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Discussion Starter #1
Ok, some of you may remember I posted this same topic a few months back. Well I still haven't solved it?? Here's my situation. I have an all original 69 Z, DZ 302, matching everything. I'm having an idling problem. Once the car is brought up to operating temp it will idle for a few seconds then slowly choke itself off and stall. Today we finally have it at a point were it idles now but still wants to stall. It will idle steady for a while, then drop itself off a few hundred rpms, then bring it self back up. It eventully stalls though.
Here's what we've done so far: Completely rebuilt carb (Professionally, then we went through it a month later), adjusted floats on car, adjusted idle screws anywhere form 3/4 turns to 1 1/2 turns, (currently the car is at 1 1/4 turns on the idle screws and this is the best/longest wev'e gotten it to idle), installed my distributor into DJD's camaro and test to ensure it's operating correctly, checked, adjusted,ran and rechecked valves to be at .30, plug gap .040, timimg is at 15 deg initial, temp hold 180.
This all started after I had a blown head gasket (March). I had the heads psi tested, replaced gaskets, heads, intake etc.. and installed new distributor.
Today I found the rear of the intake gasket to be blowing oil out, just behind the distributor, making a huge oil mess. Other than a loss of oil problem and a mess, could this cause a vacuum leak, affecting the idle??
This problem has not affected performance, the car runs strong, just doesn't want to idle. Any suggestions/comments would be greatly appreciated. I have kept a log on what I've done to fix the problem, if more information is needed please let me know.

Thanks DJD for all the help and the use of your camaro. Just to let you guys know what type of a guy DJD is, he has more man hours under the hood of my Z than he does of his own car. Thanks for the help and tech info.

Mr.G

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Jess - Camaros Limited Nor-Cal
69 Z/28 Lemans Blue
 

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A vacuum leak is the first thing that I would check for. When I put my car together it was doing the same thing. You say that the car picks up RPM and then drops down and then it does it again. Sounds like the car is "hunting" to me. If the car is blowing oil out of the back of the intake, that my friend, is a vacuum leak. You really can't do anything (adjustments/tuning) until you get that taken care of. No matter how you adjust the carb, timing, mixtures, plug gaps, etc the car will be the same. Fix the vacuum leak and let us know how it runs.

I almost forgot, my car did the same at idle. What happened with me is that the vacuum leak was making the carb bring in way toooo much gas and the car would load up and die. At higher RPM's it doesnt' matter b/c the car can burn the fuel easier. Make sense? It's a vacuum leak.

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1969, X-44, Export Model, Hugger Orange, Std. Int., BC Rear(soon to be a BT 12 bolt), PDB, GMPP 350HO, M22 Supercase, SSM Lift Bars, AirGap, Holley 750, FlowMaster American Thunder Exhaust, FlowTech Headers

[This message has been edited by Judd (edited 11-04-2002).]
 

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Discussion Starter #3
Thanks for the reply. Wasn't sure if that would cause a vacuum leak, just found it yesterday. I'll get on that and keep you guys posted. Thanks again.

Mr.G

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Jess - Camaros Limited Nor-Cal
69 Z/28 Lemans Blue

[This message has been edited by MrGrumpy (edited 11-04-2002).]
 

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Well.... Is an oil leak out the back of the manifold actually a vacuum leak? The spot that the oil is coming from is adjacent to where the dist shaft goes into the manifold. This kind of equates to a crankcase breather as I see it. I don't want to say it isn't a vacuum leak but I can't see it sucking air into the manifold and expelling oil on the block and bell housing. The fact that the back of the manifold isn't sealed correctly might lead to an intake runner not being sealed properly as well.

Jess has gone through hell since he has brought his 302 back to factory specs but I think we are just about there. We have step by step eliminated one thing after another. The dist has a clean bill of health as it performed flawlesly in my car. After he got the carb back from a prof carb shop, it had a whistle when you cracked the throttled and was full of cheap parts. The whistle seemed to be getting worse and the engine idle still flucated from 900rpm up to about 1400 rpm and if you didn't keep your foot on the gas it would slowly die... I had Jess get a carb kit and I went through it! (this carb was new off the shelf when he got it last year!!)

Here is where we stand right now. Idles but flucuates between 1000 and 1100. We should be able to get this down to 900 rpm but can't. The worst part is at 1100 you can't hear that 30-30 cam that gives the DZ that distinct idle. To get it to idle we have the initial timing set to 15-16 initial with no vacuum advance in the picture. Idle mixture screws are 1 1/4 turn out. Factory setting on this is 1/2 turn. I run between 1/2 and 3/4 turn on my carb. (similar 780 vac sec, 2 power valve carb) If we lean it out it wants to stall, I can raise the idle and it it recovers but now idles at 1200 and fluctuates up and down +- 300rpm and dies. If I richen it beyond 1 1/4 turns it doesn't seem to have an impact so I know I'm right on the edge of the idle ckt. (at least we're still on the idle ckt) If we lower the initial timing the flucation starts all over again.

Jess has tripple checked the valve adjustment and I can't think of anything else right now. If you think I left anything out just ask!!

Thanks,

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...Dennis
"The '69, the '96 our local club"
and the "daily driver"
 

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Want to find a vacuum leak?

Get a 5 inch PVC pipe and cap it with a cap

Drill and tap for a shop air fitting. Install fitting. Install an air regulator, adjust for 3-4 psi of air.

Connect shop air to 5 inch cap made. Remove air cleaner and install PVC cap in place of air cleaner removed. Turn on air supply.

Use soapy mixture and spray intake system. Watch for bubbles. If manifold is leaking, oil fill will expell air.

I would also check to see if fuel is dribbling from venturis at idle. If it is, then, fuel level set too high.

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Everett "OBJECTS IN THE MIRROR DISAPPEAR UPON RAPID ACCELERATION"
 

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Since you went into details, I would bet the farm that it is indeed, a vacuum leak. My car had the exact same problems. Not similar probs but, the exact same problems. An easy way to check if the car has a vacuum leak is to squirt/spray some ether or starting fluid around the intake and base of the carb. If the car picks up idle when you spray it you will know for sure that it is a vacuum leak. Did you guys put a spacer under the carb? Did you check to see if it was "true." I had a leak there with my cheap Summit phenolic spacer. If the spacer is wet it too would be considered a vacuum leak


Again, I went through the same thing with my car. It was running rich, fluctuating idle, ran great at higher RPM´s but the plugs were drowning. BTW, how do the plugs look? Set the timing to 10 BTDC and 36 total advance. Another thing is that the TACH on my car was jumping all over the place. Then we thought that the carb was too big for the motor since GM recommends the 600CFM and we had put a 750cfm on it. Changed jets (down), advanced the timing, retarded the timing, fattened the mixture, leaned it out and then out of curiosity we checked for vacuum leaks and BAMM! there it was right on the back of the intake which in turn screwed the intake runner gaskets. So, we changed the intake gaskets, put the original #72 jets back in the 750cfm and set the timing again at 10 BTDC and 36 total advance and the car now runs like a champ.

Just humor me and check it for vacuum leaks. If I´m wrong I´ll buy you both a cold one
When I read the original post I thought that I had written it since it was so similar to my problem. I could be wrong but as you stated, you have to check the easy most obvious stuff first. Wish I had.

Good luck

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1969, X-44, Export Model, Hugger Orange, Std. Int., BC Rear(soon to be a BT 12 bolt), PDB, GMPP 350HO, M22 Supercase, SSM Lift Bars, AirGap, Holley 750, FlowMaster American Thunder Exhaust, FlowTech Headers
 

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Floats were a bit low and bringing them up to just below the site plug helped some.

Oil fill is in valve cover not intake would an internal leak still manifest at the breather? I like the forced air idea. A 1320 ft drop cord and my compressor in the trunk might make for a hell of a trip down the track!!

No external vacuum leak unless at the back of the manifold. It seems to blow not suck but that hasn't been tested. Since this mill has 11:1 pistons the curve has been set to keep the total timing down. Design was 12 initial and 8 vacuum from a manifold source. CA has 91 oct high test unless you run race gas so keeping part throttle timing mild is important for street driving.

Jess I have a propane torch and we can retest for leaks with it. You also mentioned that the under side of the manifold had signs of pitting, maybe an internal leak there...

Keep the ideas coming,

[This message has been edited by DjD (edited 11-04-2002).]
 

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Pull off the vacuum line and check valve at the Brake booster when the car isn't running. If there isn't any vacuum in the booster, indicated by an inrush of air when the check valve comes out of the grommet, you have a vacuum leak in the booster. The rubber cup behind my master cylinder was leaking for about a year and I never heard it leaking. Brakes were heavy and a bit stiff, but not overly bad. This raised my vacuum in the manifold by about 1/2".


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Mark Canning
1969 Indy Pace Car
350/300HP RPO Z11
My 69 L48 - 350/300HP Engine
 

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Discussion Starter #10
Thanks for all the ideas guys. I'll try anything. Just some more background. Everything in the engine compartment, engine included, has be replaced or rebuilt.
I'll check the brake booster idea today. My Z has to go sleep over at DJD's tonight. Found a water leak in the foundation of my garage. break out the jack hammer.
As for octane I run a mix of 100 and 90. Sometimes I put the 105 when I can get it. That 11:1 doesn't like plane 90 octane.
I like the air test, the propane next to the disrtbutor and a hot engine makes me a bit nervous. I'll try that, I know the intake gasket has to be replaced because of the oil issue. As for the intake, when it was off I was told the rear was pitted, so they used a little more sealant. I guess not enough. Thanks for the replys. I'll let you guys know what happens after I get her back from DJD when the garage is done.


Mr.G

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Jess - Camaros Limited Nor-Cal
69 Z/28 Lemans Blue
 

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I had an unstable idle in my 302 but mine was just slowly dropping RPM's at idle when fully warm and not recovering. Probably not the same issues but one thing nobody has mentioned was the exhaust heat riser passage. It may be sending too much heat up to the carb and causing the fuel in the bowls to boil. This condition will be made worse by fuel additives or high octane fuel. If you have a stock carb with the choke stove, you can block the drivers side heat riser passage with a flat stainless steel shim but leave the passenger side open. That allows the choke to still get heat but stops the majority of the excess heat from boiling the fuel in the bowls. You can verify this condition using a bucket of ice water and a towel. Soak the towel in the ice water and then wrap it around the bowls when the idle is unstable and see if it stabilizes. If it does, you need to block the passage. Worth a shot, right?

-Mark.
 

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A couple of thoughts - if it has pushed the intake rear seal out, there's excess pressure in the crankcase; check the PCV valve to make sure it's working, as that's the crankcase "exhaust" route. Is there oil in the air cleaner? If so, it's being "blown" out through the "intake" side of the PCV system because it can't get out through the PCV valve. If the side gasket seals are good, you won't have a vacuum leak from a blown end seal that affects how it runs - it'll just make a mess. When you put it back together (after checking the seal on the side gaskets and looking for oil in the intake ports on the heads that would indicate a bad gasket seal near the bottom of the ports), use RTV instead of the crummy rubber end seals.

Idle instability can also be caused by the vacuum advance not being fully deployed at your idle vacuum level; as the manifold vacuum varies at (rough) idle, the vacuum advance can "dithers" and keeps changing the timing.

Another cause is the centrifugal advance coming in too early, and with a rough idle, it does the same thing - it "dithers" and keeps changing the timing, as it's idling "on the curve"; it should be calibrated so the curve doesn't start until 100-200 rpm above idle, so you're strictly on initial timing (plus fully-deployed vacuum advance) at idle for timing stability.

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JohnZ
CRG
'69 Z28 Fathom Green
 

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So, Doctor. What is the scoop? Figure it out yet?

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1969, X-44, Export Model, Hugger Orange, Std. Int., BC Rear(soon to be a BT 12 bolt), PDB, GMPP 350HO, M22 Supercase, SSM Lift Bars, AirGap, Holley 750, FlowMaster American Thunder Exhaust, FlowTech Headers
 

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Jess had an emergency that is gonna keep us from working on his prob for a few days (his garage sprung a leak and the concrete floor will have to be busted up and replaced) I have his Z in my garage and will be parting it out if he takes too long to come get it!!
 

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LOL. I´ll start putting my parts list together then


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1969, X-44, Export Model, Hugger Orange, Std. Int., BC Rear(soon to be a BT 12 bolt), PDB, GMPP 350HO, M22 Supercase, SSM Lift Bars, AirGap, Holley 750, FlowMaster American Thunder Exhaust, FlowTech Headers
 

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Discussion Starter #16
Thanks for all the replys. I'll get started as soon as I get my garage and Z back. I'll keep everyone posted on the trials and hopefully the fix.
Thanks DJD for storing my car till my garage is fixed. Can you believe the HOA want me to park it on the street. Can you say Gone in 60 Seconds.
A quick one: will this problem also cause hard starts, like the car just turns over and over then finally starts?


Thanks,
Mr.G

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Jess - Camaros Limited Nor-Cal
69 Z/28 Lemans Blue
 

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Discussion Starter #17
Ok guys, got my garage finished and my Z back from the sleep over at DJDs. I replaced the intake gaskets, took my time an was real meticulous about installing the gaskets and intake. I used the copper/orange RTV ( nice touch!) for the front and rear seals.
Ok here's the bad news, car is still having the idling problem. I checked to ensure there was no vacuum leak at the brake booster. The was no oil in the air cleaner also checked the PCV and relpced to ensure.
John Z, you were saying something about the centrifugal advance coming in to early that the car would be idling on the curve maybe causing this problem? How would I check this? DJD is this what you were explaining on the phone? Also, would this come in to play with the vacuum advanced canisted disconnected. I ran the car yesterday with it unplugged. I'm reachin fellas, all out of ideas? Would changing the springs in the distributor effect the idle or does it just play a role off idle? Thanks guys for the help.


Mr.G

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Jess - Camaros Limited Nor-Cal
69 Z/28 Lemans Blue
 

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You can remove the rotor and put a rubber band around the advance weights which will lock out any centrifugal advance, and then it will be forced to idle with only initial advance and vacuum advance.

If you are then able to achieve a stable idle, it would indicate that the centrifugal advance is coming in too early (centrifugal advance should only kick in above idle), changing your idle timing, causing the idle instability.

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SteveN
'69 Camaro Coupe
'96 Camaro Coupe
'69 Corvette Convertible
 

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How do the plugs look? Have you tried a hotter set?
Do both idle mixture screws have the same effect or does one side seem dead?
Do you have manifold heat passages blocked?
David

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Check my web page for First Gen Camaro suspension info:
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67 RS 327 original owner. 69 Camaro Vintage Racer, 65 Lola T-70 Chev SB Can-Am Vintage Racer
 

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Discussion Starter #20
I drove the car today to a toy drive, just to get it out an run it alittle. I went with a colder plug a while back when I was tring to get the car off the race fuel, pinging on straight pump gas. For the plugs they look ok to me, there not built up with carbon, they look a little white if I remember right. I'll checkem tomorrow. When I started it today it backfired through the carb really bad and the passenger side blew black soot type stuff all over the wall??????? also a few times today it wouldn't start, like it wasn't getting something, fuel, spark??? It would turn over and over, like I had the coil wire disconnected.
I still need to check the curve and distributor thing. I was talkin to a guy today that had some problems similar when his MSD box wasn't getting enough voltage. Would this cause my problem? My thinking is because it runs fine with the stock distributor with the pertronics but doesn't with this distributor. Is this distributor get spark to run but not enough?? but we checked my distributor in DJD's car, and it ran perfect? Just tring to eliminate things.

Thanks,
Mr.G

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Jess - Camaros Limited Nor-Cal
69 Z/28 Lemans Blue
 
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