85 K5 4x4 - carb issues? replace carb?

[Dawson Clawson]

1985 K5 Silverado 4x4.
5.0L 305hp
Sparkplugs, wires, and Distributor cap/rotor we already changed.

The carb is an original quadrajet, from what I've been told. Haven't IDd myself (not sure how, exactly - I'm car-tarded). I've already taken it to the mechanic to unstick a power valve and change the EGR valve. They sprayed some solution in it and let it sit overnight. It runs much better at idle and cruising speed.

However - If I'm sitting at a full stop and depress the gas pedal to give it a teensy weensy bit of gas, the K5 hesitates like it isn't hearing my foot. Just really slightly. If I give it a bit more, it does better - no hesitation. It did this before I had it fixed, was fine for a week or so, then back to what it was before.

The mechanic told me that it's most likely the best I'll get without replacing the carb. Doubtful to effectively troubleshoot over the webs, so I guess I'd like to know what would be the best carb to install?

I've read here that Quadrajets were the best carbs for 4x4 Blazers. Would that be the case? I don't go off-roading yet. I don't race myself down city streets. I'm a pretty conservative driver since I'm still fixing issues as they arise.

Lastly, I'm more interested in a clean running truck than I am horsepower or gas mileage. I just want it to purr at rest and go when I tell it to. Not pussyfoot.

Thanks for your help!

 

[1-ton]

It sounds like the "well plugs" on your carb are leaking fuel. This is a common problem with old Quad carbs, and will lead to the problem you are having. A new Edelbrock "Performer" series carb should fix the problem, with 650 CFM and electric choke.

The Edelbrock carberators do not meter fuel as well as the old Quads did, so you will need a fuel pressure regulator to go with the new carb. These Edelbrock (unless you get the more expensive off-road series Performer) carbs are terrible off-road carbs due to there lack of fuel metering ability, but work great for every-day street use. I think Holly's are too tempermental to weather changes for daily use.

 

[paratrooper307]

You also might want to verify that your timing is correct, improper timing can cause hesitation off idle. If you're looking to replace the carb, try Mountain Man Fuel Systems. The send you a nice rebuilt quadrajet for a good price and you send back the old one. They do quality work, including sealing the well plugs.

 

[diesel4me]

HMM--I think an '85 had an electrified Q-jet with a computer??...if thats the case it will need someone with experience with those carbs to set it up right...I had a El-Camino with one,you had to use a dwell meter to adjust the pintles in it,and it had a TPS switch too,if it wasn't adjusted just right,it hesitated and idled crappy...I eventually ditched that carb and put a "old" Q-jet on it,along with an earlier HEI distibutor and left the computer wires to the carb dissconnected...then it ran nice!..

 

[paratrooper307]

It is computer controlled. I dropped mine right on and it worked fine with no adjustments necessary. If you do switch to an older style, if you have the 700R4 trans, you will have to make a provision for the trans lookup as it is tied to the CCC and the TPS.

 

[496truck]

The mixture control solenoid is a common failure point and will cause the hesitation you describe.

To make an easy check, top front drivers side of the carb there should be an electric connector, maybe blue or teal. Unplug it. The check engine light will come on, but you can drive it. Drive it, see if the hesitation is gone. If it's gone that's your problem.

Personally, I'd replace the intake and carb with an Edelbrock set up or old q-jet and eliminate the computer from the truck. You could fight with this carb for years trying to get it right. The problem will come back again and again.

Ultimate fix would be to upgrade the engine to TBI injection. As old as that TBI tech is, it's miles ahead of those old computer controlled carbs. Runs great and clean, gets better mileage and is easy to work on.

 

[Dawson Clawson]

The mixture control solenoid is a common failure point and will cause the hesitation you describe.

To make an easy check, top front drivers side of the carb there should be an electric connector, maybe blue or teal. Unplug it. The check engine light will come on, but you can drive it. Drive it, see if the hesitation is gone. If it's gone that's your problem.

Personally, I'd replace the intake and carb with an Edelbrock set up or old q-jet and eliminate the computer from the truck. You could fight with this carb for years trying to get it right. The problem will come back again and again.

Ultimate fix would be to upgrade the engine to TBI injection. As old as that TBI tech is, it's miles ahead of those old computer controlled carbs. Runs great and clean, gets better mileage and is easy to work on.

Ideally, I'd like it to be computer-minimal. I know there are some computer parts on these trucks and I will eventually do my best to phase them all out since I don't have to get emissions testing anymore (here in Texas, it cost me 15 bucks to get a safety inspection!).

I'll see about identifying this carb and the trans and reply back. It sounds like it would be better to trouble shoot if I know this info.

 

[82355]

Lastly, I'm more interested in a clean running truck than I am horsepower or gas mileage. I just want it to purr at rest and go when I tell it to. Not pussyfoot.

Ideally, I'd like it to be computer-minimal. I know there are some computer parts on these trucks and I will eventually do my best to phase them all out since I don't have to get emissions testing anymore (here in Texas, it cost me 15 bucks to get a safety inspection!).

I'll see about identifying this carb and the trans and reply back. It sounds like it would be better to trouble shoot if I know this info.

Those two posts seem slightly contradictory. I would suggest swapping in a TBI setup after reading your first post.

Martin

 

[paratrooper307]

If the carb is the right one, the mixture control solenoid plug will be gray (closer to tan really). If you have an automatic its going to be a 700R4 unless somebody has swapped it. The computer carb is bad for those that want to do a lot of tweaking or modifcations to the carb or mixture as it doesn't tolerate those so well. If you want a smooth running carb with decent mileage (for a heavy, square-bodied, carbureted truck) stick with the computer carb, you can get them rebuilt for a reasonable price or do it yourself. A lot of people don't understand or aren't familiar with the quadrajets and particularly the computer controlled ones and swap them out for inferior or less efficient carbs. TBI will give you better mileage than any carb.