Hard Starting Chevy

[swissarmychainsaw]

I have a 1984 Chevy Silverado; 305 ci 700r4 carburated that is hard to start.
125K miles on it.

Just did a basic tune on it, plugs, wires, dist cap. This did not change how it runs. It was a bit easier to start with the old stuff! Idles a bit rough, but once warm it runs great and gets 21mpg at 65mph with a 500lb motorcycle in the back!

Here's what it does:
After running the choke flap is perfectly vertical. (so I think the choke opens properly).
In the Morning I press the throttle down once or twice (same results) and the choke flap closes all the way.
Trying to start it though it chugs and huffs and puffs and bounces around, it spews black smoke (like unburned fuel) much to the happiness of my neighbors.

It looks to me like the choke is opening and closing properly, so I'm not sure what to do here. I'm tempted to just replace the thermostat on the choke, but it seems foolish to just start replace stuff I think works.

Any thoughts?

thanks!
--Nick

[MARKDTN]

Hard to start hot or cold or both? How about if it sits a few hours vs: overnight?

[swissarmychainsaw]

Originally Posted by MARKDTN

Hard to start hot or cold or both? How about if it sits a few hours vs: overnight?

Should have made this clear: Only when cold, as in after it sat overnight.
If it's a warm day (mabe over 60 degrees) it starts easily.

After it has been running for a while then if it sits, it start right up with just the turn of the key. (I'm assuming the choke flap is wide open at this point, aka it's "warm")

[MARKDTN]

Could be all the fuel is running out of the carb at night. This is a common problem with old Q-jets. I'm not exactly sure how to fix it, some plug in the bottom I think? I would try some morning with it cold pouring a little fuel into the carb, button it all back up, and try to start it. If it starts right up, you can look at this more. I also seem to remember that there is a difference in GM and inexpensive aftermarket fuel filters. The cheap ones can allow fuel to drain back to the pump. The GM and good aftermarket ones have a rubber flap/check valve that keeps the fuel in the carb.

[tucsonjwt]

If you have only cold start problems -
Considering you are in San Fran, then your choke should completely close when you depress the accelerator to the floor once, then remove your foot completely from the accelerator. Once the truck starts, the choke should open almost all the way very quickly, since the ambient temperature is not very cold. If the choke valve is sticking (carboned up, gummed up, etc.) then the air mixture will be too rich and you will have the symptoms you describe. Here is the way I would check this:
1) Depress the accelerator all the way to the floor once - remove foot from accelerator. This should set the choke valve completely closed.
2) Open the hood, remove the air cleaner cover, see if the choke valve is all the way closed - pull back on the throttle bracket all the way while pushing down on the choke valve with your other hand. The choke must be completely shut - just a tiny bit of space between the choke valve and the carburetor will cause the truck not to start. My guess is you will find a slight bit of movement possible in the choke valve when you manually try to move it completely shut. Make sure you pull back on that throttle bracket all the way before pushing the choke valve shut - otherwise the choke valve may still be open slightly but you will think it is closed.
3) Turn the ignition key. If the truck does not start - depress the accelerator half way to the floor.
4) If the truck still does not start, you have verified that it is not because the choke is not closing all the way.
Buy a can of gumout carb spray cleaner and go somewhere the neighbors won't be irritated by you revving the engine. When the engine is good and warm and running, remove air cleaner and pull the throttle back to rev the engine, while spraying carb cleaner on the choke valve, shaft, and throttle linkage. Spray more down the throat of the carb. Don't let the engine stall when your are doing this. Use up the whole big can of carb cleaner. Chances are this won't fix the problem, but your carb will look nice and clean You will then be into a carb repair/rebuild situation. If that is the case, I would look for an experienced Qjet rebuilder who can guarantee the work. I have had no luck with aftermarket brands or exchange rebuilds - others have different experience. Since you are getting good gas mileage on the highway, I doubt that you have any serious problems with that carb. Don't let somebody "fix it" so you get 10 mpg on the highway.

[geezer#99]

Sounds like your choke just need the choke plate open further after it starts. To adjust the opening amount there's a screw located above all the choke linkage. Phillips head. It's directly above the black cap on the side. After you start it when cold screw it in a bit and watch the choke plate open. Set the choke plate about a 1/4 inch open. or where it runs best.

[silvereagle07]

Did you change the timing when replacing the distributor parts? Maybe you need to check the timing.