theboilermaker

first afew specs. The motor is a 73 4 bolt main that I built last summer before i went to school. it is bored 40 over and has flat top pistons with 624(I think) heads. Unfortunatley what I don't know is what cam is in the motor. The engine was given to me. The cam had very little wear on it, and the previous owner of the motor said that it ran very strong. So not wanting to fix something that wasn't broke I left the cam. I figured I could swap cam when I go to Al heads. that said I bolted on the cc carb and timed the motor. Now I am running EXTREMELY rich. I have read here once that with a high duration cam it is neccessary to drill out idle passages to get the mixture leaned out. What is my best course of action? and if this is neccessary does anyone have a picture of what needs to be drilled. Being a college student I do not have alot scratch that, much of any spare time to work on the car. any help would be much appreciated. Thanks guys. I don't know what I would do without this site!!!!!

Doom86

You shouldnt need to drill anything unless you have some very radical setup.

Do you get a "service engine soon" light? (got the codes?)

You'll need to trouble-shoot the fuel mixing sensor's. Throttle position sensor, Mixture control soleniod, Coolant temp sensor, and Oxygen sensor. Make sure they are all hooked up, and the ECM wire (i think its a 4 wired harness) is hooked to the distributor.

You'll need a dwell meter and digital volt meter to do so. You should have these already if you're trying to tune this type of setup.

I'm betting you need to set the dwell of the MCS with the IAB (Idle Air Bleed) adjustment on the carb . If you're not getting any service engine lights, with mixture related codes, this is where i'd look for answers. The IAB is for fine tuning the fuel mixture in the cruise and idle circuts. It also effects idle to off-idle response, if its really off.

theboilermaker

Just checked the dwell. It hovers around ten sometimes jumping to twenty. I am going to go up and check the O2 after a quick snack. does this seem like the correct course of action? Seems to me that if the O2 was bad then it would be sending a lean signal causing the motor to run rich. please let me know if my logic is flawed!

Doom86

were you using the 6 cylinder scale? You want it to bounce around 30 on the 6cyl settings. (mine slowly bounces from 25-35) If you got headers make sure you get the gases real hot to get the meter working right. I gotta pull mine up to 2000 rpms for 5-10 seconds to get it hot enough at idle.

id check the TPS second after the dwell is set.

You arent getting any trouble codes then i take it?

You cannot always trust the ECM to tell you whats wrong. A good example is when my TPS sensor's tang broke (so it wasnt working at all). It never once set off the SES light but it sure made the motor run like total garbage. it was like this for a good 2-3 weeks of driving.

theboilermaker

so you would check the tps before the O2 sensor I am reading my factory manual and it seems to me that the O2 could easily throw it into full rich.
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ohh and I think the first time I checked the dwell I was checking it wrong. I went back and read some more and I read a few places to pull the ebrake block the wheels and put the tranny in drive. I did that and got a better reading about 20, but the car idled like total crap. hunting and lurching. I had to turn the idle stop screw almost all the way in to get it to stay running.

-- btw that was on the 6 cyl scale in answer to your question

Doom86

Most deffinately check the TPS first. But you have to set the dwell first, exactly like i said before. To fine-tune the dwell you want the transmission in drive, and someone holding the breaks in. But setting it in neutral/park is very close.

Set it to 30' on the 6 cyl scale before you go any further. If you are not getting any variation of the dwell by adjusting the IAB you may not have the exhaust gases hot enough for the 02 sensor.

theboilermaker

I am looking for the tps test in my manual, it is a voltage check is it not?
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could it not also be low voltage from the mc solenoid?

Doom86

yep, just back probe it. Its a 3 prong harness; i think its the bottom and middle you need to back probe. paper clips help lot for this.

should be .48-.60 at idle. around 3.8-4 volts at wide open.

having the dwell set right smooths out idle considerably. it even raises it a few hundred RPM's, which is why it needs set before you set the TPS sensor. Adjust the idle on the carb will also adjust the TPS at idle. So if its out of wack on the dwell, you adjust to carb to compinsate idle speed and it in turn throws off the TPS.

the MCS is controled by the dwell (you can also test it using resistance).. if you here it ticking away, its working; if the dwell is set, its working right.

theboilermaker

and the way to adjust the dwell is with the IAB isn't it? doesn't that require a special tool?
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I am confused at what you mean by back probing? is this just the voltage across the two terminals?

Doom86

No the IAB can be adjusted with a flat-head screw driver easily. Just about any size will do. If it isnt exposed you have to remove the 2 rivets with a drill that hold its "tamper proof" tab in place, it literally takes about 10 seconds. just try to not get any shavings down in the carb.

you're exactly right about back probing. stick a peice of paper clip, or something to that effect in the back of the harness where the wires go in. You can get the nodes on the volt meter in there too, but it may ruin the weather proofing on the harnes..

theboilermaker

man I don't think I can thank you enough
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I'm going to go see what I come up with. Thanks again for your help. If I'm lucky it will be just that easy.

Doom86

no problem, i wrestled my CC qjet for a long time till i started researching what made it tick. they are great carbs IMO.

heres a pick i took for you real quick from my parts carb. just to make sure there is no confusion.

theboilermaker

I played with the IAB for awhile and got alittle improvemt, but it is still definatley rich. I think I may have lost the cat. I was focused on the IAB screw and not the cat when I smelt the distinct smell of a red hot cat. at the same instant a little smoke began rising from that side of the car. I think it was the undercoating baking. I shuther down quick and got a fan on the cat trying to slow the reaction. at the same time I also noticed that my charcoal canister was making a gurgling sound. This doesn't seem normal to me. Lastly I tried briefly to get the voltage of the TPS. and couldnt. I was using my old snap-on dwell/multimeter and tested it on the battery and got a reading of 12.4 when I tried to test the tps I didn't even get a bump or bounce in the needle. Should I be looking for a new tps? or would you still be looking at O2 becuase i am running rich REALLY rich. lastly, the motor still "hunts" untill about 1300-1400 rpm. This is even reflected in the dwell sliding around by at least 6-7 degrees when I am trying to get a solid reading. For instance I had it pegged on thirty for about 15 seconds tonight, then all of a sudden it dropped to about 23. After that I couldn't get much adjustment out of it. My thought was maybe the connection was just weak. Any thoughts? Thanks for the help. I need to pick up a rochester book so I can start learning more about the system, there just isn't enough time with school!!!! Thanks man. Doing this alone would take me weeks with my schedule.

theboilermaker

I got up this morning and played with the tps some more. When the ignition is on and the car is off the voltage is about 2 volts. This doesn't change when I turn the car on. I didn't get a chance to check it hot. also. now the Dwell is really low. hovering around 10. So I went to the IAB to try to adjust it. I could put the IAB anywhere and it wouldn't change the dwell at all. one last thing. to get the motor to idle I have the idle stop screw in so far that the plunger by the TPS wont come close to contacting the throttle. If I adjust it so that it does the car wont run. Any idea's?

Doom86

did you try heating up the exhaust gases by pulling the throttle and letting it idle at around 2k for a good 10 seconds? I know on my car the dwell doesnt change until the 02 sensor takes control of the mixture (when it gets hot enough). the factory spot for 305's is 3.5-4 turns up from the bottom. DO NOT TURN IT TIGHT when you bottom it out! richer is down, leaner is up on the IAB.

sorry about not telling you how to properly check the TPS, you have to have the ignition turned to "on" but not running. If you unhook the harness and back probe it you should have 5 volts. if its all hooked up it should be as i said above. you might be getting 2 volts because the idle screw is in so much, the computer thinks you are driving around at 1/2 throttle.

you have to have to idle screw tunred in all the way to get it to stay running? what does it do when its backed out where it should be? does it start, stumble and die? will it not start?

theboilermaker

The car will not even start with the screw where it belongs. As far as the IAB adjustment. i have it WAY out and it is still running rich. I was reading in my factory manual that anything below 2.5 volts is a bad tps.( I think) I will check when I get home tonight. btw. I did have the system up to temp. I had it up to 2500 for about 30 seconds. I keep noticing that you aren't mentioning the O2. Is there a reason for that?

Doom86

well i think you need to figure out why its taking so much throttle to get it to start and run before going any further. If the idle screw is turned in completely then the TPS is going to be way off as well.

I honestly dont know what would be making you need so much throttle to start, it isnt the 02 sensor, that is for sure. how's the choke working? Is it closing completely before you start it cold? have you tried starting it and backing the screw out? hopefully someone else can help out too, ive never had this hard starting problem my self, i'd start with the choke and go from there though.

theboilermaker

Could this be the idle mixture screws?

Doom86

almost certainly not the idle mixture screws. they really dont do much on these carbs. the IAB has much more authority over the mixture.

you gotta answer questions to figure this out. it doenst take much to start a cc qjet engine. the computer has practically nothing to do with it, it doesnt even start mixing fuel until the 02 sensor is up to heat, and the engine coolant is aswell.

You need to figure out why you need the idle screw in that far to start the engine before going any further.

What's your timing set at?

VnZo

Heyy guys I just wanna say thanks for the great thread, I just put a new remanufactured "stock" carb on my new 350 and it wasn't running all the way right especially the idle after driving it and having it set high allready but this gives me a few more ideas on what to do, im not done with it yet

theboilermaker

I want to say that the timing is at 10* but I am at school untill thursday so I won't be able to get a light on it until thursday night. What should the timing be? And also, It will die even if it is warm and the screw is turned to where it should be. Thus I don't think that it is a choke issue. I would like to think that it is just a timing issue though.

trumps2000

iTrader: (2)

I'm having similar problems with my 350 swap. Things to check for:

1) I noticed on my CC quadrajet the float was set too high causing a hesitation.

2) As I understand it, when cold, the computer sends the M/C solenoid a constant 30deg signal until it warms up and enters closed loop, if you don't see this you should check your temp sensor.

3) Make sure the hose to your MAP/VAC sensor is not plugged. You should probably check the voltage from it too.

4) You didn't mention anything about the idle mixture screws, have the caps been removed? If so a good starting point is to lightly seat them then turn them 2 - 3 turns out.

Not to steal your thread, but maybe someone could shed some light on this for me. My motors been running really rich as well. Rich enough to foul plugs in no time. Reading the sensors with a scanner, at idle the dwell is 54deg. When I rev it to 2000 RPM the dwell jumps to 23deg. I then purposely leaned the carb at idle while it was running. My (new) O2 sensor read 0V (fully lean) yet the computer was still sending a lean signal (48deg) to the M/C solenoid. The TPS (.48V), the BARO (~4.5V) and MAP (~4.5V) seem to be in spec. Not sure whats wrong here?

theboilermaker

the plugs are out, but I havent checked the float or the mixture screws yet. It ran ok on the 305 so I wouldn't think that much adjustment would be neccessary UNLESS it was a cam issue. I wish I could give the specs on the new cam, but I am really clueless. It was a gift from an old hot rod buddy of mine. I decided to run it to see if it made good power. It sounds pretty mean, but I measured the lift with a micron before installing it and I don't remember it being huge.

theboilermaker

I got the timing light on the car this afternoon. The timing was around 25-30 degrees when I first put the light on it. I changed the timing to 10 degrees at idle. (with the est unplugged) but instead of idling better the idle speed dropped and I think that it idled rougher. Does this make sense. Should the IAB be looked at next? What about IAB and mixture srews. Should I set the initial timing at 10 degrees and then play with them, or is there another order to go about this? What should my timing be for a mild/medium 350?

theboilermaker

I'm going home this weekend and really need your guy's opinions on this so I can get it running correctly. I have read of people have more than 20* of advance at idle. Where should I be at? would 20-25 be rediculous? please help. I want this thirdgen in paint and on the road, but I have to get the motor figured out first

naf

iTrader: (7)

I'm going to assume the carb and all sensors are working correctly and we haven't opened it up and played with anything.

1) Let's set your base timing (with EST wire disconnected from distributor) to zero. Plug wires back up when done and clear code. Idle speed may drop some with lower base timing but don't worry too much about it. We can bump it up later once everything else is set.
2) Set both idle mixture screws four turns out from lightly seated.
3) IAB four turns out from seated.
4) Check all vaccuum hoses again.
5) Make sure choke blades are full open (90 degrees up).

Start it up and see if you can get it to idle at around 700-800 rpms. See if unplugging the TPS and CTS makes any difference. Once we get it idling and know everything works we can work on adjusting it for proper dwell.

I'll be around the house all weekend working on mine and I'll check here through the day.

theboilermaker

Thanks man, I will go run out and get the tools for the idle micture srews. I have been unhooking the wire ( I think) there was no factory disconnect point where there should be when I went to time the new motor. So I dug through my wiring diagram and I am 95% sure that I have split the correct wire and have placed a splice in it. Hopefully I have an update for you by tonight

naf

iTrader: (7)

"I have been unhooking the wire..." is this the EST wire? The one that plugs into the back of the dist? factory disconnect point? This is the CCC distributor right? What wire did you splice? The EST should plug into the dist or have a plug junction on it depending on year.

But again, don't worry about timing too much.

Trumps: If your O2 was reading 0 volts, the ecm shouldn't yet be using it to adjust mixture and the dwell, wherever it was at, shouldn't have been roaming but would be giving a steady reading and the reading would depend on TPS setting. If you want to start a new thread, I'll look into it.

trumps2000

iTrader: (2)

Well it was in closed loop because the coolant temp was warm enough, but I purposely leaned it out to see whats working and what not. This tells me that my O2 still works (its new so it'd better!). But the puzzling thing is that the computer still responed with a lean command despite the O2 sensor. I have a spare computer so I might just swap it in and see what happens. I've been using a scanner to check things out. I wonder if I should buy a dwell meter and check everything out with it. Unfortunately I'm still in the middle of classes, so I'm strapped for time.

theboilermaker

[QUOTE=naf]"I have been unhooking the wire..." is this the EST wire? The one that plugs into the back of the dist? factory disconnect point? This is the CCC distributor right? What wire did you splice? The EST should plug into the dist or have a plug junction on it depending on year.

I have the 87 factory manual for my car and it specifically stated that the plug should not be removed from the distributer. I also could not locate the factory splice in the wire (on the passenger side by the ac/ relays) where it was supposed to be. Napa was closed when I got hom, I will run out in the morning and get the mixture tools. I have been adjusting the IAB lately as was suggested earlier. Would you start with the two screws in the base of the carb?

naf

iTrader: (7)

theboilermaker: Set everything like I outlined earlier, then start it. You'll need the tool for the mixture screws, you'll have to set them so the IAB is brought into its range for adjustment. I'll have to look for the factory splice in mine, I've always disconnected the dist plug.

Trumps: Don't swap the computer yet. The ecm won't go into closed loop until it also sees a voltage signal from the O2 sensor, so you probably weren't closed. You'll know it's open when the dwell reading varies about +/- 10 degrees in a slow, continuous, pendulum motion. It will vary from 50% when closed, looking at TPS readings, but the needle won't be ranging. ECM is simple but does "learn". Saw your profile, what discipline are you?

trumps2000

iTrader: (2)

Theboilermaker:
Just a heads up, I had trouble getting the IAB and float guage tools, seems nobody makes'm anymore. The mixture set screw tool you shouldn't have much trouble finding.

naf:

trumps2000

iTrader: (2)

Theboilermaker:
Just a heads up, I had trouble getting the IAB and float guage tools, seems nobody makes'm anymore. The mixture set screw tool you shouldn't have much trouble finding.

naf:
I'm an electrical engineer, always loved electronics but I've always been pretty decent with a wrench and not bad at software either.

The scanner I've been using reads that its in closed loop and was 48 degrees to the M/C. Before I leaned the carb it was sending this same lean 48 signal but once I reved it to 2000 RPM it dropped to 23. I've checked all the sensors and they seem to check out fine. Though the MAP sensors starts out at 4.5V at idle and goes down when I give it more throttle, but I think thats the way its supposed to work. When I get a chance I'm going to record the readings of all the sensors.

naf

iTrader: (7)

Trumps: Scanner may indicate that it's closed, but was the dwell ranging? Start a new thread or PM, I'll check in the morning.

I'm civil and took Fortran WATFIV in '82 with punch cards (math was first, civil came later).

Doom86

The wires you need to be unhooking from the distributor are the ones in the 4-wire harness that are brown i think (not sure if they are all brown, its been a while). You shouldnt be needing to "splice" anything, these distributors have a dongle that the wires harness plugs into.

Id make sure i was setting the timing correctly before messing up the mixture control screws. If you've never touched them it would be the last thing to check. You said this carb ran fine before the swap right?

theboilermaker

it ran well on my 305 with a stock cam. so many variables change with the new motor I don;t know where to start. My biggest question is if I have done nothing to the carb why is it running rich on a motor with more displacement. The only thing I can figure by dwell etc is that the computer is being told I am running lean when I am not.

naf

iTrader: (7)

When you connect the dwell meter it's probably giving a steady reading at a constant rpm and turning the IAB won't affect it. When it's operating in true open loop the needle will range from a setting ~+/- 10 degrees and a small turn of the IAB will cause it to jump to one side then pendulum back until it finds a new setting it likes then start the +/- ranging again.

When you installed this system on a new/different motor the carb is too far out of adjustment and the ecm is not getting sensor readings that are close enough for it to recognize and adjust to. It's essentially stuck in it's "last known good" setting. The dwell will change, but it's only using the MAP and TPS. The ranging tells you it's in true open loop and receiving feedback from the O2 sensor.

Stick the dwell meter on it and if the above isn't the case we'll look elsewhere, but it is the most likely.

theboilermaker

I think you hit the nail on the head. I couldn't adjust dwell with the IAB to save my life. Should I go with the idle air screws then?

naf

iTrader: (7)

Try to bring it in with the idle mixture screws. When you screw them in to seat them (lightly) count the number of turns, just for reference. Doesn't really matter if you didn't, but either start with them four turns out or try half a turn out past stock setting until you can get some dwell change with the IAB. Give it a few minutes with each change. Usually a 5-6 turns out is good enough.

You may want to reset the ecm after each change. I usually don't but it may be quicker to react.

If you have to go past 8 turns out you may need to adjust rich and lean stop of MC travel.

theboilermaker

I set them both to four and the dwell is moving between 27 and 33. THANKYOU THANKYOU THANKYOU

and I'll throw my ME into the mix as well

naf

iTrader: (7)

Good luck with the new motor. If you need anything just holler.

Always looked up to those ME guys.

theboilermaker

Thanks again to you guys that helped out.

trumps2000

iTrader: (2)

Glad to see its working for you.

My cars still giving me trouble, but I'm beginning to think its ignition related. Maybe NAF can help me with in a new thread.

theboilermaker

Trumps: I don't have my carb books with me here at school, but I beleive earlier you stated something about 48 degrees of dwell being a lean signal. I beileve that 10 degrees and below is a lean signal telling the ecm to go full rich, and a 50 degree and below signal is a rich signal telling the computer to go full lean. If it is dropping to 23 under throttle It would appear the O2 was working. Have you adjusted the idle screws?
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Also, what is your timing?

trumps2000

iTrader: (2)

Well this weekend I had some time to work on the Z. I checked my sensors via the scanner and this is what I read:

Key in RUN position, but engine off:
TPS .48V (4.6V WOT)
BARO - 4.68V
MAP - 0 inHg - .54V
5 inHg - 1.46V
20 inHg - 4.22V
O2 - .44V
CTS - 12 degrees

Engine running, warmed up, idling @ 1000 RPM:
Choke fully open
CTS - 83 degrees
MAP 4.4V
Dwell ~ 45 degrees ( tried bringing it in but it doesn't respond much)
The O2 sensor voltage was jumping around .1V - .7V

So it appears to me that all the sensors work. Now while it was running it was misfiring. After it rains it tends to kick a trouble 41 or 43, indicating a problem with the igntion, but after reseating the EST connector it usually is fine. When I reved it to 2000+ RPM the tach started to jump around. So am I in need of a new distributor?

theboilermaker

How old are the plug wires, cap, and rotor?
and
what is your timing?

trumps2000

iTrader: (2)

Timing I have set to 4 degrees initial. The cap and rotor were new (sat around awhile, but otherwise new) Well its fouled two sets of plugs, its now running the first set after I cleaned them up again. I'll buy new again once I get this stubborn thing running right. The coil in the distibutor is an Accel Supper Coil I bought from a friend.

theboilermaker

I'm running 12 degrees of timing, I would normally start with about 8 degrees. You could have detonation not misfiring

naf

iTrader: (7)

Trumps:

Tach jumping is usually a sign of ignition problems. Take your coil and control module in to autozone (or clone) and have them tested. Ohm out your plug wires, they should all be the same and check for play in the dist shaft. Does timing jump around with est disconnected? Don't buy a new dist yet there's too much else to rule out first.

Oh yeah, I think theboilermakers est splice is only on fuel injected motors??

Did you rebuild this carb? are mixture screws exposed? Where exactly are you now and how did we get here?

If your dwell is not responding to changes in IAB then it's not in true closed loop. Don't assume that a dwell reading is any indicator of the true rich/lean nature of the mixture unless it's ranging. 0.1~0.7 are lean readings and you would expect the dwell to be on the low side of 30 degrees to compensate.

cheppibear

My tach was jumping some years back, turns out the coil blew a hole in the dist. cap.

I replaced cap, rotor, and coil and everything was good.