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Old 01-27-2011, 03:31 AM
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New Chevy 350 Backfire issue

I have a crate 350.

New Edlebrock performer carb & manifold.
New MSD Street fire
New plugs/wires

Timing 16d. advance

Starts fine, idles fine, rev's up slowly OK.

A fast rev up backfire/pop.
Test drive it chugs, sputters and feels like its missing.

Any suggestions?

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Old 01-27-2011, 06:04 AM
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Go over the firing order and make sure it`s correct. Check it for vacuum leaks. Check it for correct fuel pressure.
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Old 01-27-2011, 06:33 AM
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timing 16d ?? is that total advance or initial advance should have in the 30s (i like 34- 38 depending on the engine ) check for tight valves
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Old 01-27-2011, 07:12 AM
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350 Chevy Pop/Backfire

New MSD went in yesterday with new wires too. Rotor pointing @ 5:30/#1 Cyl. @ exhaust blow out or TDC?

Fires up great, idles great.

Firing order: 18435672

Have adjusted valves - loosened to chatter the tightened to quiet +1/4 turn. So should be on the looser side. went thru all twice to make sure they were all just right. Once I get a 1,000 miles on or so I'll readjust them.

I've done the timing with a light and then by listening to the motor.
Timing light with no vacume attached is 16d advanced.

Listening to the motor while adjusting the distributer puts the advance about 28d. advance, then I have to turn it back some due to hard start.

If I slowly rev. it up its fine. With a quick rev up it pops/backfires. Then an attemt for a test drive is just seems to be missing, runs rough.

I'm just stumped??

Does any of this help?
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Old 01-27-2011, 07:41 AM
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At the present time, leave the initial timing at 16 degrees BTDC with the vacuum advance hose dis-connected and plugged. After setting/checking the initial timing, re-connect the vacuum advance hose to a full manifold source. The idle rpm should increase. Lower it back down to 650-750 with the automatic trans in DRIVE using the throttle stop screw. The idle rpm in PARK will be about 850. If you have a standard trans then adjust the idle to a little below 800 with the trans in NEUTRAL.

Checking/setting the timing with the engine above 800 RPM will yield an incorrect figure because some centrifugal (mechanical) advance will begin to come into play around that rpm.

Next thing is probably where your problem is. It sounds like you have a lean backfire when going to WOT quickly. Check that you get a flow from the accelerator pump squirters immediately when the throttle is even slightly advance. If you don't, then adjust the linkage so that you do. Next is to increase the squirter size by going two sizes up.
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Old 01-27-2011, 07:51 AM
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Quote:
Originally Posted by CJSam
New MSD went in yesterday with new wires too. Rotor pointing @ 5:30/#1 Cyl. @ exhaust blow out or TDC?

Fires up great, idles great.

Firing order: 18435672

Have adjusted valves - loosened to chatter the tightened to quiet +1/4 turn. So should be on the looser side. went thru all twice to make sure they were all just right. Once I get a 1,000 miles on or so I'll readjust them.

I've done the timing with a light and then by listening to the motor.
Timing light with no vacume attached is 16d advanced.

Listening to the motor while adjusting the distributer puts the advance about 28d. advance, then I have to turn it back some due to hard start.

If I slowly rev. it up its fine. With a quick rev up it pops/backfires. Then an attemt for a test drive is just seems to be missing, runs rough.

I'm just stumped??

Does any of this help?
Your firing order is off, should be 18436572 swap 6 and 5
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Old 01-27-2011, 08:17 AM
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Quote:
Originally Posted by isky1843
Your firing order is off, should be 18436572 swap 6 and 5
Yep, I missed that in his post. Check this first.
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Old 01-27-2011, 08:25 AM
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Quote:
Originally Posted by CJSam
Firing order: 18435672 I'm just stumped? Does any of this help?
If it wasn't a typo, there's your problem. Your going to be mad and happy in 5 min. time!
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Old 01-27-2011, 10:50 AM
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well said frisco. i missed the 5-6 to
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Old 01-29-2011, 04:25 AM
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350 Back fire fixed

You guys here are AWESOME! What a cool forum. I followed all the different suggestions to make certain I covered everything. isky1843 you nailed it. I guess I have a bit of deslexia or whatever.. However THANK YOU ALL so much!! It runs great.

Very Respectfully,

CJ
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Old 01-29-2011, 04:36 AM
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Quote:
Originally Posted by CJSam
You guys here are AWESOME! What a cool forum. I followed all the different suggestions to make certain I covered everything. isky1843 you nailed it. I guess I have a bit of deslexia or whatever.. However THANK YOU ALL so much!! It runs great.

Very Respectfully,

CJ
Mad and happy, mad and happy, What I tell ya! When I do stuff like that I could kick my own butt if I could reach it,

Good to hear you got er goin'
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Old 01-31-2011, 12:25 PM
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Great! Glad to hear you got it goin. The little stuff gets everyone. A couple times in a haste, I have got the firing order right but going the wrong way around the distrubitor
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