Okay, picked up a used factory 327 chevy (1967 impala ss) motor a few months ago for my kemp, up until a few days ago it ran fine, no bullshit, smooth shifts (turbo 350) etc..... All of a sudden I roll up on a red and the fuckin thing starts shaking, idle drops and stalls out twice, thank god I got home, just had to rev to about 1500 in park and burn out at every light!Ha! Anyway here's what I got: Stock 327 chevy, no modifications to drive train I know of Turbo 350 Tranny non-lockup out of el camino (seriously doubt this is the problem) Stock Rochester Carb, NOT A QUADRAJET, it's an old 4gc four barrel model pre-67 Aftermarket full length headers I'm racking my brain trying to figure out what the hell is wrong with it now. I replaced the points, cap and rotor were good, wires good, plugs new, pcv valve is good, no detectible vacuum leaks, fuel pump is fine, no fuel leaks, tried screwin with the idle mixture screws in drive no real difference detected in idle or vacuum. The ignition system is good all around. When I throw it in park seems to rev fine about 900 rpm, Throw it R or Drive and idles where it should at about 550 rpm, but runs like shit! It seems like it's skipping a beat, it shouldn't be the timing cause' I set to spec at 8 degrees advanced, and set point dwell at 30 degrees, by the book. Would appreciate any feedback if someone else has experienced this, am I overlooking something or do I need to rebuild or replace carb? Thanks in advance
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Sounds like a vacuum leak in the lines, intake or carb. Spray a little starter fluid around when its running and it will tell you where it is. How many miles on the motor, could be a timing chain slipped a tooth?
I dont particularly know about that tranny but how about the vacuum modulator in it?? The key seems to be it happens when it is put into 'drive' gear and presswure changes to bands/clutches.
I have chased my tail on a carb problem before on a 383 super bee which was in beautiful restored show condition.I could not tune it correctly. I finaly pulled out the compression guage and found two wounded soldiers. I overlooked this because of how perfect everything seemed. I would recommend a quick compression check to make sure you have a sound engine. If the cylinders aren't balanced then it never will tune right. You will also get a better feel to the condition of your "new" motor.
I don't know anything about this particular setup, but it sounds like the timing is not advancing through the vacuum lines to the distributor when in gear.
I would toss a carb kit into it just to rule it out, it probably needs it anyway. But squirt some carb cleaner around the base of the carb first as previously suggested to ferret out a vacuum leak. Sometimes a minor one won't show until there is some load on the engine. Bob
I had a modulator go bad and suck a tiny bit of fluid in, richening the mix and smoking like crazy. also, I have seen the rubber line get cooked because of tight headers and become a vacuum leak, 3 feet from where you expect one. Replace with a steel line, solved.
Try slightly adjusting the idle mixture screws. If they don't have any affect on the idle then you can be pretty sure that the idle circuits in the carb are gummed up which would be my guess. It gets enough fuel to idle with no load but not enough to idle smoothly with the extra load of being in gear.
If your vacuum advance is hooked to manifold vacuum the diaphram may have shit the bed. disconect at the carb end and see what happens.
The motor in my truck acted simliar after I first got it on the road. the motor was a junkyard engine and I didn't bother re-building the carb. One day on the way to work it wouldn't idle at all and was running lean at low speed but ran fine when I gave it more throttle..... I had to keep reving it. I bought a carb kit and some carb cleaner and rebuilt it in the parking lot.... that fixed it it has been fine now for 9,000 miles.
I really don't have any other suggestions but I think you could rule out a bad cylinder. If I understand you correctly, this problem showed up litterally from one stop to another. That means something broke or cracked from the time you took off from one light and arrived at the next. I'm guessing vaccum leak or tourque converter. Good luck.
Have you tried a vacuum gage on it yet? That would be the acid test to see if it is something internal or external. If the motor runs rough but the gage is steady, it would be external & vice versa. Bob
Do you have fuel pressure? I know it sounds stupid, but your pump might be dying. Just a wild ass guess since I can't hear your car...the other ideas I see here are better, but what the heck, anything might help.
If you've got another coil handy, swap it out. I've had them work fine at idle, but break down under load. If the transmission modulator is allowing leakage, you should see some smoke at the tail pipes. The fuel filter in the carbuerator might be a good place to look also, especially if it's the old brass "Rock" type.
Had a similiar experience with me Ford motor. Acted like vacum but I could find no leaks and the gauge showed good vacum. Found that the intake had sucked the gasket at one port. New gasket, problem solved.
Also, suspect the carb float. The phenolic ones get logged and sink, sometimes. Behaves just as you described. I had an 80's Caprice that ran best at 80 mph; anything lower was too rich. Rebuilt the carb and all was well. The floats are hard to evaluate; maybe someone on here knows how much they're supposed to weigh.
Classic case of insufficient information for informed troubleshooting. Don't be suprised if reading the responses make you even more confused. Good luck.
my thoughts check the inline carb filter wires plugs ditch the points alternator not charging until revved fuelpump
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I know this is an old post, but having the same issue and wanted to see if anyone has any tips. I have a 66 c10 with 327 and th350. engine vacuum is 18" at 800 rpm and fluctuates intermittently between 17-18". has performer intake, new 1406, new HEI, new plug wires. cyl#1 had 80 psi and all others 120, plugs are old. Timing is set to 4 BTDC Do you think the low compression on one cyl could cause rough idle and low 500 rpm when in gear? idle fluctuates 100 rpm 700-800rpm.
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