What's new
CK5
Register an account today to become a member! Once signed in, you'll be able to participate on this site by adding your own topics and posts, as well as connect with other members.

Advice needed on a friends truck

76k5blazerr

76k5blazerr

Git-er-dun
 Premium
Joined
Nov 13, 2013
Posts
1,587
Reaction score
744
Location
North Carolina
I'm working on my friends 78 blazer for him, it's got a 400 with an edelbrock 1406. He recently got it back out from sitting for 6 months or so. He brought it to me and I have so far replaced the master cylinder, calipers, pads and collector gaskets for the headers, it had a major exhaust leak. Now I'm trying to get it to run good. I just rebuilt the carb. Took it for a test drive and it is still stumbling off idle and running rough up till about 2000 rpm and then it smooths out. It was missing before the carb rebuild and I found out a plug wire was bad so I put a new one on it and now it's better but still missing on driver side. Going to pull plugs when it cools down. What do you guys think about the stumbling issue? Need ideas, trying to get it done and back to him by the weekend.
 
Check timing, might want to advance it a little to help with a stumble. Also check for a vacuum leak causing it to go lean off idle.
 
Greg Ducato said:
Check timing, might want to advance it a little to help with a stumble. Also check for a vacuum leak causing it to go lean off idle.
Click to expand...
I was thinking vacuum leak myself, his truck still has the factory cruise control and stuff so there are miles of vacuum hoses. Is there any vacuum lines I should check first? Ones that would make the biggest difference it the way it runs if they were leaking? I also will borrow my neighbors timing light and check the timing. What should it be at? 8-12 BTDC?
 
check any and all vacuum lines, it only takes one, make sure distributor receives full manifold vacuum, not timed vacuum
 
Excuse my ignorance... I have never really had a problem with vacuum lines since I've had my old trucks. How exactly do I tell if I have a bad line? Do I need one of those vacuum gauges or can I feel it?
 
You can do the squirt bottle trick. Fill a bottle with water and squirt on the lines, and any gaskets that affect vacuum. They will temporarily seal up from the water, and you will notice it idle better for a second.
 
10-12 btdc is where I'd start. I just tuned a 350 I put in a Nova (pulled from a 76 truck) motor needed 10 before it ran right, and pulled hard from idle at 13 btdc. It also had a Edelbrock carb.
 
I think I would change the plugs, wires, cap, rotor, fuel filter. Plus check the timing, vac leaks
 
Possible the accelerator pump cup dried up after sitting that long...that can cause a hesitation or lag when you step on the gas..(it may get better and even go away if the fresh gas swells it back up to size again )..
As suggested already,a vacuum leak can do much the same thing too..
I use a can of carb cleaner,with the straw nozzle--spurt some on suspected areas like hose ends that may be split,gaskets between the carb and intake--you'll hear the idle be affected right away if you find a leak..

Also make sure the vacuum advance works ,you'll hear the idle speed go up when you connect its hose to manifold vacuum if its working...also ensure the centrifugal advance weights are not rusted stuck and "snap back" when you turn the rotor by hand and release it..

I bet more than one plug wire isn't 100% if you found a bad one too..
 
diesel4me said:
Possible the accelerator pump cup dried up after sitting that long...that can cause a hesitation or lag when you step on the gas..(it may get better and even go away if the fresh gas swells it back up to size again )..
As suggested already,a vacuum leak can do much the same thing too..
I use a can of carb cleaner,with the straw nozzle--spurt some on suspected areas like hose ends that may be split,gaskets between the carb and intake--you'll hear the idle be affected right away if you find a leak..

Also make sure the vacuum advance works ,you'll hear the idle speed go up when you connect its hose to manifold vacuum if its working...also ensure the centrifugal advance weights are not rusted stuck and "snap back" when you turn the rotor by hand and release it..

I bet more than one plug wire isn't 100% if you found a bad one too..
Click to expand...
Yeah, after watching some youtube videos i'm going to try the carb cleaner trick tomorrow, accell. pump rubber pieces were fine when i was in the carb today. Borrowed neighbors timing light so tomorrow going to check timing and for vacuum leaks. Im betting I find a big one. Hopefully I do cause I'm running out of ideas! I too think the plugs and wires need to be replaced but thats the kind of thing he can do on his own so if he wants i'll just let him replace them.
 
Wont hurt to make sure all the plug wires are on the right cylinders too--its easy to swap #5 and #7 for example,and that will make it run lousy at idle and rough till it gets up some RPMS..

I found those 2 wires swapped on more than one truck I bought that "needed a valve job",according to the previous owner...:surepal:
 
On that 1406 carb you have 3 settings in the throttle pump arm. You can switch to the lower hole and get a quicker throttle pull out of it to remove some of the stumbling hesitation.

Also if you rebuilt it you may have noticed a few filter screens in the kit, One that goes on the fuel intake, and another down inside the carb.
You can use one or the other but not both.
Don't do what I did and install both screens, it slows down the fuel flow too much.
There are a bunch of tech videos on the Edelbrock website that can be helpful.
 
pblaze725 said:
On that 1406 carb you have 3 settings in the throttle pump arm. You can switch to the lower hole and get a quicker throttle pull out of it to remove some of the stumbling hesitation.

Also if you rebuilt it you may have noticed a few filter screens in the kit, One that goes on the fuel intake, and another down inside the carb.
You can use one or the other but not both.
Don't do what I did and install both screens, it slows down the fuel flow too much.
There are a bunch of tech videos on the Edelbrock website that can be helpful.
Click to expand...
Just adjusted the timing and sprayed down the vacuum lines, no leaks that I can see or hear. Going to test drive in a bit and see if it made a difference, seems to idle a little happier, if it's still stumbling I'll switch the arm to the lower hole.
 
Ok so just took it around the block, not stumbling anymore off idle, so that's good. Still kinda shaky when getting up to speed. Still misfiring also, going to pull all the plugs tonight after work and check them out. New plugs and wires may be the ticket.
 
I agree fuel filter, check fuel lines, could be trying to close at certain speeds. If it is HEI might consider the spring kit for timing advance, clean dizzy good. Full tune up. Oil change can't hurt either. Since you rebuilt the carb I assume you have the air fuel mixture set. I always did mine using the tach and then seat of the pants test.
 
Plug wires go bad with age. If one was bad they all need to be changed. Run your hand along wires. If you get a jolt you will know they are bad. Or mist wires with water when dark. You will see them arcing all over. If it has a HEI dist, remove cap and rotor. If the back side of rotor has a burn mark in center, it needs to be replaced. Also remove vacuum line from dist. Plug hose and take a test drive. It could be the vacuum advance
 
You must log in or register to reply here.

Latest Posts

Top Bottom