Yea....my engine is hurting.

Runs on after I shut it off.
Runs very rough until 1000RPM.
Very irratic idle.
Sometimes it will idle 600, sometimes 800, sometimes 1500, when fully warmed up, it just picks its own speed.
Idles smoothly at whatever speed it picks, but "jumps". The idle itself is very rough, but I can account that to overlap or something. But it also has a "jump", the randomly occurs and literally shakes the car. My buddy got in, told me the roughness of the idle was normal, then he felt the car jump, and he agreed something was wrong.

Comp Cam Xtreme Energy 268H
Protopline Vortec
Edelbrock Performer
670 Holley Street Avenger
.125 Domed Sealed Power Pistons, 10.7:1


How close does my timing have to be? Is my compression complicating the issue? I mean, the engine is being REAL sensitive to tuning. I put the timing light on it, I keep advancing it until it stops running on after I shut it off/shooting out the carb. Basically it will shoot out the carb and not run if it's too retarded and it will should out the carb and run on after you shut it off if it's to advanced. So I just kept moving the timing mark 1-2 degrees at a time until it would run smooth, rev, and not run on after I shut it off. I had it timed at 8 degrees advanced but it wouldn't rev, was very dirty. So I had to advance it to like 10-12 degrees, but I'm having problems with the car engine running on after I shut it off.

I just don't know what to do. I'm getting like 9MPG, its running rough as hell, idle quality is nearly nonexistant. But as soon as I get above 1000RPM she pulls smoothly. I can take it to 4000RPM if I want smooth as hell. I cruise around at 1500 RPM nice and smooth. I take my foot off the gas and brake and as soon as it drops below 1000RPM it gets rough (ok, rough idle is the overlap at lower RPMS I can deal, but it also "jumps", to me the roughness is something I can hear and slightly feel. Maybe the tach has a 50-100 RPM variation to it below 1000, thats just a rough idle, but then there is the random 250-300RPM "jump" that occurs. That shakes the car.

With the compression I'm running is my ignition going to have to be VERY exact in order to keep it from running on after I shut it off? Could the carb be rich and extra fuel is casuing the runon for a little?

Why is my MPG so bad? My buddy built a 350 as well, same cam, RPM performer manifold, 462 ported fuelie heads. His car idles SMOOTH, gets 17MPG.

I didn't tune the carb, the person who helped me build my engine did. He said he had to bring my idle mixture screws out 2 and 1/2 to get it to run. The flaots are set, when the sight glass is out and the fuel pump running it BARELY drips out the sight, which is what the holley manual calls for. I dont' see why my gas milage is so bad, my buddy is running a 600CFM holley on his, out of the box he set his floats, set his mixture screws to 1 & 1/2 (like its supposed to be) and his 350 is running like a champ.

Is my compression killing me? Is it the vortecs? What is it?

Any help would be GREATLY appreciated.

I'm running RTLS42 (the coldest plug for vortecs), #1 plug was pulled, looked PERFECT.

 

The compression ratio is too high.
Should have built it with flat top pistons.
You re going to need more than 92 octane to run this motor properly.

Set the timing using a advance timing light. (or get a balancer timing tape) {Mr gasket}
Set it to 32-36deg at high rpm. with the vac adv disconected. Full advance may not occur till 4500-5000rpm with stock advance springs.

Initial timing should then be 12 to 16 degrees
at idle. If not the distributor will need to be recurved.

You want lots if initial timing at idle. 14-20 deg then you want the timing to advance smoothly to 32-36deg at 3000rpm.

then connect the vac advance to ported vac.
Vacuum advance should add an additional 15deg at high vac cruise. ( hiway) but none at idle.

The power valve in the carb will have to be changed.
get a 4.5" power valve.

The power valve is opening and closing at idle causing the rpm fluctuation.
Set the idle screws to achieve best idle manifold vacuum and idle speed.

 

may be a good idea once u have the carb apart to install the power valve blow-out protection....

summit sells them for older module hollies that dont have PV blowout protection for under 10 bucks i think... that comes with a pre-set (or least suppose to be, mine wasn't and i had to measure the depth) drill bit for installation...

 

F-Bird, think Sunocos Ultra 94 will help? I'm running Mobil Super 93 right now.

Would an upgraded cooling system help? Everyone I talked to said 10.7:1 was the borderline....I think I'm experiencing that "borderline" ability to street 10.7

 

You'll need Sunoco 94 at a minimum.

If you can get Sunoco GT-100 use it.

You can spike up the Sunoco 94 using Tolene. or 110 octane unleaded race gas.

Tolene is used in many octane boosters and race gas.

Tolene is very high in octane.

You can buy tolene in gallons and 5 gallon pails from a paint supply store.

if you cooling system is pooched, fix it.
What is the water temp?

You can buy Sunoco GT-100 here

New Jersey

For Additional NJ Sites:
A-1 Racing Specialities
(800) 783-2262

Prospect Point Sunoco
224 Route 35 North
Pt. Pleasant Beach, NJ 08742
(732) 295-3377

Sunoco Ultra Service Center
Tre 46 & Howard Blvd
Ledgewood, NJ 07852
(973) 584-5114

www.racegas.com

 

When I built the engine everyone told me I could run 10.7.....that it's been done a million times and that I could manipulate my ignition timing in the summer when it got warm. Then again, I was told the swap would be done in 2 weeks, and that was in August.


Thnx for the info 88'

 

Heh, maybe I should just buy some 70cc AFR 195's....think that would drop my compression enough. 1 thing's for sure, the motor can't come out. If I REALLY do have too much compression it's worthless to *** around with the timing. I have it at 12 advanced at idle already. It wouldnt' stop stalling w/o anything less than 10*.

 

i run 10.5 1 year round with no problems.. well a lot of detonation until i got the timing perfect.. but after I got it tuned right it's ran great ever since, in the real hot days of summer sometimes i have to back the timing out a few degrees but other then that shes fine... as far as your tach bouncing around at low rpms, have u verified that you have no vaccum leaks? that could also make proper tuning a bitch.. as far as it dying when you adjust the timing, make sure your adjusting the carb to compensate as well...

 

Well with like 8* timing, it wouldn't rev, I could keep it running, but when I reved the engine it would hesitate real bad, then backfire out the carb. Move the timing up to 10-12* and it reved all the way up fine. Ive taken it up to 3500 nice and smooth. Too much advance at idle though and the engine runs on after I shut it off.

 

IMO, your combinaton should be fine. THe pistons you are running have a .100 dome, right? With the vortec heads and 93 octane with a bottle of octane booster you should be fine with about 33 to 35 degrees of total timing, based on my experience. You might want to check out the carburetor and the ignition curve. These two things will have the most impact on weather or not this thing will run or not.

 

Just reread your post, and my 72 PU has a similar configuration to your car. I had a 775cfm Demon (one of the first Demons) on my truck when I first did this engine and it would not run to save my life. The carb had set for a long time and surely the seals were all dried up, but I went and bought the Holley Street Avenger 675 cfm, put it on the truck, and she fired up idled very nicely. As I said earlier, I still think your combination will run fine. There is just something little that you are missing. Keep on keeping on, you will figure it out.
:rockon:

 

I've got the 670 Street Avenger. They're supposed to be really good, easy to tune carbs.

I've got .125 dome, advertised 10.7:1 with 64cc heads. Everyone I talked to in real life told me 10.7:1 could be done.

The car has no trouble when reving, my ignition problems seem to be under 1500RPM. 12*+ of advance that low RPM is too much for pump gas? Cause I'm not pinging up high...

I just dont' know what to think, cause I know 88 knows what he's talking about. Then again there are countless people who say they used to or are running 10.5:1+ CR on pump gas. I'm having problems with ignition, so maybe I cut it too close.

 

It sounds like you have a pretty bad vacuum leak. Where are your throttle blades set at idle?
Your compression is fine, stop worrying about it.

 

Actually we noticed the same thing on a 80 vett build. Comp reccomends and Ive post it a couple times that you not run higher then 9.5:1 with the XE268. After we curred our compression problem it ran much better, although it still wanted more advance at idle. A happy medium for it was around 15* base and 950RPM N 850 D. Any lower and it was shakey. I dont like this cam, it acts like a big cam but doesent have the cohones up top to back up its low end aditude. It would probably be great in a mild 400.

 

Your compression ratio is too high for the engine to run properly on 92 octane gas, ( and very borderline for 94 octane) but that is not the reason your car won't idle.
if the motor is running hot because of some ignition timing,fuel mixture or cooling system problem the high
compression ratio will just make it worse.
Poping, spitting back fireing and dieseling is a sure sign of a motor with overheated combustion chambers
or a lack of octane. Could be other things too like a tight valve lash, lean afr, overadvanced or retarded timing. bad cooling system.

You should be able to get the car to idle properly thou.

Look for an air leak (vacuum leak), change the power valve in the carb, check over the ignition system, get a advance timing light and set the timing properly.
Pull one plug wire at a time and see what cylinder is the offending cylinder.
If the carb throttle blades are too far open at an idle it
will tend to run on when you shut it off. (retarded timing)

Remove the carb and look at the throttle blades from the bottom. the transfer slots should be just exposed on all 4 barrels equally.

note: you will always have to spike the fuel with octane
or run reduced total timing from optimum to aviod detonation at WOT.

What does the water temperture guage say ::?

 

Another thing, you have a Holley. Check your power-valve. Maybe try another carburetor on there that you know is good.


I had to print this thread by the way. Thinking that compression will have some bad effect on idle has to be a first. Compression has nothing to do with idle. You could have 14:1 static compression ratio and idle fine all day on 87 octane.

 

Yes it could be a bad power valve or other malfunction in the carb, too much valve lash and several other things like you said.

 

Stealth, is this the first time running the engine since a cam install? If so, are you sure the cam is installed correctly?

 

There are 3 things that are bothering me:

1] RPM "jumps" at idle and anytime the engine is under 1000RPM and not under load. I'll look into a power valve to see if that helps.

2] The engine "runs on". It doesn't deisel, pop, or backfire. I'm not sure if any of you are familar with run on. I have to turn the car off in drive so it doesn't do it. Temperature has no effect, I can fire the engine up after it sits for 8 hours in the cold, drive 1 mile, shut it off, it will run on. I could drive 10 miles and it will run on. I could drive 10 miles and it won't run on. Its intermitent. My only thoughts is ignition timing.

3] The biggest thing is that I'm getting 9 MPG. I'm getting absolutely terrible gas milage, even my bosses 440 big block gets 12 MPG, and he doesn't have OD. My boss has a rich/lean sensor so I'll have to work with that. I swear I can smell the engine running rich at idle. Do idle mixture screws affect fuel when the car is driving? Or only at idle? I'd have to rejet the carb in order to change the fuel delivery under load?

88: I wasn't able to get my temp gauge to work. Took the factory pice off the m05, screwed it into my block, put the green wire from my harness and nothing. Can't even get the temp gauge to "ground" out or whatever. Either that green wire is wrong or the temp sensor is bad. I don't even know which one the gauge went to. Can I buy one ? Part #?

Oh yea, my radiator leaks, but the leak is very high so my fluid level is not low enough that it doesn't work, it still flows, it leaked when I had my 305, and the 305 never overheated. I don't believe my idle/run on problems are cooling related, because the car doesn't have problems when under load. I've driven for 30+ minutes non stop w/o problems, it's when I turn the car off and have to idle when I get into problems. If anyone has a part # for a stock replacement on an AT car it would be welcome, I just dont' want pay 600$ for a becool.

305: The cam is in correctly. He installed the cam in my buddies 350, and his 350 is running perfect. (the one I mentioned above) He installed it straight up.

 

"run on" is the same as "dieseling".

Caused by a lack of octane. Further aggravated by a inproper ignition timing, a lean cylinder, etc etc and a bad cooling system.

The fuel is lighting off even with the ignition off
even at idle. (auto, pre-ignition,) In exteme cases it will even detonate, even at idle.
The high compression ratio, low octane fuel and improper ignition timing is causeing the motors' combustion chambers to overheat (possibly glowing hot spots) creating the run on. (after a drive)
Haveing the carb throttles open further than nessessary
at idle just adds to the problems.

Some cars us an anti-dieseling solenoid on the carb to help reduce this.

Get a water temp guage. They cost a lot less than new
engines.

The engine's crank balancer could be slipped or the timing tap mis-located causeing you to mis adjust the ignition timing.

I would advise you not to drive the car until you get to the root of the problem.

 

88: You have any idea what I need to get my gauge working? It's the stock gauge in my instrument cluster. I have no idea what sending unit need to buy and screw into my block/head so I can hook my wire to get my water temp.

My plan is this:

Ignition timing and using oxygen sensor to do a rich/lean tune to get the car running "right". If it still is having problems even when running stoich and with good ignition then I'll spike some octane boost in it.

Hopefully it won't come to that and Sunoco 94 can keep me happy. Thought if I'm having this much trouble in the winter, I can't imagine it during the summer.

 

Lets say I have retarded ignition timing, a cam with a moderate amount of overlap, and my carb throttles are open to far at idle.

My boss was showing me the idle mixture holes and the slits in the primaries....that if my blades are open to far the idle mixture screws dont' do much (which explains why he had so much trouble getting them to work)

Do water temp gauges go bad? Or is it more likely the sender goes bad....cause I got my gauge to work, 10-15 minutes of highway driving and it only read 140 degrees.

Oh yea, I drove 12 miles to my bosses house, shut the car off, no run on. Started it up after hooking my guage up and ran the car for a few minutes to see if the guage would read, no run on.

Drove home another 12 miles, it ran on. An octane problem should be consistent no? I just don't think it's octane, maybe the compression is making the timing/carb problems worse, I was reading a book I got for xmas, pontiac ran 10.75:1 and 11:1 for years on the GTO.....and everyone I talk to says 10.7:1 is fine on 93 octane, if you are very well tuned. Tomorrow I'm going to pull a valve cover and find EXACT TDC, and I have an oxygen sensor and a rich/stoich/lean gauge.

 

Back in the muscle car era, there was "muscle car" fuel to match.

The high compression GTO's , HeMi's and Ls-6 Chevelles
etc all required Premium Leaded high octane fuel.
We used to run them on Sunoco 260 (about 102-104octane. The laws of physics haven't changed.
93 octane is not enough.

"Lets say" we stick to reality. Finding True TDC on your balancer sounds like a good start.

 

My boss has a 67' Fury with a 440, 10:1, he runs regular, his car doesn't run on or ping. I thought maybe that a big block had different characteristics, or my cam could affect it. But as you said, I'll do TDC and go from there. I appreciate all the info.

 

About a year ago I got a '84 carb'd 305 Z28 and the thing has been nothing but problems. The guy who owned the car previously must have had his brain replaced with a walnut, as all the vacuum lines were incorrected placed, wiring for all the electronic was hacked off, and the car just generally ran like crap. Anyway, the car is all stock except for a huge friggen fan, and a 4 bbl edlebrock carb, and has No *****. My brother and I have gone through the WHOLE damn car fixing every little thing, but we still have the same problems as listed by the original poster. We have adjusted the mixture on the carb, there are no vacuum leaks, and checked the timing. Basically, we have done everything in the intial post, and have all the same problems still. Last night we just looked at the car, trying to figure out what it could possibly be. My brother knows everything there is to know about TPI cars, and a bit about carbs, and he is at a loss. Here are all the symptoms as of date.

*irratic idle (idles high, as though choke stuck, even after driving for thirty miles in an arizona summer)
*runs even after shut off (have to put it in drive to shut it off)
*runs rich (all the time, no matter what adjustments)
*misfires (plugs recent, plug wires replaced)
*timed correctly, yet runs like a dog, (timing adjustments dont seem to help. Tried degree by degree adjustment, nothing worked.)
*have to push to full throttle to accelerate. (this is recent, as off last night)
* p.s care of the previous owner, there are no electronic sensors functioning on this car.

Im sure there is more, I just can't think of anything. Everyone who replied to the initial post asked about vacuum lines being connected. I ASSURE you that they are all connected. I wake up early on a work day to look over the car to see if I find anything, and I have disconnected each vacuum line and reconnected it according to the Carb's instructions MANY a time. The carb is recent, but if I can't figure anything else out I'm going to get it warrantied. Maybe it is just faulty? PLEASE PLEASE PLEASE HELP!
Thank You!:hail:

 

The first engine I rebuilt, I failed to put break in lube on the cam. We kept thinking it was the carb, cause it ran like crap and it would backfire through the carb. The cam had some flat lobes tho.
Have you looked into that?

 

ok.

A. why are you using the coldest plugs for vortec's?

go with the normal heat-range plug for vortecs.

B. what are your plugs gapped at?
keep them between .035-.045

C. What kind of distributer are you using?? please tell me you are not using a CC-HEI. and if you aren't try replacing the cap and rotor, and the coil.

D. GET A VACUUM GAUGE. make sure all your vaccum ports are hooked up properly. i.e. the timed vacuum port that your vacuum advance on the distributer is hooked up to, has NO vacuum at idle, and does have vacuum at higher rpm. try disconnecting and pluging ALL other vacuum sources on the carb, and see if that helps the idle.

E. using the vacuum gauge, tune the idle mixture screws to attain the highest vacuum.

F. set your timing up for highest vacuum, then retard it a few degrees if it is pinging. because it sounds like maybe your balencer slipped. so the timing mark might be off.

G. was your cam degreed?? a improperly degreed cam could cause what you are describing.

H. are your valves lashed correctly. if some are too tight, they will cause the valve to never fully close, and your motor will run really poorly, lash them when they are running and go 1/4-1/2 a turn.

I. get a fuel pressure gauge, and see how much fuel pressure is getting to the carb. if the carb is starved for fuel, your motor will run lean.

hopefully one of the above should help.

 

All these replies and not a single one mentions the distributor location? I know I've dropped mine in once before and just being off by 1 tooth caused nearly every problem your describing.

 

Scott:

Cam is in right.

Carb is getting 7PSI steady.

Heres what happened over the weekend.

I retimed the car and got it to the point where it didn't run on and drove fine.

Guy who helped me build the engine(rob) pulled the distrib vaccum advance off the ported vacuum and put it on full vacuum. For some reason he is obsessed with running the engine on full vaccum not ported vacuum. Right now running on full vacuum the engine has not run on in about 30 shut offs in a row. The idle has stabilzed as well. I had it running like this with the engine running on the ported vacuum, but he switched it for some reason. It seemed to be a timing problem, I had the engine about 10-12 degrees advanced, when I rehit it with the timing light the marks had slipped back, so the engine was retarded, which explains the run on.

My only concerns are that my gas milage still seems pretty shoddy (11-13MPG). The engine runs "fine" as it is off full vacuum. The problem is the engine still does not respond to idle mixture screw adjustment or idle screw adjustment.

Now rob admits he doesn't understand why the engine doesn't respond to the idle screw or idle mixture screws. He said that normally if you turn an idle mixture screw 1/4 turn that you should see a noticable difference in engine behavior, whereas my engine you could do a full turn and you might see 1" of water column change. You can do a full turn of the idle screw on the carb, and the RPM may only change 50-100RPM. The engine has NEVER responded to idle mixture screw or idle screw adjustments. Ive been led to belive that they should be sensitive, and my don't seem to be. Rob showed me how the idle mixture screws work with a 750 holley he had sitting around, the slits in the primaries below the throttle plates. I might just pull the carb off and see if the plates are open so far at idle that they aren't doing anything.

My idle is very low, i have to REALLY screw the idle screw in to get a high idle....

 

Have you tried turning the idle screws all the way in with the car running? If the car continues to run there goes your problem... You have some sort of internal leakage going on. Another thing may be that you have some sort of vacuum leak or something causing your throttle blades to be open up too far and the carb is completely out of its idle circuit...

 

Is there a way to tell if the carb is out of the idle circuit?

I will def screw my idle mixture to full tomorrow.

 

If the car continues to run (at all) with the idle screws in the carb is either out of its circuit or you have some kind of internal leakage (like a powervalve). Another thing you could look for is, look into the carb while the motor is idling. If you can see fuel dripping or any form of wetness within the venturi or on the blades ...you have one of the above problems (internal leak or carb not in its idle circuit, or both)

 

For first , iam from Germany so if my english is not the best .. sorry for that

Thank you for all the information posted over the last 2 years they where very helpfull

I just wanna let you guys know what happens to me …

I built a chevy 350 a bolt .040 over

Scat Cast steel crank , Scat pro competition rods, wiseco forged Pistons

Lunati Vodoo cam ..703 and their microtroll Lifters

Dart 180 iron eagle heads , Manley valves

Weiand street Warrior intake , 750 Holley with HP Mainbody billet base and metering plates

It just stars at first firing ( a bit loud I thought ) used breakin oil ( royal purple) broke in for 20 min at 1800 rpm

Dizzy is a new msd streetfire set at 12deg base ,full w/o vacuum to 34 deg

Could not get the mixture right ( slots where just about 0.03 uncovered … installed a wideband O2 Sensor … very rich ..like 11:1 goes up and down all the time…

Car runs like crap power only in high RPM

Vacuum gauge … only 9HG instable at 800 RPM , at 700 RPM the neelde bouced around fro 4 to 8 HG

Tried all… like othe plugs ( heat range ) tried different airbleed / jet combinations, PV`S,

Float level and so on … A/F jumps around ….

Readjust rockers… ( half turn … 3/8 turn ) ….nothing helped … grrrrr

Compressiontest was low (135 to 145 psi) Calculated should be around 9.8:1

Maybe a vacuum leak in the valley …

Ripped all off … guess what I found … all exept 4 of the brand new lifter ( hydraulic)

where rock solid … no movement of the plunger even with big force they didn’t move …

so as I adjusted them I opened the valve instead of moving the pluger to the right position …..

result the valves never closes …..

a tip from here : check , even new parts ,for function and you can save a your self a lot of trouble

installed new lifters ( checked them before )….now he is running flawless full adjustable …. Very happy now

I hope this helps