Carb adjustment, choke and backfire

[CharlieC]

Never mind… I think I found my answers.

Charlie

 

[cheavyk10]

I would start with the timing. Especially if you have an aftermarket cam.
What's the timing at when you're all in? (Around 3000 rpm).
Do you have vacuum advance? Make sure it's plugged into the full vacuum port.
For an example my small block like 16 initial 36 total and it's only has a small cam, intake and headers.

 

[CharlieC]

Thanks.... After I submitted the thread and start poking around, I found most of my answers (choke adj, mixture adj. and recommendation to set the timing about 12' at idle). I figure I need to get all that squared away before addressing my occasional hesitation/backfire. The dist. is a stock HEI with the external Accel coil with I think an advance weight kit. The dist. is what, almost 50 years old now? I'm probably going to swap it out and go back to a standard HEI setup if problems linger. After I did the wire swap and start looking around in the back, probably 50+% of the insulation on the wiring going from the coil to the dist. had deteriorated inside the plastic loom, replaced all that.

This is all old school with a timing light and the timing tab, I don't have any way to measure timing that high up or at least I don't think I do. I do need to confirm I have a good vac port on the carb for the dist. I did disconnect from the dist. and plug the carb port when I took my reading.

Thanks!
Charlie

 

[cheavyk10]

I disconnect the throttle return spring and set the engine at 3,000 RPM and then check the timing that way if I'm by myself.

 

[CharlieC]

My problem would be the timing tab only goes to 16' and there's no OBD port to tie in to, so I'll have to settle for the 12' at idle. :-)

Charlie

 

[Wes Harden]

Total timing at 3000 rpm is nice to know for performance. Base timing of 12* is not unheard of, it is a little high for stock sbc. Try 8*. It is not causing the back fire. The back fire is either mechanical, valve sealing, exhaust restriction. Electrical, spark jumping to wrong cylinder. Or fuel ratio,

 

[CharlieC]

Thanks... I'm hoping the issue is either electrical (given my wire deterioration I mentioned earlier) or largely caused by fuel being off. The block and heads were redone maybe 30k miles ago, though many years... and my exhaust (after the headers) is really too big IMHO @ 3" which I intend to go back to maybe 2.25 with some Thursh Turbo's to replace my Flowmasters. At some point, the idea of pulling heads became not as exciting as it used to be.

None of us here have really new trucks... is a damn near 50 year old dist with 100k miles on it an obvious thing to replace?

Thanks
Charlie

 

[Wes Harden]

Yes I agree, best to stay with a factory or brand name dist. My current dist is a new ac Delco from Rockauto. Complete coil to gear, has 20k+ miles. Replaced a billet proform 3rd one. I caution against the no name billet chinseium. Maybe a brand name like Accel or Malory. The store brand summit or jegs not so much.

 

[Blue85]

Is the vacuum advance tied to a direct or ported source? Easy to tell by disconnecting the vacuum can (and plugging the line), but way different timing settings. If you're at 12 degrees at idle with vacuum advance enabled (direct), then overall the timing is retarded.

 

[Chickntrk]

He said he disconnected the vac advance when he set timing, only difference between ported and manifold is at idle. If you’re hooked to manifold then you’ll be advancing the timing at idle, ported won’t advance the timing until the throttle is opened but it happens as soon as the throttle is touched.

 

[Blue85]

I did disconnect from the dist. and plug the carb port when I took my reading.

OK, I missed this earlier.

If you’re hooked to manifold then you’ll be advancing the timing at idle, ported won’t advance the timing until the throttle is opened but it happens as soon as the throttle is touched.

Yeah, that's what I was saying. Timing was measured at idle.