Carb Choke Plate to Provide TBFI Properties

[Joseph812]

I guess that if I could afford to drive the car much, I could justify spending a few hundred dollars for a new carb.

[shadows]

you are missing the point
you've been going round and round
there are basics you are missing

[Joseph812]

Saying to take it to a mechanic was way missing the point. That was missing many points really, probably more than I should bring up. One that I did mention is that the car is most likely beyond economical repair, and that means a mechanic working on it might be considered ethically questionable.

Also, if I don't mention the basics, that doesn't mean I haven't thought about them, and it's not necessarily wrong going round and round, because as time goes on, the situation has to be re-evaluated, often looking at things again. In general, reviewing options is a good thing, not bad.

I have many reasons not to take it to a mechanic. I'd say that you wrote that for public consumption, and I found it lacking sensitivity toward me, to put it mildly. I ask that if you find my thread tedious and annoying, please ignore it.

Thanks and take care

[Joseph812]

I'm going to try to forget about that unfortunate spat, no hard feelings toward Shadows. I was feeling better about the car running again and that scrape really sapped a lot of that away. But so here goes.

I have ordered the repair manual and hopefully that will detail the operation of the accelerator pump and let me know how easily replaceable it is. A working acc pump would work wonders just by itself.

On another note, I was thinking more about the choke plate dynamically being able to do some adjustment of the fuel/air mixture, which led me to a possibly easier alternative to consider. One goal is to be able to richen up the mixture just enough to get beyond that warm-up period where the engine can't develop any power, when pressing the gas pedal causes stalling.

Its runability has greatly improved since I did that suction therapy on the carb, by totally choking off the air for a few seconds and cranking the engine. That was when it seems that blockages got sucked out of the carb passages. Now it runs as good as it did years ago. Maybe doing that sucked rust out of the way--fuel tank rust that somehow got past the fuel filter.

Back to the choke idea--the first thing I want to do is see if the plate can close all the way, and if not, why not. I suspect that someone left it maladjusted for some reason, possibly during work on the emissions improvement they were trying to get years ago, after which, the whole runability issue began. Maybe the carb came with the maladjusted choke plate, and it was still like that after they put that new carb on there several years ago. Once it passed that emission test, it was good enough to get by. And, I didn't care much then since I was doing a lot of work on my electric motor drive system, including charger and motor controller, that I designed all from scratch and installed on one of my bicycles.

My goal is to discretely do some things without adversely affecting the emission output. But since I only drive very rarely when I really have to, it's not critical if the emissions aren't perfect, especially since the car has 200,000 miles on it. I doubt that I drove it much more than 1000 miles in the past ten years since I can't get out there much and don't want to go out much, anyway. I would have liked to set up car sharing with my neighbor, and then have just one functional car between the two of us, but he went into the nursing home. And, I ride the bicycle down to the produce market to get food, for the most part.

[Joseph812]

I thought it would be good to get back and update about this project. I will just summarize the last things I did because the whole story of what I've done on this project is too long.

I got a repair kit for the carb and replaced the bad components in the accelerator pump circuit, I should add that at least the top seal (for the accelerator pump rod) was bad. I could tell it was working better after that, but still not good enough, by far.

Since I then had the exploded diagram of the carb that came with the rebuild kit, I could see there was also an auxiliary accelerator pump (diaphragm). It seems to be much more than auxiliary, though, since how it was operating was keeping the rod-actuated pump from doing much of anything.

The way the "aux pump" was behaving was to absorb the pressure from the rod-actuated pump (which is implemented through the gas pedal). So, the aux pump was dissipating the pressure the rod pump was trying to generate, not letting enough pressure to build to push gas out into the throttle body.

As far as I can tell, the aux pump must always have engine vacuum on it so that when the engine loses vacuum from fuel starvation, the aux pump diaphragm relaxes and tends to force gas into the throttle body and also permits the rod pump to build pressure so it can add to the injection effect.

I noticed that the hose going to the nipple on the aux pump housing was not having vacuum all the time. Why, I don't know. Best I can figure to do on this car is to splice into the manifold vacuum going to the choke pull-off and run that to the aux pump. Last night when I tested it like that, it made the engine functional as far as I can tell. Didn't get a chance to test drive it, though.

It turns out that the aux pump does basically what I had originally thought of trying with the choke plate last summer when I considered using a drop in engine vacuum to cause extra gas to go into the engine automatically. I had actually considered trying to add an extra external pump of some type, even, at one time. I'm glad that I know how to get the carb do that now in pretty much it's stock state.