350 running rough
 

hey guys i got a 72 gmc 1/2 ton 350 4 speed. the motors got 20,000 since a complete rebuild. its got a quadrajet and i put some headers on it (stock headers off something?) anyways its my DD 30 miles a day. i run scrap 75 miles away every weekend and cruse alot. i wrap the engine up often and sometimes run open headers if im tweaking my exhaust. i have purple hornies 18in header mufflers with about 4.5 feet of 3in with turn downs.
now my problems started when i got the pickup last summer. if it was 60 degrees out it would hardly start, i mean it would start but wouldnt like to keep running. and if it got any colder then that it sucked. anyways i finally acted like i knew what i was doing and adjusted the 2 air fuel? screws. i finally got it dialed down and it ran great for awhile. then one night it was -10 outside and i started it up and it ran on like 4 cylinders for about 10 minutes then it got warmed up and started running right. its done that a couple more times when its been about 15 degrees outside and i cold start it. so anyways the pickup was running great and i was in a town about 20 miles away and i bought a magazine and sat in my pickup idling reading the magazine for about 20 minutes then i drove home. i was on the interstate and the pickup kinda jerked twice on the 20 miles drive. almost like the engine stopped running for half a second. that was about 5 days ago and its got to it will hardly run. i thought it might have been running rich cause it was popping out the exhaust when i was just driving normally, and doing that half second stop alot. anyways i pulled a plug and the (i forget what its called but its not the electrode tip, its what it arcs to) anyways that was almost white(the plugs have about 1000 miles on them) so i turned the 2 air fuel screws out but it didnt much better, its drivableish now. and i got a carb kit that my neighbors going to help me put in so mabey tomorrow. the only thing is that i gassed up in the other town so mabey there was something in teh fuel and mabey plugged the filter? ive gassed up since then. anyways im going to the shop and hopefully ill get it fixed. but any input anyone has would be greatly appreciated! thanks

Re: 350 running rough
 

If you rebuild that old Q-jet, it will probably need a throtthe shaft rebush. The shafts that the butterflys are on will "egg out" the holes and cause some serious vacuum leaks. A competent carb shop can do it. There are also rebush kits available for the DIY guys.

Gary

Re: 350 running rough
 

ya the guy i have helping me knows his stuff and he said if the bushings were wore out he knows a guy that can rebush them. any ideas as to whats wrong with my engine? i havent had time to check it yet but hopefully ill get to it tonight

Re: 350 running rough
 

have you changed the fuel filter or just thought about it?

ever try throwin a gan of fuel treatment like berrymans in the tank?

maybe try a fuel pumping capacity check?

has the gas tank ever been cleaned out??


you can throw carbs at a problem allday long but not getting a steady reliable supply of gas it wont run right with any carb you care to use

Re: 350 running rough
 

You haven't mentioned if you did anything with the distributor. HEI or points type, if points, are the points set properly, is timing set right, plug wires in good condition? There are quadrajet tuning manuals on the web but the quickest things to change out to remove doubt are the distributor parts. These points wear and if you're using it as a DD, they need adjustment. A dwell meter is good or you can do it by ear. To adjust timing, you'll need a timing gun. You can rent these from the autoparts stores.

As for the carb, what I've done in the past (no expert for sure), is turn both mixture screws all the way in and then back them out the same number of turns and start there. Is the choke working properly?

Lots of things need to be run down first.

Good luck-this board has lots of experts!
:gmc2:

Re: 350 running rough
 

i put a new cleanable brass? filter in about 2 months ago (the one in the carberator) i put a new fuel pump in when i started driving the pickup (6 months ago) ive never heard of berrymans but ive ran lots of stuff in the tank like seafoam and carb/injector cleaner. the gas tank has never been cleaned while ive had it. it only sat 2 years before i got it. ill check the filter and run some more cleaner through it. ill also spray some carb cleaner in the carb. one thing i think i forgot to mention is that the vacuum line that hooks into the air cleaner was unhooked so mabey something got sucked into it? thanks for your reply!

Re: 350 running rough
 

ok its got points. when i started driving the pickup (6 months ago) i put new points and condensor in it. i set the timing up to 12 and set my dwell. i put new wires on it when i started driving it and spark plugs 1000 miles ago. a guy told me that the points might have went bad cause the springs lost their tension(i hit the red line on occasion) i havent put new ones in yet but i cleaned the points with some emery cloth. also i put a newer distributer cap on there. i checked it and it seems good.
im thinking tomorrow ill get a new coil, points, condensor, rotor, and cap?
also when i was adjusting my carb i could turn it down untill the engine started to slow down then i turned it the other way and i got to 4 full turns out and it still didnt slow down, i was afraid of turning them all the way out so i turned them out 2 turns from slowing down from the bottom.

Re: 350 running rough
 

ok so it turns out my points were burnt so i put some new point in it and when i had the air cleaner off my boss came up and said my vaccume lines were all messed up. we fixed teh lines and it has never ran better!

Re: 350 running rough
 

Sweet... :)

Gary

Re: 350 running rough
 

Good to hear. That's why a lot of people go to HEI to eliminate the whole points thing. I still have points-it gives you something to tinker with.:lol: