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.

[yuccales]

Originally Posted by brad_man_72

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

Well said!

[Tkmadone]

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

[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

[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.

[Sillyoldman]

Sorry if this has already been stated but I'm too tired to read the thread. I'd find TDC and drop the dist again. I think the issue is most likley in your heads. Properly adjust the valves (not running) or at minimum check for a loosened rocker nut. If it backed off, replace it. It will just back off again.