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68 327 Rough Runner

 
Dusty Diamond
I love my Chevy Chevette!
Posts: 4
Joined: 09/15
Posted: 09/13/15 07:00 PM

Hey guys- I just inherited a 68 327 Camaro and I'm having some issues getting it to run smoothly.  The car is super straight, has good fluids, rebuilt Edelbrock carb, clean plugs and a brand new battery.  The thing fires right up and revs really nicely in N, but once I throw it in gear it feels like it's gutless when put under any kind of load.  It sort of chugs it's way up through the RPMs.  It'll get places, but it's hardly a strong running machine at this point.  

I'm decent with a wrench, but this is my first small block V8 so I'm starting from scratch here.  I'm hoping to troubleshoot as much little stuff as I can before handing it over to a mechanic.

Thanks in advance! So excited to bring this baby back to life  Laugh  

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Just Try It1
My first time was in a Chevy
Posts: 165
Joined: 08/14
Posted: 09/13/15 10:23 PM

do you have access to compressed air???

count the half turns of the idle mixture screws as you lightly seat them.. then remove them...  give the idle mixture screw hole a 1 second shot of carb spray followed instantly with a blast of compressed air.  give it another blast of  carb cleaner followed by another blast of compressed air.. do both sides..  reinstall the idle mixture screws and lightly seat them then back them out the same number of half turns you counted when you started this..


what this does is blow out the idle feed restriction and the idle air bleeds...

those get debris sucked into them during normal operation ... especially when there is no air cleaner mounting gasket.

Afbidlecircuit Zps7ccb467d

35D5824f C301 4A1e 9D64 0Dbfe2c6dd71 Zps98f001e9

i cut away an old primary booster i had laying around from a water damaged AFB  

AFB AVS Primaryboosterdiagram Zpse535929c


you could have one side clogged and the other working fine..

you will know when you get it clean as you can at that point slowly come off idle to almost any speed and back down to say 1000 rpms then slowly up to 1500 and back to 800 rpms then back up to 1500 rpms again.. without moving the throttle so fast you are working the accelerator pump.

the idle circuit is controlled by the idle mixture screws..
the idle transition circuit is controlled by the idle feed restriction and the idle air bleeds.  

no amount of jet. metering rod or power valve spring changes will effect off idle flat spot issues.. as the primary main circuits are NOT FLOWING ANY fuel until above 1400 to 1600 rpm..   you can see the primaries start flowing with a mirror held so you can see down the primary bores..  at what rpm does the fuel start flowing from the booster ring..   everything below that is IDLE TRANSITION CIRCUIT..

it is totally possible that you have debris in the float bowl that has clogged the tiny passages..   look at the sediment i shook out of an thermoquad.. CAM01676 Zpszkhscgl5

i had actually rebuild that carb only a few days before.. handed them a quality fuel filter to install in line..  well.. they installed their clear fuel filter.. and that let all that sediment thru and clogged the carb again..

CAM01710 Zpswzjgvivb

CAM01711 Zpspxevyuhh

lastly... if your base idle speed setting is WRONG.. you could have exposed too much of the idle transition slot like this image...

Idlefeedpassageidletransitionslot Zps9d39547c

do you see the marks i added where the primary throttle setting should be at..

Holleyidletransitionslots Zps6a6ff870

if you are NOT Running a PCV valve.. may need one to allow you to have the best base idle speed with the primary throttle plates at the perfect position..  

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Just Try It1
My first time was in a Chevy
Posts: 165
Joined: 08/14
Posted: 09/13/15 10:29 PM

can you perform another test for me... this takes only about 5 minutes..

Wmdprhm


test 5 is kinda hard as you don't have an underhood fuse block..   you can perform test 5 between the positive battery post and the thick red wires into the horn relay on the inside of the radiator support..

test 6 is important also..  i broke the output wire on the alternator on my 67 camaro 327.. burned up my alternator in a second..  

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Dusty Diamond
I love my Chevy Chevette!
Posts: 4
Joined: 09/15
Posted: 09/14/15 10:01 AM

Interestingly enough, I went out with my multimeter to perform the above test and I was greeted with a dead battery.  I jumped the car and then disconnected the negative terminal so I can investigate where I might be getting a power drain.  

I thought the initial culprit was a bad battery, but it looks like there might be a power loss somewhere in the system Frown  

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Just Try It1
My first time was in a Chevy
Posts: 165
Joined: 08/14
Posted: 09/14/15 10:46 AM

please... SLOWLY recharge the battery on a battery charger.. at no greater than 10 amps setting on the charger..  if you have a 2 amp charge setting and your battery has been dead for a few days.. you will need to do it that way..   till you can perform the first part of the voltage drop test  to check the percentage of charge..

and please don't pull a battery cable off with the engine running..  you will blow the diodes in the alternator and will usually either burn the fusible link or drain the battery if just one of the diodes shorted..

diodes have a voltage and current rating.. most alternator diodes are rated at 25AMPs at 100 PIV.. peak inverse volts..  when you pull the battery cable off.. if the alternator is putting out current.. the voltage will increase in the split second that the voltage regulator needs to shut down the charging system to over 100 volts..  this will blow the diodes..

charge your battery up... hook up one cable.. touch the other cable to the battery post.... if it sparks.. something is drawing current..  you can hook a test light between the negative post and the negative battery terminal.. if the test light comes on.. there is something on..   because of my experience in auto repairs.. disconnect the battery again..  disconnect the output wire from the back of the alternator..  put some tape around the ring terminal..  do the one battery cable on and the test light in the  second one test again... if the test light is now out..  your alternator is blown out. .  

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Dusty Diamond
I love my Chevy Chevette!
Posts: 4
Joined: 09/15
Posted: 09/14/15 12:55 PM

So, I jumped the car (this was before I read your message) and measured the voltage on the battery terminals when running- 13.78. Turned on the lights and the radio, and it measured 12.95.  I let the car run for a few minutes and then shut it down.  The battery measured 12.10 as it sat.  I went inside for an hour or two and then went back out to take a reading on the battery terminals and the multimeter said 6.6?!  I
disconnected the negative terminal and took another reading and it read around 11.  

I also connected a test light between the negative cable (disconnected) and the positive terminal and the light did not go on.  

I'm going to grab a trickle charger tonight to give this battery a proper recharge per your advice.  Any idea why the volts would fluctuate so crazily with the negative cable on/off the battery??

Thanks a ton for your help man, I really appreciate it!  

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Just Try It1
My first time was in a Chevy
Posts: 165
Joined: 08/14
Posted: 09/14/15 01:11 PM

diagnostics with a DISCHARGED or DEAD battery don't give you a decent result..

something may be staying on..

with a fully charged battery... you can with a digital volt meter that reads at least 10Amps DC... you can perform this... engine off.. headlights off.. doors closed..

Current Draw

this is the volt meter that i use.. its cheep .. amazingly accurate..  and it has a 20Amp DC setting..

http://www.harborfreight.com/ac-dc-digital-multimeter-37772.html

its also not auto ranging.. which DRIVES Me crazy personally... having to wait as the meter cycles thru all the ranges for several seconds..  

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Dusty Diamond
I love my Chevy Chevette!
Posts: 4
Joined: 09/15
Posted: 09/25/15 02:40 PM

Quick update here.  I pulled the carb and blew out the idle mixture ports with carb cleaner and compressed air.  I also replaced some of the cracked rubber vaccuum caps.  Also checked the float bowls and they were clean as a whistle.  Put it all back on, and it fired right up.  Problem is, it's running no better.  Short bursts of throttle make the engine completely hesitate and it's barely able to chug it's way out of my driveway.

On the electrical side of things, I've found that I've got a parasitic draw and have worked my way through the electrical but haven't gotten it all sorted yet.  For now, I'm leaving the battery cables off until I can find what's draining the battery.  

Would it be logical to assume the battery dying issue is probably not related to the rough running issue?  I'm going to pull the fuses again and see if I can get that test light to go out when connected to the neg terminal and cable this weekend and see if I can find the main power drain.

Thanks for any help you can provide!   Confused  

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