New have engine question

[1shot1yote]

Hi I'm new to the forum.  I have an 83 chevy but i've put in a rebuilt vortec engine, it's all stock no hot cam or anything.  Running a carb intake and edelbrock 1405.  The motor doesn't seem to be running on all cylinders.  I have tried two HEI distributors.  One new and one used.  I have checked valve adjustment twice but i'm going to triple check again in the morning. 

It seems to idle ok and run good under full throttle.  The carburetor was used, I have not rebuilt it but I've cleaned it twice.  The one thing I did notice was that the check ball under the brass weight is missing.  Could this be my whole problem?  If I pull the spark plug caps on the # 3, 5, 2, or 8 cylinders it doesn't seem to change the idle at all.  This seems wrong to me.  It had new plugs after the rebuild and I've put new plugs in it again.  When I slowly rev up the engine it seems to have a stumble around 1400 rpm.  It will surge and then fall off.

I will add I'm running a Summit external fuel pump, but I think I've ruled out over pressure cause I've unplugged the pump while the motor is running and it doesn't change at all.  Oh yeah brand new Accell plug wires too.
Any new ideas would be greatly appreciated, I'm pulling my hair out trying to figure this out.

Thanks
Justin

[rich weyand]

I'll repeat the advice I gave another fellow earlier this week:

Check that the vacuum advance is connected to the proper port.  This is real common with Edelbrock carbs.  The vacuum advance should not be connected to the passenger side port (ported vacuum).  It should be connected to the driver's side port (manifold vacuum), which is about the same amount off center on the carb on the other side, and a little lower.

Check to see if the choke is working.  Take off the air cleaner with cold engine and note position of choke plate.  Turn ignition on (no need to start engine) and observe choke plate.  After about 5 minutes, the choke plate should open fully.  If choke does not open fully, check choke electrical connectors for 12 volts whenever ignition is on.

Check ignition timing.  With the vacuum advance disconnected and the hole in the carb plugged, 12* BTDC at idle should be a good timing number to start with.

Check the idle mixture.  Screw the idle mixture screws in all the way (not tight!), then back out two turns.  Start the engine and set the idle to 700 rpm.  Back the screws out 1/4 turn.  Faster or slower?  If faster, back them out another quarter turn.  Keep repeating until it runs slower, then turn them in 1/2 turn.

If none of those do it, check the float levels.  For this you will need gaskets: http://www.jegs.com/i/Edelbrock/350/1499/10002/-1.  Adjust the float levels per page 8 of the Edelbrock carb manual: http://www.edelbrock.com/automotive_new/mc/carbs_acc/pdf/carb_owners_manual.pdf

Let us know how that stuff works out.

[454Man]

If you pull the plug wires and there's no Change id buy a plug wire tester. Or connect your timing light to see if your getting spark to the plugs....not going against the previously advised.

What's under the hood??? If you have to ask maybe we shouldn't race...

[1shot1yote]

Carb is a 1405 manual choke.  So choke plate is all the way open.  Vacuum advance is connected to manifold vacuum port. 
Timing is set to about 12 degrees BTDC.  The IMS screw on the drivers side will change the idle when I turn it, but the one on the passenger side doesn't seem to do much.  I've checked the plugs with a spark plug grounded out against exhaust manifold and I'm getting good spark.  Have also checked with timing light.  When I had the carburetor apart the last time I set the float levels.  Maybe the carb is just wore out, it was used.  I'm pretty much out of ideas.

Thanks
Justin

[Irish_Alley]

just thinking. but its weird how every other plug in the firing order is screwing up.

[rich weyand]

just thinking. but its weird how every other plug in the firing order is screwing up.

Yeah, and it's the first and last on the P side, but the center two on the D side.  Weird.

That P side idle screw gives a hint.  Sounds like the orifice is clogged up.  No fuel from one-half of the carb at idle will certainly !@#$ things up, and if it's not a dual-plane manifold could result in the stated symptoms.

Pull the P side idle screw out, shoot some carb cleaner down there, and let it sit a bit, then replace the screw and adjust.  See if you can get that side operational.

[1shot1yote]

I checked all the valves again so I'm positive it's not valve related.  I'm going to buy a carb rebuild kit and try that tomorrow.  I think I've ruled out everything else.  I'm hoping that fixes it.

[Engineer]

Ok, are you running a dual plane intake? Look at the intake runners on your intake.

If you have a dual plane (factory type) the right hand side of your carburetor feeds cylinders 2, 3, 5, 8.

Since you say the truck runs fine off idle then we can direct our attention to the idle circuit on the right hand side of your carburetor. Are there idle mixture screws? Is the one on the right screwed all the way in stopping all fuel flow?

Ignore your ignition, there is nothing wrong with it.

[rich weyand]

I already told him to clean out that idle passage, but sounds like he'd rather rebuild the carburetor.  For practice, I guess.

[1shot1yote]

Intake manifold is a square bore design dual plane, Summit racing for Vortec heads.  I've taken the carburetor apart twice and cleaned it.  I started out with the IMS screws one and a half turns out.  Like I said the carb was used so it could maybe use a rebuild.  I'll try some carb cleaner in the idle screw ports and see if that helps.  I need to get the check ball that goes under the brass weight because that is missing.  I'm not sure how much of an issue that is? 

Thank you for all the replies any new ideas gives me something to check.  I'll try a few things tomorrow and report back. 

[rich weyand]

OK, so let me talk about that dual-plane manifold for a moment.  The idea of a dual plane manifold is to have each half of the carb feed half the cylinders.  Each side feeds every other cylinder in the firing order.  What this does is reduce the intake pulses by half in each side of the manifold.  Since the firing order is 18436572, that means that 1, 4, 6, and 7 are fed by one side of the carb (driver's side), and 8, 3, 5, and 2 are fed by the other side of the carb (passenger side).  Those last four numbers sound familiar?

When you say 2, 3, 5, and 8 act like they're missing, and you have a dual-plane manifold, we think "OK, one side of the carb is buggered, and it's the passenger side."  Then when you say that "The IMS screw on the drivers side will change the idle when I turn it, but the one on the passenger side doesn't seem to do much," we can confirm what we already knew, the passenger side of the carb is buggered.  Both of those screws should affect the engine the same way. 

So something is wrong on the passenger side of the carb, and one place to start is to make sure that idle passage isn't plugged up.  It could be something else on that side of the carb that is affecting 2, 3, 5 and 8, and then the idle screw doesn't do much because that side of the carb is buggered for other reasons, but that is one thing to make sure of.

I'm not sure what you are talking about when you say "the check ball under the brass weight", but would it be on the passenger side, perhaps?  You don't mean the fuel valve under the float, do you?

[Irish_Alley]

OK, so let me talk about that dual-plane manifold for a moment.  The idea of a dual plane manifold is to have each half of the carb feed half the cylinders.  Each side feeds every other cylinder in the firing order.  What this does is reduce the intake pulses by half in each side of the manifold.  Since the firing order is 18436572, that means that 1, 4, 6, and 7 are fed by one side of the carb (driver's side), and 8, 3, 5, and 2 are fed by the other side of the carb (passenger side).  Those last four numbers sound familiar?

When you say 2, 3, 5, and 8 act like they're missing, and you have a dual-plane manifold, we think "OK, one side of the carb is buggered, and it's the passenger side."  Then when you say that "The IMS screw on the drivers side will change the idle when I turn it, but the one on the passenger side doesn't seem to do much," we can confirm what we already knew, the passenger side of the carb is buggered.  Both of those screws should affect the engine the same way. 

So something is wrong on the passenger side of the carb, and one place to start is to make sure that idle passage isn't plugged up.  It could be something else on that side of the carb that is affecting 2, 3, 5 and 8, and then the idle screw doesn't do much because that side of the carb is buggered for other reasons, but that is one thing to make sure of.

I'm not sure what you are talking about when you say "the check ball under the brass weight", but would it be on the passenger side, perhaps?  You don't mean the fuel valve under the float, do you?

listen to this man, if you want to fix your ride.

[1shot1yote]

Thank you for the replies.  I did not realize that the passenger side of the carb fed those cylinders.  I wish I would have asked this question about a week ago I could have saved some time.  I'll see what I can get figured out in the morning.  The check ball I'm talking about is for the accelerator pump.  It's under the squirter nozzle there is a brass weight and then a little check ball. 

[rich weyand]

That's the pump discharge weight and the pump discharge ball, numbers 37 and 38 in this diagram.  This check valve keeps the accelerator pump from leaking gas into the primary barrels unless the accelerator pump is providing a minimum pressure.  It will be hard to tune the carb properly without this in place, but it will not cause the problems you are reporting, and in particular will affect both sides of the carb equally.
http://www.volvord.com/view.htm

Pull the idle screw, fill the passage with carb cleaner, let it sit for a bit, then blow it out with some air and replace and adjust the screw and see what you get.

[1shot1yote]

I would like to report back that the problem is solved.  I bought a carb kit this morning and a gallon of carb cleaner.  Completely disassembled carb and soaked for and hour or two, and then blew everything out with air.  Reassembled with new carb kit and all is well.  Both IMS screws work as they are supposed to. 

I have a question about tuning.  I adjusted the idle mixture screws as per manual.  But now the idle is a little too high and the air screw is backed completely off.  How do I get it to idle down a little more. 

Thanks to all for the help, especially Mr. Weyand.