Help with diagnosis??

[CCCC]

1972 Longhorn, BB 402 with 4 speed manual. Almost ready to take this long-delayed project to the paint guy - realized that the truck had not been on the highway for a while - so went out to test.

Ran fine at low speed on 3 miles of gravel, hit the pavement and ran it up to 60mph. After a mile or so, it slowly lost power/revs and eventually would not even idle. Normal temp and oil pressure before it died - no odd noises. Good fuel delivery to carb (filter OK) and would start but not gain any revs - stalls when asking for revs/power under load. Towed it home.

First thoughts and efforts:
Fiber cam drive gear wear and off timing?: Removed timing gear/chain cover - still fiber gear in there and some slack in chain - will replace all. But - timing match up not off enough to cause such a problem.

Has stock dist, so maybe PO defeated the resistor wire that decreases running voltage to ign points and maybe they are fried. Will remove dist check this next, as well as bad dist cap, etc.

Problem with dist drive - at drive end or in dist shaft? Will check this too.

Bad coil function? Do these old coils die slowly, or suddenly?

Other estimates from you folks? Thanks for any ideas.

[geezer#99]

First check tightness of distributor.
If slightly loose the normal rotation of the rotor will make the distributor rotate and retard your timing.

[zosoppp]

Perhaps a faulty electric choke not coming off once engine is warmed?

[So.Cal.Super]

You said Fuel filter was good. the one inside the Q-jet
(I'm assuming stock set-up) or do you have another one maybe between the pump and the tank? filter sock inside the tank good?

when it cooled down did you try and drive it again? just wonder if after its cold it felt like it has all it's power back.

[LockDoc]

-
I think you are getting way too deep to start with. It sounds like a fuel delivery problem to me. Fuel sock on the in tank pickup tube may be sucking up debris from the bottom of the tank once the fuel started sloshing around, from the first drive after sitting so long. It could have the wrong fuel cap on it also. Since it is a '72 it would have originally had a non-vented cap on it and if the emissions stuff was removed and the extra lines capped off the non-vented cap would need to be changed to a vented cap. That would cause the symptoms you are seeing....

LockDoc

[CCCC]

Thanks for thoughts so far - maybe missed it but I do have good fuel flow to and into the carb - temporarily removed that small in-carb filter. The accel pump squirts gas, etc. It did not sputter or lunge at all as it was quitting - not like running out of gas or vapor lock.

I needed to check that timing gear/chain setup anyway as part of the plan - and now know that one needed to be replaced anyway- have had those OEM fiber gears break and cause trouble.

When cooled it will star with effort and run at low rpm - will not rev up much and simply dies if I try to pull load even in low gear.

Am still thinking timing/dist problem and maybe way out of time due to slippage as someone noted.

Other ideas? Thanks for all.

[snipescastle2]

If you had left your ignition on for any prolonged time, listening to the radio etc...might have burned the points up(unless you have HEI)
Another possibility is the plugs/wires might be in need of changing. With regards to fuel problems, just because the filter appears to be fine, there could be dirt or debris stuck in the needle and seat preventing the float to rise.
I'd say look closely at your points, most likely issue.
Ben

[67 chevelle]

how long did it sit , over 6 months maybe bad gas

[Chknlyps2]

Does it still have a points distributor?

Many years ago I had an old 6 cylinder I swapped out that had been sitting for several years. Ran great for 15 or so minutes until it slowly lost power and quit running. after almost giving up I checked the points and the fiber rubbing block wore down from the lube being old and dried out and the distributor cam getting a little rusty & rough from moisture.

[special-K]

Could it be a fuel problem that is settled in your carb? Is it an ethanol fuel? No sludginess in the filter? Perhaps poor fuel flow through carb.

[VetteVet]

If your tests on the ignition and gas are ok, Check the mufflers for mice or rats nests clogging up the exhaust flow.

[snipescastle2]

I've heard stories that mice had actually made their way into the combustion chambers of engines of cars that sat in barns,garages, ETC. That's very possible indeed.
Ben

[swamp rat]

As soon as it dies before you do anything else pop off that air filter and make sure its squirting fuel before you try to restart or hit the gas pedal, i agree with the bad sock or filter thoughts above, if the old pick up sock is falling apart it can plug a filter, also if the truck has incorrect fuel lines ( not fuel but vent hose) it could collapse, or if the line directly under the tank is still the original line it can also collapse from the vacuum created by the pump

Take the coil off and shake it if it fells like its got oil sloshing in it replace it.

Its been sitting a while so unless it was doing the same thing before then its not the cam gears

[Grumpy old man]

Sounds like a fuel issue to me also .

How many times have you seen where someone has done a new engine swap or even a new carb without cleaning the tank or at least changing the filters and end up with these type of problems ? Toss on a new $400.00 carb and fuel pump and leave the $5.00 filter or run rubber fuel line ? Happens all the time ...

[67 chevelle]

Originally Posted by special-K

Could it be a fuel problem that is settled in your carb? Is it an ethanol fuel? No sludginess in the filter? Perhaps poor fuel flow through carb.

After rereading your initail post , I'm agreeing with special-K , I just had a holley that sat awhile , and it got alittle junk /sedimemt stuck between the inlet , caused all kinds of issues , flooding mostly , this new gas turns to junk quick

[CCCC]

Had to take a short break from the fixit project - and have decided to replace that OEM fiber-toothed cam gear and the timing chain while it's apart - too much slack in that chain and those plastic gears make a mess when finally they give up - and they always do at the worst time.

Once the timing gear/chain is back in and I can spin the engine I can check the dist setup/points/etc. I do have strong fuel flow to the carb, so in the meantime will go inside the Quadrajet to look for the kinds of problems that special-K noted.

I'm going to also look for rat nests while waiting for the parts. Full report - or some more questions - later. Thanks for all suggestions.

[special-K]

Smart. I had the new Cloyes double roller under my seat ready to install that weekend. You could hear the chain slap the cover after a rev. My boss asked to borrow it to run an errand, he came back walking. He probably horsed it while I had been babying it. Hauled it home, new timing set and push rods, no good, bent valves. At 120k miles I ended up with a rebuilt engine.

[CCCC]

Originally Posted by special-K

Smart. I had the new Cloyes double roller under my seat ready to install that weekend. You could hear the chain slap the cover after a rev. My boss asked to borrow it to run an errand, he came back walking. He probably horsed it while I had been babying it. Hauled it home, new timing set and push rods, no good, bent valves. At 120k miles I ended up with a rebuilt engine.

Last week I quickly ordered the gear/chain set as well as push rods, manifold gasket, etc. for this one as soon as it quit - knew that even if this problem cause was not the gear failure, I would need the stuff for this one or another one. That fiber tooth deal was a stupid move by GM - only a matter of time/miles until they go.

[CCCC]

Ok - got this figured out. Truck had pretty much been sitting waiting for clean-up and paint - with only occasional start/run events to keep it alive. Putting it under load on the road brought out the gremlins.

special-K was on the right track.

Solving became complicated due to two causes. Three fuel filters - one between tank and pump ( a little gritty), one between pump and carb (more gritty) and the small one in the carb - which had the check valve insert. The check valve was stuck and filter quite dirty with very fine material - hardly could blow through it at all. Have no idea what that fine orange-ish stuff was. Most of the crud in the line probably went right in there once running on the road. Installed 3 new filters. Started and ran fine in the garage.

But, it would still fade or run out of gas going down the road. Took off the fuel pump and found two things - diaphragm was not intact and gas was going into the crankcase, and the PO had instaled a SB pump on this BB (took a while to figure that out - but the arms are different lengths). Got the correct new pump on there, changed the oil/filter, and drove it 120 miles to the paint guy.

However, it wants to run somewhat rich at times so am thinking there may be a needle/seat/float problem or leak-down issue in the Quadrajet. A rebuild job seems to be in order there - or maybe replace the Q-jet with something aftermarket. Looking for dependability and economy. Any suggestions there?

Thanks to all who chimed in on this.

[Steeveedee]

Dependability and economy with a Q-Jet. Correctly tuned, I've seen guys turn some surprising times in the quarter mile, and drive to and from the track to boot. You can try Carmantx at V8Buick.com, or Ken at Everyday Performance (also on V8Buick.com). Either can make that carb like new. You can go to Cliff Ruggles if you have time. He wrote the book on Q-Js, but has a one-year waiting list, last I checked.

[special-K]

Carb doctor in PA does ethanol-ready rebuilds. The Q-jet is your best bet. You can't beat the spread-bore design for overall driveability. Running on primaries you get better mileage than a 2bbl but bring on the secondaries and gain more than double the CFMs and all your motor can give

[Dirt's72]

I took my quadrant carb from my 72 big block to skinners here in town. They do all the carbs for mild to wild. Pete had his done there as well for his bb 72 RV.
Mine is running good. The price was right although I can't remember exactly what it cost but was very fair.

[CCCC]

Thanks to all three of you for the carb info - very helpful. I will stay with the Q-jet. Actually have experienced pretty good luck using good rebuild kits with them in the past going al the way back to whatever was in my 62 Impala with 327. Was that a Q?

I don't have a spare Q to get ready to install before I bring the truck home so will have to wait. Maybe it's finally time to take a carb to an expert - especially if they can adjust/modify for this ethanol crap. The place in Alb would be most handy - but will look into the others.

Thanks again.