My crappy 1976 Chevy Nova(250 I6, auto) has been giving me problems since day one. I needed to by a car to drive to school and get decent MPG, and I ended buying this turd cause I didn't have any time to look around for a good Ford.
Here's my problem, it wants to stall right off idle because there's a "flat spot" in the lower end of part throttle. It's fine if a accelerate very gently but when it hits the flat spot it just cuts out until I give it more gas. It's noticeable when a rev it up also. It does not matter how fast I'm going, as soon a I hit the "flat spot" it cuts out. Here's a list of the parts I've replaced or installed:

Re-manufactured carb
manual choke kit
vacuum advance control
cap/rotor
plugs/wires
fuel filter
air filter

Plug gap and timing are within spec, and even when I play around with the timing and with gap there's no effect. Getting a strong blue spark from coil, and at idle it's pulls 16-18 inches of steady vacuum. There also seems to be a miss at idle, it has an erratic shake and pops through the exhaust. I checked for vacuum leaks and there's no cracked hoses or unplugged fittings. It will do it with the EGR and EFE unplugged and capped off.

The only other thing I can replace is the HEI module in the Dist. but the parts store guy said they are an all or nothing type of part, meaning if it were bad it wouldn't run at all. I really need to get this fixed before I drive back to school(82 miles one way) on Monday night. Please, if anybody could help me out then I swear the next vehicle I buy will be a Ford. Thanks!!!

 

Ben, I see nobody has given you any advice, constructive or otherwise. Maybe its because we're talking about a chevy, or even worse, a 1976 nova. So I'll offer this bit of advice: Cut your losses and make a planter out of it. Some nice yellow gladiolas might set off the turd brown those often came painted in. Sorry I couldn't help more than that friend.

If your knuckles ain't bleeding you did something wrong.

'72 F-250 "Hi-Boy" 4x4, Dana 60/HD44, FE428 @ 400+ ponies , NP435 4-speed, custom suspension w lift, mud on black.

 

It sounds like your timing has slipped a tooth. Your vacuem is decent but that flat spot sure sounds like a timing problem (also the pop through the exhaust). If it ever popped through the intake manifold that would really make me think it was timing. I thought it was your accelerator pump on your carb but you took care of that. If it has a zillion miles on it I'd say that you need to pull the water pump and pull the timing gear cover to see if the marks on the gears line up.

Don't feel bad driving a nova... I spent time for a while in a Vega (went through 3 motors).

98 F250LD 4X4
Slotted Rotors

 

I see that you've replaced the carb with a reman one, did check the accelerator pump just in case? With the engine off, remove the air cleaner and hit the throttle, if you see an initial squirt of gas then the accelerator pump is fine, if not it needs to be replaced. I hope this helps.

Kevin

 

It only has 94k, and I don't think it jumped a tooth. It has the crank gear and the cam gear meshed together(no chain). Today I went around the engine with a bottle of propane and found a small leak. I fixed that, and the idle smoothed right out and I gained a couple inches of vacuum. But of course it didn't fix the problem. The pump shot in the carb is good.

The day I drove the car home I barely noticed the flat spot. After I gave it a tune-up it got worse. And now after the new carb and the new vacuum advance, it's even worse. Now when it hits the flat spot it's feels like somebody turned off the key.

Any more suggestions?? I'm totally lost here.........

 

Try putting all of the old stuff back on. You said it seemed to run better that way. maybe the tune up was just too much. I don't know though. My girlfreinds mom used to have this pos 79 impala with a 305. We did the same thing. New carb, tune up, air filter, you name it. I could not figure out what was wrong with that heap of junk.

People who say it can't be done should not interrupt the person doing it.

 

I had a '76 Ford Granada that had the same kind of flat spot on acceleration. It would stumble right when you were speeding up to merge on the freeway.
I took it to a shop where they pulled the distributor and put it on a SUN machine and tuned it.
After that, no more flat spot. It ran like a raped ape.

 

The distributor is the only part I have not replaced yet. And by the process of elimination it's next. How much would it cost to have my distributor tested and repaired? Looks like I can expect to pay around $150 for a reman. one, I'm going to try and get my old one fixed first.

We'll see what happens next.....

 

We had a granada, or was it a monarch? I don't remember. But after you got the distributor fixed did you have to fix the saggy rear? My dad could never get his level. He should have just chopped the front springs and made a lowrider.

People who say it can't be done should not interrupt the person doing it.

 

I take it it's a "point type" distributor, otherwise I don't see how the 'strib could cause it. Sometimes the shaft bushings get so worn down they allow the shaft to wobble, but that doesn't account for the flat spot on accelleration.

I know this about Nova's, (GM in general, come to think of it) you can get a leak in the power brake booster unit (if it has one) that constitutes a major vacuum leak. -Think about the size of the vacuum line that runs to it.

This one is a little hard to detect, because who thinks of the brake booster when dealing with this type of problem?
One of the signs to watch for is a hissing noise heard from inside the car...

Observations:

The problem gradually increased after you bought it.

It acts like a classic vacuum leak.

The carb is new, and presumably good.

* NOTE: Vacuum problems characteristically cause higher than normal running temperatures, same as adding Oxygen to a torch flame increases heat

Chevies are also notoriously sensitive to valve trouble. One miss-set valve, or a collapsed lifter that someone adjusted instead of trashing & replacing could free up again over time and throw the valve adjustment right out the window...

I wouldn't trust any part of the motor except what you know was bought new, at this point.

If you can - take it back to who you got it from, and make them fork over the cash you are out on the deal, since they MUST have known what was going on, and compensated for it just enough to wish their trouble on YOU.

 

It actually has an HEI ignition, but the more people I talk to the less I think that it's the problem. The '75 and later 250's have an integral intake and cylinder head, I've heard they are prone to cracking. Every symptom points to a vacuum leak but I sure can't find it. Which led me to believe it may be something else. Also, the car does not have power brakes(or power anything).

Thanks for all the help even though it's a chevy!!!

 

Ben, if you think it's a vacuum leak, spray WD-40 around where you think the leak may be and when the engine rev's you've found your leak. The WD-40 will get sucked into the leak. Good Luck.

Kevin

 

BOSS_358, never had a problem with the suspension. Always seemed level. I could always tell a Grenada or a Monarch coming down the road. Every one I ever saw had the PS hose hanging in a short loop under the car!