Idle and acceloration...

[Nunyas]

Hi all,

I've been having some problems with my '76 B lately. The last thing I did prior to these problems showing up was replace the check valve on the exhaust air injection manifold, and clear out a blockage in the hose and consequently the inlet on the gulp valve. Initially after doing the above the car seemed to idle ok, but it hesitated under acceleration if i didn't slowly get the RPMs up to about 2K prior to letting the clutch out. Today while coming home from work I discovered my gulp vavle got stuck in the full open position and as a result it idled extremely lumpy and was a major pain to try and get to accelerate. I managed to get her home, and while poking around under the hood found the stuck valve and found the cause for it sticking. However, its still idling somewhat erratically now. I've triple checked the gulp valve and it definitely isn't stuck open anymore. Although, while checking it I did notice a ever so slight suction on the gulp valve intake. It doesn't seem bad and I would have to hold my thumb over the hole for 30 to 60 seconds to even notice that it's trying to suck in some air.

I poked around a bit more and cleaned the rotor (the distributor cap looks fine) and cleaned the plugs (1 & 2 were white'ish a result from the gulp valve getting stuck i suspect, and the 3 & 4 were a light golden brown).

Thinking my problem has to do with the mixture, I played around with the mixture some it's set to 3 flats from full rich (1/2 turn). Its still using the ZS carb, but it was converted to manual choke before i got the car. However, no matter how much I adjust the mixture I cannot get rid of the hesitation under acceleration. Also, as I mentioned earlier my idle seems to be a bit erratic now. If I try to set the idle for anything under 1500 RPMs the idle gets really really lumpy, and acts like it wants to stall (but doesn't). I thought I had set a good idle/mixture at some point, because I was able to get the car to idle smoothly at 1000 RPMs. But then after I let it idle for a few minutes it started to alternate between periods of lumpiness and smooth idling.

I should mention that when I got the car it always ran really really ritch, and upon inspection I found that the mixture needle retaining pin was bent into a 'C' shape and basically allowed the needle to sit in its housing with no spring tention. I've 'Mc Guyvered' a retaining pin to hold the needle below the level of the pin, but for some reason I think it may be causing the car to run too lean now. But I'm not absolutely sure because the symptoms are confusing me.

Also, I had a mechanic look at the car to help me figure out what all needs replacing for SMOG inspection and he pointed out to me that I have a *HUGE* dent in my catalytic converter (the stock cat was replaced with a 'universal' cat that now resides under the drivers floor pan) and what sounds like marbles rolling around in my muffler.

Any of you know if there is a single component that could cause my lumpy idle and hesitation (I say hesitation but it feels almost like mis-firing until the engine hits certian RPMs) under acceleration? It's really begining to annoy me because nothing I've done seems to help the idle much and I cannot get rid of the hesitation at all.

As always, I appreciate any input you guys may have.

 

[SilentUnicorn]

Hi Nunyas
My toyota with F/i had very similar systems,i r/r'd the egr valve it seemed to overall aggrevate the problem. turned out to be sucking air in from some rather weak fuel lines. so far anyhow...


I your case however i would toss the converter and muffler, i know you cant toss your converter but certianly replace it, and the muffler as well. Sounds like it is very possible that your exhaust my be possibly partialy plugged, not allowing your engine to breathe well. Marbles in the muffler? ...kewl.. /ubbthreads/images/graemlins/wink.gif

mark

 

[timbomath]

Hi Nunyas, Whenever my 79 (de-smogged) with ZS exhibits the symptoms you describe it's been because of an over lean situation. Adjust the needle a 1/4 turn to the right (richer)and see if it makes a difference, that may be too much but you'll at least get an idea if this is the problem. This is assuming you've done all the other usual stuff first: plugs, cap & rotor, valve adjust, fuel filter, etc. You can get the correct retaining pin for $5 from Moss or Victoria British, having the right stuff usually works best. The settings to put the air-mixture control in the middle of its range are: 2 full turns back from 'tight' for the big plastic plug and 2 1/2 turns for the center brass screw. Check for vacuum or air leaks as Mark suggests and make sure float level is correct and fuel pressure is adequate. That being said, let me also add that it will never idle like a Camry (or even a Ford for that matter).
Lots of luck'
Tim Matheis

 

[Nunyas]

Thanks for the tips guys. I've reset the air mixture screws back to middle, since I know I've tinkered with it in the past and didn't notice any changes to how the car ran (the last setting they were at was all the way in). It started raining on me before i could finish, and i couldn't get her restarted to move into the garage. So, i'll have to finish up with the adjustments tomorrow.

mark - yeah, the cat. and muffler are certainly on my list of things to replace.

Tim - I realize that it will never idle as smooth as any of the modern 4 cylinder cars (many of which i can't tell if they're running or not except for the exhaust sound), but I do expect my B to idle smoother than it does. Currently, it feels like the entire car has been turned into a 'Magic Fingers' bed that you find at many a motel... And stepping on the gas just amplifies the lack of smoothness. It's almost like its only running on half the cylinders.

 

[Nunyas]

Tim - I was just looking at MossMotors.com and could not find the pin that i referred to earlier. So, I double checked in Moss's and VB's catalogs and neither of them have the part listed. Which now has me questioning whether or not the pin belongs in there. If you look at the cut-away view of the piston at MossMotors.com (https://www.mossmotors.com/Shop/ViewProducts.aspx?PlateIndexID=28999) you'll see that they don't list it, nor do they show one being there.

I assume I'm correct in thinking that there should be a holding the needle in position, because without a pin the needle would be 'slack' and be susceptible to changing its position at will (to an extent). If i remember correctly, when i got the car it always ran extra rich (black smoke from the exhaust), and while i could lean it out some there was always black smoke present (without the pin it was varying the thickness of the smoke). With the pin installed, the black smoke is gone.

 

[timbomath]

Nunyas, It's #11 on the picture you linked to (it is not labeled in the cut-away picture)and is NA. (Looks like it is available from VB #3-6066 screw, needle locking.) It is a spring-loaded screw-in assembly that screws in the hole in the side of the piston with a pin that fits in a channel on the needle shoulder and keeps it from falling out yet lets it move up and down with adjustment. With your damper cap removed insert your mixture adjusting tool and turn it tight to the right (full rich) and back it off almost 2 full turns to put the needle in the middle of its range. It would be pretty hard to make something else work correctly. I'm sure I have an extra on a spare carb (a good thing to have when you're using the ZS). Let me know if you can't find one.
Tim

 

[Nunyas]

Tim-My interpretation of "Screw, Needle Locking" is the screw that goes into the side of the piston and prevents the needle from falling out of the bottom of the piston (this is what happens when I loosen it to place the *pin* in position above the needle). "Screw, Needle Locking" is this part:

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This is the location of the *pin* that I was referring to:

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I have the "Screw, Needle Locking", but I had to fab a pin to go above the needle (the car always runs far too rich without it). At least, I think a pin belongs there since I've read reference to a pin in that location here: University Motors, Ltd. . But seeing a lack of the part I 'fabbed' in any of the catalogs that I've looked through makes me wonder if it should be there.

 

[timbomath]

Nunyas, The only reference to a pin I can see in the UM article is the 'pinned tube' the allen wrench fits in. This is talking about the adjusting tool with the pin on the side to fit the notch in the piston to hold it in position while adjusting so the diaphragm does not tear. There is no pin in the area you have circled on the drawing because this would keep the adjusting screw (the short fat brass screw with allen socket and o-ring) from actually screwing into the top of the needle assembly. Which if it doesn't, means you actually have no way to adjust the needle height because the adjusting nut is held in place and draws the needle in or out as it screws into the top of the needle assembly. Your pin is probably just lowering the needle closer to its proper height which is what makes it run better with it in. From my measuring to bring the needle close to its proper height, screw the adjusting nut all the way to the right, (full rich- this brings the needle up and allows more gas past it in the jet), then back off (lowering the needle in the jet and closing off some of the gas flow) 2 - 2 1/4 full turns. This will probably still be a little rich, road test and continue to lean it about 20 deg. at a time until you notice hesitation or power loss.
Lots of luck,
Tim

 

[Nunyas]

Thanks for the information Tim. I think I've gotten her to run as smooth as she is going to get without replacing my exhaust (still stumbles a little from normal idle speeds, but not bad). If I go any richer she'll be belching out black smoke /ubbthreads/images/graemlins/frown.gif

I reread the UM article and the part that spoke of the pin that i fabbed myself is under "RUNNING RICH" section 5 (just above "RUNNING LEAN"). It would seem that the needle only comes as an "assembly"? Mine appears to have "disassembled" itself sometime prior coming into my ownership, because the car ran far rich even when I set the needle to full lean condition. I 'fabbed' a pin to go below the threads that the adjusting screw goes into to hold the needle in a fixed position relative to its assembly, and verified that it all moves in and out of the piston as it should, via turning the adjusting screw clockwise and anti-clockwise.