1987 Monte Carlo SS 305 Quadrajet Tuning Issues - Hot Rod Forum : Hotrodders Bulletin Board
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Old 10-24-2016, 08:23 AM
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1987 Monte Carlo SS 305 Quadrajet Tuning Issues

Hey everyone, I'm having trouble tuning this CCC carbureted 305 Monte Carlo. I rebuilt the carburetor because it had leaky gaskets, but ever since I've rebuilt it it runs insanely rich. I reset all the carburetor parameters to as close to stock as I can but it doesnt help. I ended up with the lean stop backed out 3.75 turns, the IAB screw backed out 4.75 turns, and the mixture screws set at 1.5 turns out. Plunger travel is exactly 4/32, but I plan to tighten it up to 3/32 to see if that changes anything. The carburetor runs nasty rich no matter what, so I pulled it apart and epoxied the well plugs, still no change.


I plan on measuring the TPS voltage and also setting the dwell on the mains.


With these CCC cars, how do you set dwell? Should I start adjusting the lean stop, the IAB, or the mixture screws first? Also, can the O2 sensor cause this change? From what I read, the O2 sensor doesn't do anything until the car is warm and it's in closed loop? Are the main metering rods supposed to pulse at idle as well? I've noticed they still do their normal 10mHz pulse at idle.


Also, what's the best way to go about removing the Rich Mixture Stop Screw plug? Drill into the plug just enough to break the surfance and drive in a small screw?


I'm 100% lost on tuning this car and any help would be greatly appreciated.

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Last edited by HeavyChevyDeluxe; 10-24-2016 at 08:43 AM.
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Old 10-24-2016, 09:24 AM
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Quote:
Originally Posted by HeavyChevyDeluxe View Post
I'm 100% lost on tuning this car and any help would be greatly appreciated.
You must get a Chassis Service Manual and follow the adjustment process EXACTLY. If you simply try messing with things, you'll just be chasing your tail. There are special gauge tools used to set up the solenoid stop. Without these, you'll never get it right. The mixture control solenoid dwell setting is measured on the green single terminal connector that's in the harness in front of the carb. Use a regular dwellmeter set on the six cylinder scale. Adjust the idle mixture screws to get about 30 deg dwell.

Of course, you must ensure that everything else is properly connected and working. For example, I had one CCC car were the air switching valve in the A.I.R. system had gone bad. Fresh air was blowing directly at the O2 sensor while in closed loop mode. The ECU read this as Too Lean and ran the mixture control solenoid full rich. There is no code to set for this problem, you have to use traditional troubleshooting skills. There are unfortunately a lot of similar failure modes in the CCC system that won't set a code.
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Old 10-24-2016, 09:41 AM
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Thanks Joe! I don't even know where I'd come across a service manual.. cool that's what I thought. The green wire is also pin B on the ALDL connector under the dash isn't it? I've basically set up the carburetor to the same settings as someone on the 3rd Gen forum, which he's running the H.O. 305, should be close I hope.

I don't think the smog pump is even hooked up anymore, last I checked it had the belt off, but I'll verify that when I'm home.

Shouldn't the carburetor run at a predetermined parameter when in open loop? So technically if the carburetor is fine and the o2 sensor is bad or getting a bad reading, it should run well until it enters closed loop operation and gets feedback from the computer?
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Old 10-24-2016, 09:58 AM
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check for codes.. you know how to jump the A and B terminal..

hook up a dwell meter to the Green terminal indicated.. set it to 6 cylinder mode.. does not matter that you have a V8.. its the readings you are getting... 0 to 60 degrees of dwell to match the manual.

at idle. if everything is properly adjusted .. you should have 28 to 34 degrees of dwell. slowly bring the motor to 2500 RPMs.. you should have somewhere between 28 and 40 degrees of dwell.

did you use the J shaped tool to set the adjustable air bleed screw in the top of the air horn.. that makes a HUGE difference..

you can test the Diverter valve by unhooking the hoses into the air injection check valves and plugging some heater hose and shoving it over the air injection check valve hose barbs.. you should ONLY have air flow from the diverter valve into the upstream check valves at cold start for about a minute until the system goes into closed loop..

i actually have that manual. i have to go now.. but i actually have some instructions for adjusting that carb ... someplace in one of my many computers.

you will need a carb dipstick... a set of the adjusting tools for the double D and the J shaped tool to adjust the air bleed height in relation to the lean setting..

its all crazy complicated.. are you in the los angeles area.. i have scan tools for that system also.. lets you look at live data.
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Old 10-24-2016, 10:28 AM
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Thanks Wayne. Will it be necessary to check for codes of the CEL isn't illuminated?

I was going to make my own J strap tool to check height. I found a specification stating the top of the air bleed should be 1.756" from the top of the bottomed solenoid.
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Old 10-24-2016, 10:54 AM
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Quote:
Originally Posted by HeavyChevyDeluxe View Post
Thanks Joe! I don't even know where I'd come across a service manual..
Ebay, for starters.

Quote:
The green wire is also pin B on the ALDL connector under the dash isn't it?
No, it's specifically for checking mixture control solenoid dwell.

Quote:
I don't think the smog pump is even hooked up anymore, last I checked it had the belt off, but I'll verify that when I'm home.
That was merely intended to be an example of a failure mode that can cause full rich running without setting a code. There are others. If hardware has been disconnected, you need to verify that hasn't inadvertently disabled the CCC system.

Quote:
Shouldn't the carburetor run at a predetermined parameter when in open loop?
Yes, MC solenoid dwell is fixed at 30 deg in open loop mode. Now, if the CCC system is disabled for some reason, the MC solenoid is deactivates and the primary metering rods stay in the up position - resulting in a full rich condition.

Quote:
So technically if the carburetor is fine and the o2 sensor is bad or getting a bad reading, it should run well until it enters closed loop operation and gets feedback from the computer?
Yes, though that's again only one possible failure mode.
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Old 10-24-2016, 06:57 PM
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Did you follow the instructions on the sheet supplied in the overhaul Kit?


Sounds like the float may be set to high.


Getting the rich stop and lean stop set before the carb is assembled is pretty important. Most important adjustments in this carb.


The idle air bleed is a cinch .
Sounds like you made the base adjustments correctly to me. JMO
You can make the base adjustments without the "special" tools if you know what to do.


The jets have a step on them where the setup tool rests. It is made to adjust the lower limit (Lean stop) to its correct height. That measurement would be 1.07 inches with the paddle held down to the lower limit stop, measuring from the "step" on the jets to the bottom edge of the paddle that contacts the top of the metering rod.
From there the rich limit is set to 4/32 as you said.



I am still thinking you have the float level wrong. or Maybe the wrong gasket.
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Old 10-24-2016, 07:06 PM
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Lean limit tool I have :


Thexton 403 GM CCC Carburetor Lean Limit Gauge Brand New | eBay


I have the other tools for stop adjustments, and the J hook for the air bleed.


I lost my TPS adjust socket though
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Old 10-24-2016, 07:09 PM
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This is a nice tool for mixture adjustment:


http://www.thexton.com/carb-adjustment-tool-p-26.html


Sadly, someone borrowed mine, I just didn't know it. I miss that tool.
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Old 10-25-2016, 01:15 AM
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check your private messages... just in case you have not logged in.

there is a lot of stuff to go thru ... chart A2 is one of the first steps... fixed dwell between 10 and 50 degrees. is a good starting point..

by the way.. if you learn this system.. is is the basis for most of the current engine control systems out there today.

a scan tool will help.. but they are almost impossible to find..

i don't know how far in texas this is from you.. but i would leap all over this.

https://killeen.craigslist.org/tls/5799948632.html

you won't find another so easily.. and you will find it works for so many GM cars back from 1982.. including the fuel injected versions.. think crossfire.. TBI TPI LT1.. and of course.. all the years of feedback carbs after 1982 or 83 when then went to a 12 pin diagnostic port..
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Old 10-25-2016, 10:15 AM
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Thanks gentlemen for all the info and replies.. I'm finally gathering enough info to have a rough understanding of these carburetors.

Just a heads up I metered TPS voltage and found it to be high, about .68 volts. So I dropped it down to .45 volts with a primitive adjusting tool I made from 3/16 steel brake tubing.. this changed nothing. Still runs like crap.

I also noticed the cap and rotor were old and corroded.. replaced those and still no change. Still rich.

So now I'm scratching my head once again. The plan is to remove the carburetor and thoroughly inspect it to ensure the gaskets are correct and that everything internal to the carburetor is in good condition. I'm sure it is, as I've already looked through it, but I'm beginning to suspect that the MCS is messed up somehow or some way.. no matter what I adjust the lean stop to, the MCS plunger travel is not affected.. it only changes if I turn in the rich stop.. so I am planning to yank it apart again.

I'd like to recheck float level. According to when I disassembled it it was low (3/8 as opposed to 11/32 per the spec table).
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Old 10-25-2016, 10:29 AM
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The qjet has plugs on the bottom of the main body that can leak causing you to run rich.

To test if this is your issue pull the carb and set it on a towel with the top removed. Fill the bowl up and let it set up to a day. In most cases you will find the towel getting wet in a short period of time if the plugs are leaking.

Another thing to check is that the carb was not put together wrong. You would be amazed how many "quadra junk" carbs I've gotten for free because after a rebuild they "still" didnt run right only to find that the metering rods had been damaged (mostly tips bent) during rebuild.


Most of the time (being where I am and not having emissions testing) on the ccc qjet cars we replace the hei and carb with non ccc versions and if the car has a 700r4 we set it up to run without a computer.
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Old 10-25-2016, 11:11 AM
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You can convert to a junk yard tbi for under $200.
In some cases you might even be able to get the intake in a partout with blown engine kind of deal.
Rebuild the tbi for around $60 and never look back.




Tbi is so easy to rebuild a 6 year old could do it as long as they watched out for the regulatior spring.

You are so close most will be a plug and play. The wiring harness are totally different. Your basically better off doing a harness swap. Its tons easier then you may think.

Like I said your in those years between no brains and tbi it's easy and cheap to upgrade.


You have the system I hate. It can tell you about a issue but can't adjust much to fix it.

Tbi can lean out a over rich condition, gives better fuel atomization, and better idle quality. If you have ever needed to stop and change jets half way up a mountain or flooded in the winter then tbi is for you.


I have a few crates full of older carbs. Crates with ones that worked great when pulled and ones that are just parts. I may have only one or two tbi units right now thpugh.
As once I put the tbi on after a hour long rebuild they stay on till The thing leaves my possession. The ones I do have are from engines I have destroyed the bottom ends on.

The only issue you may run into is your abs. I am in the dark on what kind of abs you currently have and If it will work with tbi or not.
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Old 10-25-2016, 12:06 PM
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I already epoxied the well plugs as a precaution while I had it off the first time.

In regards to the measurement tool being 1.07" for the lean stop, I've read elsewhere and found a manual on setting these carbs up. They stated the tool is 1.304" in length to set the lean stop.. or am I reading incorrectly?

I plan to pull the carburetor off when I'm home.. the car will idle so much cleaner if I stick a pick down the air horn and hold the MCS down so it won't do its thing.. making me think that I have the lean stop set way too high or a bent metering rod. The carburetor will still run if I unplug the MCS and turn the mixture screws in :\

Seems to me that something isn't right. I believe it's getting fuel from an unmetered source. I'll update yall this evening once I've started digging in and after I've read through the pages that Wayne sent me via PM.
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Old 10-25-2016, 12:08 PM
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I still have an ignition issue to mess with anyway. I replaced the cap and rotor and still have an intermittent misfire on cylinder #1. I swapped the wire with a spare I had that is known to be in working condition and #1 still missed intermittently.
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