350 Not running smooth - Team Camaro Tech
Engine General Engine Discussion.

  • 2 Post By scblucam
  • 1 Post By partsguy57
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post #1 of 9 (permalink) Old Jan 23rd, 20, 12:58 PM Thread Starter
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Location: North Carolina
Posts: 161
350 Not running smooth

Hi guys,
I'm having trouble with my engine in my 69. It doesn't run smooth or even stay running especially when cold. I need to have the idle up to 1000 for it to stay running..
It is a 1971, 350 with I think a 2 bolt main. It has a Comp cam 12-423-8 276/282. Dur @.050 is 224/230. Lobe Sep 110. Lift 502/510. It's a hyd roller.
Alum intake (EPS) and alum heads (E210).
It has a Holly 630 vac secondary.
Tremec TKO600
Chevy HEI

So, What should my idle be?
What should the timing be?
Is this the correct carb for the set up?
Can I go bigger on the carb after I get it running correctly?
Hope someone can help, Thanks.
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post #2 of 9 (permalink) Old Jan 23rd, 20, 01:40 PM
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Re: 350 Not running smooth

With that cam idle would likely be around 750 for a smoother idle but you would need to fine tune that once you get your timing set while using a vacuum gauge to get the highest vacuum

"why" it doesn't idle smooth or run could be several reasons.

Does the choke work? (when cold)
Are the valves lashed correctly?
What is timing advance now?
what is vacuum?
Are the plug wires on the correct order?

The 630 carb is OK. Can you run a bigger one, sure but you need to get the motor sorted first

"Generally" timing at idle with vac line plugged can be 6-15 (12-13) degrees with full advance (2500-2700 rpm) about 32-35 degrees

Confirm your plug wires are good and routed correctly
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post #3 of 9 (permalink) Old Jan 23rd, 20, 02:02 PM
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Re: 350 Not running smooth

"Confirm your plug wires are good and routed correctly"


I had my plug wires on/off a dozen times while troubleshooting my rough idling 383 stroker. I'd checked the routing and firing order multiple times and for whatever reason (mental block I guess) I repeatedly installed the #6 and #8 plug wires backwards. Had a eureka moment and it's run smooth ever since.

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post #4 of 9 (permalink) Old Jan 23rd, 20, 06:10 PM
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Re: 350 Not running smooth

Maybe I missed it but, did it ever run good or did you just get it and have a problem?
Everett#2390 and allanjs like this.

68 302 M20 - 85 IROC Z
The older I get the faster I was.
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post #5 of 9 (permalink) Old Jan 23rd, 20, 07:39 PM
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Re: 350 Not running smooth

Start at the basics. Compression test. Good compression it can be made to run well...

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post #6 of 9 (permalink) Old Jan 24th, 20, 07:46 AM
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Re: 350 Not running smooth

Yes to all of the above!
Start with basic troubleshooting. Has the car been sitting for a long time? Maybe the gas is bad. Newer gas with ethanol doesn't age well. My car needs to run for a few minutes before it runs well.
Check all of the plugs, maybe one of them isn't firing.
Maybe you have a plug wire crossed or loose and it's not delivering power to the plug. While you are checking the plugs and wires you can do a compression test.
Then check timing and vacuum. If all of that is good then play with the carb.

69 Camaro L48 SS350
M20 4spd
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post #7 of 9 (permalink) Old Jan 24th, 20, 08:22 PM
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Re: 350 Not running smooth

I have a cam similar, and mine is cold blooded. Check for vacuum leaks, if none set idle mixture screws to get the highest vacuum, I'm at three turns out with a 670 aveneger, but it has a slightly stinky idle. Don't know what compression you have but try adding some timing, I'm running 18 initial, 36 total by 3000, it likes it. Idle should be no higher than 800, and make sure you idle slots are not exposed to much, just a small square is what you want. Make sure your plugs are good, correct heat range, good wires, all the usual stuff.

1969 Camaro LM1
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post #8 of 9 (permalink) Old Feb 16th, 20, 09:24 AM Thread Starter
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Posts: 161
Re: 350 Not running smooth

Sorry I haven't got back to you guys. Had a unexpected death in the family and things have been off.
I can answer most of your comments with one statement. All parts are good and in working order.
The car runs pretty good when warm.
The timing is 12/36. I can't find my vacuum gauge so I need to get a new one before I can answer that.
Bottom line is I'll recheck all of the suggestions and see what comes up.
The gas idea seems possible, I only drive it about once every two months but I do use Sta-Bil.

Thank you all very much and wish me luck.
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post #9 of 9 (permalink) Old Feb 16th, 20, 01:20 PM
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Re: 350 Not running smooth

" fine tune that once you get your timing set while using a vacuum gauge to get the highest vacuum"

OH, PLEASE, stop all that incorrect info about setting initial timing with a vacuum gauge, IT DOES NOT WORK. Timing is set specifications, not voodoo with a vacuum gauge that makes things worse.

With that cam, I'd shoot for 14 deg/BTDC @ idle of 750 rpms. Then, I would connect the MODIFIED vacuum advance into FULL MANIFOLD VACUUM, NOT PORTED.

MODIFIED VACUUM ADVANCE should give an additional 10 crankshaft degrees AFTER the engine starts up, for 24 deg/BTDC IDLE degrees timing, once again, after engine starts. Set carb and idle speed after getting timing/vacuum advance correct.

Vacuum advance modifications: Stop down the advance degrees available, Crane stand alone stop plate will fit any GM vacuum advance, (complete FREE info and pictures package on how to do it RIGHT, ask for them).

[email protected] The cost for the Crane stop, p/n 99619-1, and the screw and washer to mount them (from YOUR local hardware store) are under $5.00, and YOU install them (drill/tap one hole, install plate, flat washer, hex head screw, trim off excess threaded screw length from underside of advance mounting plate, mount, adjust, done).
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