Loss of Top End power

[AndrewM]

Hey all, new to the group and new proud owner of a 71 C20 350 V8. I have been driving without problems for around a week now but just ran into some problems. I filled my car up with regular unleaded (E10 I'm assuming) and when I went to drive it started losing power in 3rd (top gear) when I would get above 35 mph. I limped home but noticed it wouldn't like me to try to get above 35 after that.

I've noticed the oil pressure runs fairly high, and upon inspection, the PCV tube is cracked but still has suction. I replaced the oil and filter yesterday with 10w30. I haven't done anything other than that.

I'm a beginner at all of this so any help is greatly appreciated. Thanks!

[Steeveedee]

Can you get engine speed in the lower gears, or does it run out of power that way, as well?

[4carbcorvair]

I would start with fuel/carb issue. Check your filter at the carb inlet first.

[AndrewM]

Originally Posted by Steeveedee

Can you get engine speed in the lower gears, or does it run out of power that way, as well?

It only seemed to run out of power when I was in 3rd and trying to go above 35. Lower gears responded well without any of the bucking/loss of power feel.

[bill3rail]

Check fuel filter, sounds like it is starving for gas.

Check fuel pressure also.

[Coley]

Use intelligent, methodical process of elimination.
Start with making sure your engine is in time and your distributor hasn't slipped.
In my opinion, set the timing to 10-12°....and do this before you touch or adjust the carb.
Always timing first.

Next up....front to back...check every single rubber hose connection to the carb and the intake manifold looking for vacuum leaks....including the ever important brake vacuum hose.
You can test hoses by carefully 'clamping' them with a set of pliers and waiting for 5-10 seconds to see if the engine runs better (or worse).
Check all (4) carb to manifold bolts and make sure they are not loose.
A vacuum problem is not uncommon at all with a 'sudden' or new problem in the way engines are running.....

Start with that and we will work through this.

Coley

[HIGHWAY BY THE SEA]

Those symptoms EXACTLY mimic the time that my 68 stepside had a clogged fuel filter (some neighborhood kid put red clay in the gas tank). Clean tank,fresh gas, new filter, and it ran perfectly!

[AndrewM]

Thank you all for your responses and feedback on this. Coley, I really appreciate the thorough advice on steps to take and will update everyone with what I find. I do know that my PCV tubing is split at the carb housing. Does anyone know if they make just the tubing, because the valve still seems to be working well (it rattles when I shake it).

lots of projects on this truck to get it where it needs to be. All help and insight is thoroughly appreciated!

[geezer#99]

Pcv hose is just a hose.
How could the bung (port) on the carb be split.
Take a pic for us.

[Coley]

To replace the pcv all you need to do is go into any auto parts store and order 24" worth of 3/8" rubber fuel line (equivalent)...then cut it to length and add a new pcv valve...you'll be good to go.
Again, make sure you check out the brake/booster vacuum line as well....if that leaks that is a real drain on the motor and I think that it too is a 3/8"ø rubber hose.

Coley

[AussieinNC]

If you are going to replace the booster hose, make sure its brake booster rated vac hose...

Lower quality hose may suck closed and you will lose brake assist...

This sounds lust like a clogged fuel filter sock on end of pickup tube in tank...most likely got some bad fuel...maybe even water....

Pull the fuel filter off off the fuel line...and drain it into a glass jar...water will settle on bottom of jar...

Stay safe...

[AndrewM]

Originally Posted by Coley

Use intelligent, methodical process of elimination.
Start with making sure your engine is in time and your distributor hasn't slipped.
In my opinion, set the timing to 10-12°....and do this before you touch or adjust the carb.
Always timing first.

Next up....front to back...check every single rubber hose connection to the carb and the intake manifold looking for vacuum leaks....including the ever important brake vacuum hose.
You can test hoses by carefully 'clamping' them with a set of pliers and waiting for 5-10 seconds to see if the engine runs better (or worse).
Check all (4) carb to manifold bolts and make sure they are not loose.
A vacuum problem is not uncommon at all with a 'sudden' or new problem in the way engines are running.....

Start with that and we will work through this.

Coley

Coley, thank you so much for this thorough checklist.
-I started with the timing and got that straightened out, but I feel like the distributor still has some play even after it was tightened.

-I think the fuel line is restricting the flow at the top bend, so I plan on replacing that, but already replaced the fuel filter and that seems to have helped tremendously. She runs over 55 now which is nice!

-I still need to replace the PCV valve on the Right Valve cover, as there is no rattle.

-I plan on replacing all of the hosing and performing the 30k maintenance, as I don't trust the previous person.

Thank you all for your help and input!