A Shocking experience -- Pulling plug wires

[ronzet]

LBC Gurus...

So, my A is back together after the head gasket adventure.

It runs well but idles miserably...

I used the ol' pulling the spark plug wires (the SHOCKING experience) to see which cylinder is bad and found that 1 and 2 cause the engine to run worse... 3 and 4, however, made little to no difference, although the spark from the cable to the plug is nice and sharp when placed in proximity to the top of the plug
....

I pulled the #4 plug, put the cable on it and set it against the block, and started the car to check for spark at the electrode.. nice and sharp, replaced and then repeated on the #3 plug, same result.

I am VERY suspicious of the rear carb (that <span style="font-style: italic"><span style="font-weight: bold">in general</span></span> feeds #3 and #4 cylinders.

I have tried to adjust it to see if there is a change in condition... to no avail....

Any suggestions????

 

[Steve_S]

Are you sure the carbs are balanced? Are the floats set properly? Do the pistons rise together?

 

[ronzet]

Steve,

Thanks for the note.

I did balance the carbs, with the aiflow balancer tool, before I had torn it apart fixing the head gasket....As I think about it, even then it had a rough idle .. It is, if anything, more pronounced now.

I have no answer to your troubleshooting queries, yet...

However, before I start dismantling the air filters and ancillary hardware to access the carb intake....

Is it your considered opinion that the back carb, and maladjustment, are a potential cause of the symptoms I have articulated???

 

[DrEntropy]

I'm late as usual, but Steve has suggested the same thoughts I have. Rear carb as suspect #1. Check for vacuum leaks at shaft and mount as well. Try that before you pull filters, etc. Spritz something (carb cleaner, WD-40, etc.) on the two holes at the body of the carb where the shafts go thru, and around the mount gaskets. If there's a leak, it'll be evident.

<span style="font-style: italic">
EDIT: Be advised! Carb cleaner is FLAMMABLE and you should be cautiously UN-liberal if you use that!</span>

 

[GB1]

<span style="font-style: italic">
EDIT: Be advised! Carb cleaner is FLAMMABLE and you should be cautiously UN-liberal if you use that!</span>

UN-liberal with a fire extinguisher in the other hand :wink:

 

[Steve_S]

Another consideration would be fouled plugs, but I would still suspect the rear carb or fuel delivery to the rear carb based on your symptoms. Have you tried swapping front and rear carbs and see what happens?

 

[DrEntropy]

Ooohhh.... new diagnostic technique!

I'd want step-by-step pix. :smirk:

 

[jlaird]

Yep, me as well. Not sure you can swap front and rear carbs.

 

[Hap Waldrop]

Have you tried swapping front and rear carbs and see what happens?

That would be a interesting set of carb linkages

 

[ronzet]

Gentlemen...

I could mount them upside down... (imagine a devil with a smirk here)

Actually, If I could swap them it would be a great way to trouble-shoot it... but a bit too much work at this point.. removing all of the linkage and then trying to figure out how it goes back together afterwards....

Just to pose a theory... If, in fact, the fuel is not getting to the jet on the back carb, it would have a rough idle and then, at speed, the front carb would be providing the fuel and the air as the back only providing air into the manifold. I do sense a lack of pep even at speed.... (If pep can be associates with 62 HP)...

Anyway, based upon the comments, 'me thinks' my suspicions are, at this juncture, warranted.... soooo.... let's take a closer look at the back carb...

Any comments on a Webber conversion???

By the way.. I do miss the little emotion faces that we once had at our disposal....

 

[dklawson]

Well, the (tongue in cheek) suggestion was made to swap the carbs. How about swapping the plugs and seeing if the poor running condition stays with the cylinders or with the plugs.

Out of curiosity.... When you balanced the carbs you had to have the throttle linkage loose. How about the choke linkage? Did you have it disconnected and the fast idle screw backed out?

 

[DrEntropy]

All too good. Ron, ya have an imbalance. Doug has hit it with a ~completely~ independent front-to-rear starting point. :thumbsup:

 

[ronzet]

Actually guys...

When I balanced the carbs before the head gasket schtuff, the linkage was loose, permitting each carb individual adjustment....with an SU Airflow meter...

In this current situation I have adjusted (balanced) the carbs, also individually -loose linkage -- and the AIRFLOW is balanced. The problem with the balancing assumes that the fuel flow is properly -- well-- flowing.

That is the rub.. I suspect that the jet in the rear carb is either inoperative or marginally operative... ergo, no fuel reaching the throat.

Steve had suggested a fuel delivery problem and DrEntropy concurred. There are quite a few other things that I have checked and have eliminated several other possibilities. I am now pretty sure that the fuel feed (jet) is bad and the corroboration helps... Although the proof in the eating -- so to speak.

I will undertake the removal of the rear carb and check my rebuild thereof....

Thanks for your comments and suggestions... I will let you know.

 

[Deleted member 3577]

The fuel level in both jets should be the same...
lift the needles out of the way.
Try sucking the fuel out of both jets to start with.
Then turn the fuel pump on until it stops clicking.
Check to make sure the fuel is about 1/8" to 1/16" from the top of the jet.
Adj float to give correct fuel level.

Another check would be to run the car as you normally do and pull the plugs to check color.
(The 1st thing I always do anyway)

 

[DrEntropy]

It strikes me that this "seat of th' pants" approach to finding and fixing "driveability issues" is part of the charm of our old lumps. What fun woukd there be in connecting a multi-prong plug to 'em and reading OBD-II codes?!? Scant challenge in that and hardly a chance to learn what's going on inside the beast. "Replace the X Thingie". feh.

I consider it arcane knowledge, not obsolete information.

Not unlike wizardry. :laugh:

 

[Deleted member 3577]

Yep...I find myself using a more intuitive approach as time goes on.

After I thoroughly figured out how they work, I can figure out why they're not working much easier.

So far as carbs go....
Everything has to be exactly the same between the 2.

So something is different...

What is it???....

Could be just some gunk lodged in the jet where the fix is as simple as momentarily putting your hand over the carb to clear it.

Could be something really goofy like a needle valve that works sometimes & not at other times.

 

[DrEntropy]

Yep...I find myself using a more intuitive approach as time goes on.

After I thoroughly figured out how they work, I can figure out why they're not working much easier.

Words of pure wisdom, Dave. And they apply to about everything in life, cars to computers and particle physics.

...now if I could just figger out how wimmen work...

 

[dklawson]

Ron, in my first post when I asked about the linkages being loose I'm sure you had the throttle linkage loose.

I was more concerned about having the choke linkage loose and the fast idle screw backed out. I have forgotten to loosen and back-off the choke settings on my car and found that while airflow was balanced, the idle appeared to be wholly dependent on one of the two carbs.

 

[ronzet]

dklawson,

Thanks for the comment. In my post I was trying to be as clear as possible in explaining the steps that I have taken to troubleshoot the problem. I THINK that I had backed out the fast idle screws but will check it again.

I had rebuilt the carbs during the engine rebuild. I find myself questioning the rebuild of the carb since, as I mentioned, it never has run as smoothly as I would wish even though, throughout my de-bugging, I have fussed and fiddled with the carbs to get an even idle....to no avail.. It just has not run as well as it should... Having eliminated most of the other causes, I keep coming back to the carbs....

'Tis not a major project removing and disassymbling the carbs to check my work.... I wish that I could swap the carbs - front to back - as Steve had suggested - but that is not a possible alternative...

<span style="font-weight: bold">UNLESS... someone knows a way to check for fuel flow before I tear it apart????</span>

 

[Steve_S]

The "suggestion" to swap carbs front to rear was a joke, just so we're clear. It can't be done. :wink: