79 Chevy C10 350 need to pump gas 3x on cold start and be fully warm before move

[brody287]

Hi everyone,

I'm a brand new user here so first off let me introduce myself. I just purchased a beautiful green 79 Chevy C10 with a 350 from my father in law, which was his dad's farm truck before he passed. It's in great shape, well taken care of, but of course it has some things that need fixing.

It runs beautifully when it is warm, but when starting cold I have to pump the gas exactly 3x and then start it, and give it gas as it starts. Then I need to keep my foot on the gas while it warms a little or else it will stop, it won't idle until it is warmed up. If I try to drive away before it is warm it will die, but only in drive! I'm always able to put it in reverse and back up, but it won't go forwards until it is nice and warm.

I'm a complete newbie to these trucks and I'm a fairly inexperienced backyard mechanic, so please don't hesitate to dumb things down for me. My first thought is I need to adjust the choke or the idle. So I did my best to adjust the choke so that it's just closed when cold and fully open when warm, and that seems to be working alright (it wasn't far out anyway), but I haven't touched the idle yet. I am a bit perplexed because the truck will idle fine when warm, so it doesn't seem to me like I need it to idle higher, but I have heard that if it's not idling high enough it will die on take off, which sounds like my issue.

Another piece of the truck's history is that the right auxiliary tank had a hole in it (rust I'm assuming) that was patched before I purchased it. Perhaps a fuel pump has gone bad? I have a vacuum/fuel pressure gauge to test if I knew where to begin! Any thoughts on where I should start to diagnose this issue?

Thanks

[zieg85]

In a perfect world...Cold start, once to the floor to set the choke and put the carb on the fast idle cam.  It should stay running and be smooth through warm up.  Anything shy of that something is removed, not adjusted or something else. 

[JohnnyPopper]

First off welcome to the site, you will find a lot of help here.

On to your problem, as Zeig pointed out, your choke is the problem.

If it goes closed when cold and opens when hot, you half way there.

There is a linkage that moves a stepped cam that the idles screw rests on when cold, this opens the throttle wider until it gets to OT (operating temperature)

The steps are low to highest depending on how cold coil is.

Look for some of Stuart Griffins posts, he linked a classic PSA (public service announcement) that shows the full details of how chokes work.

[brody287]

Thank you both this is really helpful. Will try and adjust the fast idle screw (didn't even know it was there until now!) tomorrow morning when the truck is cold. If I'm correct, I should tighten it to increase the idle speed when the engine is cold before it heats up to operating temperature, since my problem sounds like a too-low idle problem.

[VileZambonie]

Before you start messing with adjustments, verify the choke closes when cold and opens when warm.

[brody287]

Before you start messing with adjustments, verify the choke closes when cold and opens when warm.

The choke has already been adjusted and seems to be working great. It's closed when cold and open when warm.

Today I adjusted the fast idle screw. At first I turned it in a couple turns and got almost no difference, so I let the truck cool down again and then tried again later. I found a video that said a good bench setting was to take the screw to the bottom, then back it 4 turns. I did that (which was quite a lot further in than it had been when I started) and it seemed to work much better the second time, it started right up and idled steady! So much better in fact that I am suspicious that I didn't wait long enough to let the truck get cold (though I had never even got it to a steady idle the first time). Will try again in the morning so I know it's absolutely cold.

[JohnnyPopper]

Nice!

Now can you send a pic please?

[brody287]

Johnny,

Here are some pics of the truck.



So far I've replaced the wheel cylinders on the rear brakes, replaced the valve cover gaskets, the rear main seal, the oil pump and oil pan gaskets, and given a general clean. My next problem is that my carburetor has these "double D" screws for the mixture screws . Everything I've seen suggests they should just be flathead screws but instead I have these flat blades sticking out. Might be able to adjust them with needle nose pliers?

The truck still doesn't start and run quite right when cold. When I tried it again the next day it seems to start worse now. So I'm still mucking with the fast idle cam a bit. Eventually a carburetor rebuild is on my list of things to do as I'm sure that will help a lot. Until then I'm just trying to get the carb tuned as much as possible the way it is now.

[JohnnyPopper]

Did you search for stu griffin's lock down posts that had the 'Proper Choke' commercial?

It could be the answer to your prob

[brody287]

Did you search for stu griffin's lock down posts that had the 'Proper Choke' commercial?

It could be the answer to your prob

I haven't been able to find it. I've tried searching for "stewart griffin lock down" or "stewart griffin choke" etc., but haven't been able to get to what you're talking about. If you know where to find it could you link it here?

I adjusted the choke a tiny bit richer and adjusted the fast idle cam screw in another turn, and I had great results yesterday! Still three pumps of gas, but she started and idled without any extra help from the gas pedal, and then went into gear and drove away about a minute later (though it threatened to die). Although, it was 29 degrees celsius yesterday versus the 12 or 16 we've been seeing lately, so the temperature difference may be contributing to things.

[brody287]

Ended up rebuilding the carb because with COVID I figured, I've got the time and I might as well give myself the best chance for success here. I did that, and troubleshooted some issues (I have a thread over in fuel systems & drivability about it) and I've managed to get it idling when cold now! Very excited about that. Thanks for the help.

[JohnnyPopper]

I reached out to Stu, he just sent me this, it's hilarious but very helpful!

https://www.youtube.com/watch?v=_BTEdWt2V3s&t=103s

[carmen77]

This is hilarious. I love it!


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