After tune up, hard to start

[swissarmychainsaw]

Hey folks!

I'm teaching my 10 year old how to be a gear head squares junky. So far so good!

1973 Suburban 350/350. GM HEI ignition (likely from an 80s era truck).

Had the truck about 5 years and never did any tune up on it.
It has always been very easy to start when warm.

Cold (after a couple days sitting) it would do the typical "crank, crank, crank - where's my gas - crank, vroom"

Finally started to miss, and was not running on all cylinders (all the time), so we replaced
* plugs
* Plug Wires
* Distributor Cap
* Rotor

After my "tune up" it's been not wanting to start when warm, and requires several seconds of cranking.
So I've been fiddling with the timing a bit.
Assuming that when you do cap and rotor you have to reset the timing

I unplug the vacuum hose from the distributor vacuum advance to do this.
Warm it up, then set "initial timing" (at idle).
Originally I put it at about 14 degrees BTDC, (hard to start)
and today I bumped it down to 10 degrees.

What should this be at, and will small differences (say going to 11!) make a big difference?

Thanks! I really want this thing to fire right back up again!

[geezer#99]

In this case I’d say it’s not your distributor.
Changing cap and rotor shouldn’t change your timing.

Are you sure it’s not flooding a little?
Flooding causes poor hot starts , missing and sounding like it’s not firing on all cylinders.

[swissarmychainsaw]

Originally Posted by geezer#99

In this case I’d say it’s not your distributor.
Changing cap and rotor shouldn’t change your timing.

Are you sure it’s not flooding a little?
Flooding causes poor hot starts , missing and sounding like it’s not firing on all cylinders.

Well after changing plugs/wires/cap/rotors, it runs really good, and the "not firing on all cylinders" is gone.
Now its just hard to start!

How can I tell if it's flooding?

[geezer#99]

Look in the carb for excess fuel.
When you finally get it started when hot does it blow a little black smoke out of the tailpipe?
When starting it hot do you pump the gas pedal before cranking? Or just barely touch the pedal?

[swissarmychainsaw]

Originally Posted by geezer#99

Look in the carb for excess fuel.
When you finally get it started when hot does it blow a little black smoke out of the tailpipe?
When starting it hot do you pump the gas pedal before cranking? Or just barely touch the pedal?

I'll check the carb, look for a black puff.

When starting warm, I don't touch the gas. Or if I do its just a blip.
In the past all you had to do was turn the key when warm (as you should I feel) - you likely shouldn't have to give it any gas with the carb bowl full of fuel.

So the change here was "new cap & rotor, wires and plugs". I'm scratching my head as to why it starts differently, but now I have changed the timing, hoping that was the culprit!

So is my 10 Degrees a reasonable start?

[geezer#99]

Yup!
10 is good.
My 84 with Rochester wouldn’t start hot if I even had a thought of or had my foot within a few inches of the pedal.

What did you gap the new plugs at?

[Dead Parrot]

Changing the rotor shouldn't change timing as long as the hold down bolt for the distributor was tight. If the bolt was loose, then you might have turned the dizzy while swapping parts.

Possible you accidentally changed the choke a bit while reaching over the carb to the dizzy. Stray elbows and such.

Double check all the rubber hoses. Did the THERMAC vacuum hose get hooked back up? Assuming stock air breather. IIRC - the pipe comes out where the choke linkage is and is easy to miss. Left open, it is a vacuum leak.

10* is good. Mine likes 12. Hard to start if I go more. Timing marks will vary a bit from motor to motor. Trying to perfectly match someone else's settings rarely works.

Normal HEI plug gap is .045. Your truck specs probably call for .035 if it was originally a points dizzy.

[1976gmc20]

In the past, I've had a certain brand of plugs not work well right out of the box, at least for certain applications.

A GM pickup should start when warm by just turning the key and releasing it without even waiting to hear it start. At least all of mine always do/did unless there was something wrong. Carb/Tbi didn't matter; just click it and it was running.

Funny, I've had best luck on timing by setting by ear. When we moved to a lower altitude and my old pickup was pinging, I read up on the recommendation and borrowed a timing light and it ran like sh1t. So I started over and set it by ear and it was great, but way more advanced than recommended for ~3500'.

[swissarmychainsaw]

" Normal HEI plug gap is .045. Your truck specs probably call for .035 if it was originally a points dizzy. "

This is a good call. I don't remember off hand what I gapped the plugs at, but I'll bet a dollar it was .045.
I'll check if the rain lets up a minute!

[Dead Parrot]

Originally Posted by swissarmychainsaw

" Normal HEI plug gap is .045. Your truck specs probably call for .035 if it was originally a points dizzy. "

This is a good call. I don't remember off hand what I gapped the plugs at, but I'll bet a dollar it was .045.
I'll check if the rain lets up a minute!

Just to clarify. You probably want .045 to take advantage of the HEI. I doubt the difference between .035 and .045 with new plugs would make much difference on getting an easy start.

[swissarmychainsaw]

Plug gaps are at .045, so I'll leave them.

So you guys are right, the carb is sputtering gas out the top when you try and start it, ti's wet with gas (on the choke flaps).

So, I guess my next step is to get the number off the carb, order a kit, and rebuild the thing. Never done a Q-jet before. time to talk to Cliff!

I found a video on line that shows you how to "poke your float with a stick" to help clear any debris that might be holding the needle open, and that convinced me that I need a new float valve (or should check mine). When I did this, it started up (i.e. did not leave me stranded)
https://www.youtube.com/watch?v=MszBzWTVfx0

If you like long winded country boys and want to see the inside of your Q-jet, Tyler has a bunch of great videos:
https://www.youtube.com/watch?v=3_Ljs7COiuE