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Carb -- To Rebuild, or Not to Rebuild

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GA72TR6

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My 78 Midget shows signs of running rich...hesitation under a heavy foot, black fouled plugs, occassional backfire, and hints of black smoke at the tailpipe. Cleaning and replacing the plugs solves the symptoms temporarily, but after 15 miles or so, she's back where we started. The hesitation is no good in heavy traffic...gunna get swashed....or just stuck somehere having to call AAA.

I'm opening the water choke this week to see if she's opperating properly (runs like the choke's on all the time) but if that's not the culprit, I assume I need to look toward the carb. I can adjust the mixture with a special tool I have to order and, since I have to pay S/H anyway, was considering a carb rebuild kit and new needle "while the hood is up."

Assuming the H20 choke is OK, is the total carb rebuild going a bit too far to solve my problem, or should I just start by turning the adjustment screw and keep on driving? My goal is to just get solid throttle response, stop fouling my plugs, smoking, and smelling...and be able to get out of the way in rush hour traffic! Any wisdom you can share?
 
You didnt say how many miles on the carb, but it sounds like the water choke is stuck or is bad, also check the rubber diaphram in the dashpot if they tear or get a hole in them they run real rich. Most of the other guys here dont like the Bosch platinum plugs, but ive never had one foul. Good luck
 
Water chokes are notorious for giving problems. There is a procedure out there for checking them. Do a search on this forum to find a link for it. Also, make sure your ignition circuit is healthy before adjusting on the carbs. A good many carb problems end up being ignition.
JC
 
I vote for the bad diaphram. In a Spit with same engine I experienced similar problems PLUS giant balls of flame out the exhaust on over-run and about 15 MPG. Bob
 
If you are getting back fires, check your ignition timing. Then check out this article about the ZS choke...

https://theautoist.com/zs_water_chokes.htm

I would say unless you have a good reason not to rebuild the carb, I would rebuild it anyway. It will only improve your driving experience.
 
I prefer Webers myself. I looking to see if I can squeeze a Holley into the midget. /ubbthreads/images/graemlins/smile.gif
 
Though there are those here to disagree, I find Weber carbs as bullet-proof as SU's when properly set up. The only unit in the "fleet" here without a 40-DCOE Weber induction system is Diesela. If I could pump diesel fuel thru one she'd be "shod" with 'em as well! /ubbthreads/images/graemlins/devilgrin.gif
 
Morris, EXCELLENT article! It got it printed, laminated, and inserted in my shop manual's "appendix" this morning. I read it right AFTER I had finished following that same procedure, fumbling through a less-than-well-illustrated shop manual. The only thing I didn't check was the proper function of the heat mass device using a hair dryer (whoops!), but I'll see if everything else does the trick before opening her back up and dumping coolant all over the floor again (plus, that little joker is expensive!). Everything else checked out and I cleaned up things which did seem a bit "sticky."

While the "hood was up," I also replaced the diaphram (which didn't appear to be damaged, but for $7, you might as well while it's open).

I'm going to adjust the major/minor mixture controls on the side of the carb (thought the only one was inside the daspot piston via a specialized alen wrench...live and learn). Then I'll slap in a new set of clean plugs and drive and see what happens over about 20 miles.

Regarding the backfiring, it only did that when the plugs were truely filty and, after posting, I realized that I had only about 1 gallon of gas in the tank, too, so she might have been starving.

If you clean the plugs and drive, it works fine for about 5 miles, then progresses to sputtering over the course of the next 10 miles or so. Clean plugs, repeat. Could make for a long cross-country trip! Since its a progressive problem, I don't think spark/timing is the issue.

Since the popping, I removed the fuel filter "just for fun" and found rust behind the filter on the tank side...looked like my grandfather had been spitting tobaco into my fuel filter!!! So, I'm putting a new tank and line kit on order and refrshing the filter. The old filter appeared to be clearing most of the garbage from the carb, but I wonder if that rust could have been my problem all along?

Updates to follow adjustments to the richness screws...hoping for happy motoring soon!
 
Well, I made the richness adjustments and she certainly does idle better/smoother, but their's still black smoke and stinky at the tailpipe after running for about 20 minutes and the plugs are getting blackened again. The H2O choke and the in/out lines are getting nice and warm, but I'm guessing the choke is still on. A new heat mass sensor (I assume the culprit since it's the only thing I didn't check) is about $70 and a manual choke conversion is about $110. Anyone have an argument one way or the other? I'm leaning toward $110 to replace the whole unit and take control from the cockpit where I don't have to get my hands dirty!
 
[ QUOTE ]
Anyone have an argument one way or the other? I'm leaning toward $110

[/ QUOTE ]

I wrote you a PM, Robert. Did you not rec'v it /ubbthreads/images/graemlins/confused.gif

There are TWO conversion on the market. One is a SERIOUS PITB to do and the other ABC. I stock the ABC one and it's a lost LESS that above. /ubbthreads/images/graemlins/grin.gif

Please contact me direct.

/ubbthreads/images/graemlins/cheers.gif
Ed
 
You can pick up a chock conversion at your local big box auto parts store in the "HELP!" section. They run about $15. Probably not as nice as the ones offered by Moss, VB, etc.

I would seriously reccomend rebuilding the carb and replaceing the needle before doing the manual choke conversion. You can lock out your water choke so that it does not activate at all to see if it is actually the source or your rich problem.
 
Morris, your suggestion is intriguing. How would I go about "locking out" the water choke to find out if it's the culprit? Also, I noticed at the tail end of that article you linked to in a prior posting a reference to turning the H2O choke housing which allows the choke to turn on/off sooner/later. Sounds like a potential spot for calibration?

I was VERY careful when I disassembled and put it back together exactly like it was. However, as the article suggests, a PO could have put it back together incorrectly anyway, so I may have replicated an earlier problem. It's hard to tell from the pics in the article and from catalogue diagrams - do you know what positions the water inlet and outlets should be at in relation to the carb if everything is hooked up properly?

Along similar lines, when I reinstalled the heat mass sensor over the choke, I inserted the little metal operating arm of the choke into the curved slot on the inside of the sensor, making sure it fit into the slot and through the coil that’s inside the sensor (like it was before). I assumed this was the correct fitting, so as the coil inside the sensor expands and contracts, it moves the choke on and off. I assume that’s how it goes together, right?
 
"Morris" said:
[ QUOTE ]
You can pick up a chock conversion at your local big box auto parts store in the "HELP!" section. They run about $15. Probably not as nice as the ones offered by Moss, VB, etc.


[/ QUOTE ]

Just so you can do a DPO type job?? /ubbthreads/images/graemlins/pukeface.gif

So that you become a CDO?? /ubbthreads/images/graemlins/nopity.gif

I happened to be picking up a couple cases of oil for shop today and checked out "HELP" section. That is NOT a "choke Conversion" by ANY stretch of the imagination!! /ubbthreads/images/graemlins/nonono.gif

A REAL kit contain FOUR machined parts especially for the CORRECT job. Plus cable and items to stop the water flow.

Course I've only been doing this since these cars were NEW. /ubbthreads/images/graemlins/angel.gif

What ever blows your dress up or whatever floats your boat!! /ubbthreads/images/graemlins/thumbsup.gif

/ubbthreads/images/graemlins/cheers.gif
Ed
 
To lock out the choke enrichment, you must force the spade looking thing at the top of the picture below, to the other side (left side) of the choke housing. I have done this in the past by inserting a small dowl that forces the "spade thing" to the left.


Zs1005.jpg

picture courtesy of TheAutoist.com


Before doing this, remove the three screws that hold the heat mass housing on and remove the black plastic insulator. Now fire up the car. If everything is working, the "spade thing" should move from the right all the way to the left. If the "spade thing" does not move as such, then the small vaccuum hole that runs between the carb and choke body is probably clogged. This would cause your choke enrichment to be on all the time.

While you have the heat mass housing off, let the car warm up and check the movement of the coil. Mark it's final position on the heat mass housing. You can use this mark to help you calibrate things when you put it all back together.


Another thing you may consider checking is the float bowl level. If it is too high or running over, it can cause your car to run really rich.

I agree with Ed that the HELP! choke conversion is cheesy. But it will work if you are on tight budget. If you are not on a tight budget, go ahead and rebuild the carb and buy a good choke conversion.
 
I think I've ruled out the "water" portion of the water choke. The choke is possitioned just like the one in your pic, Morris. The sensor heats up and, when warm, the little coil inside the sensor moves nearly 1/2 inch from right to left (from the driver's perspective) after just a few minutes. I assume that's enough, as it moves nearly all the way across the arched opening.

Next, I moved the "spade thing" inside the choke body. It only moved when you press the accelerator, which feels like it "releases" it, and when it does, it moves from right to left about an 1/8 turn. Is this sufficient movement to turn the choke off, or is it still on? With a little force, it feels like it could go farther and the movement doesn't appear to be terribly smooth.

When I do this, there appears to be a little less smoke, but it's still there and the car still sputters under acceleration, smokes black, and stinks a bit too much for a positive "public appearance" at the local Starbuck's.

Think it's just gummed up between the choke and carb? I'll tear that apart and clean that tonight. If that doesn't work, how would I go about checking the float bowl level?
 
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