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And don't be surprised if you don't have that horizontal, spring looking thing between those carb throats. That's a hot idle compensator and not on all models -- Right W. Guy ?
Verne- I suppose I'll remove the air cobe again to team that vertical passage. Thank you, I missed it! All the others are totally clear.
Test drive a few minutes ago no change. Still improving idle speed by going "full lean" on the minutes screws. Car still runs better than ever, but I know I can't keep "feeding it cheeseburgers."
Verne- I suppose I'll remove the air cobe again to team that vertical passage. Thank you, I missed it! All the others are totally clear.
Test drive a few minutes ago no change. Still improving idle speed by going "full lean" on the minutes screws. Car still runs better than ever, but I know I can't keep "feeding it cheeseburgers."
Benton,
Just so you know, the marks left on the inside of the throttle bore are made when the blade is closed (engine not running). When the engine is running and the throttle arm is against the stop screw, the blade is open somewhat. What I mean is that mark you see is not an indication that the blade is at a "good" position when it's running.
Now you say there's "no change". Does that mean you can completely close off the idle mixture screws and the engine will still run?
Benton,
Just so you know, the marks left on the inside of the throttle bore are made when the blade is closed (engine not running). When the engine is running and the throttle arm is against the stop screw, the blade is open somewhat. What I mean is that mark you see is not an indication that the blade is at a "good" position when it's running.
Now you say there's "no change". Does that mean you can completely close off the idle mixture screws and the engine will still run?
Verne
Verne- yes, there is no change in the situation- taking the mixtures screws all the way in continues to raise the idle.
And yes I understand there is a visible ring where the blades close, I was hoping the amount of the "slot" visible in the photo would be some help. The blades are indeed closing- at least to the eye. I can dismount the carb and take a photo of it underneath but I was attempting to show that the vertical slot has a tiny amount showing below the blade - again to my eyes.
The saga continues. The car isn't stumbling in the least and shows no ill effects other than smelling a little rich and the all-important symptom of the mixture screw issue... This issue is consuming me.
If anyone would be willing to take a phone call about my ongoing issues please PM me, I may need to skip ahead and speak to someone about all this. I will be happy send my phone number or call you whenever you prefer.
I feel like I'm clogging up the forum relentlessly posting about my issues.
If anyone would be willing to take a phone call about my ongoing issues please PM me, I may need to skip ahead and speak to someone about all this. I will be happy send my phone number or call you whenever you prefer.
I feel like I'm clogging up the forum relentlessly posting about my issues.
I'm sure you are just LOVING the repeated teardowns, but I wanted to point out a couple other places that need to be free of any blockage.
Under the venturis you will see two holes (toward the front of the carb) These are the passageways for the idle vent in the venturi to reach the mixture screws. At the bottom of each of these holes, there is a small hole that leads down to the mixture screw. Spray some solvent in each one and make sure it comes out of the threaded holes for the mixture screws. (screws removed)
Also, when you have the venturi clusters removed, make sure this hole in the side of the emulsion tube is also free of blockage.
I feel like I'm clogging up the forum relentlessly posting about my issues.
There are plenty of people trying to help you, so there's no need to feel that way. People just get annoyed when they give suggestions and the poster doesn't come back with results, in which case, they feel like they're wasting their time.
Chin up. Every problem has a solution, and you are putting in the effort
Verne- thank you for both replies. and for the clearly marked photographs. I'll probably do these tomorrow early afternoon. I think I have #2 photos cleared but I do need to check a prior post for one more hole to check on that assy.
As for your photo showing the carb body holes to the mixture screws, I will check them well also. I suspect they are flowing - only evidenced by the fact that they react to closing by helping the mixture go lean.
I will complete this work.
I *feel* like I may have a primary or secondary not closing but I haven't read how to adjust. Just yet. The only reason I'm thinking this- from a rudimentary standpoint is that the mixture screws are having an effect, idle quality is good in all cases, so good that the over rich situation seems to be coming from a metered source- as it produces a very reliable idle...
Still puzzling and thanks again for the time!
Last edited by ChattanoogaJSB; 04-30-2016 at 09:03 PM.
Yes, you should check that your secondary throttle blades are closed fully at idle. It's a mechanical linkage and not difficult to check. When idling warm, you could also press your finger down on your hot idle compensator to see if the idle changes.
There are many things that could be checked but it's difficult to list them all. This would be a lot easier if I had your carb on my bench, but this is cruising season and I know you want to find a quick cure.
Well, Verne...I removed the air horn and cleared/checked all the passages you were kind enough to reference. I also bathed the Pistons for the metering rods and the metering rods in my carb cleaner. I didn't think the Pistons were binding (and they aren't) but I just wanted to be thorough.
It was a little difficult to blow through at least one of the idle circuit passages you mentioned in the main body of the carb- so I had hoped I had fixed the issue.
After a thorough warm up- no change. Idles nice at 600, takes power well, does not smoke (at least from the car view) etc. but the mixtures screws leaned still improve idle speed. So it's still rich.
The primary and secondary actions are both closed- to the extent I could discover anyway. The secondaries don't respond to any "push" closed and they operate open normally. The choke fast idle is not in play.
I am about to say it's time for a pleasure cruise- health effects be darned! I am mindful that I've probably been hard on it driving it this rich.
As of now the mixture screws are closed, idle adjusted back down to 600.
I'm sorry those other suggestions didn't solve the problem. I'm obviously shooting in the dark which is a good way to miss the target.
Did you remember to press down on the hot idle compensator (brass lug) while it's idling warm?
IF that doesn't produce any change, I'm afraid I'm out of blind suggestions.
I *feel* like I may have a primary or secondary not closing but I haven't read how to adjust. Just yet. The only reason I'm thinking this- from a rudimentary standpoint is that the mixture screws are having an effect, idle quality is good in all cases, so good that the over rich situation seems to be coming from a metered source- as it produces a very reliable idle...
Still puzzling and thanks again for the time!
While the AFB is more sophisticated than a Holley in many ways, the linkage adjustments are primitive. The accelerator pump link is one area where plyers are the primitive tool, and the secondary linkage is another. On the passenger side the long linkage arm can hold the secondary plates open. There should be a few thousandths clearance between the linkages to allow the secondary plates to close, and the tabs bent toward the carb body set the secondary shaft travel stops. These are all set with plyers and adjusted by eye.
I'm sorry those other suggestions didn't solve the problem. I'm obviously shooting in the dark which is a good way to miss the target.
Did you remember to press down on the hot idle compensator (brass lug) while it's idling warm?
IF that doesn't produce any change, I'm afraid I'm out of blind suggestions.
Verne
Verne! You have been a tremendous help to me along with the others. Thank you for the time and effort. I will attempt the hot idle compensator next time I warm it up. My reading indicted it would lean out the mixture to combat vaporization under extended hot idling scenarios so I don't know if it will help me since my rich mixture problem is trouble even at modest engine temps. But- surely- I will check it also
Again, many thanks!
Mark- I'm still giving your mega-vacuum "nuclear" option some thought. And soul searching my courage.
While the AFB is more sophisticated than a Holley in many ways, the linkage adjustments are primitive. The accelerator pump link is one area where plyers are the primitive tool, and the secondary linkage is another. On the passenger side the long linkage arm can hold the secondary plates open. There should be a few thousandths clearance between the linkages to allow the secondary plates to close, and the tabs bent toward the carb body set the secondary shaft travel stops. These are all set with plyers and adjusted by eye.
Thank you! I will dig back in tomorrow and see what I'm missing. Although both sets of Venturi seem closed, I am obviously getting fuel introduced in a very metered way.
I'm certainly eliminating possibilities with everyone's help.
Just wanted to let you know I'm not going to drop the ball responding to the sage advice I'm being given...
Benton, it sounds like you have cleaned all the internal passages at this point so the Mega Vacuum technique will most likely produce nothing at all. It only works to suck small blockages past the obstructions. Has no other value.
Glad it is running smooth and you can enjoy it.
Benton, it sounds like you have cleaned all the internal passages at this point so the Mega Vacuum technique will most likely produce nothing at all. It only works to suck small blockages past the obstructions. Has no other value.
Glad it is running smooth and you can enjoy it.
I can enjoy it, just have to suspend that nagging feeling.
Obviously I've improved things overall, the garage smells much less of fuel on shutdown.
I did order a rebuild kit for it, enough to allow me to tear it down and soak it for a few days in the middle of the week. Cannot hurt. I have also found that donor 3721 carbs are pretty cheap if I want to try my hand at another carb main casting or other parts.
Truthfully once I began correcting a few things I was fascinated to see how well the old engine could run, but before I spend more than a casual amount of money on it I should allow that I'm thinking hard about a Blueprint 355/390 crate engine in the fall, and just put the original to rest on a stand.
The converted manual choke has indeed been tied open and the fast idle cam is likewise disconnected - the only thing I noticed today is that the choke piston vacuum junction to the carb body had no gasket, and seemed a tad bit damp (the piston itself). I blocked off the vacuum passage entirely with some spare gasket. No test drive, both kids are home but I doubt this will make any difference.
Thanks again for the wisdom men- will write back after the rebuild.
This is an extreme long shot in the dark WAG, but I (as many others) have been baffled by the way your idle mixture screws behave.
After thinking about this for a while, I remember having some carbs back in the era of crude smog controls in the late 60s/early to mid 70s where the idle mixture screw function was actually reversed from the norm. In other words, full in was full lean and full out was full rich. They were set at the factory and then 'sealed" with plastic caps - which were usually soon crushed with a pair of needle nose pliers so the mixture could be richened up.
So - do you know the history of your carb? Is it original, or a later replacement? Possibly a smog era carb?
I said it was a long shot at best - but it might just explain the way yours has behaved, at least in part.................
04-30-2016, 10:44 AM
