popping though carb out of nowhere!

[barleywilkerson]

truck just started popping through the carb and hesitating really bad... checked and rechecked the timing before this happened and everything was running perfectly... went for a 20 mile trip(yes, that says 20) and about 3/4 of the way there the truck started acting up... had to leave it parked for fear of a breakdown...

any ideas why it would start popping through the carb and hesitating?

edelbrock 1904 on edelbrock performance intake, 350 engine...

[454HO]

Mine did that when it wiped a cam lobe.

[ont_guy_38]

Originally Posted by 454HO

Mine did that when it wiped a cam lobe.

My thoughts excatly.remove valve covers and look for broken or missing push rods.If you dont find any start engine and see if all of your rockers are moving like they should be.If not then a cam lobe would be the problem

[barleywilkerson]

that doesn't sound promising... any more common ideas first? need to move truck asap...

[jermasaurus]

You would probably notice if you had one, but my holley did the same with a good size vacuum leak.

[barleywilkerson]

hmmm... push rods... wish i could find my rocker adjuster tool(s)... went to the parts store the other day and nobody even carries them anymore...
i might end up selling the damned truck VERY soon... seems like every time i fix something, something else goes off it's nut...

thanks guys... any other ideas, i'm listening...

[Srubydo1986]

mines been doning that i think it a need of a new cap and rotor cause it not doing so hot. But that not a big deal anymore cause i have to take the motor out now.

[454HO]

Do a compression test. You can borrow a gauge from Autozone.

[87 STEPPER]

Well i think everyone is going to big to fast you said you made some timing adjustments BEFORE this happened.

Sooooooo i'd look at the distributor and see if it came loose and moved throwing the timing out.

Also check all connections to the dist. and all vaccum connections make sure that the ign. wires arn't touching the headders or manifolds and grounding out.

Check all the basics first then if you can't get the truck to run smooth then pop the valve covers off and look for any obvious damage bent pushrods or broken intake valve and exhaust valve springs.

If that looks good have someone turn the truck over while you make sure all the valves are actuating.

If that looks good then check your mechanical timing by bringing #1 to TDC and see if the dist. rotor is in it's correct phase. if not correct as necessary.

If the truck is still not running right pull timing chain cover and check the timing gears and chain also recheck the mechanical timing and see if the cam and crank are in time with #1 @ TDC.

If no problems are found by now then i'd say pull the cam and visually inspect it for any obvious defects.

Good luck.

[hotrodmtodd]

You definitely want to check all the external stuff FIRST, but more than likely you probably have a flat exhaust lobe on the cam, or a stuck, burnt or bent exhaust valve. Hope it is just a crossed wire or a loose or damaged upper valve train component. The cracking sound is usually caused by exhaust gas that is not able to escape via its normal route. Good luck to you, Mike

[454HO]

Another very simple check - remove the oil filter, cut it open and check for metal. May not be 100% conclusive, but if a cam lobe is worn the metal has to go someplace.

[77 350 Shorty Wide]

What year of truck? Do you have point or electronic Hei ignition? If points they could be burnt of worn throwing off the dwell and timing. This happened to me years ago with a dual point distributor. Tore into the timing chain and replaced it thinking it jumped a tooth or two. It was only the dwell difference between the two sets of points that was throwing everything off.

Hope you find the problem and it's an easy fix.

God Bless, Terry

[1975stepside]

BEFORE you go unbolting a whole lot of stuff, why not do this simple test for a vacuum leak first? Get some spray carb cleaner or even a can of WD 40 will do, and lightly and SLOWLY spray around all your vacuum hoses and connections. If the engine smooths out at any point where you spray, there is your vacuum leak. Odds are pretty good you'll find a hose cracked somewhere, or one you accidentally knocked off or loose while playing with your timing. Sometimes the power assist brake diaphragm has a crack in it, and will cause a vacuum leak as well.

Good luck!

[bigpig72CST]

I had a similar problem a few years ago, it would run ok for a little bit, then start popping and hesitating. It was as simple as a cracked distributor cap. I assumed the worst at first too, but started eliminating the easy stuff first. With a flat lobe, or some of the other suggestions, wouldn't you hear it hammering at higher rpm, or making noise in general?

[Alex1]

sounds like a cam lobe - unplug one plug at a time -if you get it to stop then I'm pretty sure that's the issue. It's happened to me 2x's!

[BLE 'BURBAN]

Double check yor plug wires too. You may have gotten a couple crossed up when you did the tune up.