weird 86 k10 problem

[benoit454]

Ok first off some info, 86 k10 short bed, fresh rebuilt 350, stock gm intake, headers, summit cam/lifter set, stock rings and bearings setup(replacement) stock heads, brand new aftermarket edelbrock 600 cfm manual choke carb. Autolite double platnum plugs.

Well first edelbrock I had started flooding over and leaking gas out the throttle shaft, it had 90 day warranty which is total BS!!!! So bought a new one.

Thing ran fine for a couple weeks, now it's acting up.

Here's the problems, sometimes hard start after running, drove it about 5 miles, shut it off, waited for like 30 minutes, tried to refire, cracnked for more then 30 seconds and wouldn't fire, had to hold it to the floor, then it finally tried, puffed out fuel smoke badly, and died, tried again, same deal to the floor, fired, smoked, had to rev it up hard. Done fine on the way home, no problems driving it seemed. Also seems to have a dead miss in it at low throttle or idle, after about 1/3 or more maybe 1/4 throttle the miss goes away and revs smooth it seems, if you hold it there.

Now here's where it gets a little weirder, put gas in it, seemed to do fine, didn't have that happen again, still kind of rough like a miss at low throttle, but drives fine, just in the mornings on first start and rev in park it's rough, sounds like a miss or running on 6 or 7 plugs instead of 8.

Now that wasn't the weird part, it started doing it again, and just like the first time the gas hand read 1/4 tank. Put gas in, same deal, no hard start but slight miss on first start. Runs fine. Runs fine when it has hard starts, just a real PITA to start after warmed up, and when it hits it smokes, usually have to hold the gas down to start it. Doesn't act as if it runs out of gas, but once you put more in it usually or at least hasn't yet had hard starts as long as it's not on 1/4 tank!!!!!

Anybody have a clue or idea? The fuel pump is new, i think. return line is plugged off. it used to be hard to refire with the line unplugged so we plugged it off. Since then it's always started great on refires. Just developed this problem like 2 weeks after new carb, and nothing else changed. Been doing it for about a week to a week and a half.

Only thing I can think of is to readjust the mixture, set idle speed, check plugs, replace if black, check all plug wires which are new also. Maybe change out with another set. Possibly change out the distributor cap also. Recheck timing, shouldn't have changed, unless the clamp let loose and it jumped. it has been popping and backfiring every once in a while maybe once then not again for awhile.

This trucks been one problem after another I swear I think it's cursed, it's never been right. So far I've jerked out the knocking 305, which we had changed oil sending units, and tuned up, still wasn't right, cleaned carb adjusted it, changed cams, added headers, changed carbs, wires, plugs, then had to rebuild a 350 because the 305 knocked. Can't get the tv cable to adjust right, found the TCC solenoid unplugged ever since we had it, like 2 years later. had to change dashes, guages messed up, gas tank leaked, sending unit stopped working. Now I'm having a th350 built to replace the pos 700. Radiator was plugged, and leaking, changed it, heater core blew, changed it, one hose went then changed it, another went, so now it's all new hoses, and cooling system. Now this, what next. my old man is fit to be tied, he's talking about trading it off for sure. he's really pissed that nothing ever helps it. had new tires put on, lift kit, exhaust almost everything's new, and still nothing but problems.

[84 400]

Wow it looks from your car domain that you have put so much into that 86. And iot does look great by the way but looks don't mean anything compaired to a good runner. could it have somthing to do with your sending unit in the tank being clogged or somthing? That is the only idea i have on it but it sounds like you got all the things listed to check / change first. And i do see that you have replaced the sender. I am stuped but i do not have as much knowlage as other members o maybe they can help you. Good luck

[benoit454]

No I never changed the sender just cleaned up a spot and reground, I changed the guage cluster just for that reason, but it never healped, same with the oil pressure and temp switch, i changed them because the guages didn't work, so then they still didn't and I changed the guage cluster.

Now i got mech. oil pressure and water temp. I've had the tank out before, and I've replaced every piece of rubber line, just not metal ones. I'm thinking of changing the fuel filter out also. it's an aftermarket in line clear deal up top.

[benoit454]

Just another update, it was acting up bad the other day on 1/4 tank, and last night I put in about 4 gallons, so it wasn't on 1/4 tank, started fine this morning, drove fine, started up everytime today just fie, had about 5 or 6 stops and starts or more also. No problems.

Seems it only happens at 1/4 tank.

[mitch1965]

Are you sure that when the gauge reads 1/4, that is really is 1/4? Sounds offbeat, but maybe you are just sucking the very bottom of the tank. I suggest pulling the tank and making sure it is clean. Clean the pump intake, check the sender, clean the ground lug before reattaching everything. I've seen this more than once. Especially since it ran fine by just adding some fuel to the tank.

[piecesparts]

Try going to the basics and eliminate ALL of the outside influences on the motor. First set the timing on the motor (try setting it at 12 degrees BTDC)m second set the carb idles (I use a vacuum gauge, but adjust for a good smooth idle), then eleminate ANY smog garbage for controlling the tranny. Use the basic vacuum to the tranny modulator and that is all. Are you still trying to use the EGR valve? If so, this could be your problem. It may be stuck off of it's seat.

As for the fuel pump return being plugged. I tried removing my return and had a serious bogging problem, when I tried to accelrate hard in city driving (fuel overheating). I had installed an Edelbrock street fuel pump. I solved this by mounting a new bottom plate and added the return line back to the pump. I now have no coughing, sputtering, or bogging when I drive.

Take a look at your cap and rotor on the dizzy, my son's truck was runnung rough and when I opened it up the rotor was half gone.

Stock GM intake, which edelbrock carb are you using? Is it a replacement for the quadrajet or is it a 1406 design model. Have you check for a vacuum leak around the base of the carb?

When you put gas into the tank (at the 1/4 tank reading) how much gas are you putting in? A short bed truck's tank holds around 16 gallons and you can squeeze it to almost 17, if you work at it. I can usually run my tanks to dry before switching them, so there is a remote chance that your fuel tank sock is dirty or collapsed. This was a common problem in those years.

[rfmaster]

Benoit

I would check fuel pressure at the carburetor. I presume that your truck has a conventional mechanical fuel pump which has to suck fuel all the way from tank! If it is old you may have starting problems since there is greater tendency to flood by flooring carburetor. You may have a pinched fuel line or clogged fume return line from charcoal canister.

Do not give up – old trucks just require more attention and a lot more patience

[benoit454]

fuel line hasn't changed or got pinched, charcoal lines are plugged off and not used at all.

It's just what I said the truck does fine, no problems when it's above 1/4 tank.

Truck is hard to start and acts like it's flooding if it's on 1/4 tank, but runs and drives fine once started.

The wire and terminal were cleaned and crimped last dec. I had the tank removed but didn't clean inside. I bet I need to I heard from someone else the sock was dirty. i thought thoose were only on the fuel injected ones?

Block mounted factory replacement fuel pump.

As far as a miss or running rough, yea carb needs tweaked and tune up, cap, rotor, and wires.