Truck running better at 37.5 BTDC instead of 12 BTDC?

[crazzmc]

My truck has been giving me some problems - slight fuel smell, some white smoke. Got my timing tape on and finally got a chance to look at my timing. I was super surprised to see it running at 37.5 BTDC. I adjusted the distributor brought it down to 12 BTDC and now it smokes even more and has more of a smell. It even cut out while going up a hill from a stop and I had to put it in low gear to get it up.

I am running a rebuilt 302 with a C4 Transmission.
I have a 1-3-7-2-6-5-4-8 firing order and because of that I assume I have a roller cam.
Got a Holley 4160 750 CFM Carb on it
Idling around 750-800 and about 550-600 in drive.

I am pretty sure my timing is right because of the photos below:






Just trying to understand why it runs better so far off, any ideas?

[Ranchero50]

Was the vacuum advance on or off? Also how much timing chatter are you getting with that Chinese dizzy? When I had one on a TBI converted marine 350 it was all over the place as the RPM's rose.

[sargentrs]

Unless you have a really souped up engine, that Holley 750 cfm is way too much carb for it. Hook up a vacuum gauge to manifold vacuum and tune your timing to achieve max steady vacuum (18-20) then see what your timing reads.

[crazzmc]

Was the vacuum advance on or off? Also how much timing chatter are you getting with that Chinese dizzy? When I had one on a TBI converted marine 350 it was all over the place as the RPM's rose.

That is exactly what happened. I took the vacuum advance out and set it to 14 degrees BTDC it is running much better. Still got a fuel smell and a tiny bit of white smoke from the pipes but much better overall. I'm not sure what you mean by timing chatter, but my timing belt/fan area only kinda chirps on full lock out of my steering wheel (I have power steering).

Everyone says these chinese HEI distributors are pretty cheap and crappy, I am considering an alternate solution, but because I have a roller cam I will need a steel gear on the bottom correct. I just don't know what to get because I only see HEI Distributors with steel gears on the bottom.

Unless you have a really souped up engine, that Holley 750 cfm is way too much carb for it. Hook up a vacuum gauge to manifold vacuum and tune your timing to achieve max steady vacuum (18-20) then see what your timing reads.

Yeah everyone keeps telling me that. I was thinking of trying out the Holley 600 cfm, but I don't really want to spend the extra money. I don't know what jets are in here but I did change the power valve from a 6.5 to a 5.5 which helped it run a little smoother. The person who I bought the truck from said it was recently rebuilt and the guy wanted to make it into a 'racing truck' but kinda gave up halfway and sold it. all I know is that it has a roller cam inside, not much else.

I am idling right now at 900 in Park 650 in Drive and I am getting about 18 on my vacuum reading.

I also need to install a PCV valve but my rear is being used by the brake booster and my front port is being used by my tranny, should I splice into the tranny line with a t-connector or something? Someone said that I can also go directly into the intake manifold just not sure about this.

[DuckRyder]

You can get a different gear for the other distributors.

Is the 750 a Vac Secondary?

[sargentrs]

The tranny line should go in the intake. Timing chatter is when your timing light jumps around instead of being a straight consistent line on the harmonic balancer. I like to time my engine to max timing. Rev it up to around 2500 rpm and dial the distributor where your timing reads around 38*. Let the initial fall where it wants to. Then bring your idle down to around 750 rpm and tune your carburetor with a vacuum gauge to achieve max vacuum at idle. Then timing again, idle, carb. Usually takes about 3 passes to get it steady.

[crazzmc]

You can get a different gear for the other distributors.

Is the 750 a Vac Secondary?

It is a Vacuum secondary. It’s a Holley classic 4160 750 Cfm carb

The tranny line should go in the intake. Timing chatter is when your timing light jumps around instead of being a straight consistent line on the harmonic balancer. I like to time my engine to max timing. Rev it up to around 2500 rpm and dial the distributor where your timing reads around 38*. Let the initial fall where it wants to. Then bring your idle down to around 750 rpm and tune your carburetor with a vacuum gauge to achieve max vacuum at idle. Then timing again, idle, carb. Usually takes about 3 passes to get it steady.

I might be getting some but I’ll confirm again tomorrow morning. Yeah I was reading about setting “total timing”. I’ll give it a shot tomorrow. After doing some more tuning today I was running at around 18 on the vacuum at about 850 idle with a 14 BTDC. Initially I was idling at 1,100 but after driving it around a bit (despite already being warmed up) it lowered itself to 850 and has sat there the rest of the day as I drove around periodically. Still around 600 in drive. truck seems much happier though