truck runs like crap since i set timing? how to check by vacuum?

[dropped72shortbed]

ok so i borrowed a timing light to check my timing on my truck last week.

i started at 5deg BTDC, truck was running pretty good, just had this sputter kinda backfire noise when i stepped on it if the engine was cold or really hot. i bumped it up to 8deg BTDC and it started doing it more. so i figured if i moved it back to 4 it take it away. so i set it back to 4 and it idles really smooth and good. except when i take it up above 2300rpms is does that sputter/backfiring thing non stop. did i mess up the vacuum advance or something?

i remember someone telling me just to play with the timing till i got good vacuum. should i just do that? i have a vacuum guage, should i just hook it up to the part on the carb where the vacuum advance usually hooks up to?

any other ideas how to fix? i mean the truck still runs but its kinda undrivable now.

[conman]

I would look elsewhere for my problem. 4 to 8 degrees shouldn't be causing you that big of a problem. Just make sure your vacumn advance is unhooked and block off the vacumn hole on carb. How new are your plug wires, and/or plugs?

[69 longhorn]

I agree with conman,I think you have other problems to look at. (plugs ,wires points ,ect). To set timing with a vacumn guage,(if stock eng).....try to shoot for 18-20 inches of vacumn @ idle. This will be a general setting,& you will have to listen for the best setting(how smooth it runs,how it accelerates,& check for spark rattle when pulling hills). Good luck....69 longhorn.

[KO]

I agree it's probably not the timing. As mentionde I would check the electrical system. You may have a wire crossed, happens alot with 5 & 7. Also make sure your wires are in good shape had a miss when one would ground out because of a burnt wire. With the popping though I had something similar happen when my carb wasn't right, would run good until I reached about 2800 rpms then start spitting/sputtering. Make sure the choke mechanism is operating proper.
Good Luck, Ken.

------------------
Ken Floyd
72 C20 350HO
82 Honda Silverwing
2001 Silverado

[REPO1]

If you still have points style distributor, I would go ahead and change them out. For the small price of a new set, and for the little time they last, I would get them. That sounds like they might be the problem.

Reid

[71GMC_3/4T]

I always had good luck with Napa Echlin points back when I used points. The other brands would float out over 3000 rpm.
A couple of other things to check would be the centrifugal advance and the vacuum advance to be sure they're working.

[COBALT]

I agree totally. Those new points from NAPA are the way to go.

One thing, though. I recently had a problem with my points, and it would miss out all the time, not just at RPMs above 2K. It would miss out at idle. I'd start thinking about the carb. Hell, just do a complete tune-up. You might as well, considering you'll end up checking everything anyway.

------------------
'69 3/4 ton C20 2wd w/ 350ci/400THM and a wood bed!
'69 3/4 ton Custom 20 2wd w/ ORIGINAL 350ci/4sp Manual and a wood bed (parts beast).
Seattle, WA.

*See pics of my trucks and project at www.webshots.com!

[704x4]

I guess the first thing that i would try to change is the mechanical advance.

if it's worse with more advance and it got better when he backed it off until it got up over 2000 rpm

i would say that the mech advance is opening to much

you can buy a kit at the parts store with new weights and at least three different pairs of springs and good instructions

try a little heavyer spring and see if it clears up

just my .02 worth

[71402BB]

after you buy those new points don't forget to set you dwell!

------------------
71 SWB Stepside, was a 250, now is a 402 Big Block with 4 speed and 3.73's

72 LWB 4x4 350 4-speed 3.08's posi wearing army olive drab green (SOLD!)

68 BURB 50TH LOOKALIKE with built 350 4-speed 4.11's and posi

[bigjimzlll]

and a condenser too...rotor...cap...check your plugs..while you have them out..replace them too...