My 85 has issues,

[f6john]

I have been enjoying my late fathers 85 Silverado but some issues are really bugging me. It has a 99% original 305 - 350 Turbo automatic with 61,000 miles that I'd like to get a few years of use before an engine swap. It starts fine. It idles rough, rougher some times than others, but it never dies. Off idle acceleration is ok, don't feel as if it's missing or anything, but the tranny shifts hard out of 1st to second which doesn't seem right. The really annoying thing it does, you can be rolling along at a steady speed and light acceleration and the thing just doesn't respond. Apply more throttle and still nothing, let off the throttle and reapply and usually it will pickup and go on. Other times when you increase the throttle it feels as if it actually goes slower.
I am a fair mechanic but I'm terrible at diagnosis. Once I figure out what is causing the problem I can usually correct the situation. But with this truck I don't know if it's the carb, fuel delivery, ignition, timing, tranny or what. I could just start throwing new parts and pieces at it and stumble on to something, but most of the time when I take that course of action I wind up spending a lot of money and still have the same problem.

 

[RetroC10Sport]

With the tranny shifting hard, I would be checking for vacuum leaks first. Particularly vacuum lines.

I'm sure others will chime in here as it's been a long time since I've played with carbs and 3 speed transmissions.

 

[Swims350]

does it have OD or not? If it's got od or it's 4 speed then it's 700r4 and tv cable might need adjusted.

If it's 3 speed th350 not sure unless the lockup converter is causing issues.

 

[RetroC10Sport]

350 turbo, he says.

 

[Swims350]

yea but whether or not it is, that's another story, if it's a th350 more then likely it's a th350c for the year, unless it was changed.

 

[f6john]

3 speed with the lock up converter.

 

[Old77]

Does it have a shift kit in it? Shift kits can cause it to shift hard as well. I'm going to guess no but worth asking.

 

[f6john]

No shift kit. No emissions testing in my neck of the woods either. This thing still has the smog pump and everything. I'm just not sure what I can delete without causing other problems.

 

[Swims350]

no emission you can junk it all, smog pump, plug the air lines or put on headers, ditch the egr, all that crap and extra vac. hoses.

Might be time for a fluid and filter change.

 

[Old77]

I'm with swims! Ditch all that stuff and see where you're at after that and changing all the fluids!

 

[Irishman999]

That hesitation is most likely the accelerator pump in your carb. How long has the thing sat? I had similar problems with my quadrajet and rebuilt it with a "JP Sorsen kit from Autozone, it fixed the problem for months but I just switched my truck over from Quadrajet to a Carter AFB 600 cfm.

Before buying the kit try blocking off all the vacuum ports and just running a single line from the special distributor port to your vacuum advance.

 

[Irishman999]

Just in case you weren't sure which one is supposed to go to the distributor here's a picture. Your tuned vacuum port is the on picture just to the right of the fuel filter, The rest can be blocked off. The bigger port at the top front of your carb (not pictured) can be left open since its just a vent for the bowl.

You must be registered for see images attach

 

[f6john]

That hesitation is most likely the accelerator pump in your carb. How long has the thing sat? I had similar problems with my quadrajet and rebuilt it with a "JP Sorsen kit from Autozone, it fixed the problem for months but I just switched my truck over from Quadrajet to a Carter AFB 600 cfm.

Before buying the kit try blocking off all the vacuum ports and just running a single line from the special distributor port to your vacuum advance.

I found out by looking at a receipt for tires, that the truck was driven 4,000 miles in the last ten years, which I know could be the reason for a lot of the driveability issues. I've driven it about 2,000 miles (about 5 years worth) in the past two months. I'll start pulling the smog stuff and do a change out of common service items and see where I'm at. The carb could be the biggest problem I have. I do have an Edlebrock carb sitting on anther motor that had very little use but it has been sitting idle for over 12 years so it would need to be checked out too. I don't know if it would bolt up to the factory four barrel manifold anyway.

 

[Old77]

Yeah, sitting mostly undriven for that long of time can cause issues! Sometimes not driving something is worse than driving something a lot!

 

[Irishman999]

I found out by looking at a receipt for tires, that the truck was driven 4,000 miles in the last ten years, which I know could be the reason for a lot of the driveability issues. I've driven it about 2,000 miles (about 5 years worth) in the past two months. I'll start pulling the smog stuff and do a change out of common service items and see where I'm at. The carb could be the biggest problem I have. I do have an Edlebrock carb sitting on anther motor that had very little use but it has been sitting idle for over 12 years so it would need to be checked out too. I don't know if it would bolt up to the factory four barrel manifold anyway.

You can bolt that carb up no problem, I really wish I took pictures of my mine while I did it. You can get an adapter from Autozone or Orileys for 20 bucks, it lets you bolt on any squarebore after market carb to your spread bore manifold. I also had to buy a 10 dollar throttle cable adapter and throttle post.