Need help with an acceleration issue

[semperfiguy98]

Hello all!
Longtime lurker here. I usually don't post a lot because I typically find my answers using search. However this one has me stumped. 86 Suburban K20 350 with th400. CA emissions, totally stock engine was rebuilt recently. I bought it cheap because it had issues. The transmission leaks, the brakes are shot, needs front wheel bearings, rear wheel cylinders, etc...
When I bought it, it was drivable, but barely. I set the timing to factory spec(8 degrees @ 700rpm), tried adjusting the carb but no effect. Found a few vacuum leaks and fixed them. Got a rebuild kit and disassembled/rebuilt the carb with a new float set to 3/8(spec). New fuel filter and air filter, idle screws set 4 turns out. Starts up great, choke works ok, idles at 700rpm, vacuum is rock steady 21 inches. Now here's where it gets fun...
I put in gear and crack the throttle to about 40 percent and it accelerates well. If I mash the throttle then it takes off hard but if I let up then it feels like the engine wants to stall for a sec and then it picks back up. I haven't made a full power run for more than 200 yards because it's not legal yet so I can't leave my long driveway. Funny thing tho it doesn't seem to do it in reverse. It'll light up the tires in reverse, only in drive do I have this issue. I'm sure it's just a minor annoyance that won't manifest itself on a longer acceleration run.
Any thoughts or ideas? Thanks in advance!

 

[Rusty Nail]

Hella rich @ 4 turns out. I thought it was more like 1.5 - 2.5 turns...
Connect vacuum gauge and adjust to highest possible vacuum.
I kinda of think you may suffer from actual fuel DRIPS upon deceleration? One way to find out!

 

[semperfiguy98]

I'll turn then in and see how it goes looking for best vacuum. Can you explain what you mean by the second part of your reply? Fuel drips? And how can I find out?

 

[Honky Kong jr]

If it does it only forward it could be a float related fuel starvation issue or possibly fuel pump failing and causing fuel starvation.

 

[Rusty Nail]

Well, drips rather than a SPRAY. Should be a nice spray down the carb, never drops of gas. Only way to tell is by looking...

hope this helps! Good luck Mr. Four Turns.
That other dude is only trying to make your life more difficult usin all them big words!
Reverse is geared VERY WELL, it is naturally badass. It has a great ratio!

 

[Snoots]

If it does it only forward it could be a float related fuel starvation issue or possibly fuel pump failing and causing fuel starvation.

It does sound like that. Perhaps a low fuel bowl level?

 

[semperfiguy98]

Ok I did some looking. Looking down the barrels when is idling(warmed up) and there's no dribbles at all. I goose the throttle and I get two strong jets of fuel. Idle screws are now both 2.5 turns out. I got a chance to take it out on a long stretch of road and did some pulls. From a dead stop, it pulls hard for about half a sec then doesn't pull as hard but still pulling for about 1.5 seconds, then back to full power. I'm thinking air valve needs a tiny bit more tension. Does that sound logical? Thanks again for the help.

 

[1987 GMC Jimmy]

It sounds logical to me. Lighter acceleration that's contingent on the primaries goes well, but only when you go harder on it and potentially need the secondaries do issues arise. It sounds like you've gone through it well because I would have suggested going through the vacuum system before you took the air horn off, but that aspect sounds like it's in tip top shape.

 

[semperfiguy98]

It took weeks to get all the vacuum leaks fixed. I had to get a smoke machine and fix leak after leak. The egr, choke pull off, and intake gasket were leaking. Half the hoses were split. The hose to the transmission modulator was disconnected. It was a mess. I'm a forklift mechanic by trade and before that I was a jet mechanic in the Marine Corps. I just don't have much experience with carburetors. I'll make some minor adjustments tomorrow and report my findings.

 

[1987 GMC Jimmy]

Wow, you didn't play around with them. I've used smoke, too, but not from a smoke machine. I've also used the old starter fluid method. Good luck and hope it works out!

 

[Honky Kong jr]

Smoke is the way to go.

 

[shiftpro]

Smoke is the way to go.

 

[semperfiguy98]

Ok gents. It seems to run much much better now. I can floor it from a stop sign and not worry about it stalling and embarrassing me. Thank you all for your help. As I progress in the repairing/rebuilding journey, I'm sure I will draw upon your knowledge many times. Now I get to go see if she'll pass smog. Stupid CA.

 

[shiftpro]

Stupid CA.

"Stupid CA".... You're being nice.
Glad you got your rig running better.