Engine problems -- slight backfire ... - The 1947 - Present Chevrolet & GMC Truck Message Board Network

71sub · 08-04-2003, 09:25 PM

I've got a mid-80's 350, Edelbrock Performer intake and HEI with 700r4.

Installed new Edelbrock 650cfm vacuum 2nd's and new spark plugs gapped @ .045's.

While idled @ ~ 700 RPM, no problems -- but once I put into gear, I get backfire sputers on the passenger side AND I have no
power out of engine --- used 2x the amount of gas today going to work !!!!

VERY frustrated. I've followed Edelbrock carb tuning tips
--- back out 2 full turns, turn in clockwise ( one side at a time ) till RPM drops and put back a 1/8 turn. BTW: timing's at 8 degrees.

What am I doing wrong --- what else do I need to check ?

HotRod929 · 08-04-2003, 09:58 PM

Sounds like you might need to advance the timing a bit more. My 350s running at 13-14 degrees advance. I could b e wrong though.

HotRod

Class of 69 · 08-04-2003, 10:11 PM

If the carb was only thing changed before the problem developed, I would look for a vacuum leak. Strongly suggest rechecking the plug wire location. Sounds like you may have crossed two.

71sub · 08-05-2003, 12:18 AM

Well --- I removed the carb and blew air through the port vacuum inlet and installed a 1/2 riser.

Power has been restored to engine -- but still backfires on the passenger side, not at idle anymore, but during acceleration.

Does that mean I too rich or too lean ?

Thanks for all the guidance !

jcueckert13 · 08-05-2003, 12:22 AM

i think that means it is to rich but why is it only happening on one side

smokekiki · 08-05-2003, 08:43 AM

Check to make sure Your plug wires are in the right order and there is no crossfire.I would advance the timing a little.Mine with hei runs best at 12 btdc

tripp · 08-05-2003, 10:24 PM

make sure you check the firing order and timing. i had the same thing happen to me and it caught my carb on fire!

lngbed71 · 08-05-2003, 10:32 PM

My guess is vaccum leak, check the manifold "T" fitting directly behind the carb, on the manifold. Sometimes if this is off it pulls additional air right into the right side causing backfires and sputters as you describe. You may also want to check the vaccum port on the rear of the carb itself to see if there needs anything connected or plugged off.

08-04-2003, 09:25 PM	#1
71sub Registered User Join Date: May 2002 Location: Stockton, CA Posts: 169	Engine problems -- slight backfire ... I've got a mid-80's 350, Edelbrock Performer intake and HEI with 700r4. Installed new Edelbrock 650cfm vacuum 2nd's and new spark plugs gapped @ .045's. While idled @ ~ 700 RPM, no problems -- but once I put into gear, I get backfire sputers on the passenger side AND I have no power out of engine --- used 2x the amount of gas today going to work !!!! VERY frustrated. I've followed Edelbrock carb tuning tips --- back out 2 full turns, turn in clockwise ( one side at a time ) till RPM drops and put back a 1/8 turn. BTW: timing's at 8 degrees. What am I doing wrong --- what else do I need to check ? __________________ 71 C/10 : 350 / 700r4 ; Ford 9" posi 3.50 with 31x10.5 rear tires, single drive shaft, C-notch, 2.5" drop spindles, keyless entry 71 Suburban 350/350 -- caddy tail lights, keyless entry, late model seats, billet Autometer instrument cluster 70 Ford Torino -- 351W (balanced & blueprinted ), C4, VDO gauges

08-04-2003, 09:58 PM	#2
HotRod929 Registered User Join Date: Mar 2002 Location: Bondurant, IA but in Worcester, MA for school Posts: 767	Sounds like you might need to advance the timing a bit more. My 350s running at 13-14 degrees advance. I could b e wrong though. HotRod __________________ 1970 Chevy C-20 350 V-8 Turbo 350 w/ shift kit Dana 60 w/ 4.10 gears AND Powr-Loc POSI New Additions: Summit Headers 135amp alternator Proform HEI Edelbrock 1406 600cfm carb Sunpro Tach Powr-Loc POSI Edelbrock Performer RPM Intake MSD 6A Ignition Box AIM: HotRod929 Visit My Site: http://1970chevy.netfirms.com/

08-04-2003, 10:11 PM	#3
Class of 69 Registered User Join Date: Mar 2003 Location: Stillwater MN Posts: 1,166	If the carb was only thing changed before the problem developed, I would look for a vacuum leak. Strongly suggest rechecking the plug wire location. Sounds like you may have crossed two. __________________ 69 GMC K10 ..some restoration required....still..

08-05-2003, 12:18 AM	#4
71sub Registered User Join Date: May 2002 Location: Stockton, CA Posts: 169	vacuum advance Well --- I removed the carb and blew air through the port vacuum inlet and installed a 1/2 riser. Power has been restored to engine -- but still backfires on the passenger side, not at idle anymore, but during acceleration. Does that mean I too rich or too lean ? Thanks for all the guidance ! __________________ 71 C/10 : 350 / 700r4 ; Ford 9" posi 3.50 with 31x10.5 rear tires, single drive shaft, C-notch, 2.5" drop spindles, keyless entry 71 Suburban 350/350 -- caddy tail lights, keyless entry, late model seats, billet Autometer instrument cluster 70 Ford Torino -- 351W (balanced & blueprinted ), C4, VDO gauges

08-05-2003, 12:22 AM	#5
jcueckert13 Registered User Join Date: Apr 2003 Location: Edgewood New Mexico Posts: 2,088	i think that means it is to rich but why is it only happening on one side __________________ 1990 subaru legcy (daily driver) 1987 Toyota 4runner (weekend toy) 1968 C30 flatbed dually 1970 C10 longbed stepside (in pieces) 1976 Dodge Dart 1963 Dodge Dart

08-05-2003, 08:43 AM	#6
smokekiki Mike Join Date: Jan 2003 Location: west chester pa Posts: 2,474	Check to make sure Your plug wires are in the right order and there is no crossfire.I would advance the timing a little.Mine with hei runs best at 12 btdc __________________ 70'c/10, 71 suburban4x4 402bb, 72suburban 4/6 drop, 72k/5 4x4 blazer 4" lift 35 tires

08-05-2003, 10:24 PM	#7
tripp Registered User Join Date: Mar 2003 Location: Meansville, Georgia Posts: 218	make sure you check the firing order and timing. i had the same thing happen to me and it caught my carb on fire! __________________ 68 SWB Stepside 72 Cheyenne 20 72 SWB Fleetside 72 Suburban 72 2wd Blazer

08-05-2003, 10:32 PM	#8
lngbed71 Nothing fits but the oil Join Date: Mar 2003 Location: Gaston, Indiana Posts: 424	My guess is vaccum leak, check the manifold "T" fitting directly behind the carb, on the manifold. Sometimes if this is off it pulls additional air right into the right side causing backfires and sputters as you describe. You may also want to check the vaccum port on the rear of the carb itself to see if there needs anything connected or plugged off. __________________ Land of the free Because of the brave



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