No power at WOT after 5 seconds

[Duro5341]

Hey guys....

I have a 86 K10, 350 Heavy duty emissions engine, TH400, 3.08 rear end

Here's the problem

I have lots of power at WOT for 5-7 seconds, then it falls on it's face, you let off the throttle and then give it alittle....nothing. Then after 15-20 seconds of coasting it's fine. I can feel the secondaries opening, and the accellerator pump squirts fuel when pumped. When just normally cruising around town it's fine, lots of bottom end torque, and idles, and starts up great. Just looses power at 75%+ throttle

It almost feels like the fuel pump can't keep up with the carb, and it's running out of fuel. The fuel pump looks a couple years old, but that means nothing....it could be a cheap POS out of the box, it was replaced by the previous owner. I haven't checked fuel pressure yet, but what should it be at with a bone stock(all original) 350..

Anyone had this problem, or have any insight...

Thanks
Duro

[Pyrotechnic]

Is it a Quadrajet ? Check the fuel filter built into the inlet on the carb body. Usually fuel pumps will leak fuel out of the vents if they go bad, but this isn't always the case.

[Duro5341]

Ya it's a stock 4 barral Q-jet, I replaced the fuel filter last October. And I have only put 7000kms since then

Duro

[72C203503ONTHETREE]

Check the lines for leaks, may be sucking air, or the pickup in the tank may be plugged with crap. Most likely its the pump though. Try smelling the dipstick, if theres a fuel smell the pump is bad. One of the one way valves in the pump may be sticking open enough that it cant keep up with the demand. Sounds exactly what a bad pump would do though.

[71swb4x4]

Just to clarify, you replaced the filter in the carb right? Sometimes people forget that one is in there, and only replace the in-line filter.

[Duro5341]

Well it really started acting up today, no power off idle....it would fall on it's face. And I had no time at the shop to look at it, we were booked solid..........So off to the diagnostic specialist our shop deals with. He found quite a few things wrong with it, that all added up.....

Here's the list
- Fuel pump screwed, as I thaught....only 2psi on guage
- Fuel filter plugged
- Mechanical Advance in dizzy siezed solid
- Vacume diapham broken for vac advance, so no advance at all on engine
- Carb was all gummed up, and missing 2 check valve balls....previous owner must have forgot them...as I have never taken it apart
-Blew main rear brake line on test drive, as he was pulling into the shop...thank god, would have been hell with my car trailer behind it

So the carb was removed, and soaked in carb cleaner, then cleaned theroughly, the vac advance unit was replaced, and the mechanical advance unsiezed, and oiled. New fuel pump, and filter..

It's like driving a brand new truck now, just gotta do the valve seals, and rebuild the rearend, and it's new again

Thanks
Duro

[Ivan D.]

a little offtopic, but how bad are yer valve seals? I have no umbrella seals (didn't know I need them besides the o-rings, and they didn't come in the kit either) and I go through about a quart every couple of hundred miles, it smokes fairly bad at start-up but once warmed up there ain't no trace of oil in the exhaust.

[Duro5341]

Mine will smoke quite a bit at start up, sometimes for 10 minutes. Alot at initial start, and alittle till warmed up. But once it reaches operating temp, and the thermostat has opened it's gone. My plugs are starting to foul, but they will be replaced aswell

Personally I would put both style seals on, thats what I am doing....just for piece of mind.

Duro

[Pyrotechnic]

Positive viton seals are the shizzle. They clamp down on the guide and will not slide around. You mainly need them on the intake valves but it doesn't hurt to put them on the exhausts too.

[Duro5341]

Originally Posted by Ivan D.

a little offtopic, but how bad are yer valve seals? I have no umbrella seals (didn't know I need them besides the o-rings, and they didn't come in the kit either) and I go through about a quart every couple of hundred miles, it smokes fairly bad at start-up but once warmed up there ain't no trace of oil in the exhaust.

A quart of oil in a few hundred miles seems quite excessive, sounds like you may have a severe leak or something...you can't possibly burn that much without noticing alot of blue smoke. I only burn/leak about 1 liter in 3000 miles, 1 oil change. I have a small oil leak, nothing major

Duro

[Ivan D.]

Duro, I'd notice if I had a massive leak, my oil pan is bright orange so every little spec of dirt shows right up. It definitely don't mix with the coolant either, so if level is dropping it's gotta be burning it out, right? I gotta check exactly how much it needs added now, it's been over 300 miles since last top-off so this weekend I'm gonna get a fairly accurate reading on the problem..

[Ivan D.]

Originally Posted by Pyrotechnic

Positive viton seals are the shizzle. They clamp down on the guide and will not slide around. You mainly need them on the intake valves but it doesn't hurt to put them on the exhausts too.

Yeah, that's what I'm gonna get too, is there a trick to do that without pulling the heads?

[Srubydo1986]

i think the air compressor to the spark plug works i think.

[Ivan D.]

Originally Posted by Srubydo1986

i think the air compressor to the spark plug works i think.

don't that require some fancy valve spring compressor too?

[xtreme80]

Originally Posted by Ivan D.

don't that require some fancy valve spring compressor too?

Yup, but you need the valve spring compressor even if you take the heads off.

Now if I could only get off my ass and do this to mine

[72C203503ONTHETREE]

Theres a cheap pry bar type thing you can use, remove the rockers and then use the rocker stud as a pivot. Summit racing has them and even a lot of parts stors carry them. Looks like a flat piece of metal in a boomerang shape with a forked end that goes over the spring.

[Duro5341]

Seriuosly spend the $50 and get a spring compressor....last thing you want is that spring flying across the room....and hitting something, or someone

It's sprung steel, and doesn't like to be dropped on concrete/anything hard. You may fracture it somewhere. And for the serious job that it does, you don't want it failing...

Better safe then sorry, I always say

Duro

[Ivan D.]

I hear y'all... will get a decent valve compressor on next paycheck.