Dwell and choke question

[Peer81]

Hello everybody,

Two different questions in one topic.

Today was "dwell-day" . Put the vette off the ground, wheels from the floor, warmed up the engine, put her in Drive and connected the dwell meter. The meter was fixed at the 0 degrees, started turning out the air valve but after one turn saw no change so started turning in. After 3 or 4 full turns had it almost at 30 degrees and with some 1/8 increments finally has the needle dancing around 31 - 29 degrees.

But here my question. Now i "fixed" the idle problem with the air valve, but is this the same as changing the mixture screws? When I begon the dwell meter was at 0 degrees, wasn't it better to first change the mixture needles to get the dwell meter between 25 - 35 degrees and at the end fine tune it with the air valve or is my method also allright?

Second thing, if I'm correct from 0 to 29 degrees the mixture is running lean and from 31 to 60 the mixture is running rich. So I was very lean, also understandable because at this moment I'm only running the stock short style header with about 3 feet of exhaust pipe, so no back pressure.
But to continue, running lean then I would think with the air valve, when the air valve is moving down it's pushing the plunger down on the primairy rods taking them deeper in the jets to flow LESS fuel (leaner). So I should turn the air valve up to enrich the mixture. But I managed to get the 30 degrees dwell by moving the air valve in. Could somebody fill me in on this one

Of course when I have my true duals I need to reset the idle speed, TPS and dwell and then I can also see "how much" the system is richend up by the exhaust.

Second question.

I rebuild my carb like it should ( I think) but the choke isn't working like it should. Well, I need to keep my foot on the gas because the choke isn't kicking in. I set the second and last choke steps with the choke angle gauge including the unloader but I also don't know how the carb can go from the just running position to the choke steps (first, second or thirt).
Could somebody explain to me when a cold engine is just running how the choke should react and which rods should move in which direction.
Btw. I didn't check if there is 12v on the choke wire, but will do!
Thanks!

Groeten Peter

 

[Sensei]

First, you should set the air valve with a the gage, then don't move it more than about a quarter turn. If it requires more than that, go back and adjust the mixture screws.

Second, the air valve does not affect the rod position. The movement of the MC solenoid opens and closes the air valve.

Once you have the exhaust system and everything else set, everything will probably change.

Check for 12v, but also be aware, choke thermostats are bad on 90% of the carbs I rebuild.

God bless, Sensei

 

[Peer81]

Thanks for your reply Cris,

Could you explain what the air valve is doing? I think I'm thinking in the wrong way, if the MC solenoid is opening and closing the air valve I don't see how it could affect air fuel mixture.

I'll check for 12v on the wire and check the choke itself with a 12v source and ground.

Groeten Peter

 

[Sensei]

In the idle system, between the idle pick up tube and the idle restriction, the fuel is emulsified with air from the idle air bleed. The idle circuit has fuel going through it at all times (idle, cruise, WOT). When the metering rods are raised by the MC solenoid (for richer mixture), it also shuts off the idle air bleed (stops the air from being mixed with the fuel in the idle circuit at that point).

God bless, Sensei

 

[black_81_vette]

You could also chuck the feedback carb and get a non comp controlled dist and be done with it.but that depends on your local emissions testing.

 

[Peer81]

Emission is no problem over here but I have a computer and I don't care if it will take forever but it will work. I think a E4ME is far superior to a normal Rochester anyway.

btw. Checked the choke, tested it on 12v charger and it seems to turn from cold to hot about 20 to 25 degrees. Started it again and was running stationairy around 3000 rpm, so getting closer but need to reset the high idle rpm

Groeten Peter

 

[black_81_vette]

Feedback carb is better? As slow as the C4 controlls were thats highly doubtful.Besides a more hit or miss style of metering fuel parts are now very hard to find for them. Truthfully youd be better served by retrofitting a throttle body set up than dick around with some troublesome electric Qjet. Those cars had a limited range of dwell no performance oriented primary metering rods ect.But hey if you got one that works thats great.

 

[Sensei]

Feedback carb is better? As slow as the C4 controlls were thats highly doubtful.Besides a more hit or miss style of metering fuel parts are now very hard to find for them. Truthfully youd be better served by retrofitting a throttle body set up than dick around with some troublesome electric Qjet. Those cars had a limited range of dwell no performance oriented primary metering rods ect.But hey if you got one that works thats great.

I hate to flame someone here, but most of you know I have been on a mission to wipe out this sort of mis-information for years, so here goes (sorry black_81-vette, not disrespect intended).

The CCC computer system is outstanding. How many computers do you know of that can be kept outside for 28 years and still work? even if it fails catastophically, the car still runs fine to get you home, and it is dirt cheap to replace.
The computer is stupid in the best way possible. It monitors and adjusts timing and air/ fuel mixture by throttle position, engine vacuum, rpm and mainly O2 in the exhaust. It keeps the mixture at optimum efficiency during all driving conditions except WOT, at which point it allows the carb to flow all the fuel it can, which is ALOT! (see E4ME carb below)
The computer never "freaks out" and stops working because the EGR etc. is not there (it never even notices). Make all the engine mods you want, the CCC computer, like the Energizer Bunny, just keeps going, setting your timing and A/F mixture right where you want them.
The original emissions timing curve can be fixed easily, just advance base timing from the stock 6 BTDC to 12-14. Again, the computer never notices a thing, it just advances the timing from wherever you have it set. If you want a bit more agressive curve, (requiring premium fuel) replace the stock chip with a $120 performance chip.
Even if you go to a radical camshaft with very low vacuum, the computer can easily be fooled into thinking 9 inches of vacuum is 15 by a simple voltage regulator circuit, again allowing it to keep A/F mixture at optimum efficiency for normal driving and optimum performance at WOT.

The E4ME carburetor is the real jewel of this system. It is the most advanced carburetor ever made. Only the largest displacement, highest RPM engines could ever benefit from a different carb (if you have a 7000 rpm 427, you may need more than 800cfm).
Properly set up, it can deliver 800 CFM of fuel mixture at any desired ratio for WOT performance, AND STILL GIVE OPTIMUM FUEL ECONOMY AROUND TOWN AND ON THE HIGHWAY!!!!! No other carburetor can can do that! PERIOD! The people who say they can do not truly understand the difference between carburetor operating systems and the potential of the E4ME.
I have never had any trouble finding the parts I need to get any level of performance desired from an E4ME. It is the ultimate carb!

http://www.corvetteactioncenter.com...430-those-modified-engines-original-carb.html

Okay, end of Hijack/ Flame/ Rant,

God bless, Sensei

 

[black_81_vette]

Thats all well and good,price any mixture control solenoids lately? Im sure the E-Jet can be set up properly I still have the one on my 85 ss for now.But when you look at from a simple tuneability from a normal skilled person the E-Jet becomes a pandoras box.The standardQ -jet has been used used on class stock drag cars running 10s and can be tunned easly.Sure you can use The E-Jet but many if not most people do swap it out for the earlier carbs. Dont get me wrong the E-Jet works well for its intended use Just dont try buying a remaned unit they are very pricey and truthfull there are not alot of people that are educated on the proper repairs for them such as you are.All in all what im trying to say is for most part is that simplicity is best and keeps alot people out of trouble.As far as air flow requirements no argument from me on that,as any flow sensative carb is way better than its mechanical secondary counterpart on the street. CV based carb is always better at fuel metering but then again look at motorcycles constant cv and work well.And ive never seen a electric controlled carb on them. I think What caused GM and others to use feedback carbs is they all got caught with their pants down and they had no good way of controlling emissions.They tried true.. but most of the emissions parts were crude and diddnt last very long.And you bring up the fact that the early computor systems were rubust sure Il give you that but the C4 system was replaced by the C3 system I belive In 83 or 84 and its baud rate was over double of the old feedback system. So actually that brings up the question of could a guy use the later model controll box? yes in a techinical sence you could but why bother as the wiring and such would be needed and the performance gain wouldent be worth it.If I had the time and money I would convert to a tunned port set up or other FI system as the degree of tuning and performance outguns a simple carb setup.I have heard even top fuel guys are experimenting with electronic fuel injection. Dont get me wrong electronic carbs are ok when working correctly but like I said earlier there are simpler ways of gaining performance,but my hats off to you as you have a vast knowlege on these carbs.

 

[Peer81]

To continue this topic, the choke is working again but I'm not sure if my choke indicator light is working correct. When I'm turning my key from the acc. position into the start position the choke light only flashes about 0.5 sec. This is the only time the choke light will go on and I have to be very quick to see it. Is this the same way it worked on the other 81's or not? Thanks,

Groeten Peter

 

[Sensei]

Yes, my choke light does not stay on.

God bless, Sensei

 

[Peer81]

Thanks, then I can scratch that one from my to do list

Groeten Peter

 

[Peer81]

And an extra dwell question.

The books says to put the trans in drive, block the wheels etc etc. But I was thinking, is it also possible to get the rear wheels off the ground and then put the trans in drive. This way I can set the E4ME by myself. Of course this way the engine has no load and with the wheels blocked she has. So is this also a possibility?

Second. Does anybody know how much advance the ecm gives to the timing?

Greetings Peter

 

[Sensei]

Does anybody know how much advance the ecm gives to the timing?

Remember this?

http://www.corvetteactioncenter.com...ry-forum/98701-81-ccc-performance-timing.html

 

[Peer81]

Remember this?

http://www.corvetteactioncenter.com...ry-forum/98701-81-ccc-performance-timing.html

I didn't seem to remember that one, thanks!

Any idea for the blocking the wheels vs. in the air?

Greetings Peter

 

[Sensei]

To do it right, I would think you would have to block the wheels, but I'm not sure it is all that critical.

God bless, Sensei

 

[Hib Halverson]

(snip) I think What caused GM and others to use feedback carbs is they all got caught with their pants down and they had no good way of controlling emissions.They tried true.

You may think that but you're wrong.

. but most of the emissions parts were crude and diddnt last very long.

I'm not sure I agree with that, either. It depends on what standard you use to judge durability. If you use the standards which existed in the late-70s/early-80s, when those systems and components were developed, a lot of those parts lasted a very long time.

And you bring up the fact that the early computor systems were rubust sure Il give you that but the C4 system was replaced by the C3 system I belive In 83 or 84 and its baud rate was over double of the old feedback system.

C4 was only used on the 1980 Calfornia cars and a few other GM vehicles produced in 1979 and 1980. The C3 (Computer Command Control) was introduced for 1981 on Corvette and a few other cars. It is true that both processor clock speed and the baud rate used to communicate with sensors, actuators and with diagnostic equipment over the serial data line was increased almost on a model year basis. Those early processors (80, 81, 82 and even 84) were so slow that the engineers benchmarked them with a sundial. Sometimes problems would have to exist continuously for several minutes before a code would set.

So actually that brings up the question of could a guy use the later model controll box? yes in a techinical sence you could but why bother as the wiring and such would be needed and the performance gain wouldent be worth it.If I had the time and money I would convert to a tunned port set up or other FI system as the degree of tuning and performance outguns a simple carb setup.
I have heard even top fuel guys are experimenting with electronic fuel injection.(snip)

I write web content for a Top Fuel team and I'm not aware of any Top Fuel operation which has a serious development program going with EFI. No one in their right mind would spend the kind of money it would take to perfect such a system unless the NHRA gave a clear signal that it was going to start allowing electronic controls of any sort in any of the Pro classes. In fact, at this point in time, I think the "winds" are blowing in exactly the opposite direction. That's why T/F, F/Cs, TAD and TAFC and so forth use all kinds of mechanical/pneumatic timing devices to control the clutch, the fuel injection and so forth.

My belief is the real "future-development" effort in the Nitro Classes is focused on bringing back full quarter-mile racing, getting the speeds below 325 and going to a smaller engine, say 410-420 cuin from the current 500 cuin.

Where NHRA may start allowing EFI is in Pro Stock, but I think it'll be a year or so before we see that happen.

Now...it is true that NASCAR is looking at EFI to replace carburetors in its touring series, but I think it's going to be a few years before we see EFI in Cup. They'll try it in Truck and the NWS, first.

I'll guess that NHRA is watching how NASCAR rolls out it's EFI engines.

 

[LanceB]

I don't even have a choke on my 81 anymore...boxed up. Runs great without it. I am sure I am going to get reamed for saying this!

 

[Peer81]

I don't even have a choke on my 81 anymore...boxed up. Runs great without it. I am sure I am going to get reamed for saying this!

Lookup "the Netherlands" with Google Earth, then you know why I need one.. hnoes

Greetings Peter

 

[LanceB]

I do have to let it warm up a little bit when it gets real cold but it runs surprisingly well no matter what the weather is doing. Cold weather it seems to really hum. I always planned on going back and putting a new one on, but if it isn't broke don't fix it eh? I won't drive it if there is salt on the road tho so pretty much a 30 degree or higher driver.