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Old 10-14-2004, 09:01 PM   #1
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I'm Rich!

Well at least my engine is...I'm pulling my hair out over how rich my engine is running. Here is the deal:

On the last two trips I've noticed smokey exhaust and a rich smell mostly at start up and idle. This week I had a friend follow me up a local hill and he reported a noticable amount of black/brown smoke from the exhaust when under load. I have also been going through fuel pretty well lately. At first I freaked out that someting big was wrong but a compression check showed all eight between 155 and 160psi. No oil consumption, no oil in the breather, no oil on the plugs, etc....so phew!

But all eight plugs are sooty - very sooty. Tailpipes are sooty - very sooty. As a baseline, here is a quick review of some of last year's related maintenance; rebuilt carb, new mechanical and electrical fuel pump, all new fuel filters, new air filter, pvc valve, breather filter, brand new distributor cap rotor and coil, new accell wires, new platinum plugs, all new vacuum tubing, new exhaust headers, new free flow exhaust.

Since my [albeit inexperienced] carb rebuild was to factory spec (no hot rodding here) and I can't directly adjust the mixture on the QJet (without cutting in to the baseplate and exposing the idle mixture screws) I'm thinking about things like plugs and timing.

Basically I'm grasping at straws as to how to isolate this issue and solve it.

Tomorrow I'm replacing the sooty platinums with good ole' champions and I'll quadruple check the timing....but I could really use a fresh perspective and some new ideas on things to check.
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Old 10-14-2004, 09:18 PM   #2
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Q-jets . . . . bah

Did you replace the float in the Quadrajet?
Have you checked manifold vacuum?
Did you check timing centrifugal advance?
Did you check vacuum advance?
Are you sure you had the carb vacuum advance plugged when you set the timing?
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Old 10-14-2004, 09:37 PM   #3
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Quote:
Originally Posted by swebster
Since my [albeit inexperienced] carb rebuild was to factory spec (no hot rodding here) and I can't directly adjust the mixture on the QJet (without cutting in to the baseplate and exposing the idle mixture screws) I'm thinking about things like plugs and timing.
Swebster,


I hate to be the one to break this to you, but the best thing you could do at this point is to gingerly remove the Q-jet, carry it lovingly away from the vehicle, then toss it with all your strength into your neighbors yard while yelling expletives. Feels better now, doesn't it?



In all actuality, the Q-jet is an extraordinary carb, with a limited lifespan. Yours it appears, has used it's up. When new, around the mid 60's, they were amazingly fuel efficient and powerful. As the years progressed though, without the benefit of new molds from GM, the 'ol Q-jet started it's decline. Although there have been many changes and updates, all the way through to a quasi-computer controlled version, the casting, as in your case, has had it. Rebuilding yours won't help, remanufacturing (not the same) might, but that's not something you or a mechanic can do.



The two main problems on your Q-jet are most probably the welch plugs inside the main body, which come loose and leak fuel, and the fuel well in the center which tends to warp over time and...leak fuel. Both are common problems, with companies like Champion and Tomco making kits to attempt to reseal them, but it's not worth the effort at this point.



Two obvious options at this point would be to buy a new Edelbrock Q-jet, made with a brand new mold and many improvements by Weber-Redline, the actual manufacturer, or buy a Holley 'remanufactured' Q-jet. The reman is 'much' less expensive than the Edelbrock, but you may need to go through 2-3 before you get one that works right. The Edelbrock, although pricey, is a much-improved design, even though it is visually similar to the old one. You would have to offset it's cost with the expected use of the vehicle.



Although the Holley remanufactured Q-jet can work fine, I would not recommend Holley's 'new' aftermarket replacement. It is a variation on their performance carbs, and although it is a good design for a daily driver, doesn't tend to like extended periods of inactivity, and usually needs to be rebuilt quite often if it sits unused. This isn't always the case, but common enough to be problematic. I hope this helps.


John-Boy
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Old 10-14-2004, 10:26 PM   #4
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Quote:
Did you replace the float in the Quadrajet?
Have you checked manifold vacuum?
Did you check timing centrifugal advance?
Did you check vacuum advance?
Are you sure you had the carb vacuum advance plugged when you set the timing?
Replaced the float. Manifold vacuum at idle is close to 20 inches, 10 at 65 mph (this as measured by the dash gauge - in know i know not the most accurate gauge but it what I got

Replaced the entire distributor this spring including centrifugal advance, vacuum advance, pickup, coil, cap rotor - everything. (old dist had some sticking weights)

Timed with the vaccum advance disconnected and the tube plugged.

Quote:
the welch plugs inside the main body, which come loose and leak fuel
Thought about this one. I did not seal these when I did the rebuild and should have. One of my ideas is to pull the carb and seals these with JBWeld as a last ditch effort. Also can check main body gasket for leaks. The casting was perfectly straight when checked and the carb was providing good economy with good looking plugs prior to the rebuilt. I rebuilt it because the secondaries where not working correctly among other issues related to performance.

I looked at the Edlebrocks before. There is also a west coast outfit that has developed rebuilds specifically for RV use as well. I'm really hoping to keep this carb long enough for me to fund an FI conversion next year. Hate to spend the bucks right now on something I don't want to keep.
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Old 10-14-2004, 11:05 PM   #5
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Quote:
Originally Posted by swebster
The casting was perfectly straight when checked and the carb was providing good economy with good looking plugs prior to the rebuilt. I rebuilt it because the secondaries where not working correctly among other issues related to performance.
Is this an accurate description, the vehicle performed OK, i.e., not rich or black smoke before rebuild, only after? That could help determine the problem. What performance issues were you having? For the secondaries, there is a choke linkage kickdown lever that won't let the secondaries open unless the choke is 'full open'. If that lever is misadjusted or stuck in some way, or otherwise not functioning, the secondaries would never open regardless of engine temperature and/or throttle position.

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Old 10-14-2004, 11:11 PM   #6
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I think John-Boy is on to something. My GMC never ran right after i rebuilt it, until I disconnected the auto. choke and put on a manual choke.
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Old 10-15-2004, 07:09 AM   #7
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Prior to the rebuild the secondaries would not open due to gummed up linkages. I originally got into all of this when the MH would not climb hills on a trip (read Help - MH can't climb hills for more info).

I did have a problem post rebuild with the choke partially closing when warm but that was corrected with a replaced heating element connector. Now the lockout releases with full open choke and the secondaries open fine.

Does this info help?
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Old 10-15-2004, 07:46 AM   #8
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My 80' Oldsmobeater does the same thing until it gets warm. It's issue is clearly the automatic choke. It is a temp based unit and when it's less than 70 degrees, it tends to run VERY rich and while sitting at an idle for even a few minutes, I get two black soot marks on the pavement. Not that I think it is the same issue as yours, but just thought I'd add it just in case yours runs well after it gets to oper temp.
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Old 10-15-2004, 08:33 AM   #9
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Twink,
Yeah...mine is definately very rich on startup. I get the soot marks on the pavement as well. Once it warms up it runs fine; no stumbling or bogging, oo other typical "too much fuel" symptoms....but even after a good long ride the plugs are very sooty and I still get some dark smoke from the exhaust even at idle.
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Old 10-15-2004, 08:41 AM   #10
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Quote:
Originally Posted by swebster
Prior to the rebuild the secondaries would not open due to gummed up linkages. I originally got into all of this when the MH would not climb hills on a trip (read Help - MH can't climb hills for more info).

I did have a problem post rebuild with the choke partially closing when warm but that was corrected with a replaced heating element connector. Now the lockout releases with full open choke and the secondaries open fine.

Does this info help?
OK, let's see if I've got this right so far. Secondaries did not work before, you've cleaned the linkage and replaced either the divorced choke spring and/or it's linkage, and now the secondaries work fine. If the choke opens fully after engine runs for approximately 5 minutes, then it to is fine.

Door #2, the engine did not run rich or black smoke before rebuild, but does now. If you know the choke is functioning correctly, then the problem is in the carb and associated with the rebuild. Possibilities are;
1. The new float has a hole in it and is full off fuel, not allowing the needle and seat to close.
2. The float adjustment is incorrect, causing the same problem.
3. The needle and seats have dirt/debris in them (can be quite small, and still be problematic), causing the same overflow problem
4. Bent/missinstalled metering rods.
5. Loose or uninstalled jets

These aren't the only possibilities, but the most common. If the info in paragraph one is correct, then I would remove the top of the carb again and check for the above listed items.

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Old 10-15-2004, 09:32 AM   #11
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John-Boy,
I certainly suspect something with the rebuild could be the issue - after all I did it myself and it was the first carb I've ever done (if you don't count the side draft strombergs I had on my 280zx in college ).

As a "book learner" I followed along with the book "Rebuilding Your Rochester Carburator" very closely. Triple checked everything but certainly could've done something wrong.

I plan to replace the plugs and check the timing today at lunch and run her. If there is no change then the carb is coming off and I'll run through the list; float setting, seal the welch plugs, check the needles and seaths, check everything again and see what's left.

Still hoping I can use this carb for a bit longer.
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Old 10-15-2004, 09:48 AM   #12
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Quote:
Originally Posted by swebster
Prior to the rebuild the secondaries would not open due to gummed up linkages. I originally got into all of this when the MH would not climb hills on a trip (read Help - MH can't climb hills for more info).

I did have a problem post rebuild with the choke partially closing when warm but that was corrected with a replaced heating element connector. Now the lockout releases with full open choke and the secondaries open fine.

Does this info help?
EEEEEEKKKKKKKKKKK!!!!

Did you play with the screw on the top curb side rear of the carb?

Getting the top door for the secondaries to open by simply revving the motor with no load should not be easily done.

Lets start with baseline idle mixture.

You have a vacuum gage so VERY easy to set. get it idling about 750rpm. Watch the vacuum gage and adjust till you pull the highest vacuum. The premise is the higher vacuum you pull the more efficient the motor is running the closer to a stoic fuel mixture. After you find that high point give both idle screws a 1/8 to 1/4 turn lean (clock wise). At idle you best running lean because it will load up if your at all rich. No load at idle so problems from detonation. Gets the stink out at idle. The transition from idle to the mains on line is handled by the accelerator pump so it should not make a dead spot coming off idle unless there is a problem with the accelerator pump.

Now if you messed with the spring tension on that top door add a little tension back That will help lean it out a little buy lessening how much the secondaries come on. If you did not mess with it then try lowering your float level.
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Old 10-15-2004, 10:37 AM   #13
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Quote:
Originally Posted by 59toaster
EEEEEEKKKKKKKKKKK!!!!

Did you play with the screw on the top curb side rear of the carb?

Getting the top door for the secondaries to open by simply revving the motor with no load should not be easily done.

Lets start with baseline idle mixture.
toaster - I don't even know what screw you are talking about so I doubt that I "adjusted" it on purpose.

The secondaries do not open at all under no load. I know they open now only because after the carb rebuild I ran her up and down some hills with the doghouse and air cleaner top off to see what the carb was doing. Man do they open! Sounds like an airplane toilet flushing....scary!

If I remember correctly I'll need to remove the base plate and cut out the plugs in front of the idle adjustment screws.
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Old 10-15-2004, 10:51 AM   #14
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I have nothing useful to add, you guys are already above my level of expertise.

But I do like your use of 'imagery', and enjoy reading your thread.

Quote:
Originally Posted by swebster
Man do they open! Sounds like an airplane toilet flushing....scary!
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