Timing / Idle Mixture / Vacuum question

[Irish_Alley]

When the engine is cold..............wouldn't all the exhaust pipes be the same temperature?   Cold?

lol nope they warm up pretty fast i was saying do it when its cold cause if you wait they will be too hot to touch

[Irish_Alley]

I felt the exhaust manifold right after starting the truck from cold, and they all seemed to get hot at the same rate, after about 30 seconds they were too hot to touch, does that seem right?

see and he understood me but
since its running good when cold hows the choke operating?

[bswilson80]

Choke closes correctly, and opens as truck warms up.

[Irish_Alley]

what kind of exhaust are you running?

[bswilson80]

Just the OEM manifold and what appears to be run of the mill true dual exhaust that exit behind the rear tires, no markings are obvious, is there anywhere to look to tell?

[Irish_Alley]

just trying to get an ideal. my truck will pop every couple seconds out the exhaust but i have open heads. my buddys blazer will also not as much as mine but his does it he has true duals coming out in front if the rear tires with no mufflers or cats. and his 72 jeep with 5.0 also does it it also has true duals all these are mud trucks except for the jeep we just got that thing running after sitting for 20 years lol

[travisr1988]

my truck pops on decel, not as much or often since I bumped timing to 12*. My '92 s10 blazer had a dynomax muffler and it popped no matter what I did, I actually started liking it. on that exhaust the pipe was 2.5" with a 3" tip, so on decel cold airwould rush into that 3" tip and hit the 2.5" pipe it'd pop. The colder the weather the more it popped and louder it popped.

[bswilson80]

My cousin has an old Bel Air that pops on decel too, but his sounds nice, like an old engine that has more to give than he's asking out of it.  Mine just does it at standstill and it sounds like I have a bunch of dwarves with hammers stuck in the bed of the truck trying mine their way through the metal.  Not that cool.

[Fairlane514]

Full manifold vacuum is better anyways. The motor should run cooler as well.

[travisr1988]

mine doesn't pop under 50 or so mph, just when decel from highway

[rich weyand]

travisr: Check the location of that vacuum line from the distributor.  On decel is when I would expect the location difference to matter.

[travisr1988]

travisr: Check the location of that vacuum line from the distributor.  On decel is when I would expect the location difference to matter.

It runs to a port on the bottom of the carb, my dad put it there and said it should be there to keep the vacuum advance from advancing at idle.

[rich weyand]

OK, here is a pic of the Qjet showing the ported and non-ported vacuum connections.  The distributor (for best performance) should connect to the non-ported vacuum.  Ported vacuum was a trick to meet emissions specs at idle, but was not the best choice for best operation.
http://www.gtoforum.com/attachments/f50/9784d1293232179-who-has-best-book-help-me-convert-quadrajet-img_20101224_163810.jpg

[travisr1988]

OK, here is a pic of the Qjet showing the ported and non-ported vacuum connections.  The distributor (for best performance) should connect to the non-ported vacuum.  Ported vacuum was a trick to meet emissions specs at idle, but was not the best choice for best operation.
http://www.gtoforum.com/attachments/f50/9784d1293232179-who-has-best-book-help-me-convert-quadrajet-img_20101224_163810.jpg

Is that the same for the side entrance fuel line style? if so I believe mine is on ported, I'll switch it over I guess, which means (if it goes back to the way it was before) my timing at idle will be something like 18* will that be ok?

[rich weyand]

Changing the vacuum port shouldn't change the timing at idle because you are supposed to set the timing at idle with the vacuum line to the distributor disconnected!  If you do not disconnect the vacuum line to the distributor vacuum advance when setting your ignition timing, the ignition timing will be WAY off.  I would set the timing to 16* BTDC with the vacuum line disconnected, and then make sure you don't hear any detonation when, say, flooring the engine from a slow speed while going up a hill.  If you do hear detonation, back it off to 14* BTDC and test again.  If you need to back off again, 12* BTDC should be safe for just about any engine setup.