frostindahouse

Hey Guys,

So I apologize for the lengthy post, but I wanted to list everything ive done so that someone has the best chance of helping me.

SO I have a 1986 z28 manual with a carbureted 305.

I just rebuilt the carburetor and was super happy that I managed to pull that off. I bolted it back on, and replaced one of the vacuum hoses (the big one that goes from the front of the carb to the oil chamber)...Although I think i need one size smaller..it fits but its not super snug.

Anyway, I went for a drive...and it was ok for like 20 min untill it started acting really choppy and idleing really low and then the check engine light came on and the car died. I opened the hood and saw that hose came loose so I reconnected it, and it fired up fine.

Over the past couple of days I have been adjusting the idle every time I start it (cold idle) but right now its a little too low (around 500RPM)... and warm idle is a little too high (around 1000rpm)

Anyway, this last time I started it up it ran like complete ****...I pressed on the gas and it was stuttering and everything, and I went around back and there was liquid oil out the back like it had shot out of the tail pipe. I pressed on the gas and some more came out...I didnt actually watch it because i had to get in the car to gas it, but there was noticeably more on the passenger side then the drivers side.

It died like twice, but I started it again just wondering what the hell was going on(it has ran fine for a year and ran even better for the last week since the carb rebuild)...I found that after it warmed up though, not only did it run fine, but it no longer spit oil (or another black liquid..not exactly sure it was oil)..I took it for a drive and it pulled and reacted fine...no more loss of power or stuttering or oil spitting...

A friend of mine said it could be the seals??? But I didnt see any blue smoke or anything...A little white smoke, but it was really cold (like 45 degrees) so I figured it was just heat.

So...any ideas?

sailtexas186548

iTrader: (2)

could be condensation in your exhaust mixed with carbon so black water came out.

The running funny could have been the cold, or a number of things. Its pretty extreme to have black liquid oil come out of your exhaust so i doubt it was oil

frostindahouse

Thanks for your reply!

Well it was cold wet and rainy, so that is a logical explanation, and certainly better to hear then a big job of some sort.

I would think that if oil was in the engine at all I WOULD be seeing blue smoke right?

So looking at these issues separately and as a coincidence, what could cause a car to run bad and stumble while cold but be fine when it warms up. I'm aware the low idle is probably a contributing factor, but that is slowly sorting itself out (the car warms up pretty quick so i can only adjust the cold idle for a tiny bit, and then have to wait till the next day for it to be cold again). Any idea of what to for symptoms of this problem?

HF_monster

did you readjust the choke when you rebuilt the carb? did you remove the idle mix screws and check for damage? and did you make sure the plugs in the bottom are sealed with epoxy when you cleaned the carb?

ASE doc

Good call. Also, cold idle with choke closed should be 1,800 on initial startup(highest notch on fast idle cam). After throttle snap, idle should drop to 1,200. Then after warm up, idle should settle down to 550-600. Idle mixture screws should be set at about 2.5 turns out. Best to set them using a gas analyser.

frostindahouse

Readjusting meaning engaging it with the spring? if so then yes...I wasn't aware there was any adjusting needed...


I removed the screws, but didn't really look for damage...the thread doesn't seem broken if thats what you are asking.

Yep, with JB Weld, I let it sit over night before I put it back together.


REALLY???

I was reading the sticker on my hood and it said 700 and 800, so I assumed 800 was cold idle and 700 was warm idle.

So I hate to be the newb here...but everyone keeps saying "2.5" turns out...What exactly does that mean? does it mean that I screw it all the way in to where the spring is fully compressed, and then I rotate it 2.5 turns, each turn being a full 360 degrees out meaning counter-clockwise?

Secondly...There is a screw right near the fuel inlet on the passenger side...thats the idle after throttle snap right? The screw on the drivers side under the TPS is the warm idle right?

If all of that is true, then how do I adjust the idle BEFORE the throttle snap?

Thank you everyone for your help!

**EDIT***
Could that liquid be gas? I just went out there again, and it stumbles, almost like its misfiring when its cold, but as soon as it warms up it runs fantastic... is there anything that would make a carburetor not work while its cold??? From my understanding the choke only controls airflow right? but is there anything that actually limits the carburetors ability to gasify fuel when its cold?

HF_monster

for the mixture screws yes turn it clockwise untill it seats be carefull not to over tighten and damage the screws. from there 2.5 full turns counter-clockwise.

your warm idle should be 700-800 RPM.

the screw on the drivers side is the idle RPM screw.

The choke needs to be set by distance to the choke tower I cant remember what it is off hand.

Bobbyz

iTrader: (1)

I would looking into intake gasket seal. i had a similar problem and that's what it turned out to be for me.

ASE doc

I apologize if I misinformed you. I didn't notice that your car is manual trans. Auto V8 car generally idle about 550-650, depending on application. The choke setting HF Monster refers to is with choke pull-off activated(vacuum). Its generally about 1/4 inch. There should have been an adjustment guide with your rebuild kit.

To adjust initial start up idle, before throttle snap, the engine needs to be completely cold. With the choke adjusted properly so that it closes completely(align the notch in the choke thermostat with the center of the rich/lean marks on housing), sweep the throttle once by hand and release it. The choke should snap shut firmly and the fast idle cam should now be at it highest point. Start the engine and adjust the fast idle screw to the desired high idle idle without disturbing the fast idle cam itself.

The fat idle cam can be manually set to fast idle by opening the throttle, lifting the the end with the weight on it and lowering the throttle to rest on the cam. However, the fast idle setting will only be accurate with the choke closed which must be done with the engine fully cold.

frostindahouse

ASE DOC,

Thank you!

I just went out there to do all of this...my choke seems to be functioning correctly (it snaps shut when I open throttle).

My choke pull off...I pushed the lever in and then put my finger over the vacuum port, and I observed it still moving out ever so slightly...a tiny tiny bit....when I let go of the vaccum port then it released back to its resting place...do you think its bad? or is it normal for a tiny bit (1/10 and inch max) of play?

Another thing I think I should mention at this point:
When I rebuilt the carb, I was looking closely at NAF's thread here:
https://www.thirdgen.org/forums/carb...-ccc-qjet.html

And I came accross this picture:



If you look at that little silver metal rod in the bottom left of the carb...Mine was bent outwards, away from the carb....Observing that his was straight and that the linkage actually relied on that piece, I bent it back and insured that it caught the linkage like it should.

***BUT**I cannot adjust the idle at this point anyway...My car stutters and idles really low when cold...Im not getting any codes, but it sounds like a big block rumble...almost like it is misfiring...and some liquid shoots out of the exhaust at high throttle...I think its gas....I observed the very second it hit open loop though and it instantly went from a broken rumble to a healthy steady idle...I saw no change on the choke or anything like that at that second though...

Do you mean the gasket in between the carb and intake? There was two in my rebuild kit, I put on the closest matching one...I dont think either one matched the one I took of 100%...Should I try the other one?

ASE doc

The fact that it runs well in open loop and falls apart in closed loop tells us that mechanically the engine and fuel system are fine. In open loop, the engine and carburetor are operating entirely on their own with no input from the ECM. Once the system goes into closed loop, the ECM uses information from the O2 sensor to control AFR via the mixture control solenoid. It is possible to misadjust the MCS to the point where the ECM cant manage AFR effectively but then I would expect to see the engine run poorly even in open loop.

Check the TPS. Its a common mishap to break the plastic TPS rod, causing the TPS to read full voltage at closed throttle. The TPS should read about .5v at CT and 4.5v at WOT. Test the CTS for resistance. It should read about 3,400 ohms at 70 degrees and 185 ohms at 210. Also, test O2 voltage as the system goes closed loop. Is it going high? From the sound of your symptoms, it sounds like the engine's going lean, so if the O2 is reading correctly, it should read low voltage(about .2-.4v). If it's reading high(.6-.9) then the O2 may be bad. To verify, pull a plug and see if its really light in color, like lean AFR.

A scan tool would be of great value right now. It would allow us to see what's happening as the system goes closed loop. Is the MC solenoid responding to the O2 sensor? Is O2 voltage responding to changes in MC solenoid frequency? Id say not. The term "feedback" is based on the relationship between the O2 and the MC solenoid.

frostindahouse

OK, perhaps there is another thing I should mention.. (this was my first carb rebuild)...

The MCS is that little plunger that goes into the center of the carb over the float right? I didnt count the turns when I took it out, and I read somewhere that I should tighten it only 4 turns...so thats what I did...It still seemed kindof loose and not all the way tightened.. and the little cap sticks out of the top of the carburetor...could that be the problem? Should I try to tighten it down a little more?

Also, its official...I only got 77 miles to a full tank of 87 octane gas. Before the rebuild I used to get at least 100-110, granted It has idled for a collective amount of 20-30 minutes.

For the TPS, im still a bit confused on how to check the voltage..Ive done a search and couldnt really find anything other then posts just saying to check the voltage...how would I go about doing that?

The o2 sensor was replaced about a year ago, but ill check it.

And what is a CTS?

A scan tool just might make its way into my inventory...I'll look them up.