carb issue????

[kasearch@ix.netcom.com]

I am experiencing an issue with my 1969 428/C6 CJ Mustang. The car is stock, numbers matching in every way, with all the original components. It was running poorly, so I gave it a full tune-up. (Fouled plugs). That is all that was done. After the tune, it was re-timed to specs, it started, and ran well – until I put it in gear. Once shifted in to reverse, or any of the drive gears, it heavily bogs down, immediately stalling the engine. Checked for vacuum leaks – NONE.

The carb was RESTORED in July 2019 and looks great, and used to run great. I began checking the carb for adjustments, and by using the vacuum gauge, I discovered a couple of things.  I am carrying 12 "vacuum on a steady needle at idle. In trying to adjust the air/fuel on the metering block (FYI- Holley 4150  9510-U, LIST 4609), I started with the recommended 1 ½ turns out. When adjusting the passenger side air/fuel, I was able to achieve a little better vacuum reading with minimal adjustment. While attempting to adjust the driver's side air/fuel, when the metering screw was turned all the way in, it had NO effect on the carb or the running condition. Turning it out caused it to run too rich. I could never get it to a point that I could shift it in to any gear without the bog. Any suggestions or thoughts?  Problem in the idle circuit? Only a bad metering block?

[TLea]

Very few carb restorers will take the time to remove well plugs in metering blocks and properly clean/un clog. Without that a carb will display exactly symptoms you are describing

[Bob Gaines]

The plugs in the metering blocks can be a pain to take out which is why many rebuilders bypass taking that step.

[FL SAAC]

Very few carb restorers will take the time to remove well plugs in metering blocks and properly clean/un clog. Without that a carb will display exactly symptoms you are describing

a big plus one on this

[Drew Pojedinec]

Depending on idle speed and tslot exposure, is a common thing that a cj style carb can idle with a mixture screw closed.

Is pretty rare that putting an engine in gear stalls due to a rich condition, typically the opposite is true. An engine leans out significantly when a load is placed on it.

If it was one of mine, contact me. If not, why not discuss with the builder?

I would look for outside variables tho. You mention "it used to run great."

This makes me pause and wonder what may have changed, carbs are really feedback devices of sorts, they only really react to given inputs.
Something as simple as initial timing changing could cause an otherwise perfect running carb to become a basket case.

Drew

[Royce Peterson]

Something as simple as initial timing changing could cause an otherwise perfect running carb to become a basket case.

Drew

This is true. Often "carb problems" are electrical in nature.

[rockhouse66]

Do you have a vacuum signal at the ported vacuum line while at idle?  I assume you are using ported vacuum to the distributor advance.

[kasearch@ix.netcom.com]

I do have vacuum at the distributor port. And I did email the restorer of the rebuild on Saturday. But what does it mean when stated that "Often "carb problems" are electrical in nature."

[shelbydoug]

When you are getting opinions on what the issue could be, in a large way, you are just getting feedback on the "likeliness" of the cause by symptoms described. Those are the symtoms that you have observed and they may not be 100% comprehensive?



In some ways, you have overlapping symptoms that are indicative of various possible causes.



I like the thought about questioning the positioning of the throttle plate in regards to the idle slot.

That could explain the lack of response to the idle adjustment screw.


Likewise, the lack of attention to the "emulsion tubes" is right in there as a possible cause. So the only thing that you can do is go down the list, one by one and verify that each of these items is NOT the cause.

Personally I have had issues with Holleys suddenly loosing their ability to idle without stalling.

This has always in my case been caused by an issue with the idle air bleeds or slots either being clogged or blocked OR an issue down in their wells (which for me is rarer).

It doesn't take much for a speck of something to block them individually or both simultaneously.


There are well replacement plugs available that are exactly like the originals.
So don't hesitate to consider removing them to verify that the tubes are thoroughly cleaned out of any kind of debris or even a corrosion build up.

They are not difficult to do but it is carb surgery and it needs to be put on the work bench and will take some time if you have never done one before.


It is probably unfair to blame the "rebuilder or the restorer" for lack of attention in those details since it is so easy to clog the idle air bleeds on a Holley to begin with.


The other thing is that, yes, you can send the carb to a competent carb tech but usually these folks have stacks of work in front of them before they can get to you so plan on a long down time if you go that route.


What electrical issues? Have you verified that the advance in the distributor is function properly? Have you verified that the points cam has zero play, side to side?

[rockhouse66]

If you have a measured vacuum signal to the distributor advance at idle then the distributor is advancing.  When you put it in gear, the vacuum drops and the distributor retards and the engine no longer has sufficient idle speed.  This is just one of many possibilities.  If your restorer adjusted the secondary butterflies improperly that is one possible cause of this condition.

[Royce Peterson]

But what does it mean when stated that "Often "carb problems" are electrical in nature."

Just that. Drew mentioned that the distributor initial advance may have changed. I would make damn sure the distributor is correct before I claimed I had a carb problem.