wits end

[Fleetlover]

posted a week or so ago about problems with my 250 . Have had truck for about a year and during decent weather would run it when I could Never ran strong and always needed to be fully warmed up to run decent . I always suspected a vacuum problem but did not have time to address it . About 2 months ago it started to get progressively worse and got to the point where it would hardly go down the road but once in a while would run smoothe at a steady rpm then act strange when I let off gas and run rough again . replaced all vaccum lines installed new carb at which time noted that PO never fully tightened a couple manifold bolts . Replaced manifold gasket . Cleaned fuel lines and installed new fuel pump volume tested and OK . Still would barely run. PO or someone installed HEI I have replaced cap rotor ignition module plugs wires. Will start and idle ok then sometimes just stalls out . If started and given gas just stumbles and dies and sometimes will restart easily and sometimes not . Timing is pretty much where it was when it ran ok . At the truck show yesterday someone said it will turn out to be something simple and you will feel like an idiot . I would happily be an idiot if I could take my truck for a drive . Oh and to make things even nicer when I opened the hood to install the plugs end of last week I had a hole in may radiator . The fun never ends . Any input greatly appreciate Thanks George

[Professor]

Fuel supply problem? Check everything from the carb back to the tank: all lines, filter(s), pump, fuel tank pick-up.

[tom hand]

First do a simple check...HEI's used with cheap rotors will tend to fire thru the rotor and fry the mechcanical advance. Pull the rotor and make sure the advance works smoothly. If that is not the problem, do a compression check to make sure the motor is OK

[oldsub86]

Simplistic advice but we were always taught in the old days to verify fuel and spark first. If you can isolate the problem then at least you will not be throwing parts at it.

Do you get good spark at the plugs?

What do the plugs look like? Are they black and fuzzy which would indicate too rich? What does the exhaust smell like - any indication it is too rich - black exhaust?

If not too rich then is it too lean? You might want to open the carb and check the float level. A new carb does not mean it is set right or that it has not suffered some damage in transit.

If all of that checks out then maybe time to look a bit deeper. Check cam timing. Should be able to get some idea by pulling the valve cover and checking that the valves open and close in sequence with the piston going up and down -

Are the valves opening - could the cam be worn to the point where the valves are not really opening much - you would still get compression as the valves would close.

Is your distributor timing way off? Once you have it running, have you tried advancing or retarding a bit to see how it runs? The timing marks on the balancer may not be where they should be if it has been changed or has spun on the rubber.

Are you getting advance on the distributor? Can check with the timing light to see if it changes with rpm.

Try a vacuum gauge to see what that can tell you. Will come with instructions on what to look for.

Have you checked to make sure that the plug wires are in the right sequence? - firing order

Are all of the wires and plugs ok? Easy enough to damage them in installation or removal. Pull off one wire at a time while it is running to see if it makes a difference - if you pull a wire off of the plug and it does not run worse, then you have isolated the cylinder that is not performing for whatever reason - might want to have a set of insulated grip things when you do that

Grounds often cause trouble in older vehicles - are the headlights bright when you turn them on? Are the cables to the starter good? Can't recall offhand where the main power feed is but often related to the starter - are the grounds clean and tight?

What voltage are you getting at the distributor? Is it getting a full power?

Keep us posted.

[Orion 762]

Was the yellow wire to the starter coil removed when the HEI was installed?? On my 71 with HEI, the PO had left this yellow wire (on outside post of starter coil) installed, and it was intermittently grounding out against the header. Truck would "die" when I did left turns with brakes applied (fine all other times).

This wire (yellow one) can be removed. No longer needed with HEI. Also make sure the HEI distributor has a good + lead coming from the firewall. It's supposed to be a new 12 gage wire carrying 12v from your ignition key. On my truck the PO had incorrectly used the old "+ HV coil wire" to power the HEI (this incorrectly delivers only about 7-8 volts to the distributor).

Simple to check anyway . . . good luck.

Orion 762

[73stepside]

i had a 74 nova that did the same exact thing but it had points. i put 4 carbs on it before i got a good one. you may also want to check the module in the hei it might be bad/getting too hot. you will want to opt for the gm module most others aren't worth the money.

[Fleetlover]

Well here's the idiot fix of the month ( year ?) After work yesterday decided to take one more look before I set the truck on fire and let it burn in the driveway JK I had a rachet in my pocket so I says Lets give that float bowl a little whack before trying to start it up again Presto started up idled pretty good fiddled with the idle screw a bit and its better than it's been in ages . apparently either something got by my dual filters or somebody left something in there when it was rebuilt Gonna pull it apart and see if there's a bunch of crap in the float bowl . Course I still can't drive it til I fix the radiator .

Orion Yes the PO cut the yellow wire and it's in a pretty safe place The ignition lead was also replaced with a heavy wire .

Thanks everyone

[Bernie]

I had a 250 with much the same symptoms. I could never get the intake manifold to seal to the cylinder head. Finally gave up and replaced it with a 350.

[Fleetlover]

Bernie Interesting Wonder if the intake could have been warped . Will proceed with the 250 for now but eventually will likely install a SB w\4 speed