While my car is in my shop getting the rear suspension upgraded, I thought I'd attempt to also diagnose the motor's issues. Here's the scoop:

'70 L46 (all orig except holley carb) conv 4speed (overall, the car is generally in mediocre condition at best)

Bought it online. Was supposed to be a "perfect, and rare car." I got hosed...Lesson learned, bigtime burned Anyway,

Symptoms:

Smoking especially upon starting with a bit of a miss, both clear up, but not completely when engine becomes warm. Does not seem to have much power/torque at all. I have to really rev it up and dump the clutch in 1st gear to spin the tires.
Also, I was putting premium (93) fuel in it since it was supposed to have 11:1compression. But just to see if it made a difference, I've been running low octane fuel with no knocking / pinging etc......performance still sucks, and I'm assuming the compression is nowhere near 11:1....

Car has 130K miles (supposed to be actual ). Motor was rebuilt in the 115K range by previous owner's dad (YIKES) who was "a great mechanic." PO said his dad put "flat-tops" in it..... Car runs "OK"....but just seems very wimpy, esp for a 350/350 vette.

What I've done:

New points/plugs/air filter/fuel filter
adjusted the throttle cable to allow full excursion (WFO)
got carpet out of the way of accelerator pedal
Leaned out the carb (Holley) a bit
Adjusted the timing (several times

Nothing seems to help....it's just running like a sick dog.....zero power

Help please! THanks....

 

I would start with a compression test and a leak down test, that will give you a good idea of the general condition of the motor.

 

Is that procedure described in an accessible, previous thread????

 

Compression test = remove all plugs, lock carb open and turn motor over, using a compression gauge in each spark plug hole. (1 cyl at a time)

Leak-down test: put air hose adapter at each plug hole, bring cyl to top dead center and apply air. Check for air coming out exhaust or intake, this will identify valvetrain wear. Pressurizing the coolant tank or the crank would indicate HG failure or poor ring seal.

http://en.wikipedia.org/wiki/Leak-down_tester

 

consider a distributor rebuild ,new springs and weights.if the compression is ok consider a newer cam .

 

if he put flat tops in it ,lord knows what other " improvements " were made

 

Hey Doc, sorry off topic but did you have your Vette at Siriani 3 or 4 weeks ago? I live in SA too...

 

Smoke is never a good sign.

Black is normally a rich mixture. White is oil.

If it smokes when first started up, oil leaking down to the cylinders. Normally past the valves. It may go away until the car warms up, then if starts to smoke again, it is leaking past the rings.

This is by no means a concrete diagnosis, just seat of pants experience.

A compression check will, indeed, indicate one or both of those symtoms exist.

 

It sounds like u are at the bottom of the learning curve for your "old school" vette. Well this is where a lot of the fun is just getting to know your car and what u can do to it for better performance. And like others have said a compression test will not only tell u the condition/cylinder sealing of the engine but how hot the compression ratio and cam are.
U want to fix that miss and tune in a good timing curve into that distributor. Also need to tune the carb with jetting and adjustments.
All this doesn't cost much money but takes a truck load of patience. U won't learn all the tweaks and fixes overnight but if u give them time and effort u will have a much better running car and understand anything that comes up in the future.
That smoking on startup is just the vlv seals and a common trait of the stock seals on a sb chevy. U can deal with those anytime but will need a air compressor and valve spring compressor to install good seals - when your ready.
My first recommendation is to buy a service manual - even a Chiltons at PepBoys - so when receive advice u can bounce it off the service manual to make sense (take all the "free" interenet advice for what its worth).
Or u can always find and old school carburetor tune up shop somewhere nearby if u need to. Please update your profile so we how the car is equipped to help you - also where you are located can help.
A miss can be several things like a tiny hole in plug wire insulation (heat damage) - open the hood at night and have a look for sparks - or even if a plug was dropped while installing (broken).
I sounds like u want to start with timing so let us know what u have for initial, mechanical, vacuum advance and the timing curve u are using and if u have a specific question,
cardo0

 

When any engine is modified with a new timing chain set and/or a new cam & lifters, (or all of the above), - there is always the chance that the cam/valve timing isn't correct which will kill performance big time !

If the cam wasn't degreed when installed and is installed retarded - all bottom-end torque will be gone , the bigger the cam the worse the problem.
Keep this in mind if all the tuning doesn't sovle your problems.

If it's been [I]rebuilt[I]and still smokes , then you have to wonder what else wasn't done correctly !?

Good luck !

 

I'd yank the engine out of the car, put it on a stand, and pull it apart. You can spend a lot of time, risking a scratched fender screwing around under the hood, or just pull the engine, for a really good look. Learned this over the years, and have an engine picker and stand now.

 

best result in performance I ever got was having someone put it on a distributor machine given all the engine specifics and get a great curve on it. Did 10x the job I could and tried many times.
Night and day difference!!!!!
If its still doggy and your carb is Ok pull the timing cover and see how the cam is installed.

 

No, my inspection sticker is expired and the vette's been in the shop just sitting for a while.... We need to hook up sometime....

 

I agree but after yanking it out and putting it on a stand, (stick it in a corner if it is the original) I would buy a new crate engine My L46 was a dog. Much happier with the new "Year One" crate engine.

 

Wow, thanks guys.... lots of helpful info there. I really think this motor was re-built by Bubba and is probably a mess on many levels. I'm currently rebuilding the rear suspension (e-brakes and T/A's are nightmares, huh?) and should finish that this weekend.

I'll get to the motor and post my car's particulars later tonight or tomorrow.... Basically it's a bone stock 70 vert L-46 with a non-stock holley carb. I'll take some pics, and warn you ahead of time...she don't look like your car....mine's pretty ugly......

 

Believe me brother.... I have another 330 horse 350 in an old el camino....I'm very close to yanking the l46 and bag it for someone on down the line and drop the other 350 in and be done.... This is a # matching car...but it's an ole dog.... will never be a show car....

 

I can relate sort of.

Mine is also a 70 L46. Never been apart until I replaced timing chain and pulled the intake.

The PO gave me the original distributor with a "replacement" installed. Had the wrong carburetor and plug wires routed incorrectly, wrong spark plugs etc... Mine did not smoke at all.

Driving it home it ran like a total POS.

Checked compression and all was fine.
Found an original carburetor and had a rebuild kit installed and bushings installed on throttle body for butterfly.
Had the original distributor rebuilt and set up on the proper equipment.
Replaced plugs
Replaced spark plug wires with quality set.
Then we fine tuned the carb while running.

At this point we still had a slight miss. We blocked off the vacuum at the manifold and carb and she ran perfect. I ended up replacing all the vacuum lines and rebuilding all the other vacuum components showing signs of their age. In fact I would block off all the vacuum first as any leak downstream can be tough to find and will seem like a miss.

All I can say is I was grinning from ear to ear once all this was completed. I had no idea just how nice the L46 ran until it was right.

All that being said. Based on your symptoms, I would be very tempted to at least pull the heads and oil pan to see what the PO has in there after trying all the suggestions above.

Don't kick yourself. Consider this a great opportunity to learn.

Bill

 

Swapping to another engine, is my favorite way, and goes quick. When I have an extra engine I don't want to mess with for awhile, I put it on inexpensive engine cradle, rolled in a corner, with a piece of wood on it for a storage shelf. Takes up little room this way, and doesn't tie up your stand. Also have a couple pieces of 2'x8' plywood, to roll the whole thing accross the yard to the storage shed.

 

That's exactly what i did with my numbers matching engine, I put a crate motor in and will put some go fast items in/on it after i get other things done, if I grenade this motor well that would suck but at least the original is safe

 

Sounds like a plan, if you ever need/want any help let me know, I'm not the sharpest tool in the shed but I can turn a wrench and be that extra pair of hands that's sometimes needed

What part of SA you live? I live in Timberwood Park, just east of Camp Bullis...