Engine symptoms - diagnosis?

[desertPOS]

I have a '69 C20; 350/quadrajet, TH400, ho52 RA. Anyway, the truck runs great overall, but during initial startup when it's cold I have to give it extra gas to keep it going for about 10 seconds or so. If I don't give it any extra gas it will start up and run for about 2 seconds then it dies (I always pump the pedal three times before I start it cold). Other than that it runs very well. However, it does diesel a little intermittently when I shut it off, and during all operating temperatures seems to stumble if I put the pedal down all the way (like cuts out for a half second, THEN accelerates). Anybody who can tell me why or how I can fix this would be much appreciated!

FYI, Things I've done recently to the engine are new fuel filter and HEI ignition. First things that come to my mind are possibly haven't gotten the timing set perfectly, never tried to 'dial in' advance curve on new distributor (cheapo from sumit). There is also some fuel leaking from the front of my Qjet that I haven't traced out yet. Thanks for the help! I just want it to run a little better...

[Chevyholic]

How old is the PCV?

[desertPOS]

Coudn't honestly tell you. How come? I've owned the truck for about 6 mos.

[dznucks]

if these problems existed before you did the work you mentioned, i would say that it is a choke issue on the carb. the dying during initial startup is def. a choke problem. i dont have experience with a quadjet but typically all the carb systems depend on the choke and idle setting being properly set. you could have timing issues too, but i would start with the choke first.

when your motor is cold the choke plate on the primary side of the carb should be just barely cracked open. somebody will chime in here and be able to tell you more about setting that on your qjet.
good luck

[lofly'a]

i agree the choke is likely your issue.

[68gmsee]

Not sure what qjet/choke you have, but on mine it is adjustable.

I adjust it is when cold or fist thing in the morning.
Loosen the choke cover screws and rotate until it closes.
Then rotate backwards until just barely starting to open up again. Depending on how cold it is in your part of the country, you may have to move it one way or the other to adjust properly.

Always make sure that it is completely open when hot.

Dieseling can be caused by carbon buildup or timing. Check the timing to make sure it is correct first then get two cans of your favorite fuel cleaner.

Mine was doing that last week. I adjusted the timing (slightly advanced) and poured 2 cans of STP fuel cleaner. Worked great.

[cdowns]

if the gas is leaking out of the carb onto a hot engine i'd make that my first priority prior to truck burning up/a little gas makes a big flame

[desertPOS]

well it gets pretty damn cold here in southern california I mean this symptom happens when engine is cold/ not at operating temperature. It's nice and sunny and warm outside. Good advice though.

Thanks for all the other responses, have some good directions to check out... Timing I feel like I'm guessing on just a little bit. After putting on the HEI I've heard people say all different numbers for where the timing should be set at. I would have to double check, but I believe I ended up at about 10* and it was running well (minus the minor issues). I'll try the fuel cleaner and recheck the timing.

As for the fuel leak, yeah you'd think I'd check on that, huh! It's very small and I figure it evaporates as soon as it drips. There's not like gasoline pooling up on top of the engine. Can't be helping my mileage though! Thanks again...

Originally Posted by 68gmsee

Not sure what qjet/choke you have, but on mine it is adjustable.

I adjust it is when cold or fist thing in the morning.
Loosen the choke cover screws and rotate until it closes.
Then rotate backwards until just barely starting to open up again. Depending on how cold it is in your part of the country, you may have to move it one way or the other to adjust properly.

Always make sure that it is completely open when hot.

Dieseling can be caused by carbon buildup or timing. Check the timing to make sure it is correct first then get two cans of your favorite fuel cleaner.

Mine was doing that last week. I adjusted the timing (slightly advanced) and poured 2 cans of STP fuel cleaner. Worked great.

[desertPOS]

Originally Posted by Chevyholic

How old is the PCV?

why do you ask about the PCV?

[Wreckless_71]

haha... yeah. Leaking fuel can cause some problems in the future. I had a recent mishap involving a broken fuel line, hot headers, and a flaming 14"x4" fuel soaked air cleaner... needless to say there is a fire extinguisher mounted in my truck now.

[El Jay]

and during all operating temperatures seems to stumble if I put the pedal down all the way (like cuts out for a half second, THEN accelerates).

I'd look at the accelerator pump.
If the truck sat for a long time, it could have dried out.

[haysonj]

Before you start with the timing read this. It sure helped me and my initial timing ended up at 13* http://www.hotrodders.com/forum/dist...1-a-59033.html

[68gmsee]

Originally Posted by haysonj

Before you start with the timing read this. It sure helped me and my initial timing ended up at 13* http://www.hotrodders.com/forum/dist...1-a-59033.html

Long but informative. Good post on how vacuum advance/timing works.