Hello to all my CF friends,

I was on here many years ago when I purchased a 73 C3 Coupe. However, a divorce took her away. So...I'm sorry for my absence.

New wife who supports my long wanting for a collectable Vette. I finally purchased a 72 LT-1 Coupe all original and stock, just they way I wanted her. I still have not had the time to set the timing as the car came from Ohio and I'm sure it's off a little. Carburetor looks black which indicates to me she's running rich. When driving the car or carb has a slight hesitation when shifting into higher gears. My question is and all options are welcome. Should I set the timing and make carb adjustments or just go ahead with a rebuild? Or...replace the carb with a new Holly Street avenger? Or does anyone recommend something better.

Thank you for all the help and advice my fellow CF members.

Regards,

Gregg

 

Welcome back to the forum. Wait for a moderator or administrator to move this thread to the C3 Tech section of the forum.

 

Moved to C3 Tech.

 

My understanding is timing comes first and foremost. Timing affects the carb settings but the carb settings don't affect timing. After that I'd opt for a cleaning and re-gasketing the carb.

 

Thanks for the insight Drifting,

It’s been a while since I’ve worked on Chevy 350”s however, I’m looking forward to getting deeper into it. Are you referring to the gasket under the carburetor to the manifold? In which case I assume you recommend taking off the carburetor to clean it correct?

 

You're welcome, 2nd Gear.
My username is 67:72 - the Drifter and 2nd Gear monikers were instituted by Admin several weeks ago.

When I commented gaskets, I meant a "rebuild" kit for the carb. It's my own pet peeve that it's called a rebuild kit since all you're really doing is cleaning and putting in new needle, pump, and gaskets. You'd have to remove the carb to do this, so replacing the carb to manifold gasket(s) would also be in order and it comes in the kit.

 

Sorry 67:72,

yeah that was my thought. I will get the timing dialed in first then pull the carb and rebuild it. I do like to keep everything original as possible always. I was just thinking a larger carburetor would give it a little more guts. However, again I’m not opposed to just rebuilding the original carb. Thanks again for all your help.

 

E-mail member Lars for his papers on timing. his E-Mail is V8fastcars@msn dot com. Do the timing and curve first. Also ask for his carb tuning papers.
Another important thing is to set the lash on this as it is a solid lifter car.....I think Lars has papers on that as well.

Jebby

 

Hi Debby,

Thank you for the reply. What is the curve and lash? Sorry, not familiar with these terms.

ggg

 

Sorry auto correct. Jebby!

 

Ask for Lars papers and it will explain them…..
if you are completely unsure though….you may want to find a seasoned pro to work on it. Although everything can be explained….if you have never done it…..I don’t recommend cutting teeth on an original LT-1.

Jebby

 

An original LT-1 should run really... really ..... well as is with all stock parts. It just needs a really good performance tune. Not a regular tune-up. Please use all the original parts. They will be hard to improve upon. It was one of the best built and most powerful small blocks of the muscle car era.
The main part of a performance tune, which works really well on these engines, is it needs a lot more timing, do not use the original "book" specs. Use the specs from Lars. Roughly 36 degrees total and about 15 degrees initial, with manifold advance, not ported. That is the most important part, and you do actually want to change it from what it was originally, it will run far better, run cooler and stronger, and even get better gas mileage. No one looking at it will ever see a thing different, and you will enjoy the way it runs. Chevy set them roughly 8-10 degrees retarded from "optimum" for very early primitive emission control reasons.

Then do a basic tune-up, which on these which consists of new plugs, wires, setting the valve lash, carb gaskets, etc. All of that is minor compared to the timing.
I had an LT-1 for 30 years, and it ran really well, and I loved it. Now I am just going bigger, a lot bigger

You may even have the TCS system still functioning, which is Transmission Controlled Spark, and that retards timing even more, until top gear.. That can make it hesitate badly. It can be easily by-passed / disconnected. Just look it up.

Fixing the timing will make it gain like 30HP, it was set that bad by the factory. If someone tells you to use the label or book settings, just smile, and "run".

 

Hi Leigh1322,

Very good advice and interesting, thank you. Lars sent me all the tuning specs and more to get this LT-1running they way she should, Do you recommend changing the points? I believe the car has an advanced ignition system, that I'm not familiar with. In a CF thread I read that using these points were a good upgrade,

MR. GASKET DISTRIBUTOR MECHANICAL ADVANCE CURVE KIT, thoughts on this product?

I have had the car for about a month. It came from Ohio and just haven't had time to dig into her. I decided to completely make my garage they way it should with a new epoxy floor system and complete re-organzed and clean. I figure if you're going to have a classic car like this one the home or environment should be pristine.

Regards,

Gregg

 

Yes that "curve kit" is good. However do not use the weights, your OEM ones are better. You just need the springs and maybe the bushing. IIRC it is the lightest spring, or a medium, or one of each that makes it work. You want the full centrifigal advance to be "all-in" by 3000-3200 rpm. Once you get that dialed in, you may find you need to "limit" the mechanical advance to about 22-24 degrees, so you can start at around 12-14 degrees at idle. The LT-1 likes that. But you can not go over 36 degrees advance no matter what. Be sure! You do not want to hurt it! Then add 12-14 degrees of manifold vac advance, and you may have to limit that also. I have LARS's vac advance limiter in mine. That will give you way up around 24 degrees at idle/low rpm/cruise, and the engine will run much cooler. But the 12 degrees vac advance falls off very quickly when you nose into the throttle. 72s were factory set with "ported" vac advance, and it was strictly an emissions deal, and it did not work well. Unless you are into 100% correct NCRS judging, please undo it, it runs so much better. The above distributor tune-up will wake that engine up a lot, so much so that you will swear new parts were bolted on! LOL

IIRC the 70 &71 LT-1s had factory transistor ignition, but 72 may have gone back to a points setup.
In my opinion there is absolutely nothing wrong with a good points setup, the newer aftermarket "conversions" work "better?" for a while but have not proved to be reliable long term under a hot corvettes hood. Then the electronics fail very suddenly, and you are stuck on the side of the road. Do buy a good set of points though, with a high performance spring, that LT-1 loves to rev. Not chinese repros, they are no good. You will also need to add back the little lubricator pad for the distributor cam. I raced my LT-1 for 30 years with a well tuned distributor and a points setup. It loved 6500/7000 rpm! It worked great and rarely needed adjustment as it was not a daily driven car. I did have blueprinted connecting rods and ARP bolts though, and a slightly bigger cam, the "30-30" or the "off-road" one. And I had headers. You may want to hold yours back to 6500 ish rpm for safety reasons, unless the bottom end is "built" like mine was.

Good luck and have fun with it!

I am currently building my 454 the same way, to run and rev the same way. Solid cam, points, stock Holley, etc. It'll just have 100+ "more" HP/TQ everywhere.

 

Hi Lars,

Thank you for all this great information, you really are helpful and know you're stuff!

What kind of points do you recommend? Also, where can I purchase a Lars Vacuum Advance limiter? Do you recommend a certain Holley rebuild kit for my carburator? There are so many to choose from, one must be better than another.

Thanks again for all your recommendations!

Regards,

Gregg M.

 

You can buy the limiter directly from Lars (I'd assume): V8fastcars@msn dot com

Standard Motor Products makes just about all the points out there, from what I read from SWDuke, who really knows this sort of thing. SMP points are rebranded and sold as house brands - NAPA is one such. AC Delco hasn't made point sets in decades, so buying a new Delco set from an auto parts store is really just buying a reboxed SMP set. Attached is the link to an article SWDuke wrote a while back about choices of NAPA points that helped me decide what I wanted. Some folks buy NOS Delco points off ebay as they're easy to find and cheap unless you want the hi-perf that go for $50 and up.

 

i thought lars was v8fastcars@aol.com. this q jet is a very nice carb, but a pita to get right. i would email Lars-whichever email it is-and get his timing papers. the mech advance may be fine. do you have a dial-back timing light? if not, you need a TDC, 15 before and 30 before TDC mark on your balancer. then you can see all-in advance. the ignition timing that GM used was designed for emissions. you want 36 to 38 degrees without vacuum hooked up at the point the mech advance stops advancing. if it keeps advancing above 3000 rpm, springs are too stiff. if it does all it's advancing at 1500 to 2000 springs are weak or broken. now, after timing it correctly, decide if carb needs attention or not. very strong recommendation. SEND IT TO LARS! he may not be the world's foremost authority on the q-jet, but he is up there with the other 2 or 3 guys. and he has a test engine he uses to make sure everything is copacetic before sending it back. and Jebby is somebody else to pay attention to. Debby. somebody else called him Jenny recently. i hope he doesn't get a gender identification issue...

 

Gregg -
You obviously have my e-mail address since you e-mailed me for the the articles. Why don't you e-mail me and ask me..? The articles you have state specifically where and how to get my limiters. Read page 4 Note 1.
There is only one Holley rebuild kit for your carb list number. Buy the Holley Renew Kit for your list number. There's just one.

Lars

 

Black carb, assuming you mean the throttle pates, means backfires through the carb so look at timing first not the carb settings. Its also a solid lifter engine so adjust all of the valves.

 

If the throttle bores are black, it's a sign of carbon sooting caused by exhaust gas reversion up through the intake system. This is indicative of engine timing problems - most commonly retarded timing - and not a carb problem. Fix your timing: I have sent you all info on how to do that.

If you have the original carb, it's a 780 cfm Holley. The last thing you want is a bigger carb - that would be a really bad idea, and it would not make your car perform any better - quite to the contrary.


Lars