1971 cutlass ragtop , owned since new. 350 4 barrel. 34k miles. Every cylinder has 165 PSI. Heres the thing, engine used to run like a swiss watch (talking 35 years ago). NOW most of the time (95%) runs like crap, I'm afraid to drive it ! rebuilt the Q-jet, installed a HEI. (yes, full 12 volts to it). sometimes it starts right up and will idle Beautiful, slightly rev and all is fine. put the air cleaner on. restart the engine and runs like crap again, timing it set initial at 12-14 BTC. with vac disconnected. Engine is holding 60 PSI oil pressure and steady 5 PSI fuel pressure. blew out ALL the lines, dropped the tank (it is spotless) and installed new pickup and fuel sender). I've been wrenching on 50s-80s cars since 1965 & have never run into anything like this. Anyone got some good ideas to send my way? I have tried 3 brand new carbs, ( 2 NEW HEI Dist), new plug wires, search for vacuum leaks, Dist is NOT in 180 off. **even the couple of times when it was "agreeable" and idled well, holding 17 psi Vacuum, had all the "power" of a poor running 4 cyl !( like the 2nd 2 barrels were not opening (but they are ). Thanks in advance

 

After establishing dwell, setting timing (w/ vacuum advance can unplugged then plugged back in), did you establish the highest achievable vacuum adjusting your A/F mixture screws? On my '71 CS convertible I'm able to achieve 17"Hg. Although my timing is set to 12°BTDC. Check your vacuum. The fact you install the air cleaner/breather & it runs like doo doo may be indication of poor vacuum? Check for leaks - you hook up all the hoses? Are you using the TVS switch or is that deleted?

 

I feel your pain. Been chasing a somewhat similar problem all summer. Motor is running lean and wont idle perfect. Put on air cleaner it runs worse. I rebuilt my carb as well.

Used a smoke generator to check for leaks and found no leaks. Have turned AF screws out about as far as I could without them falling out and still too lean. Add fuel through the carb and idle smooths out.

Assume idle circuit isnt flowing correctly so finally gave up and sent my carb in to get rebuilt and flow tested. Hope that fixes things. It sucks not being able to enjoy these fun cars.

If you find an answer let me know and if I get my resolved Ill post it back in here.

 

What was the root cause for the timing mark being "off"? Did the balancer slip?
Have you ever replaced the timing chain?
I'd suggest making sure this is corrected first by either getting your balancer rebuilt and/or replacing the timing chain.

What air cleaner are you using? Is it the stock one? Does it clear the HEI?
Are your spark plug wires good? Could they be arcing to the air cleaner?

Could also be a crappy HEI module.

 

Note that he installed a HEI distributor.

 

Valid point...he still needs to evaluate vacuum.

 

Still have the original distributor and wires to try?

 

BRAND NEW hei (NO pOINTS FOR DWELL) ring may have slipped 20 years ago for all I know, 1st time I've checked it with a piston stop. brand new Timing chain.

 

still have the orig dist and coil but no non HEI Wires. was thinking of trying that. also, I ordered a fitting to install a Fuel pressure gauge to use with the Q-Jet. wondering if t5he pressure could be fluctuating. New pump and filter.

 

have a "smoke Can" but have not yet tried that.

 

orig air cleaner, but it does it also without the air cleaner.

 

I did not see that adjusting the" idle screws" made a lot of difference, but it does the same thing with a brand new Edelbrock 600 on it !

 

what kills me is:** I have been able to get it to Idle Absolutely Perfect** 3 times, rev a little and it's fine. shut it off, re start and does it again ! can't be the ignition switch, I've tried it with a 10 gauge wire from the battery + to the dist, Same.

 

Did you actually measure the vacuum?

 

Theres a perm gauge hooked up. best I can get is 17 "

 

Sounds simple enough - don't mean to be trite - but, you have validated you have the vacuum hoses connected "correctly" i.e. to their proper manifold &/or ported connections? Sounds stupid maybe, but I've seen folks connect vacuum hoses to the top of the air horn which does nothing for A/F mixture. You still operating w/ the TVS switch & solenoid or has it been deleted?

 

Perform the 1st test (top LH corner) and evaluate your vacuum. Your vacuum should be rock steady. The needle should not waver at all (or whatever perm gauge you're using). If its a gauge, the reading should be identical to the test in this diagram - immediate drop to 5" and back up to 17".

 

I thought you have 5psi?

 

At the top you say that timing mark was off.
Why !?...
Retrace your steps. How was engine running before distributor change. When was the turn of events ?
Something smells fishy in the timing. I suggest you take a closer look at your timing events. Check dizzy wiring for interference.
Get timing settled for smooth idle and a nice crank start. Check and note timing mark. If you can, take it out for a little run. Come back and check timing mark again. If the car starts running shitty again (idling high or low, running roughly) and timing is not exactly as you set it.
I would yank that distributor !

 

I forgot to mention.
I had a similar problem. Checking vacuum, adjusting carb, replaced timing chain, rebuilt carb.
In the end, new dizzy was junk.

 

I always ask, "Okay, what changed right before it started to run poorly?" Judging by post #1, it's the timing mark.

Investigate that.

 

I was dealing with something similar this summer. Ended up being cracked and split vacuum hoses in three different areas. I had replaced all of them when I got the car. I found them by putting a vacuum pump to each line, visually they had looked fine.

 

Just a thought...

Hew HEI does not mean good. I would check it, rotor button, cap etc to ensure no issues.

Perhaps try an known good one or your old unit.

 

Was the timing chain replaced? I know it only have 34K but it might be failing apart. A cheap replacement HEI might be worth a shot. Plus replace the wires and plugs as well. I had an intermittent miss from a bad plug wire. Make sure it is a constant 12 volt source as well. My 70S blew a couple of HEI modules due to fluctuations in voltage. If it runs the same, you know it is fuel related.

 

the new edelbrock carb has a spot in the line on it for the pressure gauge. thats What i was referring to. When I installed the rebuilt Q-Jet., it has no provision, thats why I ordered one. IT WAS holding steady 5 psi, (then it sometimes would slowly drop to 3-4 !) Fuel pump is brand new. the only thing I can think of is MAYBE the "sock" in the tank is getting plugged.(Original tank and sender, never out). I'm going to disconnect the line from tank to pump and blow it out. ALL the vacuum lines are on. manifold vacuum to trans, ported on front of carb to dist, PVC to carb base, the only line not in it's orig place is from the large canister from the tank. has not been hood up for 20 years.

 

Post #8...

 

^^^^^ THIS ^^^^^

It makes no sense that you needed to change the timing mark. If you replaced the timing chain, and it hasn't run well since, except for idling, you might want to pull the timing cover and recheck everything.

I am guessing that your cam timing and crank timing are off. Here's why:
1) You should easily pull more than 17" of vacuum on this engine unless you replaced the cam, too.
2) If you created a new timing mark and set your advance at 16 degrees BTDC, this could be very advanced in relation to the original timing mark. This could be the source of the pinging you mentioned. The engine might idle just fine with this much advance, but under load, you could be running way too much advance and pinging.

Have you tried setting the timing against the original timing mark? If so, and if it ran poorly, your valve opening and closing events could be off.

Coming to think about it, you probably could use the piston stop tool, pull the valve cover and watch the valves opening and closing as you turn the engine by hand. You should be able to determine more or less when the valve events are happening in relation to TDC this way, and this should tell you if the crank and cam are not lined up correctly.

Just my two cents.

 

my changing the timing mark had nothing to do with it. this car sits covered up in the garage for YEARS at a time. only has 34K miles. in the past,(30 years or so) the only way the car would run halfway decent was with what the timing mark was saying it was over 18 degrees advanced. the chain is "on correctly" (& am aware of how it will act if it's a tooth off). ( I've been building & (hotrodding ) engines since the 60s, (cut my teeth on 409 chevies and 406 fords) Not a Novice. I'm not trying to be a "wise ***". What has me stumped is, why will it run absolutely perfect for a few min, then shut it off, then runs like crap again. got spark, got compression, cam timing is correct, Non Adjustable valve train, keep trying different spark timing (with and without the vac adv hooked up) and the mechanical advance is working fine. I ,today, disconnected the Fuel Line from tank to NEW Pump, and pressurized the tank, only clean fuel came out. I am waiting for the fitting so I can check fuel "Pressure" with the Q-Jet on it. (I seriously suspect something fuel related). I need to go out and pull a few plugs again to see what the "mixture" may be doing. I'm 76 years old and have a bad back and 2 artificial shoulders, so it takes me "a bit" to get some things done. Please bare with me.

 

Describe " Runs like crap " !

 

when it runs "good", it runs like "new" (like put a glass of water on the hood and you won't see "ripples") ! but then it will almost act like a bad needle/seat thats leaking and making it "flood", but no gas smell or black smoke. ( don't know,maybe more like it's running OUT of fuel), but it's not. Damn I wish it was a CHEVY ! LOL. Whatever it is, it Won't Do It "Constantly", so I can't Catch it.

 

A family of mice used your 4bbl as a double-seater outhouse.

 

Question, on the front pass side of the intake manifold, there is some sort of "valve" about 2" tall, that has a 2 wire plug on the top of it and is "supposed to have" 1 vacuum line going to it. Any idea what it's for? hasn't been there for at least 30 years !

 

Thanks, hard to follow, was just making sure all tune up parts were replaced to start. If it has an in carb filter, make sure it isn't the issue, although a restricted fuel filter or pickup sock should cause poor running all the time. Did it have these issues with the Edelbrock carb, usually that is when the issues start.

 

I think you're referring to the TCS, I called it the TVS in an earlier thread. Is that what you're referring to? I'll find a picture.

 

You have AC or no AC?

 

 

Here are some threads stolen verbatim from our site. Have a look...

Transmission Controlled Spark (TCS) is referred to in the 1971 CSM as Distributor Vacuum Control Switch (same thing). The wiring diagram will illustrate the acronym TCS. Is this what you're referring to - based upon without AC or with AC. There are two wires which connect to the TCS solenoid - I think one is Black and one is Dk. Green - I'd have to look at the wiring diagram.

 

Post a picture...easier to see what you're talking about.

 

 

One Dk. Green wire & one Black Wire with Single Orange Stripe