402 just not running right(frustrated)... - The 1947 - Present Chevrolet & GMC Truck Message Board Network

**68350** · 10-20-2011, 10:19 PM

Ok, I guess I'll start off with what the engine is...

1970 402 truck block
1965-1967 396 car heads
1970 BB truck quadrajet rebuilt
HEI with aftermarket cap
rest unknown but all looked good when engine had new gasket set installed

Timing is set at 12 below TDC
Idle set at roughly 700 in park

Ok, here are my issues. It doesn't seem to want to run worth a crap when you put it in gear. By this I mean it has a slight stutter if you gas it after its in gear. It will rev up in PARK perfectly fine. If you get on it, it has alright power(nothing like my other big block truck) until about 2000-2500 RPMs, then it feels like it loses almost all of its power until it shifts, then it regains a decent amount of power. The truck has a 4.11 rearend, so I would think it should have way more snap than my 68 which has a 402/400/3.08 rearend.

Can anyone shed some light as to where to start. Also, can anyone tell me how to properly set mixture screws on the q-jet? What should the idle be at in gear, too? thanks

hugger6933 · 10-20-2011, 10:27 PM

Big blocks love timing give it some more and try agian. Try to go" all in " and set up about 34-36 @ 3000.

Lee H · 10-20-2011, 10:32 PM

What is below TDC? Did you mean before or after?
Posted via Mobile Device

**68350** · 10-20-2011, 10:35 PM

Sorry, before

**68350** · 10-20-2011, 10:36 PM

At first, it was about 18 before at idle, and it acted basically the same as far as losing power above 2-2500

Autoblueprint · 10-20-2011, 10:59 PM

Quote:

Originally Posted by 68350

Can anyone shed some light as to where to start.

Put a vacuum gauge on your engine and see what your readings are:

http://67-72chevytrucks.com/vboard/s...37#post4688437

into69z · 10-21-2011, 07:18 AM

i had a similar problem and it was due to the vacuum advance unit from the distributor was hooked up to the wrong port on the carb. I am dealing with an eldelbrock carb, it has one port for non-emission control vacuum and one for regular ported vacuum. The motor was set at 18 degrees btdc and would stumble at around 3000 rpm-switched the vacuum line and all is good. check the book on the ports for your carb-could be similar

68Gold/white · 10-21-2011, 06:56 PM

It seems like you have a vacuum leak. Plug off the PCV, and vac advance one at a time to make sure one isn't leaking.
Make sure the carb base gasket is sealing, is it new??? or used??? Ive re-used base gasket several times, but they quit making a seal, when you least likely need them to...

Idle RPM, depends on your cam. A stocker or mild cam could/should be around 750 RPM in gear, w/ vac advance plugged.

TO set the idle screws (w/ vac advance plugged), screw one in, until the engine starts to NOT to run smooth, then back it out 1/4 turn. Then do the other. Takes a little time...

IF you have an aluminum intake, The intake bolts need to be retorqued several times (only re torque them when the engine is stone cold) keep checking them until they don't loosen up any more...

**SOON2BLAZE** · 10-21-2011, 07:23 PM

My BBC is at 44 BTDC and pulls 17-18" of vacuum, idle is 750-800 rpm's if this helps

69sixpackbee · 10-21-2011, 07:49 PM

I run my 402 at 16BTDC and limit the total centrifugal to 10. Runs like a scalded cat!

69sixpackbee · 10-21-2011, 07:49 PM

Quote:

Originally Posted by SOON2BLAZE

My BBC is at 44 BTDC

??? ya mean 14 I hope

**SOON2BLAZE** · 10-21-2011, 08:18 PM

doooh!

**68350** · 10-21-2011, 09:06 PM

Well, I definetly had my fair share of dumb moments last night. I forgot to plug the vacuum advance while timing it, redid it and it maxes out at 6 before. So I am going to pull the distributor tomorrow and move it over a tooth so I can retard it a little more. I will let everyone know if it solves my issues. I checked vacuum and its dang near perfect.

Lee H · 10-21-2011, 09:22 PM

While dist is out make sure the shaft and mechanicals are free and well lubed. Springs should be light and easy to advance.
Posted via Mobile Device

jtp67-72 · 10-21-2011, 09:30 PM

Not retard it--advance it..............jim

**68350** · 10-22-2011, 11:04 AM

Well my other BB runs amazingly at 14 before, so thats where I'm going with this one.

jtp67-72 · 10-22-2011, 02:59 PM

going from 6 to 14 will do wonders --and that is advancing it........jim

**68350** · 10-22-2011, 09:30 PM

Ok, I get what ya mean by advancing it. It seems to run a lot better but still not up to snuff so I'm gonna have my uncle look at it tomorrow and tune the carb and timing. He is pretty amazing at it so I'm hoping all goes well.

jtp67-72 · 10-22-2011, 09:37 PM

you'll never have a bigger grin on your face than when driving a c10 with a good running big-block!!!!!!.............lol..........jim (well maybe when u see what LSU did to Auburn!)

10-20-2011, 10:19 PM	#1
68350 Senior Member Join Date: Jan 2002 Location: Williston, ND Posts: 2,999	402 just not running right(frustrated)... Ok, I guess I'll start off with what the engine is... 1970 402 truck block 1965-1967 396 car heads 1970 BB truck quadrajet rebuilt HEI with aftermarket cap rest unknown but all looked good when engine had new gasket set installed Timing is set at 12 below TDC Idle set at roughly 700 in park Ok, here are my issues. It doesn't seem to want to run worth a crap when you put it in gear. By this I mean it has a slight stutter if you gas it after its in gear. It will rev up in PARK perfectly fine. If you get on it, it has alright power(nothing like my other big block truck) until about 2000-2500 RPMs, then it feels like it loses almost all of its power until it shifts, then it regains a decent amount of power. The truck has a 4.11 rearend, so I would think it should have way more snap than my 68 which has a 402/400/3.08 rearend. Can anyone shed some light as to where to start. Also, can anyone tell me how to properly set mixture screws on the q-jet? What should the idle be at in gear, too? thanks __________________ 68 Chevy CST/10, 50th Anniversary, 327/th400, 373 posi, buckets 68 GMC Shortbox Stepside, 402/th400, Tilt, Tach, Bucket Seats, 3.08 Positraction 69 Chevy Camaro SS, 383, 4 speed, positraction 70 Chevy El Camino SS396, Triple Black, 454/th400, Tach 70 Chevy Shortbox Stepside 4x4, 350/th350, Tilt, Tach, Cab Lights, Bumper Guards, Tow Hooks 70 Chevy 3/4 Longbox, 350/auto, 70k, SURVIVOR 71 Chevy Blazer, CST, 350/auto 71 GMC Sierra K2500, 454, 4 speed, 4.10 posi, 37s 71 Custom/30, Open Road, 350/th400, tilt 72 Chevy Shortbox Fleetside, 496 Stroker/th400, Tilt, Tach, Bucket Seats, 3.42 Posi 72 GMC Sierra Grande 2500. 427/th400, tilt, a/c, tool and stowage, buckets/console, 3.54 posi

10-20-2011, 10:27 PM	#2
hugger6933 Registered User Join Date: Oct 2008 Location: Marianna Arkansas Posts: 7,280	Re: 402 just not running right(frustrated)... Big blocks love timing give it some more and try agian. Try to go" all in " and set up about 34-36 @ 3000.

10-20-2011, 10:32 PM	#3
Lee H Registered User Join Date: Jun 2010 Location: Upland Ca Posts: 4,147	Re: 402 just not running right(frustrated)... What is below TDC? Did you mean before or after? Posted via Mobile Device __________________ 1972 C10 SWB, Air, PS, PB, 350/350THM. Second owner. 1965 Corvette roadster, 44K miles, 327/365 SHP, 4 speed, side exhaust, knockoffs, teak, second owner (bought in 1970), Have ALL numbers matching components. My frame off restoration thread: http://67-72chevytrucks.com/vboard/s...d.php?t=556703

10-20-2011, 10:35 PM	#4
68350 Senior Member Join Date: Jan 2002 Location: Williston, ND Posts: 2,999	Re: 402 just not running right(frustrated)... Sorry, before __________________ 68 Chevy CST/10, 50th Anniversary, 327/th400, 373 posi, buckets 68 GMC Shortbox Stepside, 402/th400, Tilt, Tach, Bucket Seats, 3.08 Positraction 69 Chevy Camaro SS, 383, 4 speed, positraction 70 Chevy El Camino SS396, Triple Black, 454/th400, Tach 70 Chevy Shortbox Stepside 4x4, 350/th350, Tilt, Tach, Cab Lights, Bumper Guards, Tow Hooks 70 Chevy 3/4 Longbox, 350/auto, 70k, SURVIVOR 71 Chevy Blazer, CST, 350/auto 71 GMC Sierra K2500, 454, 4 speed, 4.10 posi, 37s 71 Custom/30, Open Road, 350/th400, tilt 72 Chevy Shortbox Fleetside, 496 Stroker/th400, Tilt, Tach, Bucket Seats, 3.42 Posi 72 GMC Sierra Grande 2500. 427/th400, tilt, a/c, tool and stowage, buckets/console, 3.54 posi

10-20-2011, 10:36 PM	#5
68350 Senior Member Join Date: Jan 2002 Location: Williston, ND Posts: 2,999	Re: 402 just not running right(frustrated)... At first, it was about 18 before at idle, and it acted basically the same as far as losing power above 2-2500 __________________ 68 Chevy CST/10, 50th Anniversary, 327/th400, 373 posi, buckets 68 GMC Shortbox Stepside, 402/th400, Tilt, Tach, Bucket Seats, 3.08 Positraction 69 Chevy Camaro SS, 383, 4 speed, positraction 70 Chevy El Camino SS396, Triple Black, 454/th400, Tach 70 Chevy Shortbox Stepside 4x4, 350/th350, Tilt, Tach, Cab Lights, Bumper Guards, Tow Hooks 70 Chevy 3/4 Longbox, 350/auto, 70k, SURVIVOR 71 Chevy Blazer, CST, 350/auto 71 GMC Sierra K2500, 454, 4 speed, 4.10 posi, 37s 71 Custom/30, Open Road, 350/th400, tilt 72 Chevy Shortbox Fleetside, 496 Stroker/th400, Tilt, Tach, Bucket Seats, 3.42 Posi 72 GMC Sierra Grande 2500. 427/th400, tilt, a/c, tool and stowage, buckets/console, 3.54 posi

10-21-2011, 07:18 AM	#7
into69z "brand new second-hand" Join Date: Feb 2007 Location: White House, Tennessee Posts: 526	Re: 402 just not running right(frustrated)... i had a similar problem and it was due to the vacuum advance unit from the distributor was hooked up to the wrong port on the carb. I am dealing with an eldelbrock carb, it has one port for non-emission control vacuum and one for regular ported vacuum. The motor was set at 18 degrees btdc and would stumble at around 3000 rpm-switched the vacuum line and all is good. check the book on the ports for your carb-could be similar __________________ Steve 69 3/4t custom camper tilt,am/fm,speed warning,air gauge,buddy buckets,aux battery, big block,p/s,p/b,a/c 67 Camaro 96 Impala ss-sold 04 hybrid Honda-saving gas for the blue truck!:b69:

10-21-2011, 06:56 PM	#8
68Gold/white Registered User Join Date: Sep 2011 Location: Ark City, Kansas Posts: 3,405	Re: 402 just not running right(frustrated)... It seems like you have a vacuum leak. Plug off the PCV, and vac advance one at a time to make sure one isn't leaking. Make sure the carb base gasket is sealing, is it new??? or used??? Ive re-used base gasket several times, but they quit making a seal, when you least likely need them to... Idle RPM, depends on your cam. A stocker or mild cam could/should be around 750 RPM in gear, w/ vac advance plugged. TO set the idle screws (w/ vac advance plugged), screw one in, until the engine starts to NOT to run smooth, then back it out 1/4 turn. Then do the other. Takes a little time... IF you have an aluminum intake, The intake bolts need to be retorqued several times (only re torque them when the engine is stone cold) keep checking them until they don't loosen up any more...

10-21-2011, 07:23 PM	#9
SOON2BLAZE Account Suspended Join Date: Aug 2005 Location: Southern UT Posts: 906	Re: 402 just not running right(frustrated)... My BBC is at 44 BTDC and pulls 17-18" of vacuum, idle is 750-800 rpm's if this helps

10-21-2011, 07:49 PM	#10
69sixpackbee Registered User Join Date: Jan 2001 Location: Sabinal, Texas Posts: 1,706	Re: 402 just not running right(frustrated)... I run my 402 at 16BTDC and limit the total centrifugal to 10. Runs like a scalded cat!

10-21-2011, 08:18 PM	#12
SOON2BLAZE Account Suspended Join Date: Aug 2005 Location: Southern UT Posts: 906	Re: 402 just not running right(frustrated)... doooh!

10-21-2011, 09:06 PM	#13
68350 Senior Member Join Date: Jan 2002 Location: Williston, ND Posts: 2,999	Re: 402 just not running right(frustrated)... Well, I definetly had my fair share of dumb moments last night. I forgot to plug the vacuum advance while timing it, redid it and it maxes out at 6 before. So I am going to pull the distributor tomorrow and move it over a tooth so I can retard it a little more. I will let everyone know if it solves my issues. I checked vacuum and its dang near perfect. __________________ 68 Chevy CST/10, 50th Anniversary, 327/th400, 373 posi, buckets 68 GMC Shortbox Stepside, 402/th400, Tilt, Tach, Bucket Seats, 3.08 Positraction 69 Chevy Camaro SS, 383, 4 speed, positraction 70 Chevy El Camino SS396, Triple Black, 454/th400, Tach 70 Chevy Shortbox Stepside 4x4, 350/th350, Tilt, Tach, Cab Lights, Bumper Guards, Tow Hooks 70 Chevy 3/4 Longbox, 350/auto, 70k, SURVIVOR 71 Chevy Blazer, CST, 350/auto 71 GMC Sierra K2500, 454, 4 speed, 4.10 posi, 37s 71 Custom/30, Open Road, 350/th400, tilt 72 Chevy Shortbox Fleetside, 496 Stroker/th400, Tilt, Tach, Bucket Seats, 3.42 Posi 72 GMC Sierra Grande 2500. 427/th400, tilt, a/c, tool and stowage, buckets/console, 3.54 posi

10-21-2011, 09:22 PM	#14
Lee H Registered User Join Date: Jun 2010 Location: Upland Ca Posts: 4,147	Re: 402 just not running right(frustrated)... While dist is out make sure the shaft and mechanicals are free and well lubed. Springs should be light and easy to advance. Posted via Mobile Device __________________ 1972 C10 SWB, Air, PS, PB, 350/350THM. Second owner. 1965 Corvette roadster, 44K miles, 327/365 SHP, 4 speed, side exhaust, knockoffs, teak, second owner (bought in 1970), Have ALL numbers matching components. My frame off restoration thread: http://67-72chevytrucks.com/vboard/s...d.php?t=556703

10-21-2011, 09:30 PM	#15
jtp67-72 Registered User Join Date: Apr 2007 Location: dequincy la. Posts: 1,465	Re: 402 just not running right(frustrated)... Not retard it--advance it..............jim __________________ Build thread at http://67-72chevytrucks.com/vboard/s...d.php?t=475791

10-22-2011, 11:04 AM	#16
68350 Senior Member Join Date: Jan 2002 Location: Williston, ND Posts: 2,999	Re: 402 just not running right(frustrated)... Well my other BB runs amazingly at 14 before, so thats where I'm going with this one. __________________ 68 Chevy CST/10, 50th Anniversary, 327/th400, 373 posi, buckets 68 GMC Shortbox Stepside, 402/th400, Tilt, Tach, Bucket Seats, 3.08 Positraction 69 Chevy Camaro SS, 383, 4 speed, positraction 70 Chevy El Camino SS396, Triple Black, 454/th400, Tach 70 Chevy Shortbox Stepside 4x4, 350/th350, Tilt, Tach, Cab Lights, Bumper Guards, Tow Hooks 70 Chevy 3/4 Longbox, 350/auto, 70k, SURVIVOR 71 Chevy Blazer, CST, 350/auto 71 GMC Sierra K2500, 454, 4 speed, 4.10 posi, 37s 71 Custom/30, Open Road, 350/th400, tilt 72 Chevy Shortbox Fleetside, 496 Stroker/th400, Tilt, Tach, Bucket Seats, 3.42 Posi 72 GMC Sierra Grande 2500. 427/th400, tilt, a/c, tool and stowage, buckets/console, 3.54 posi

10-22-2011, 02:59 PM	#17
jtp67-72 Registered User Join Date: Apr 2007 Location: dequincy la. Posts: 1,465	Re: 402 just not running right(frustrated)... going from 6 to 14 will do wonders --and that is advancing it........jim __________________ Build thread at http://67-72chevytrucks.com/vboard/s...d.php?t=475791



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10-22-2011, 09:30 PM	#18
68350 Senior Member Join Date: Jan 2002 Location: Williston, ND Posts: 2,999	Re: 402 just not running right(frustrated)... Ok, I get what ya mean by advancing it. It seems to run a lot better but still not up to snuff so I'm gonna have my uncle look at it tomorrow and tune the carb and timing. He is pretty amazing at it so I'm hoping all goes well. __________________ 68 Chevy CST/10, 50th Anniversary, 327/th400, 373 posi, buckets 68 GMC Shortbox Stepside, 402/th400, Tilt, Tach, Bucket Seats, 3.08 Positraction 69 Chevy Camaro SS, 383, 4 speed, positraction 70 Chevy El Camino SS396, Triple Black, 454/th400, Tach 70 Chevy Shortbox Stepside 4x4, 350/th350, Tilt, Tach, Cab Lights, Bumper Guards, Tow Hooks 70 Chevy 3/4 Longbox, 350/auto, 70k, SURVIVOR 71 Chevy Blazer, CST, 350/auto 71 GMC Sierra K2500, 454, 4 speed, 4.10 posi, 37s 71 Custom/30, Open Road, 350/th400, tilt 72 Chevy Shortbox Fleetside, 496 Stroker/th400, Tilt, Tach, Bucket Seats, 3.42 Posi 72 GMC Sierra Grande 2500. 427/th400, tilt, a/c, tool and stowage, buckets/console, 3.54 posi

10-22-2011, 09:37 PM	#19
jtp67-72 Registered User Join Date: Apr 2007 Location: dequincy la. Posts: 1,465	Re: 402 just not running right(frustrated)... you'll never have a bigger grin on your face than when driving a c10 with a good running big-block!!!!!!.............lol..........jim (well maybe when u see what LSU did to Auburn!) __________________ Build thread at http://67-72chevytrucks.com/vboard/s...d.php?t=475791

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