My truck has a currently well functioning, but it seems, lean calibrated (ex Ca) feedback 2150 carb, that I planned to replace with a 4v Edelbrock carb & manifold when it gave any issues.
It's given me up to 17.5 mpg, but the plugs run white - the oxygen sensor appeared near new when I bought the truck 23,000 miles ago.

A few days ago I found this mixture-solenoid delete link http://www.cardomain.com/ride/500837...ar-cab/page-3/

Has anyone done/know of this conversion?

If it gave a good tuning result, with a little more power & no negative side-effects.......the cost would be zero until I install the Edelbrock parts later.

I could also de-computer my truck (DS III ignition is already gone), & tidy the engine bay a bit more

Thanks

 

Ken - If I understand what you have, it is a DS-II ignition but still running the feedback 2150 controlled by the computer in a closed-loop mode via the oxygen sensor. Right?

If that's the case I guess I don't see the advantage to deleting the solenoid. That would give you a fixed mixture when what you have now is a variable mix controlled by the computer. In other words, you would go from a mix that should be correct for many situations to one that is correct for one situation.

I say that from having watched the air/fuel ratio meter on my truck. It is amazing to me that the apparent AFR changes so significantly over the operating range. For instance, at low speeds the Edelbrock 1406 is giving me something like 13:1 while at highway speeds it gives something higher than 15:1, which is as high as the meter reads, and that's w/o tipping into the throttle enough to lift the metering rods. Put another way, I can see an inverse correlation between air flow and AFR - the more the flow the leaner the mix.

So, if the best economy is by running an AFR of something like 15:1 then the carb isn't going to do that at lower speeds since you don't want the AFR at higher speeds to lean to the point of misfire. Wouldn't it be nice if you had a computer that could control that? One that was tied to the same signal I'm seeing, the one from the O2 sensor? Wait! That's what you have!

However, I'm not saying you shouldn't change to an E'brock manifold and carb when the time comes. I really like that combination on my 351M, even though the 2150 is a good carb.

 

Right. And despite their reputation, it seems to be working pretty well & reliably.

I guess to ask my question another way - with the computer still in control, is it possible to enrich the mix slightly (given the plug color, even with short distance running)?

Or am I making too much of it? I haven't had the truck on an exhaust analyser.

 

That I don't know. However, raising the float level might make it a bit richer. On the other hand, I'm not comfortable with using plug color to tune an engine that hasn't been on an analyser. I say that because it is possible to change the plug color by going to a colder or hotter plug. Or, by changing the ignition timing. But neither of those change the AFR, just the temp of the plug - either directly or indirectly.

My thinking is that to use plug color you'd have to have put the engine on an exhaust analyser to get a baseline so that you know the plug isn't so hot that it is cooking off the extra fuel and showing white. Or, so cold that it is fouling even when the AFR is good. Once you know that the plug color is representative of the fuel mix then you can use plug color to tune carburetion as long as you don't change the plug type or engine timing.

 

I am not familiar with DS-III, but I know on a TFI-IV system, even if you leave the carb and computer in place, without the ignition control as well, the carb does nothing, and my 84 ran full lean like yours seems to be doing.

 

I was wondering the same thing. I don't know how the computer would react, but you would think with no rpm info, it cannot make any mixture decisions and tell the carb what to do can it? It get's the engine rpm from the original distributor system doesn't it?

 

The DS-III I pulled off got the RPM from a TDC sensor down by the timing pointer. There was a reluctor behind the harmonic balancer. If that is still there then the computer could be thinking it is changing the timing, but everything else would have to be in place, like the TAB and TAD relays. I guess I leapt to that conclusion - without asking.

And, btw, I haven't been getting email notification of posts on this thread. Just happened to see y'all had posted.

 

We just had a PC melt-down, so I'm not managing to keep up.

My truck is like Gary's regarding the crankshaft sensor, which is still there.

But the previous owner's mechanic told him it was inoperative, & solely cosmetic, for inspections.
The same mechanic had done the DS-III delete for an earlier previous owner - I think because of repeat crank sensor/DSIII problems.

82F100SWB - Did you go to a non-feedback carb, in the case of your 84?

 

If the crank sensor isn't working then I doubt the computer is controlling the carb. It won't know RPM and will have its knickers in a twist to the point it would have put timing in limp-home mode. Surely it would also put AFR in some safe mode as well, probably full rich.

In that case, I think it is time to put the delete kit on.

 

Ignition should be OK because it's now DS-II, but I should get an exhaust analysis done.

It would just be good to know EXACTLY how the feedback system operates (in case there are options) before I throw this carb.

 

Not wanting to hijack my own thread, but I think there are drawbacks to the 'tunnel ram' effect of the exposed frontal intake on our trucks.

With EFI (or a correctly operating feedback carb) it wouldn't be an issue; but with a conventional carb & no oxygen sensor, you would think there must be some wild AFR fluctuations at times that are only being somewhat corrected by the power valve.

If the intake was still collecting cold air but from a location sheltered from 70mph headwinds, you would think it would be a much more stable situation for maintaining vacuum & the AFR.

 

IIRC, the computer controls the vent to the bowl by pulsing it, which changes the pressure of the air inside the bowl, thereby changing the AFR. But, that's a dim recollection. Someone on here has played with manual controls for a feedback carb and, again, IIRC, explained how the system works. I tried searching for that thread but didn't find it. Will try a bit more, but thought someone else might remember.

While I agree with the theory, my air cleaner isn't, as yet, connected to the inlet on the radiator support. IOW, I'm just running the air cleaner and neither the cold air inlet tube nor the hot air tube.

Also, I don't think the power valve would normally come into play with regard to increased/decreased air pressure. The PV, or for that matter the metering rods in a Carter/E'brock or some 2150's, open/lift at relatively low levels of vacuum (3 - 7" typically). I doubt the wind or even wind buffeting changes the air pressure at the top of the carb enough to cause the differential between manifold vacuum and that point to change much.

However, the differential does change the AFR even though it probably doesn't trigger the enrichment circuit. I don't remember which way it goes for sure, but I believe that additional pressure in the bowl enrichens the mix. (That fits with the fact that the mix leans at higher altitudes and that it enrichens with a higher float level.) So, changing the pressure into the air cleaner does change the AFR to some extent. How much I don't know.

 

Gary, Ken, the only time external airflow causes carburetor issues is with a Holley with the air horn milled off or the Dominator (4500 series). On these the top of the venturiis is so close the "stand off" cause by the reversion wave will be stripped off causing a severe WOT lean condition. Holley had a video years ago showing the cloud of fuel droplets above the venturiis. This is also the reason Weber tells you to use either stacks or an air cleaner on their carburetors.

 

A carb runs strictly on airflow through the venturi. That's it's main fuel distribution method into the engine. More airflow means more fuel. No more air can go into the engine than the throttle butterflies will allow, so any pressure from a cold air duct will have little affect unless the throttle is open a good bit. And then if you get more airflow, then the venturi will add more fuel automatically.

Everything else in the carb is just a "bandaid" or add-on to correct for conditions where airflow will not produce enough fuel.

If you are pulling a hill and the rpms start dropping, then there is less airflow through the carb and it would mean less fuel into the engine. You push the pedal down, but nothing is going to happen unless the engine can gain rpms. This is where the power valve "band-aid" comes into play, adding fuel under low vacuum situations(low rpm and the throttle is open.

Same with the accelerator pump "band-aid". Snap the throttle open, and the engine can't react and build rpm quickly enough to pull more air through the venturi to add more fuel. So the accelerator pump mechanically pumps extra fuel into the engine.

If you think about it this way, it can simplify understanding how a carb works.

 

Franklin, SUs are so much simpler, only 2 moving parts. Fully understanding how a carb works can be very rewarding, particularly if you have a very adjustable carb like a Weber IDA or DCOE series.