vette442

I have a 47K mile '71 LT-1 (dead stock) that is making me insane. It's my second one, and is running poorly - stuttering, bucking under acceleration, and the like - just like my first one (a '72) did. I sold that one out of aggravation in 1999, but would like to keep this one unless it won't run. Once at higher RPMs, the stuttering and kicking and roughness goes away (a little). I pulled the Holley since when I got the car, it was loading up and fouling the plugs and running rough as described. I pulled it in favor of an Edelbrock Performer 600 (which semi-cured my origihal '72). At first it was slightly better, but would die out a minute or two after being started and would not refire. It just floods and then starts after 10 minutes, runs for a minute or so and dies again. Soooo, I pulled that carb in favor of a Mighty Demon 650 last week. I put that one and it started for 5 seconds, died out, and I did not try to refire due to getting a lot of gas on the intake for whatever reason. I didn't even bother to touch it since then since I was so agitated. My main question is: Does anyone have a 70-72 LT-1 that runs well on a regular basis? If so, what's your secret? Have other LT-1 owners experienced the loading, folued plugs, and bucking under acceleration with these things? Thanks for any insight.... :mad

Bullshark

vette442

I had a similar problem on my 70 LT-1 Turned out I had the wrong Carb flange Gasket. I replaced it with Holley part # 108-12 which corrected the (my) problem.

Bullshark

Gordonm

Mine was original for a little while. I was running the 780 vacuum Holley and it ran fine. A friend is running the carb now and it has been OK. I since have put in a different cam heads and some other mods but i still call It an LT1. It runs great. Idle to 7000 rpm and does not miss a beat. Not saying I have never had problems but a couple of blown power valves and a stuck float once.

TJefferson2020

I had similar problems with my '70 LT1 - I have since had the entire engine rebuilt and it runs great. But before that, I bought a new Holley and it helped but it still ran badly - Although I'm not sure I think that biggest issue was that the dual point distributor dwell setting kept vibrating and changing it's setting - I noticed more vibration as the mechanical valve train would gradually get loose - and whammo! engine runs like crap. I have since replaced the distributor with a Mallory billet unit and a pertronics set up and it runs great!

Check your dwell settings - if they are off just a tiny amount the engine will freak!

pm

vette442

Guys - thanks for the tips so far. Just as an ironic addition, I was at my Corvette mechanic's tonight to drop off my '85 for inspection. He said "I was just doing carb work on that silver LT-1 you used to own yesterday - the guy could get it to barely run halfway down his driveway and it would just die out." They haven't solved all the LT-1 Gremlins on that one either yet..... My mechanic just spent 7 years doing a frame off on his own '70 LT-1 - he just can't wait to see if he has these same issues too!

BLT-71

Just a note on LT-1 issues, improve or clean up the ground on the TI amplifier it will impove the efficiency of the spark for less plug fouling. As for flooding I tinkered with many things and finally had mine under control. The exact solution I do not know.
But going out and just running the crap out of it at high rpm always helped the car and me run better.

Robert N

Also keep in mind that these engines were meant to run at higher rpms. Mine sat after what I am sure was a poor rebuild for 24 years. After getting her on the road (only the points - not the TI system - distributer was left alone. At low revs, the car bucks. Getting from first gear when stopped sucks. At 3500, no issues at all. Below 2500 rpms, the car is a PITA.

Barry's70LT1

I just noticed your post.
I have a '70 LT-1 that I consider works extremely well and reliably thru all rpms.
It sits for six months during the Winter and starts and runs well in the spring.
It's been many, many years since I have done anything to the engine.

If you are having problems getting it to run properly, then any standard trouble shooting method will work to correct the problem.

Being an LT-1 has little to do with your problems.

As far as fouling the plugs, I have AC43 plugs (way too cold for the street) and still have no fouling problems. The TI works very well.

I installed a Holley 750DP in 1971 and have been using the same carb since. The remaining items are 100% LT-1.
It continues to work well year after year with no problems.

If you have any questions, I'll try to answer them.

Barry

Les

Trouble shooting can be a major pain. Assuming that your distributor connections are solid, I'd start with making sure you're getting proper ignition advance. The distributor weights can get sticky & springs can get tired after time & keep your advance from coming in correctly. If you find that you're getting slow or incomplete advance you can get a performance spring/weight kit (check with Lars) that'll make it run better than it ever did with the factory set up.

If the ignition checks out good it probably comes down to fuel delivery and/or a vacuum leak. Carb base gaskets & vacuum lines are usually the culprits for vacuum leaks. Just a few thoughts- hope they help. If none of this helps you may need to check into the health of your valve guides & seats. Best of luck. :cheers:

vette442

Thanks a million, guys. We'll be starting in on it tomorrow evening for "Phase One Troubleshooting". I'll print out all the replies, we'll cover all these bases and see what happens.... By the way, the dwell setting (which came up in one reply) turned out to be the problem on the silver '72 LT-1 I used to own. I talked to my Vette mechanic today and he said that the distributor base had some play and would move enough during driving to knock thingg out of whack. It's much improved now.

Solid LT1

You are really not giving a lot of specifics to help solve your problem. The engine of any car need fuel, air and spark to run. The "gremlins" you are describing can be many things, poor ignition, bad fuel delivery, and MISADJUSTMENT of the solid lifter valvetrain by shade tree mechanics. My 72 LT-1 is not stock but, it also is not very tempramental in it's operation. I think you need to find a more competent Corvette mechanic if all your local guys LT-1 have "gremlins". The factory service manual can be a very good place to start to check basics like fuel and spark troubleshooting methods. The LT-1 Vette is not a good car to own if you are a "novice mechanic" because it has higher maintenece requirements than a normal hdraulic Vette. Maybe you need a nice L48/L46 or LS5 "juice lifter" Vette.