sputtering only under load CAN NOT Figure it out

[kserieskid]

hey guys ive got a sputtering problem on my 1981 chevy stepside with a 305 qjet carb and regular hei dist set up

the truck will only sputter under load, i can put it in park and rev the **** out of it but when you put it in drive and power break it it seems to run for a bit then fall on its face then come back and repeat. same when you drive it, during normal crusing speeds and mild/fast acceleration

what I have done so far
change the distributers cap rotor ignition module and the coil along with the plug wires, the plugs look fine had a mechanic at a local shop look at a plug and they seem normal.

plugged any vacuum ports open and moved the vacuum advance to a port right off the carb.

changed all the fuel filters and made im getting plenty of fuel

any suggestions will be a big help

distributer also has an advance curve kit it was there when I popped the cap off

thanks Kserieskid

[MalibuSSwagon]

I had a similar issue, with the original 305. It would run fine and cruise fine as well, but when I would give it some gas, it would buck and sputter. Turns out the timing chain was really worn out and stretched.

[Boom]

The advance should be on a ported line, when you get past the idle circuit it provides vacuum to advance the distributor. If you run it advanced all the time it could cause the hesitation you describe. I would check the timing with the vacuum line off.

[INSIDIOUS '86]

Take the crappy advance kit off and keep the lighter springs. Put on a normal center plate and weights.

Sounds like the fuel filter may be clogged and its not getting enough fuel.

[mohsinj677]

what I have done so far
change the distributor cap rotor ignition module and the coil along with the plug wires, the plugs look fine had a mechanic at a local shop look at a plug and they seem normal.

[TDS-MN]

fuel pump solved very similar symptoms for me. Had noticed some fuel weeping out there as well at one point, but not always. Figured that the diaphragm was leaking. Been a couple weeks on the new pump, and no sputtering so far. Not sure what you did to test that you were 'getting plenty of fuel'.

[kserieskid]

thanks guys im going to check the timeing on my next day off with the vacume advance on and off

with the advance curve kit im unsure why it would start messing stuff up now gunna leave it the same till i check some other stuff

im begining to think its something wrong with the jets or internal carb problem i checked how much fuel a perferctly running truck cranks out over 30 second time frame then did the same to my truck and it cranks out about the same ammount

I have checked the filters, the inline one was cloged before the sputtering happend but i replaced it along with the fuel hoses around it they were spungy. the filter in the carb was fine but i cleaned it out with some brake clean just incase.

my plan is next time i work on it is check the timeing w/vacumme and w/o vacumme check for spark dropp off when it sputters with a spark tester and see if i can turn up the fuel per say on the qjet if none of this works. and also take it to a local mechanic i trust for another opinion

Thanks a ton for the response guys its a big help

[PAPA KENT]

I had the same problem and it turned out to be the sock in the tank.It would run a little better under a load in one tank than the other so when i pulled the first tank the sock was folded over completely at the stem and the other one was folded more than 3/4 of the way.removed the socks and problems solved.

Good luck!

Kent.

[kserieskid]

Thanks PAPA KENT maybe i can put a blast of compressed air to the line and get the sock to unfold if that is the case thanks a ton!!!!

[PAPA KENT]

Your welcome except blowing air to it might be work for a little while but i really doubt it.There is a plastic type netting that the sock is made of and what i learned on mine is that once they are folded and "kinked" you might say they fold back over again and of course when they fold over they cut off the fuel supply and add suction to it from the pump and you end up with zero results.

If in the case this is your problem the only way to cure it is to remove the sock.

Good Luck.

Kent.

[motornut]

i'd womder about the vac advance but wondering how many or if any big vacume lines are plugged
check the 3/8 big hoses for cracks
choke working ok,what type?

[INSIDIOUS '86]

I've seen those recurve kits do wierd things. It's possible that the springs are so light that when you drop it in gear that the lower rpm closes the weights up and timing drops. Basically out of gear the weights are opening and way to soon.

Have a bud drop it in R while you check the timing. It should be rock steady at 12*btdc

[1986_GMC_SWB]

Long time lurker here, first time post.

I just want to reiterate what PAPA KENT said. Way back in the day, I had a '78 short wide with a 350. It began sputtering like you're describing when I was really into the throttle, usually about the time it would shift into second. We looked at timing, fuel flow, anything we could think of. The problem turned out to be the sock in the fuel tank collapsing. Tough problem to diagnose.

Good luck!

[kserieskid]

well I have to say this is one of those im an idiot moments. when I said I checked the spark plugs, I did not check them all..... all the driver side ones when I did do it. taked to my mechanic the other day and showed him whats going on. he said "that is ignition for sure, your running autolights in a chevy that's the first place to start, get some delcos and try it"

when I changed them I figured out what my problem was...... this is starting from the driverside to the pass. side. in order front to back and not firing order

id like to say, wtf

[donut]

Autolites in a Chevy won't cause that. (I've run many over the years.) A faulty wire can contribute and/or oil control problem in the cylinder is where I'd look first.

Then again, if it were just a driver, I'd probably throw a couple extra plugs in the glovebox and change them out if it starts sputtering again.

[garybanta@yahoo.com]

Checked every darned thing... replaced all fuel filters...

Replaced Distributor cap but noticed same issues.

Started to consider carburetor adjustments.

All it was was a Timing Issue..

The engine started and idled and raced in Park and Neutral normally but could not even back up a 3 degree incline without bogging and sputtering.... no power what-so-ever.

Rotated the Distributor and instant love.

Hope it helps someone.

Gary

[rich weyand]

If the distributor clamp loosens due to temp cycling because it wasn't tightened down enough, the distributor will drag retarded and you will get similar performance issues.

For plugs, I would recommend the ACDelco R45TS or Autolite 24. Autolite 24 is what all the dirt-track racers around here run in SBCs.

I disagree with the recommendation above for ported vacuum. You should also be running about 16* BTDC base timing.
http://67-72chevytrucks.com/vboard/s...d.php?t=689321

[Pontiac1976]

It all most looks like it burning oil on the those bad dark plugs. could be valve seals or valve guides.
How much miles on the heads, since compression check valves seals replaced. And if they been burning bad like for a long time then Valves guides need replaced.

[El Dorado Jim]

I noticed the spark plugs are different, the length of the electrodes and porcelain is different..the longer electrodes are hotter plugs than the shorter ones...try running all the longer type plugs and you will probably be fine...and change your plug wires to a good brand ,Belden or Borg Warner....8MM wires