[70temp455]

I want to run this past you guy to see what opinions I get.
Recently purchased 72 Lemans, 350 2bl. 165,000 on Odometer
It Ran resonable with a off idle stumble and surging at Highway speed.
Ran so-so last weekend, Started it this week and ran crappy, then I drove it and it had a bit of spuuter and on Decel sounded like retarded timing and had a "
off timing" smell.
The plan was to install a 4 bbl intake, Edlebrock 600cfm and HEI Distributor and plugs.
Upon it running crappy, I decided it was time fro the 4bbl and HEI so I installed everything and found a good 12 IGN source.
Got "ruuning" so to speek.
Can't get it to Idle below 1000-1100 Rpm so as to set the timing. Below 1000 the engine shakes violently, sputters and finally dies. when I can get it to stay running long enough (about 800 rpm) the timing mark jumps around between 4 deg. and 12-14 deg.
With vacumn adv. hooked up to Ported the timing will steady and I can set it at 12 or 14 Deg.
With vacumn adv hooked to manifold the timing jumped to 28-30 deg. (guess) which makes sense (12 + 16 vac adv = 28). Then I slowly reved the engone and the timing stayed at 28 till about 2000 rpm when it would slowly drop back down (even to less than TDC) as I slowly increased the RPM's to 2400 rpm.(ish).
I tryed driving it at this point and it simply falls on it's face.
Sooooo, what do you guys suspect is happening ? ? ?
I have a good guess but want to wait to see what Y'all think.
Thanks,
Andy

[Rob B]

Could be a number of things but I would simply start with the basics. First, I would check to make sure you have no vaccumn leaks with the intake either by spraying carb cleaner around the intake ports and carb base or simply cup your hand over the air horn of the carb or slowly close the choke plate and see if the idle begins to pick up or smooth out. Second, I would disconnect the VAC advance and set you timing at idle were it should be then rev it up around 2500-3000 to see where it is with full mechanical advance. Mess with the vac advance later, that more for a drivabilty purpose you can play with later. third, I would check all the plugs, wires in the correct firing order, cap, etc etc then do a compression test on all the cylinders to rule out any internal issues which could be a laundry list consisting of bad chain (is it the original?) worn cam/bad lifter, burnt valve, you get the picture.
Now what were you thinking???

[70temp455]

it will NOT idle (smoothly) and the timing is all over below 1100.
At 1100 rpm and the timiming set at 12 (ish) we could hook up the ported Vac. and because the throttle plate was partly opened (from the idle screw being cranked in so far) it would advance and rev way up. So when I turned the Idle speed down and we got to 1000, the plate would close enough to cut off the ported vacumn and the idel would drop way down (400 is if not just die)and no mater how hard I tryed to get the idle up to 600-700-800 the tinming was back and forth all over the place again. My brother just reminded me that we could not get it to idle smooth until we hooked up the Vac Adv , either ported ot manifold

I'd really have to do it all again and take notes, but I'm sure below 1000-1100 with vac. plugged(no adv.)
It was such a pain even to try to keep it running.
Anyhow, I'm really leaning towards timing Chain and gears , either stretch, jumped or simply so worn it isn't stable.
Andy

[70temp455]

and I sprayed carb cleaner every where and din't detect a leak. all vac lines and caps/plugs etc are new. and made sure everything there was secure.
It is a 69 4 bbl intake on 72 (2bbl) heads.
I have an Edlebrock Performer I may try.
The Carb was a month old when I put it away 4 years ago and I just rebuilt it 2 weeks ago.
I tryed my 750cfm Edlebrock on it also and it ran (or didn't run) exactly the same.
Andy

[Rob B]

More than likely the chain/gears are the problem since you had problems prior to the swap. But you don't need to worry about messing with the vac adv rather it's ported or manifold. It is NOT needed for idling purposes. If you just plug the hose from the vaccumn source your are eliminating one potential problem variable which would be an issue either with the distributor itself or an issue with the vaccumn source ported or continous. Your carb could be way out of wack in it's adjustments etc etc. That is why I mentioned about doing a compression test to at least make sure you have good cylinder pressures. Whatever reading you get, they all should within 10% of each other.

[marxjunk]

what about the timing chain? So much slop it bounces around or the teeth on the nylon gear...if theres no vac leak, youve got gas and spark..what else could it be? pontiacs are famous for eating timing chains...

i think you found the answer yourself there....

[Rob B]

If you plug the source to the vac adv theres is nothing to cause the adv to occur outside of the mechanical advance that happens with the increase in RPM'S.
In other words if your timing is jumping all over the place with it plugged, you either have a distributor problem or chain and chairs. If the timing stays the same or just varies a degree or 2 and nothing more, you have issues either with vaccumn (carb or leak somewhere) or the advance module on the distributor.

[Rob B]

Originally Posted by marxjunk

what about the timing chain? So much slop it bounces around or the teeth on the nylon gear...if theres no vac leak, youve got gas and spark..what else could it be? pontiacs are famous for eating timing chains...

i think you found the answer yourself there....

I never ruled out the chain and gears and thats probably the issue. It's just hard to believe a motor from that era would last 166000 miles on an original nylon geared sprocket and stock chain. From what your saying and maybe I'm just interperetting it wrong, it sounds like once you get to a certain RPM, it will idle/rev and sound fine but only gets wierd when you go below a certain RPM.
I'm trying to help you do a few simple things to check a couple of the key things needed for an engine to run. A compression check is simple and can eliminate so many variables and at the same bring those same ones back into play if you get so funky readings.

[Rob B]

Sorry Marx, I thought your response was Andy's.

[70temp455]

I know/knew most of this stuff when I played with my 70 Tempest up intil 4 years ago.
I didn't run Prefectly before, it does have min 165,000 mile on it. The the last day I drove it it ran really funky as I stated before. Could be it jumped a gear or (if it does/did have a Nylon gear) broke the brittle Nylon off. I had an olds 350 once that had a Nylon gear and ran great and smooth, then I was at a stop and when I went to go it had died. It broke all the nylon off the gear siting at a stop and I didn't even know it had died..
I'm going to order and relpace the gears and Chain and at least That will be new and out of the equation. Really wish I could rebuild the engine but I don'thave anywhere to do it. Someone buy me a Garage , , Please !
Andy

[bigborehunter]

worn timing chains hide well under fairly high rpm ranges due to centrifugal force making the chain stay outwards. At lower rpm, the chain can flex in and out more easily and hop a tooth that way. Industrial motors can run a long time with bad chains because its a limited rpm range. Then one day they go when starting up and take out the works.

[Lemans1970]

Originally Posted by 70temp455

I know/knew most of this stuff when I played with my 70 Tempest up intil 4 years ago.
I didn't run Prefectly before, it does have min 165,000 mile on it. The the last day I drove it it ran really funky as I stated before. Could be it jumped a gear or (if it does/did have a Nylon gear) broke the brittle Nylon off. I had an olds 350 once that had a Nylon gear and ran great and smooth, then I was at a stop and when I went to go it had died. It broke all the nylon off the gear siting at a stop and I didn't even know it had died..
I'm going to order and relpace the gears and Chain and at least That will be new and out of the equation. Really wish I could rebuild the engine but I don'thave anywhere to do it. Someone buy me a Garage , , Please !
Andy

I think replacing the timing chain and gear is a good idea whether this is causing your problem or not. My 70 has ~231K miles on it and I just recently replaced the timing chain for the 2nd time after it slipped and the engine stopped running (fortunately didn't slip so much as to bend any valves). First time was after around ~110,000 or so.

You should also be prepared to replace the aluminum timing chain cover. These typically corrode over the years. Mine was replaced with each timing chain job. Actually, the first timing chain was replaced only because the cover began leaking due to corrosion, so everything done at once. GM doesn't make them anymore, but the after market ones are great. Ames, PY and others carry them for around ~$170-180.

[70temp455]

Worn SLAP out ! ! !
Checked first by turning the crank past zero and bringing it back to zero. Then I had my brother watch the rotor as turned the crank . I got to 12 degrees before the rotor moved. Suspision confirmed. Then I torn into it and got the timing cover off (between thunderstorms). There is so much slack in the chain that it could have jumped a tooth.
Anyhow, I'll have the new NAPA chain and gear set in the morning and if it doesn't rain too much, I hope to have it back togeteher tomorrow and hopefully be able to put Fire to it.
Andy
ps The cover looks to be in good shape. It's covered in 1/2" of oil and grime and well preserved (lol)

[Lemans1970]

Congrats on finding the problem, sounds like this should take care of things.

Is the timing gear solid nylon, or nylon coated metal and are they (the new replacements) all still like that?

Also, when a chain develops slack (as per this situation), is this because the chain actually mechanically stretches, because the tensioner goes out of adjustment, because the gear wears, or all of the above?

[70temp455]

NO Nylon to be found anywhere, old or new !
time (pun) will tell if this infact actually is the major issue.
Damned rain !
Andy

[70temp455]

New timing chian made it some what better the basic symptoms (as far as I had time to check) are basically the same as before. So,
72 Lemans, 350 2bl. (7k1 2bbl heads) I just put on a circa 1969 Pontiac 4 bbl Intake, a Freshly rebuilt Edlebrock 1406 (600cfrm) and installed the HEI distributor, all at the same time.
1) Is it possible that the intake ports in the 69 inatke to match the ports on the heads ?
(I should have atlest eyeballed up the ports to the gasket but forgot in my haste to get it together)
2) Is it possible that a 4bbl is simply too much for an original 2bbl engine with 2bbl heads.
It is running very rich and I'm thinking of leaning the mixture way out to see if it will run but then my fear is that It runs too lean and I melt pistons (or what not).
3) I have an Edlebrock perfomer intake that I cand install and try to see how it runs.
A few years ago I had another car that I put a 70 350 2bbl engine in that I installed this same Intake and Carb on and could not get this same combination to run right either, so I put the 2bbl back on and sold the car.
I'm really Perplexed ! ! !
I really really need some help here !
Andy
ps on a side note, I built a 72 455 that I put in my 70 Tempest that ran perfect right from the start.

[67drake]

PIA huh?
I thought your new chain was going to fix it.
Can you keep it running and get the idle speed down if you give it more initial timing?
IMO maybe start over again. I would disconnect vacuum advance,to rule that out (As Rob said,vacuum advance is worked on last). Tie mechanical advance weights off to prevent mechanical from starting to come in,then JUST work on getting the idle speed down by giving it more initial timing if it wants it and adjusting carb air/fuel mixture screws,and try getting idle speed down. The way it is right now,when your idle speed is around 1000 your mechanical starts to come in and you CAN'T tell what initial is really at. Also,and I think you mentioned this,at about 1000 RPM you are running off your main metering system of the carb,kinda tough to get it to idle good there. Don't worry where initial is set at -give it what it wants! If you can get that idle to smooth out and lower it,you have a good starting point.
Also those balancers are 2 piece and can slip.so the timing that is showing might not be accurate anyway. You can always put a piston stop in the #1 cylinder and turn the engine over by hand CW and then CCW,and mark your balancer where the "0" mark is at both of these positions,the point between these 2 marks is your new "true" timing mark. HTH
PS-Nice weather huh? It rained here all day yesterday and this AM. I drove 1/2 way across the state yesterday to watch my daughter in a softball tournament,only got 1 game in and they called it off! Good luck with the car and the WEATHER! LOL

[gto4door]

Originally Posted by 70temp455

I'm really Perplexed ! ! !
I really really need some help here !
Andy

Maybe there is water in your fuel system. To troubleshoot, bypass the fuel coming in from your gas tank by running a fuel line into your fuel pump from a gas can with fresh gas in it.

[70temp455]

This is exactly why I ask these things.
To back up a week or so in time, I drove it the last weekend it ran OK and put $20 gas 5 minutes from home. The next time I started it (just to keep the battery charged) It idle like crap and something was amiss(I didn't drive it). Then 2 days later I drove it and it ran , Idled and drove like crap, as stated in my inital post. SO I though about the gas .
Pretty much everythin drake said I hav done. I DO try to get the initial timing set with caps on the vacumn ports on the carb and THEN, wehn I'm getting close to what it should be I remove a cap and plug in the Advance can. Thats also how I know the The idle speed screw is WAY in and the throttle plate is opened up because the port vacumn will advance the ting and RPMs.
The first thing I need to do, If it doesn't rain too much today, is go get gas. I have a 5 gal can so when I get back I run a fuel inlet hose right from the can.
Andy

[70temp455]

I have 3 questions first (becase my brain gets muddled up.(old age is setting in)
1) the dist spins CCW, correct ?
2) The Balancer (Crankshaft) turns CW , correct ? (just verified)
3) which way do I need to turn the Dist. to ADVANCE the timing? (My logic tells me CW but I'm not 100% sure of this.)
Ok, It ran crappy right before I swaped Intakes and HEI.
I might swap the 2 bbl back on and see if I can get it running good before going on.
I hate backing up , but I may have to. I changed to the HEI at the same time I swapped inatke and carb so it may be hard to diagnose 2 sytems at the same time. At least that way I can verify the HEI is not the issue.
Or I may put on the Performer intake, first and if that doesn't help, then go back to the 2 bbl.
Andy
ps. .060 spark plug gap (per 1976 Tune-up specs (which has HEI))
Could this bee too much and be an issue?