Stalling/Stumbling - Carb issue?

[86project]

Here goes - 86 C10 - auto - 305 -  Truck idles poorly, but once it warms up, it seems to run fine (but a little rich)...It does smoke at start up (leaking valve seals I think), but I haven't had any problems after it warms up - until now.  I was driving about 45, truck running fine and then it cut out...I let off the gas and it picked back up....drove it back home (~10 miles) and it pulls normal to ~35-40mph and it starts cutting out again, consistently.....even holding the throttle consitent.....no problem under heavy throttle as long as it has had time to catch up until I get into higher mph....revs normally under no load....

I am not experienced with carbs at all, but after reading some other posts, I think this maybe my issue.  Do you guys think this is the right diagnosis? Any quick checks I can do to see if I need to purchase another carb?

Hope this rambling makes sense to someone.....

[gezn2]

Fuel filters are cheap, I've seen a dirty one cause symptoms similar to what you're describing
While I was under the hood I'd look around and see if any vacuum lines were cracked open, you want to make sure the basics are right
It sounds like a fuel issue, if a fresh filter doesn't square it away then deeper digging is needed, if it was running semi-okay before this stuff started happening you might be just fine with some adjustments or 'kit'.........

[VileZambonie]

Not knowing what you've started out with an what you have I would suggest do a tune up and make sure you have no kinked fuel lines. Clean out the carb and see what it does.

[Swims350]

well we had a problem pretty close to yours in our 84, it ran rough and had troubles idling, and worse when cold, after warmed up was fine.

Sometimes it cut in and out, random speeds and throttle, and loads.

Smelled funny, like gas alot, or burn your eyes behind it in enclosed spaces, and stink, I replaced and checked everything, plugs kept coming out white and clean, it was wayy WAY too lean.

Mixture screws didn't help, carb cleaner sprayd in and on carb while running, and in tank carb cleaner, feul filter and pump, new lines, unkinked any lines particually kinked or closed, still nothing.

I ended up rebuilding an edelbrock for it and it works great now NO problems at all.

[gbskunk2006]

Don't rule out carb "freezing".  I live in Vancouver, Canada, and from about late October until early May, when the temperature dips below 50 degrees (that's 10c) in the morning, and it's damp or has been raining, my truck will run the pits for the first 10 - 15 minutes.  Once the engine has had a chance to warm up it runs like a charm.

Because it's so predictable, I sometimes will go out and start her up, then go back inside to finish my cup of coffee knowing very well that in about 5 - 10 minutes it'll stall out all on its own.  I won't go out right away as I think the heat from the engine now effectively warms the carb up.  Once I'm ready to go, I'll just fire her up and away I go

The long term fix is to ensure that the hose from your exhaust manifold to the horn on the air cleaner housing is intact.  Secondly, the heat activated sensor that operates a flap within the horn works (this is where I think my problem lies).  Theoretically, that flap should be closed when cold thus preventing the carb from drawing in the cold damp\moist air, or at least until the engine is sufficiently warm enough to counter the affects of "carb freezing".

Short term fix.  Wire that flap closed shut until late spring\summer.  I did this on the recommendation from the carb mech who rebuilt my carb for me.  Of course, your engine performance suffers a little but at least you won't be embarrassed by your truck stalling at every intersection on the way to work

[bmaier]

i had some similar symptoms/problems with my pickup and it turned out being my fuel pump, $25 to fix.

[VileZambonie]

gb skunk, you shouldn't have to wire your thermostatic air cleaner shut if it's working correctly. I recently made a post on how it works.

[86project]

Thanks for the advice guys....I was researching last night and saw a post somewhere on Q-jets that said - if you have poor vacuum due to a worn cam or bad valves that it could lead to this type of "carb problem" due to the spring being too heavy for the vacuum.  Any thoughts on this theory?

ps...I just replaced the fuel pump and installed new plugs ~ 3 mths ago....I think I'll replace the fuel filter, clean the carb and see what happens.....

Swims, your story sounds very familiar, keep your fingers crossed, maybe I'll get out of this cheap!

[Swims350]

check the plugs, see if they are black, grey or white, that'll tell you how the mixture is.

[Fordeatinz71]

i had an '86 Z28 with a 305/4bbl that started doing this...turned out it was the "fuel sock" at the bottom of the fuel pickup...a.k.a. the in-tank filter...i "fixed" it by using a blow gun, sticking it up the fuel line that came from the tank and blew the sock into the tank...it wasn't the RIGHT way, but it worked...lol

[gbskunk2006]

gb skunk, you shouldn't have to wire your thermostatic air cleaner shut if it's working correctly. I recently made a post on how it works.

VileZambonie,

What is the link to your posting?

Thx

[Captkaos]

There is a search feature at the top of the page to help you find stuff...

[86project]

I replaced the fuel filter, cleaned out the carb and found that one of the "nubs" was cracked on my Thermostatic vacuum (?) (the thing on the manifold in front of the carb).....could a vacuum leak cause this problem? I replace this unit and the issue still is happening but not as frequently....plugs are a bit coated with blow by....and when I stomp on it, it stumbles until I let off and then it'll pick back up....I have another Q-jet that I bought, do you think its worth putting the other carb on it while I try to "rebuild" the other one? could it be bad floats/jets?  Or do you think its something else?  I doon't want to go through the trouble if its a good chance its something else....