This is long but I have to give the details to fix the problems.

I also apologize for posting my vette problem on the 3rd Gen Board but I know the a lot more people on 3rd Gen than I do on the vette forum.

Car idles very poorlly when in Drive. It's a 350 with a stock Q-Jet.

Car has never idled really well, I've had for 17 years and 4 rebuilds of carb to fix the problem. The guy that had it before me rebuilt the carb once also. In 1983 it would idle when the car was in Drive and act like it was about to stall out. In 1984 I had a Isky Mega Cam installed single pattern .470 lift and 270 degree at 0 according to Isky. Idle got a little worse but not much. In 1985 the idle got bad it would die idling at a stop light unless you held the brake and gave it a little gas or shifted to neutral.

Over the next few years the idle problem got worse and each rebuild would say "idles that way cause of the cam". Isky said the cam should idle fairly well and not die when sitting at stop lights.

Car was stored from 1990 until 1998. Idle problem was never solved. I was out of the car thing cause I got married and it wasn't the right time for it, ten years later wife is kinda ok with the car thing again.

In 1998 Carb was rebuilt again, and the problem was the same or worse than ever. I called Isky up again, described the problem, they said it need a performance advance kit. Got that installed (Mr. Gasket) for about 2 days the car seemed fixed, then it got as bad as before, then worse. When I asked the local mechanics they were "sorry it's not stock can't help you" or "I don't work on corvettes" for the most part. In other words, the problem would be too time consuming to figure out.

Over the last few months, the idle has gotten worse, car had a tune up, plugs, wires, coil, points, fuel filter, air filter, timing checked and reset, carb tweaked. Then the car had a round of power surges, press the gas petal and the car po-go'd, accelerate hard cut out accelerate hard cut out. Ended up replacing the gas tank cause it was rusty and fuel line. Pogo went away, then a month later pogo returned. I replaced the fuel filter, (car has one at carb and one in line). Pogo went away again for the most part. Idle problem same.

Two weeks ago, I found a Dyno service near by. Tested the car. 160 horse power rear wheels ( 350, cam, headers Turbo 400) That was terrible!!!

Dyno guy said the ignition system almost didn't register on his computer. He mess with it to get it too read. He managed to the hp to 175. The graph was unreadable over 4000 rpm cause the points were shaking causing misfires and ignition system wasn't make a good voltage. He moved the distrubiter about 1 inch (turning) and it didn't do anything. He shook his head and was like,"I've never see that before!" He twisted some screws on the Q-Jet and basically they didn't do a whole lot. He was amazed the adjustments on carb didn't seem to do anything. Finally, he hit a combo that worked and the car idled right for about 1 minute, then it started acting up again. When he finished it was a little better.

Told me I needed a new carb and new ingition system. At when at Wide Open Throttle the Secondarys barely open. The engine pulled 30 inchs on the vacuum gauge. Dyno guy said that was proof the car should be able to idle with the Isky cam it's got. O2 sensor show the car was rich at idle. However at high RPM it was leaned out to 16.5 to 1....way too lean. In fact it leaned out too much too fast. Messing with the carb didn't change how fast it leaned out in any meaningful way was about 16.0 to 1. I checked the fuel pressure it was 6-7 pounds when trying to crank.

I did the cranking compression test. I realize I screwed it up, after reviewing an engine building book. I blocked the choke open but not the primaries and secondaries on the carb. I know this would have made some difference.

Here the data. Each was test 3 times. All plugs looked black and rich except 4 and 6 they were tan/brown and looked about right.

Engine has Mobile 1 5w-30 in it, could this thinner oil effect the test? Should I test test with 10w-30?

Cylinder 1

85 low 100max,

Cylinder 2
could not get the attached treaded in cause the A/C bracket was so tight.

Cylinder 3
65low 95max

Cylinder 4
65low 85max

Cylinder 5
65low 120max

Cylinder 6
80low 90max

Cylinder 7
90low 120max

Cylinder 8
105 low 110max

That looks pretty bad to me cause some vary by more than 25% (85peak and 120 peak 29percent variance!!!)

I did find carbon in the rotor cap and scraped some of that off.

I also found the glass insulator part of plug in cylinder 3 was broken.

The plug gaps were between 30 and 45. Which is pretty bad. I regapped all to 35 because the two cylinders that were gapped at 35 looked the best they were a light brown color. The other 6 plugs looked more black than brown. The engine has R44T's in it.

Car idled better at first. Even idled in drive for about 2 minutes. Took it for a drive. It stalled at the stop sign just like it has been. However it did seem just a tad better than it was.

Comments?

Suggestions?

Does this 350 need a rebuild for top performance?

 

With them ALL being low..are you sure the cam is in right? (not a tooth off)

Just an idea....

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ASE Mechanic/Machinist/Smog Tech

1999 NBM Trans Am
1986 Chevy 3/4 ton pick up
1981 corvette
1995 Kawi ZX6R

GO #3

 

The guy that did the cam install is one of the best around here at least.

However, I've not checked it. How would I check that?

When the car was Pogo could it have jumped timing or something like that an have gotten off?

In the current state it did dyno 175 rear wheel horse power.

 

I've never seen a SBC "jump" the chain. They usually strip the gear and quit running all together or get so loose that they beat the timing cover to death and cut a hole in it.

Did it run OK after the cam install?? (as far as power..SOTP??) Or was it "doggy"??

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ASE Mechanic/Machinist/Smog Tech

1999 NBM Trans Am
1986 Chevy 3/4 ton pick up
1981 corvette
1995 Kawi ZX6R

GO #3

 

Note he said he didn't hold the throttle open for the compression test.

Until it is done properly, the compression test will not give you good information.

Get rid of the point ignition system, either electronic conversion w/new coil, or HEI or aftermarket system (you can make the point system work, but they were always a problem with Vettes). Make sure you have the proper voltage going to the ignition (12V for HEI, for instance). Then see how it is.

In the old days, we used to say, "90% of carb problems are fixed with a set of points & plugs." Point being, many ignition problems were mis-diagnosed as carb problems. Sounds like you already know you have ignition problems.

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82 Berlinetta, orig V-6 car. Rescued w/86 LG4/TH700R with all harnesses, sensors, ECM, etc. 2.73 open. Cat-back from '91 GTA, Accel HEI SuperCoil. AMSOIL syn lubes bumper-to-bumper. Daily driver, work-in-progress (LB9 w/ZZ3 cam, exhaust, paint, etc.).
57 Bel Air, my 1st car. Currently 396 .030 over, Weiand Action+, Edelbrock 1901 Q-Jet, Jacobs Omnipack, 1-3/4" headers, TH400 w/TCI Sat Night Special conv & shift kit, 3.08 10-bolt, AMSOIL syn lubes bumper-to-bumper. Best 15.1 @ 5800' Bandimere. Daily driver while Camaro was being put together.

 

The car seemed ok, after the cam install. I as a little disapointed it didn't give a big power increase SOTP. It did seem slightly faster.

Either tonight or tomarrow, I'll redo the compression test, even if they all go up 20points the numbers will still be pretty bad.

I understand, about the points. I just got a set of ACCEL high pressure points, should I fool with these?

Would a new MSD tach drive distributer and MSD 6AL spark box, + wires and plug be a sure fix for the ingition problems?

 

have you inspected and replaced all the vacuum lines, then checked for vac leaks? you would be suprised what they can do...i was having the exact same problem (poor idle...) i put it off as being my cam, until it started to die at stop lights. i hunted around and found that the carb was leaking at the base. changed the gasket and wound up stripping the carb mounting bolt holes changed the intake, installed carb studs and now the idle is a million times better, even though it still varies slightly....but not tooo much, maybe THATS my cam (218/224 .462/.469)

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350, Comp 262, Edelbrock Performer intake 600 cfm carb and exhaust, headers

 

I'm assuming that the computer stuff is all there. Here's how you do a shade-tree adjustment of an electronic Q-Jet. Find the ASDL (assembly line diagnostic link) connector. You MUST put the computer into diagnostic mode! There are two holes next to each other that you short, but you'd have to look that up. What that will do is hold the solenoid cycle and the timing steady. Remove the plugs that cover up the idle mixture, air bleed, and TPS adjustment.

With the motor off and the choke open, adjust the TPS screw until the voltage between the middle and ground wire is roughly 0.5V. Check your specs to be sure. Now, with the engine warmed-up and idling, adjust the idle mixture screws on both sides, just like a regular Q-Jet. Go back and forth until both sides are "even". Then go to your air bleed and turn it in or out until it smooths out.

When you are done, you should be rewarded with a smooth idling electronic Q-Jet. You will know that it's set when you pull the paper clip out and the idle doesn't change. That means the computer is satisfied with what it sees and won't change it.

If the Q-Jet is set up and it's still not idling right, then it IS the cam. It's not a good idea to put such a big aftermarket cam into a stock motor. Surely, there are some good GM grinds out there that are made to accomodate the stock heads, intake, and exhaust and still wring decent performance out it.

Maybe the people at Isky can help you once you get your carb and ignition problems squared away.

 

JRR,

My Q-jet isn't the computer controlled kind. I'm doing wires, plugs and timing check tomarrow night and I'll check some vacuum lines.

thanks

 

I've been busy...with the vette...here's the Redid the cranking compression test the right way, car was nice and warm had been driven about 10 miles and rev'd at various RPM. Pulled the plugs and I know one really can't read them after they've been in and driven on...but they were a nice tan color this time instead of oily black. Had the choke, primaries and secondaries open this time. The compress numbers were a little worse this time one was as low 65 after 4 tries but all in all they were pretty close to the first numbers. one 65 the rest were in the 85-110 range. Squirted some oil in the cylinders and redid the test. 3 cylinders came up from 65-85 to 90 to 115. Guess that settled that the rings are not sealing. I was pretty depressed in denial (not the river-little pun there) for about 3 days after doing this. I had a friend helping he was not very supportive.

Anyway, replaced the rotor, cap, and coil. I was going to replace the points with my friends help but he couldn't remember how to do it. Learned later that the reason we could turn the engine over to line up the points was because it was in park...yes I know quite stupid...I hope to get the new high pressure Accel points in the car sometime this week.

Anyway this weekend I hope to get the new plug wires on and new plugs in and pull the carb. I've located a local Q-Jet tuner!!! He's got a test engine so I think the carb will get a good once over next week. That's the good news.

Local machine shop told me if I pull the engine, a stock overhaul using my old parts but new rings and pistons will cost $1000. I can get the engine redone as 383 stroker for $1500 with the old heads, the 383 w/vortec heads is $2000, 383 with GM Fastburn heads $2500, adding a roller cam add $700. This machine shop was junky and not exactly clean. I don't know their rep well enough to know if they are ones to do it. I'd like More Performance in Charlotte to do the rebuild but they are about 2-3times as expensive...I'll talk with them after I have some $$$ in hand to do something. Timing pretty bad for me to be spending that kind of $$$ on the car...If my wife lets me get the engine rebuilt it will be after tax time.

I doubt I can pull the engine myself...my friend balked at even the idea of a rebuild...and told how hard it'd be to pull the engine in my garage...he suggested getting rid of the car...I've had this vette for almost 18 years and I really don't want dump it...so I guess I'll have to pay someone...

I've not counted the total cost of all this yet...it's a real mess...looks like about $6000 for starters...cause beside engine there is a tranny problem and suspension problems (springs are toast) I've got the kit for the suspension so that's good. Good part about this car is the paint, body, interior are sound

I guess I'll work on the small stuff between now and then. I plan to order a Vacuum line kit for the headlights and wiper door...cause the car has vacuum leaks and see if I can get that fixed next. Also plan to order a new fuel line, sending unit and sock, maybe pump too. I need to nail the fuel system down.

Any suggestions?