Worst first drive ever.....

[72TealnWhite]

Bought a pretty nice 72' lwb 350 a few months back.. been working on it here and there.. mostly cosmetic .. Did do some minor tuning of the carb.. a edelbrock 1406 600cfm.. to get the idle right.. sounded like we had gotten it alright .. i had no plates yet .. so all i could gauge was a lap around the block. Had some small backfiring issues with it driving at minimal speeds.. and it would hesitate before acceleration... Well we got it to where we thought it should be and today was the day.. the test drive on the freeway.. It sounded ok. but it was hesitant still.. when it got going it sounded ok. It would backfire on decelleration or downshifting.. then i got going about 65 mph. got a thumbs up from a passer by and BANG !!!! sounded like i dropped a muffler... I looked and its definitely coming from the driver side.. i think i may have cracked the exhaust manifold... holy ****. what do i do now? The truck does run Flowmaster 40 series.. and it looks to have new pipes front to rear? Anyone know what could have caused all the hesitation and backfiring? and what about exhaust manifolds.. new ones? do i need special ones? pertaining to the block? Thanks in advance

nate

[GASoline71]

Check your timing.

Also start with a baseline of 1 turn out (after gently bottoming) on the idle mixture screws.

Read this... http://static.summitracing.com/globa...406_manual.pdf

Gary

[Leroy-B1]

Had a similar first.drive this past Saturday....finally got my truck out of shop.after.suspension work and changing it over from manual to automatic. Was on the way home with it after having all this done and lost the motor. Worst part.was previous owner had paid to have the motor gone through and supposedly only had 15k on rebuild. I even have the reciept where he had it done. After pulling the motor it was.evident that it wasn't rebuilt, simply had a set of gasket installed to stop the oil leaks and a steam bath to make look better. Previous owner paid for a rebuild though....oh well guess ill V-8 it now...feel your pain
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[stich626]

are there tail pipes after the flows?

[HavinSomeFun]

Sounds like it was running way lean and heated up the manifold to a cherry red and cracked.

[brad_man_72]

the worst drive in an old truck is still better than a walk.

[72TealnWhite]

I knew it had to be something simple ... either mixture or timing.. Sticky valves? I think the truck had sat for a year.. Well, The problem is that i don't know what this motor is all about. One guy identified the manifolds on it from a 71 vette .. so i'm not sure what else this guy did to this motor that would effect the timing.. cam.. exct. What am i looking for around timing wise on a pretty bone stock 350 with the above carb. and newer exhaust.. flowmasters.. Can't seem to get her to run smooth.. at what rpms.. do you all like to idle.. Is there anyone with the same setup and carb setup to get her to run smooth? thanks

[gonzo6869]

I have the same set up and the same problems when I first got mine.

Check your timing like mentioned already, after that go through your fuel system. Check the sock on the sending unit, check fuel filter (also look for any extra filters PO might have installed), go through the carb and clean it out (the 1406 is an easy carb it take apart and clean) and check your spark plugs and wires (PO said that new plug and wires were just installed, I found 1 burnt wire and a couple of loose plugs). Oh yeah check your fuel pressure, a stock fuel Pump will put out too much, the 1046 runs best with about 5-6psi. Hope some of this helps.

[72TealnWhite]

thanks gonzo... yeah i did pretty much all the prep work you mentioned above.. Plugs, wires, made it sound alot better.. than we tried to smooth it out with the carb. put some stuff in it to prevent sticky valves.. And the next step was get it up to about 60 mph and see what happens... and that was that. oh yeah, had just replaced the fuel filter .. ? anything to do with it? I'm thinking it was a mixture or timing issue from the start... /

[Frkypunk70]

You may want to take the valve cover off and check to make sure the rocker arms are moving up and down and the pushrods are not bent. Also this will let you rule out a worn cam. I had popping like that and found out my cam was wiped. Just a thought.

[usmcchevy]

Originally Posted by Frkypunk70

You may want to take the valve cover off and check to make sure the rocker arms are moving up and down and the pushrods are not bent. Also this will let you rule out a worn cam. I had popping like that and found out my cam was wiped. Just a thought.

Or bad timing chain.....

[Frkypunk70]

Also are you sure your not 180 out on your distributor that alway caused a lot of popping for me. I didn't see that anyone had mentioned that.
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[cdowns]

you managed to get the truck home with all 4wheels still on the ground?? so it aint the worst ever

i prefer to do mechanical stuff prior to wasting time on cosmetics

[yuccales]

Originally Posted by brad_man_72

the worst drive in an old truck is still better than a walk.

Well said!

[68 TT]

First thing is to double check your plug wire routing and firing order. It is easy to get 5&7 swapped and it will pop & backfire and run poorly if you do.

Also check to make sure none of the plug wires are hitting the exhaust manifolds. They will burn through and ground out pretty quickly. It will run poorly if that is happening as well.

Put a vacuum gauge on it and see how much vacuum it is pulling at idle. Set your air & fuel mixture screws on the carb for maximum vacuum. It will take a couple rounds through each one to get them both stable at the highest vacuum level. Once there back the screws off until it just starts to drop in vacuum. It should run the best at that setting.

[Tkmadone]

I second double checking the firing order. I've done it and it sounded very much the same as what you describe.

[GASoline71]

Originally Posted by usmcchevy

Or bad timing chain.....

This too. If the chain is stretched and jumped a tooth or 2... it can get ugly quick.

Gary

[ChevLoRay]

The 1405 I had was running .100 main jets...good for performance, but rich on the streets. Mine would gas-foul the No.2 plug every few months. When it did, it would pop in the exhaust pipes (true dual....Flowmaster 40's).

Go to www.edelbrock.com and check out their technical help pages.

When I change my 1405 for an Edelbrock Q-Jet, I had to put a heat shield on the starter because the mixture got leaner and hotter. Never did gas foul another plug and it didn't pop thru the exhaust system any more.

My bet, is that your carb is running rich.....

[72TealnWhite]

First off thanks for all the answers and advice ... Having manifold replaced, should be done tomorrow. plan then is to try the above .... thanks again
nate

[72TealnWhite]

update: maybe this truck isn't so nice after all. Exhaust manifold was cracked all the way through it was replaced . New plug wires, checked the timing, firing order, tuned carb. took it in to get looked at and apparently had a rotten distributor, bad trans mounts, and the driveshaft was about to fall off the truck .. (so he says). i had him fix all those things and wanted to focus on the motor issues. We checked everything as far as the carb, mixture, tuning, timing, .. and it still pops backfires, comes out the carb .. under acceleration and shifting gears (auto) .. and decelleration. So his idea is that something is very wrong mechanically in the engine, bad valve, bent valve, stuck, bad cylinder.. oh geez .. uh oh, is this possible.. sound familiar? Not feeling good about this. thanks,
nate

[67_C-30]

Originally Posted by cdowns

you managed to get the truck home with all 4wheels still on the ground?? so it aint the worst ever

i prefer to do mechanical stuff prior to wasting time on cosmetics

No doubt, when I first drove my dually pickup after I put the diesel, the left rear tires apparently weren't tight (I love my brother!) and they came off and ripped the custom rear fender off and one of the tires ended up in a creek about 60 yards off the side of the road. So um, that was not the worst first drive ever! -lol

[Frkypunk70]

You should really take a look under the valve covers. It may just be a loose rocker arm or bent push rod. Worse case scenario(like what happen to me) it's a worn out cam. Popping through the carb means that it's definitely valve related. Hope it's just something simple.
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[hatred]

Originally Posted by Frkypunk70

Also are you sure your not 180 out on your distributor that alway caused a lot of popping for me. I didn't see that anyone had mentioned that.
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I think this is my issue. I can definately see that the plugwires are NOT where they're supposed to be on the dist. After that it's on to adjusting the carb. Anyone have a simple way to find TDC so I can fix the timing?

Sorry to thread-jack.

Tony

[BMERDOC]

Cylinder, Distributor correlation. Cylinder #1 is the first cyl on the dr's side. Cylinder #1 on the distributor is the terminal at the 7 o'clock position looking from the grill to the firewall. Easy is relative.
Remove the driver's valve cover. Clean the balancer, paint the numbers with a bright brush on paint and wipe off before dry to highlight the numbers on it. Remove spark plugs and rotate engine (clockwise only). An easy trick is to place a screwdriver in the#1 plug hole and rotate the engine until the screwdriver stops at the top. FOR GODS SAKE DO NOT DO NOT LET THE SCREW DRIVER BIND IN THE CYLINDER!!!! Both #1 cylinder rocker arms should come up to close both valves (on the exhaust manifold end of the rocker). If you get the rocker tips at their highest point and the #1 piston is at its highest point you are at top dead center. Now, if you check your balancer and confirm it is at 0. Before you remove the distributor cap mark the dist body at the #1 terminal as close to center as possible. Remove the cap and see where the rotor is. Is it pointed at those marks or slightly faster (further clockwise)? Further ahead would mean it is advanced and that should be fine but not a lot. If you want to start from scratch loosen the distrubutor and move it so that the center of the rotor is centered with you distributor mark. You will now be top dead center everywhere and now would be time to put it all together and learn about timing lights and setting timing. If your rotor is not pointing anywhere near #1 not all is lost and you dont have to pull the distributor. Find the closest terminal and use that as #1. Go clockwise 1-8-4-3-5-6-7-2. You wires will look like hell on the cap but it will run. You can sort it out by removing the distributor and reinstalling it so that the #1 terminal is at 7 o'clock and your vacuum advance is almost straight towards the front.
Whew! Haven't even discussed that in ten years and it just flowed out of my finger tips. I hope I didn't leave anything out. Now if you'll excuse me I gotta go laydown I have a migrane.

[BMERDOC]

PS If you get the #1 piston to the top and check your balancer and its on 0 and your rotor is slow (stopped before #1 terminal) you have a stretched timing chain or it has jumped a tooth. Your valvetrain timing is slow (retarded valve train timing). You can also shake the push rods to see if they are loose (bent push rod) with the rockers at TDC. Rotate the engine to TDC according to the firing order and check each push rod and shake the rockers to check for looseness.. Also see if the valve tip is still in contact with the rocker (stuck valve). If you have a stretched chain you will have low vacuum. If your carb was tuned with a vacuum gauge you should have seen this. If you had any stuck, bent or badly seating valves or a bad cylinder this would have shown up on the gauge as an erratic needle.