BAD-HABIT

I am still trying to figure out my problems on this fu***ng thing Motor ran FINE first 40 hours or so. I then devoloped a bog/surge when going from a set idle to W.O.T. At idle sometimes its a backfire thru the carb. Also I devolped a distinct miss at cruise above 3300 and below 4500. Under hard acceleration in this range and I would get the bog but no miss till I leveled off at a steady cruise between 3300-4000. At the time of the miss I checked the plugs and noticed that instead of their previous condition they were white as ghosts!!! For the first fourty hours the plug were perfect. when all this started I pulled all the plugs and they all were the same....WHITE AS GHOSTS.....I checked them by running on a w.o.t. in which I would shut the motor off at rpm's (33-5300) and pull them and look. Well here's what I have done and found. 1)New plugs,wires,distibutor (timing verified at idle 8 degrees and at full advance 32degrees this was with old TBolt IV system and new D.U.I.-H.E.I system.)Completley went thru the carb (Edelbrock performer) and found nothing special probally since carb was new. Anyways I went up and tried every spring,jet and rod Edelbrock sold to richen this damn thing up and still NO change at all. I finished the carb up by installing the hi-flow needle and seats....I tried colder plugs and still nothing. I backed off the valves from 3/4 a turn to 1/2 and still nothing. I cheked the fuel pressure and got 4-1/2 lbs...I checked the intake and thought they were o.k. (key word here is thought) I had a "Buddy" torque it up at his garage and found out that his idea of 45ft/lbs was NOT o.k. I sprayed starting fluid around the carb base and no change in idle or rpm....I sprayed the starting fluid around the intake gaskets and WHOLA! the the engine would really drop rpm's every time I sprayed. I put a towel all around the flame arrestor( to make sure the spray wasn't getting in the carb) and still got the same drop. Well I thought(my mistake) o.k. I needed new intake gaskets (probally from the 45 ft.lbs of torque instead of 11 g.m and edelbrock calls for) Well I remove everything to get to the intake and get it off...I find the gaskets(fel-pro) look fine. But the intake (also new a performer vortec) is warped about 1/16-1/8 inch on both sides.....Great news I think yeah Im broke but I just found my problem...Sooooo I fork over the dough for a new intake (performer vortec rpm air-gap) and the recomended gm intake gaskets (the ones reccomended by G.M.,Edelbrock and Car-Craft magazine). I check the new intake with a staight edge and it checks out...I CHECK THE HEADS and they check also....I install everything back up (after fighting rain all week) and TORQUE to GM/Edelbrock specs of 11 ft/lbs. All the while using the correct sequence. Restart the motor and I still have the bog/backfire at idle....Take it to the lake and still NO FU**ING CHANGE!!!! Check the plugs and still white as a ghost. Try the starting fluid thing AND STILL GET THE SAME RPM DROP!!!!!! Well I up the torque to 20lbs and make a run and still no change....I loosen the bolts all up to nothing and retorque to 5lbs....NO CHANGE. Move the torque back up to 12lbs with 15-18 between the problem area with no help.......The leak seems to happen between the front and rear sets of bolts...On the vortec heads the intake uses 8 bolts...2 on each side up front about about 2 inches apart and 2 in the back same way...ALOT of area between the front and rear with out any bolts.....I guess my question is WHAT THE HELL TO DO Ive just lost my vaction to this damn thing and am losing what little hair and patience I have. WHY WOULD THIS THING STILL LEAK if I checked for straightness,used new intake,gaskets and correct torque and sequence. Im temped to put a heavy coat of hi-temp rtv silicone down the length of the intake and try this...At least to find out if my problem lies here or here and somewhere else......THOUGHT ANYONE??????PLEASE PLEASE PLEASE

Here is the manifold in question...Note the open area between the front and rear sets on bolt holes...

BH

Mr. Demeanor

Wow, youve been busy. I cant help with the problem but Ive been in your shoes enough time to know your fustration. If you can, take a day or two away from it. I usually figure things out when Im doing something completely different. Im sure youll get some feedback hear. Its usually somthing simple thats so hard to find.

FloridianSon

Just a thought if it is an install thing there was a service notice that Mer.changed the pattern of the sequence.On the port side starting at the front and going straight back#8 #4 #2 #6 now starboard side front to back #7 #1 #3 #5. if you draw it out on paper it will come together. Or go to the service bulletins and check it out.

jpclear

Yeah, the fuel pressure thing would really be something to check! Had a cam wear off the fuel pump drive lobe on a MK-IV big block once and we about went nuts before we found it. I do hope it's simpler than that however. It gets metal chit in the lower end brgs. when it happens. I feel your pain! --- Jer

BAD-HABIT

I called Edelbrock and they said 4-1/2 pounds was ok.....Especially at the rpm range my problem is happening at. I still want to know what everyone thinks about running the rtv silicone down between the head and manifold....I figure at the very least I can take care of the leakage there and hopefully know that the leak is my problem. If not then it's one less thing to worry about right?

BH

paradigm shift

I sure am not an expert but it sounds like you are lean. Do you know someone with a 750 or 800 holley you could borrow for a test. Someone with a setup close to yours and known to be in a good condition. Hopefully if you are lean you have not tuliped a valve or worse. When you stand on the gas and you get a backfire a lean condition can cause this. Timing and other problems can cause also but if plugs are white and you think it is lean well I would think fuel. Have you always ran 4.5lbs fuel pressure. Is the gauge right at the carburetor? Eldelbrock has small fuel bowls and can lead to running lean if fuel delivery is not correct. Good carb just has to have excellent fuel delivery. Sorry not much help just more questions. Sorry for your trouble and keep us up to date. Summer is just starting so don't give up.

BAD-HABIT

Paradigm shift-The motor ran GREAT for the first 40 or so hours...Then suddenly I got the miss and lean condition. I Havent' really had someone answer this but WHAT IS HAPPENING when I spray the starting fluid on the intake gasket "alley" between the heads and the gasket? When I do this I get a stumble accompined with a healthy drop in rpm's....What is causing the change in rpm's??? and if it is a leak then woudn't that explain my sudden condition and it's symptoms???? SOMEONE has to be bored enough to sit down and help me trouble shoot this thing out.....PLEASE (God and I really really hate begging ) I thing that this is a somewhat common problem with the vortec heads...........

BH

paradigm shift

I would agree it sure sounds like you have a vacuum leak. I would think it is odd that ALL the plugs would be white if manifold is just leaking on the ends. I would not recommend the silicone but I guess you could try it as a trouble shooting aid. You would have to make sure everything is very clean or it will not work. Do you use something like permatex #2 around intake ports on your gaskets. If heads or block have been surfaced make sure you get an even crush on gaskets from top to bottom. I have to use the extra thick gaskets on one motor I built or it causes me trouble. Usually around water ports though.

Didn't notice you were on line and I am a slow typist!

BAD-HABIT

Heads and block have not been surfaced....The instructions called for no sealeant on the gaskets as they ar a hard rubber/plastic with a silicone type crush instert around each intake port and water port. The only silicone now on the manifold is on the ends where it is to be used in place of the old cork pieces.....The leak seems to be coming from both sides more towards the center on the sides where there is no bolts... see the pic below. Whould using two gaskets be an option?

BAD-HABIT

Where can I find this service notice at? Should I use this or call Edelbrock? The heads are L31vortec truck heads I bought new from the dealer. What was the reason for the service change? That might tell somethig there.....Thoughts or comments?

Bh