Please help - warm start issue, 350 with carb

[NearNorth]

First off, thanks for this resource, I have browsed extensively over the last few years and have seen many helpful posts. This year I added a 1984 K20 to the garage and have been having a really hard time with warm starts. Hoping someone can shed some light on this. I'm not a carb guru so maybe I'm missing something but it feels like I have tried everything.

Behaviour:

Cold starts - half pres on pedal, then turn key with foot off pedal - fires up right away. I let it high idle for a minute then drive away. A+

Warm starts - If I have stopped for less than a minute or two, I just turn the key and it fires right up. A+

Warm starts sitting - If I leave it sit warm for 3 minutes or more, up to about an hour or so, the warm start is brutal, It won't start ith just a key turn. I have to give it gas and it takes a goot 10 seconds of cranking or more. Then I must hold the pedal at high idle for a good minute before I can drive away, sometimes longer. I end up starting off using both feet so that I can keep the idle high while braking with my left foot.

These are the things we did, in order:
Ignition - plugs, wires, no change, so did the cap and rotor, no change. Changed the coil and then the ICM, still no improvement.
Timing - fiddled with this and couldn't get any real improvement. Unfortunately the timing mark is not lined up with the gauge so we can only time by ear.
Then I bought a new carb - edelbrock 1406. This was a pain because i needed the spread bore adapter, had to weld a ring onto the air cleaner so it would clear the carb, then the throttle geometry got all wacked out and the cruise didn't work any more. Had to weld up some throttle plate adapters and finally got it all sorted. Worst part is, the warm start was still just as bad.

Then I tested fuel pressure, @ 7psi so I installed a holley regulator and set it to about 4-5 psi since it really feels like a flooded condition.

I am still getting hard warm starts and running out of ideas. My next step is to put a spacer under the carb for heat but then the throttle cable is going to be all wacked out again.

What's extra annoying is that I have to go for a drive and let it warm up then sit somewhere and wait in order to give it a proper test after each attempt.

I'm really starting to miss my TBI 305 in my old 87 C10 - it smoked like crazy oon startup but it started every.single.time.

If anyone has ideas about more specific troubleshooting I can do, or adjustments I can try please let me know!

 

[Swearbody]

This sounds like a improperly adjusted choke. The timing by ear is a little sketch too

Timing - fiddled with this and couldn't get any real improvement. Unfortunately the timing mark is not lined up with the gauge so we can only time by ear.

what does this even mean?? what Gauge?
DO you mean the timing tab? IM not following you on this....I want to help but dont know what you are saying there.
If youve got it timed too advanced it will cause hard starts

 

[Big Chip]

I've got the same problem with my Chevelle and I suspect the issue is the fuel boiling out when it sits after driving. I am going to try a phenolic spacer at some point and see if it helps but if someone else has a better idea please throw it out here for us.

 

[Bextreme04]

Get a TDC stop tool. Screw it into number one spark plug hole. Rotate engine by hand all the way clockwise until it stops. Put mark on balancer where it lines up with 0 degrees on the timing tab. Rotate engine all the way around counterclockwise and put another mark at 0 degrees. Halfway between the marks is your true 0 degree TDC mark. Use that to time the engine. Once you have the engine properly timed, set the idle mixture and idle speed.

Set the idle mixture by starting with a fully warmed engine. Disconnect and plug the vacuum advance. Block the wheels and set the parking break. Put it in drive. Set the idle to 750rpm. Then, adjust the idle mixture screw richer until the idle peaks and starts to go down. Adjust the idle speed while doing this to make sure it doesn't go too high while doing this. Once you have the idle set to 750 and the mixture adjusted to peak... you now have stoichiometric mixture. I tend to run my idle a little higher, so from here I adjust my rpm up to 800 and then lean the mixture until the rpm drops to about 700. This should mean the engine idles around 700-750 while stopped and in-gear. Now put it back in park and re-connect the vacuum advance on the distributor. You should now have around 800-850rpm in park and around 700-750 in gear. This should also ensure you have a decent hot start without needing to touch the pedal.

 

[NearNorth]

This is very helpful, thanks. Yes what I meant was that the timing tab does not line up in any meaningful way with the timing mark, so when I put the timing light on it it's way over to the passenger side, if I try to change the timing toward the tab it runs very poorly, so the previous owner must have changed something with the balancer. That was my first foray into using a timing light so this detailed explanation is helpful. This may be a silly question but how do I get the RPM without a tach in the dash?

 

[Ricko1966]

I've got the same problem with my Chevelle and I suspect the issue is the fuel boiling out when it sits after driving. I am going to try a phenolic spacer at some point and see if it helps but if someone else has a better idea please throw it out here for us.

You suspect the fuel us boiling out.I would verify that before I did anything. Next time it acts up open the hood take off the air cleaner, look for an accerator pump shot, if it's got pump shot I don't think it's fuel boiling out.You can take a dish soap bottle full of gas and fill the float bowl through the vent tube, this will verify whether or not it's a fuel issue. Also what carb are you running old quest can get leaky welch plugs, your fuel runs out the bottom of the fuel wells and runs the carb out of fuel.

 

[dsteelejr]

I am still getting hard warm starts and running out of ideas.

I am in agreement with the other replies in that you really need to verify your timing. When starting your timing should be retarded, not advanced.

I'm also in agreement that your carb is probably suffering from heat soak. After you shut off the engine and everything stops circulating, the temperature under the hood can rise before it cools. The carb will soak up the heat of the engine and the fuel inside the carb will boil. As the fuel expands from boiling it can push past the metering rods and exit through the jets, which floods the engine, making hot starts difficult. I had this issue on my '80 K25 with a 454, especially in the summer heat. I would have to treat it like a flooded engine and crank the engine with a wide open throttle to clear the flood. Lots of cranking and once its started it will choke you out with the overwhelming fumes of raw gasoline. This is more of a problem these days with the addition of ethanol in the gasoline, which lowers the boiling point of fuel. Was not as big of a problem back in the day when these engines and fuel systems were designed.

Other than correcting your timing issue, you can use an insulated carb spacer. I run an Edelbrock carb so I use an Edelbrock spacer #8723. Its a 1/2" spacer, so I don't think it will interfere with your throttle linkage. I had mine on a stock manifold so I also had to run an adapter plate, which was 3/4", under the spacer to mate the square bore carb with the stock spread bore manifold.

Also, On the deadhead style fuel systems where the fuel doesn't move fast enough through the line it can heat up and boil in the line and filter. Out of necessity I created a fuel return system. Since I run an Edelbrock carb I have to put a fuel pressure regulator on the line because the stock mechanical pump puts out 8psi (verified with an inline fuel pressure gauge) and Edelbrock carbs like it around 6psi. I could've bought an Edelbrock mechanical pump, which is about $140, or used a deadhead style regulator. Instead I nailed two birds with one stone and went with a return style regular, so my fuel is always circulating. It was surprisingly very easy to make and not too expensive.

After running the insulated spacer and fuel return system my hard hot starts went away. I'm not sure how much of the problem was solved because of one or the other, but together it works great.

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[SirRobyn0]

I've got the same problem with my Chevelle and I suspect the issue is the fuel boiling out when it sits after driving. I am going to try a phenolic spacer at some point and see if it helps but if someone else has a better idea please throw it out here for us.

Everyone else has already pretty much summed it up, but I'll through in and say I agree.

You should get it setup so you can time it properly, but your issue sounds like heat soak. Edlebrocks are notorious for this issue, that and being sensitive to fuel pressure. You could run lower fuel pressure to see if that helps since your already running an regulator. I have a thick phenolic spacer on mine and I run 3.5psi on my regulator, which as long as your fuel pump is producing good volume it's fine. Keep in mind adding a space will change your geometry a little bit.