Random Idle problem

[70c10stepside]

So, a few days ago. After not running the truck for a few days this came up. After it running spot on no issues what so ever prier. It'd rev at 800-900 perfectly, in park. Slap it down in gear and it'd die out. Just wouldnt do snot. Idled it up to 1100 or so, still would just die out. So picked up the a little tranny fluid, knew it was low, and that didnt help any. Advanced the timing and it sorta helped. If the motor isn't up around operating temp it'll still die out.. But if its up around the right temp it'll run perfectly at 500-600. But. Still doesn't do much in reverse, still stalls out there regardless. Advance the timing more???

Gm hei, 355, pretty high cammed 313 duration, 750 holley, 10:5 compression(around that, have to run premium), 2200 stall, turbo 400, 4.11.

All fresh, not even 300 miles probably.

Don't know exact timing, dads a mechanic but is getting me to attack stuff now lol

[70c10stepside]

Sorry, realized I added this in the build threads. Meant to put in the message board. My bad guys !

[70c10stepside]

Also, I was thinking vacuum. All lines are new, and plugged up right. No cracks or funny business. Maybe vacuum advance went???

[70c10stepside]

Nothing??
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[ChevyCruizer]

pull a spark plug and take a picture to post.

[70c10stepside]

Already replaced that. And the ones that came out were fine, just a little dirty from motor break in and valve adjusting. Just went ahead. Autolite26 premium. also already checked for intake leak, and carb gasket leak.

Only thing I can evaluate is Vacuum advance or timing. Could it be that off??? When going the motor straight up halls. Third chirps, with ease. And i have it advanced already to the point it turns over a little slow when high temp. Like when I stop for gas. With 1000cca and brand new starter
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[70c10stepside]

Advanced the timing a tad, and really just a tad and it pinged popped, and ran like a dog. Did not help a single bit. Put it back like it was and still runs low rpm in gear. Barely 500. What if I unplug the vacuum advance? I have been reading and people have done this. It fixed there issue.


What makes this so frustrating is it randomly came up. Ran spot on. Idles 900 tops in park, put it in gear and it'd be 500-600 just fine. Maybe the diaphragm in the vacuum advance blew? Or, I just dont know.. Not even 300 miles on a motor with everything new from the motor mounts up..

[ChevyCruizer]

do you have a vacume pump? if so hook it up to dist and start motor. then apply vacum to dist and your rpm should change.

[70c10stepside]

I found it to simply be a loose rocker.. Valve wasn't opening all the way, which obviously means less power... Talk about feeling like a idiot lol I heard one rattle a tad here and there but never thought it'd been THAT loose. Never got the opportunity to further investigate though. Lucky it didn't damage anything else. Motor feels way smoother.
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[ChevyCruizer]

good, glad you found it