Engine dies in gear.

[Livemeyer]

Hi all,

I'm running a 1951 5-window with a '68 327 and a mid-60's aluminum Powerglide. I have no history on the used transmission and not much on the engine either, except to say I was told it came out a '68 Camaro, but the heads are not original, they are off a mid-70's truck according to the casting numbers.

This engine has been a bit of a mystery, it seems to run pretty good, has lumpy idle, but liked to die after running a while and was fairly cold-blooded too. It had a strong odor of gasoline and spark plugs were fouled, so it was apparent that it was running too rich. So far this spring, I have replaced the Edelbrock 600cfm with a Holley 600 and installed an old transmission cooler adjacent to the transmission on the frame rail.

It has always idled really low in gear and would commonly stall out at a light or stop sign, but not always. Now after swapping the carb out, it dies right away. I thought it might be the vacuum modulator at the rear of the transmission, so I replaced it. I replaced it with an adjustable model, but I haven't made any adjustments to it. The engine fires up better and runs better with the new carb and doesn't seem to be running rich anymore. I have new spark plugs I bought last weekend but have not yet installed them.

I thought I might have a vacuum leak so I pinched off the two hoses that go to the power brake booster and the vacuum modulator, but it still dies.

I had bought an old used tachometer last year but it was reading erratic so I bought a new Auto Meter Air-Core tachometer and it is working great. So I set the idle at 1000 rpm, but when I put the truck into reverse or drive the idle drops to around 400 rpm, and the engine dies, unless I keep my foot on the gas pedal.

Any ideas? Is the transmission junk? I drove it around quite a bit last year so I wouldn't think so.

[Dead Parrot]

What's the timing?

Have you sprayed carb cleaner or similar around the intake gaskets to check for leaks there?

Did your head research specify what motor they came from? Wondering if someone swapped on a set of heads from a 350 since the bore size is the same.

[Wrenchbender Ret]

Try richening up the idle mixture screws.

[Captainfab]

I would suggest getting the timing set properly first. Then deal with the carb adjustment.

[Livemeyer]

Originally Posted by Dead Parrot

What's the timing?

Have you sprayed carb cleaner or similar around the intake gaskets to check for leaks there?

Did your head research specify what motor they came from? Wondering if someone swapped on a set of heads from a 350 since the bore size is the same.

I did spray engine starting fluid around the manifold and carburetor when I had the older Edelbrock carburetor on there, and it showed no vacuum leaks.

The heads, from my research, are 76cc smog heads from a mid-70's Chevy truck 350 engine. These are not performance heads and I suspect they are part of the problem, limiting compression. I have a new set of aluminum 64cc chamber heads that I will have a shop install soon, I'm waiting for a shipment of roller rockers and then I will deliver to the shop to have the work done. My hope was to drive it there, but I'll have it towed if I have to, but I'd really like to get this solved so I don't have to.

[Livemeyer]

Originally Posted by Captainfab

I would suggest getting the timing set properly first. Then deal with the carb adjustment.

I agree! Yet, I'm wondering what proper timing even is. I have it set at 8btdc when idling, but admittedly the idle has been all over the place and I have experimented with different timings. I may attempt to adjust the timing again tomorrow to see how it responds. I have had much better engine response since putting the new Holley carb on, but haven't experimented too much with the timing because, basically, I can't put it in gear and drive it!

[Livemeyer]

Originally Posted by Wrenchbender Ret

Try richening up the idle mixture screws.

I think tomorrow I'm going to install the new spark plugs, experiment with the timing, and then possibly adjust the idle mixture screws. I'll have more to report, then I can check back in and see what further responses I get here. Thanks.

[geezer#99]

Bump your initial timing up to 14 degrees. Your idle should increase. Turn the idle back down and adjust the mix screws for highest vacuum.

Don’t wait on those roller rockers unless they’re true rollers. Nothing to be gained if they’re just roller tip ones.

[Livemeyer]

OK, so I replaced spark plugs, bumped up the timing, tried making the idle a bit richer, and I have had some success. It's now back to 500rpm at drive idle, which is still too low, but it stays running and I can drive it around the block. One of the things I changed was a vacuum port for the distributor idle. It was coming off the lower front of the carb but I moved it to the side output that is actually labeled as such. I think this may have made the biggest difference. I think swapping in the new heads will make an even bigger difference.

[geezer#99]

The bottom port was manifold vacuum which should increase your idle if the vac pot is not ruptured. I suspect it is.
The top side port is ported vacuum. Should have no vacuum at idle.
Check your vac pot to make sure it’s good.

[Livemeyer]

Originally Posted by geezer#99

The bottom port was manifold vacuum which should increase your idle if the vac pot is not ruptured. I suspect it is.
The top side port is ported vacuum. Should have no vacuum at idle.
Check your vac pot to make sure it’s good.

Now that is interesting. When I changed to the side, timing was retarded, idle was lower, etc, had to adjust.

Now you think manifold vacuum is suspect? Could there be an issue at the manifold? I will say, it was my first time driving it after I made these changes, vacuum to the brake booster was from the carb instead of the spacer below it (between the carb and intake manifold) and the brakes grabbed hard (one of the rears locked up) when I moderately pressed the brake pedal while cruising around the block (15mph).

As for checking the vacuum pot I'm not sure what you mean or how to check, It's a new (although refurbished) Holley carb. I suppose I could try sticking my finger on the vacuum line out of the carb and see if sucks onto my finger, since I don't have a vacuum gauge.

[geezer#99]

Now that you describe it better your vac pot is likely fine.
To check it just pop the distributor cap off, hook a vacuum hose to the pot and pull a vacuum on it with your lungs. The point plate inside the distributor should move.
Vacuum for your booster can come from the back of the carb.
Your locking up brake could be from moisture (water or brake fluid) on the shoes.

[cadillac_al]

How much vacuum is it pulling anyway? My first thought was low vacuum.

[Livemeyer]

Originally Posted by cadillac_al

How much vacuum is it pulling anyway? My first thought was low vacuum.

I don't have a vacuum gauge, so I don't know for sure. I have a hunch that the 76cc smog heads on the 327 aren't helping much. I was speaking to someone else about this engine, his response was that the 76cc heads from a 350 on that 327 will make it perform like a 307.

[geezer#99]

Might not perform at all.
More like a 267.
Those heads can drop your compression below 8 to 1.

[Captainfab]

I can speak from experience that the 76cc heads on a 327 will turn it into a turd.

[Livemeyer]

Originally Posted by Captainfab

I can speak from experience that the 76cc heads on a 327 will turn it into a turd.

It sounds great, but yeah, it's a turd. I'm looking at probably picking up a newly-built 383. If I put the aluminum heads on that short block, I should have gobs of torque.

[Livemeyer]

Originally Posted by geezer#99

Might not perform at all.
More like a 267.
Those heads can drop your compression below 8 to 1.

This definitely explains why it's been such a bear to tune.

[68is4me]

Just for curiosity, what kind of distributor is it?

I have been fighting a timing issue on a 454 and getting it to run right. I am using a MSD pro billet HEI and for the life of me could not figure out why timing would never be correct. Well today I hopefully figured it out. I have been using a digital timing light, and the digital timing light does not work with the MSD dist because of the multi spark.

Just thought i would throw that idea out there. Maybe timing is not what it says.

[Livemeyer]

Originally Posted by 68is4me

Just for curiosity, what kind of distributor is it?

I have been fighting a timing issue on a 454 and getting it to run right. I am using a MSD pro billet HEI and for the life of me could not figure out why timing would never be correct. Well today I hopefully figured it out. I have been using a digital timing light, and the digital timing light does not work with the MSD dist because of the multi spark.

Just thought i would throw that idea out there. Maybe timing is not what it says.

Just using a good ol' fashioned HEI distributor. No MSD or other coil booster.

[geezer#99]

Originally Posted by Livemeyer

It sounds great, but yeah, it's a turd. I'm looking at probably picking up a newly-built 383. If I put the aluminum heads on that short block, I should have gobs of torque.

Sure you might have gobs of torque.
More than the 327 with those heads.
But there’s a trade off.
More torque but at a higher rpm.
Could be a dawg until you hit 2000 rpm.

[Livemeyer]

Originally Posted by geezer#99

Sure you might have gobs of torque.
More than the 327 with those heads.
But there’s a trade off.
More torque but at a higher rpm.
Could be a dawg until you hit 2000 rpm.

I hear what you're saying, but comparing a tired 327 at 250 horse/275 torque (probably being generous) to a new 383 at 400 horse/450 torque, I wouldn't call that 383 a dawg.

[geezer#99]

It’ll just feel like a dawg!
It’s where the torque starts to come in by comparison.
It’ll feel lazy until it hits 2500.
Many years ago I witnessed a race between a 69 Z28 and a 70 Hemi Cuda. That little 302 left that Cuda in the dust until a 100 feet from the finish. Both cars geared with 4.10’s.
I’d been lucky to at one time drive both. That Hemi with the much higher torque/hp was real lazy until it got around 2500 and then hang on.
So don’t always rely on what some numbers might say.