Thread: Chevette blues

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It's not what you know, it's who you know.

My good friend, proprietor of Hamilton auto repair, hooked me up with a NEW muffler, and a used (like new) exhaust which i was able to cut up and fabricobble into a functional exhaust. I flipped him a 20 which I thought might get us to blows before he accepted it. I told him to spend it on the wife, and he reluctantly pocketed it.

This electronic carburetor is not yet fully comprehended by myself.

Also it is supposed to be computer controlled spark advance. There is indeed no vacuum canister on the side of the dizzy. However, between the factory repair manual and the electrical manual supplement AND my own eyeball scrutiny:

This thing is a fixed spark advance.

I gotta get it running and test my theory.

Now that the intake manifold is off, that lets me peek under the petticoats. (Thanks, AvE, you corrupted me.)

The NOS fuel pump has a leaky check valve. Cam eccentric ok, push rod present. Next NOS pump is on the way. It is slightly less difficult to remove the fuel pump from above. (Intake removed) I really want a mechanical pump on this thing.

I have a mechanical/ vacuum advance HEI and a NOS non-computerized carb on the kitchen table (yep, I'm single) just in case I can't get it all straight. That's what did the trick for the late wife's diplomat. Anyone remember?

I painted the 318 Mary Kay pink and purple. She would race the local fuzz, they would block the road good and proper and the diplomat never lost.

That Police Interceptor engine had received my loving attention repeatedly. It was running a Quatrojet Dualjet which had only been made for a couple years- it's a two barrel in disguise. I had a Carter 700 sitting on the shelf, all dialed in. Her direct orders were that if she ever lost, she was yo tell me immediately, come home and I would swap carbs for a rematch.

Hmmm. Back to the chitvette. Yeah, changing out the dizzy and carb fixed the diplomat right up, but I'd really like to try to learn enough to keep the chitvette stock. The electronics and vacuum controls are not simple. The EGR was leaky, so I made a block off plate to eliminate it. Don't tell the EPA.

When the fuel pump comes in, I can get back to work.

BTW in the teardown I may have found the big vacuum leak I've been chasing. The underside of the carburetor base gasket with grid heater got folded under on one corner.

Originally Posted by firebird77clone

.....The EGR was leaky, so I made a block off plate to eliminate it. Don't tell the EPA.

You may be well aware, but just in case.... EGR was introduced mostly to allow the OEM to advance the timing more without clatter/knock/detonation with the crappier fuels and other "detuning" features back in the mid-70's. Puffing small, controlled amounts of exhaust gas into the A/F stream acts like octane to slow down the flame front in the cylinders - slower burn, no ping, no detonation.
If you block off the EGR you're going to need to re-curve your distributor, or at a minimum back off on the timing a few degrees which is going to make that little 4 cylinder even MORE anemic. You'd be much better off leaving the EGR functional. Just my $0.02, learned from experience on my '78 T-bird many, many moons ago (Intake port to the EGR plugged with carbon, blocking flow, thought it was going to rattle the pistons out on the ground).

Thanks for the info!

Removing it a step in identifying and eliminating vacuum leaks, it doesn't seal well.

The new fuel pump is on, primed and tested.

Intake manifold is on, minus one bolt (top left) which got overlooked. Everything will have to be loosened up because that last bolt won't thread in. Bummer, that little oversight will take at least an hour to remedy.

Oversight remedied.

Now to figure out where all this mess plugged in.

It's back together running about the same.

Idle is a slightly improved.

Who thinks it might be productive to try the original carburetor?

The carb currently on it is a replacement, not exactly the original. But reasonably new.

Originally Posted by firebird77clone

Who thinks it might be productive to try the original carburetor?

The carb currently on it is a replacement, not exactly the original. But reasonably new.

If you don't know the history of the current carb, I'd buy a kit for the original, boil it out to clean it well and install the kit, paying careful attention to the float level. If it has a composite float instead of soldered brass, buy a new float, too. Composites can change density over time and lose buoyancy.

Current carb was purchased new, they never got it running right. This makes me wonder if the carb was even the problem.

All I've really accomplished so far is getting it back to a mechanical fuel pump.

Originally Posted by firebird77clone

Current carb was purchased new, they never got it running right. This makes me wonder if the carb was even the problem.

All I've really accomplished so far is getting it back to a mechanical fuel pump.

Name brand carb or maybe from China? Does the carb adjust for idle mixture, changing vacuum as you go rich & lean, or giving you a clean lean & rich RPM change so you can balance half way between? When you checked the oil did you look for "sparkles"? I'd be wondering about cam lobes. Can you get away with just pulling the rockers & lifters, keeping everything in order, and looking through the lifter bores as you rotate the engine? Or check the lifters as they come out for wear? Did you check the compression, and do a leak down test to check valves? Lots of questions, I know, but you're chasing gremlins in the Chevette!

A couple thoughts for you. # 1 - the EGR valve only operates at lower rpm ranges. At wide open throttle there's no vacuum to open the valve. Just keep that in the back of your mind when thinking on power transition. # 2 - I don't remember "electronic" carbs to much and I am NOT searching for info on how each carb circuit operates because = # 3 - It's a Chevette! It's like half a car!! LOL.. What I remember most about them was it was a coin toss about what was gonna trash first, the cam or the crank! # 4 - If you are having fun - go for it - watch out for vacuum leaks, all those old parts and hoses can be a mine field for vacuum leaks..

The only adjustment is the throttle stop screw.

The computer controls the mix through duty cycle at a fixed frequency.

Compression checked good.

It runs good at higher rpm, dies if under 1/4 throttle.

I understand the cars reputation, but this used to be a very reliable great running car.

I'm not certain if it is your carb but, there were adjusters hidden behind welch plugs. See if you can locate a drawing and locate where the adjuster might be,see if a plug or cover is there and remove it - could be just what you need?

Originally Posted by firebird77clone

The computer controls the mix through duty cycle at a fixed frequency.

That SOUNDS impressive, but WHAT computer? The Chevette didn't come with any type of computer that I recall, just an ECM and it didn't control mixture. I'd put a kit in the old, OEM carb and put it on the Chevette.