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Timing issues

chev-mc

chev-mc

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Potsdam, NY
Hello all,
Thought I'd see if there is any advice to be given on this on.

78 K10 350

My truck ran great when I first got it a few years back. About a year ago when I took it off the road it ran like total crap.
I replaced the extremely worn timing chain and cogs.
Timed it and it still bogs under load and back fires.
I figured I had better replace the vacuum advance as well as it doesn't seem to be advancing when it should so that what I did today. Then timed it again. I checked the vacuum port on the Q-Jet as well and it pull vacuum when it needs to.
Its much better but far from perfect/the condition it was in when I got it. I can get it up to 4K without much problem but still get some hesitation and the occasional backfire. The last thing I can really think or would be the cap and rotor. I replaced them close to a year and a half ago. When I popped them off the brass was somewhat corroded.
Its just about 0 degrees here... I wish the truck would fit in the garage :doah:
 
What did you set your initial timing at?

You might throw a set of wires at it. I just threw a set of old rusty wires on mine because it wouldn't run right and now it runs like a champ.
 
Its weird in the emissions years , they just don't seem to run right with manifold vacuum with the stock quadrajet and camshaft .

My best settings on a late 70's motor seems to be 8 degrees at idle and ported on the quadrajet .

( my electric choke bowl venter has low signal on the full time port dunno if its all late 70's are like that or not ) .

Now all my Chevelles ( I currently own number 4 :pimp: ) loved as much inital timing as I could give them , and ran manifold vacuum off the Holley with an adjustable vacuum can .

And x2 on the wires etc , you need to replace some **** every year or two to keep her tip top :thumb:
 
Some things come to mind.
You said you replaced the vac advance unit,what about the mechanical advance which contributed to total advance? something like 35 degrees total at x rpm. You`d have to reseaarch that one. Are you sure you tapped into the correct port above the throttle plate not below giving 15invac at idle? if not your getting full vacume at idle on the vac can and setting the idle timing to your 8 degrees then dropping to -5 to 10 degrees as you crack the throttle hen recovering at high speed cruise and minimual throttle.
You mention back firing? out the exhaust of back thru the carb? a sign total timing off or valve timing off. whats your vacume reading at idle? should be 15 + - inches vac.
Personally in 30 years and over 150 vehicles I cant recall a bad cap or wires or rotor make it "bog" or "run weak",miss like hell, sputter cut out, you bet but not just feel overall weak. Next pitch black night pop the hod with it running and have a look around the cap and plugs and anywhere the wres are laying on metal or crossing each other. This revealed what looked like a lightening storm under the hood of a friends Toyota once that missed terribly under accelleration only but ran fine otherwise. The couple times Ive lost a GM ignition module it ran fine then would crap out and die,later restart and go like this for weeks then die for good eventually and have to be replaced.
Is mileage way down? carb issues,saturated float,stuck or worn needle from bouncing around after romping the truck off road. I cant imagine this but Rochesters are notorious for leaking fuel from the cast and once sealed plug on the bottom of the carb in the center,is the plug leaking like a sieve and drowning it with fuel? I dont recall what state your in but if its Ca it will never pass smog like this with it dripping fuel while idling throwing off the HC`s or?? like mad at low speed test mode.
Is it a Calif version with massive smog crapola and a 02 sensor? for $20 replace the 02 sensor, running to lean poping back thru the carb?
Im sure I can think of some more of the problems Ive faced and post em up.
 
The set of wires I just replaced didn't produce any lightning at all. We shut off all the lights in the basement so you couldn't see the hand in front of your face an we didn't see chit. The wires were brand new but put together poorly. The wires I put on were old and rusty and it still ran like a champ. I was having alot of the same problems he described...but not all of them. Long story short the "lightning method" of checking wires doesn't always work.
 
I agree 100% with you on the lightening test,IMO if there that bad you probably have had problems for a long time anyhow,just hard to diagnose over the internet. One of the biggest guessing games I had recently involved a our 83 C2500 hay wagon. I purchased it from a friend who had it the last 15 years without a glitch. It ran fine for a few monthe till mid winter when I parked it in a wet muddy area where it sat for months. It Fired it, idled fine but under accelleration somewhat loaded it would sputter and just not really get going, if on flat ground it was tollerable due to the lack of motivation to dig into the greasy mess under the hood. I literally replaced everything from the fuel pump,filters,module,cap,rotor,wires,I rebuilt the carb,bla,bla everything but the plugs which were done a year ago by me. Come to find out the plugs rusted enough around the outer edge it cracked the porcelin on several an they would misfire under load. $12 for a set of new AC`s and it ran like new again. I was so pissed I couldent see straight for weeks screwing with this thing.:mad: I was given a fiat 131 that sat for 12 years in a soggy felid and after adding some gas drove it for 6 months till I grenaded it. Ive had some real fine specimens of neglected doo risen from the dead of years sleep and would have never guessed the rusty plug deal.
 
i

i hade the same problem but my truck was backfiring under load in my intake it was my roller rockers out of adjustment and my timing was off.I went ahead and put all msd on it msd 6 box,wires,cap and rotor and it runs great now.I cant test drive it because i am rebuilbing my rear end.:mad:
 
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