot it would back fire(Partly a 4 down to 2 adapter problem as well). I then backed the timing down to 6 initial and manifold advance...still seemed a bit rough...harder starting and not as smooth....I then brought the timing up to 10 initial and ported advance....Bingo...found that sweet spot. Engine is harder cold starting, but when it's warm it only takes 1/2 a crank, and the engine pulls very well through all the ranges and when cruising I have full advance. I do have to wonder if the roughness in your engine has to do with valves or a vacuum leak?

[Clarke]

First of all, this is not my area of expertise, so I appreciate your feedback. Given the subject of this thread, I'd like to explain how I arrived at 16 degrees (in lieu of the factory spec of 7.5 degrees).

Typically, I follow specs closely, but there was a previous thread where someone was talking about advancing the timing, which I've heard so many times over the years, but never much detail on how much advance.

Many old timers I've spoken to over the years say they never use a timing light; they adjust the distributor (advancing the timing) until the motor starts to run rough (detonation), then back it off a little. (What's a little? I don't know? LOL!) I tried that with my 305 and it started running rough at 20 degrees, so I backed if off 4 degrees.

Correct me if I'm wrong, the engine achieves the greatest amount of power when the combustion process happens when the piston is at it's highest position (least amount of open area), just as the piston is starting on it's "down stroke". This is why when you advance the timing from factory spec, the engine idle increases. As you are reducing the amount of open area during the combustion process, the increased energy pushes the piston down, resulting in more power.

In the previous thread I mentioned above, I noted I completed several dozen timed runs, which consisted of cruising in 4th gear (I think 40 mph), then flooring the gas pedal and holding it until I hit 70 mph. I experimented with 7.5, 10 and 16 degrees. The times between 7.5 and 10 degrees timing were very consistent, but with 16 degrees timing the times were consistently faster. I duplicated the timed runs the following day with all three timing settings in reverse order and the results were very close to the day before.

Again, I appreciate the feedback. I obviously do not want to cause engine damage if the above justification is not correct.