The Stovebolt Site Forums The Parking Lot '60-'66 Trucks New here w/ a new 1966 c10

Just bought a 1966 c10 custom. I need your help cause im stuck. It has an i6 but the numbers say it’s a ‘75-79 block. Has a Rochester mono, manual choke, Accel HEI with a vacuum part at the base of the distributor. I bought a Carter yf to replace Rochester. They guy had JN welded a crack on the fuel inlet. The Carter has a place to screw in the vacuum tube coming from the base of the distributor. It also has a metal tube for vacuum near screw in vacuum port. I put a vacuum plug on that. There’s nothing else in the engine to put there and the Rochester didn’t have that. When I started the engine with the new carter yf it seemed like it was idlin way to high. My son backed into the garage thinking it was getting ready to explode. What can I do? What should I look for? The vacuum from the base of the distributor is tightened it the metal tube seems loose meaning I can spin it a hair between my fingers.
Thank you and many more questions to come!

High idle usually means a vacuum leak somewhere.

Post a few pics please. (Although you might need to get 5 or 6 posts up before the forum will allow you to post pics).
How did it run with the Rochester monojet?

First try backing out the idle speed screw. If that doesn't do it check to see if the throttle linkage is not letting it return all the way. Like the guys say we will need photos to get an idea & point out the parts we are referring to.
In my experience & opinion the Monojet is a better carb then the Carter YF.
George

So both carbs, the old Rochester and the new carter yf, have two holes for vacuum. One in the throat and one on the base. The Rochester had a gasjet that covered the base hole the new carter had a gasket that had an opening for the base hole. I thought maybe that was the problem. I got a gasket that covered that hole on the base and the rpms at idle are still way too high.
Would gladly post pics but I’m not allowed yet.

You can post photos anytime you want. No restrictions!

Here’s a pic from a few days ago sans carburetor.

Let me know what other pictures will help. Thanks.

I see an oil fill cap with a nipple going straight to manifold vacuum, but without a PCV!!!
That would cause a HUGE vacuum leak! That could be part of the problem.

Try disconnecting that hose at the oil fill nipple and plugging it up so the manifold can't can't suck air through that hose and see how it runs. Or disconnect it at the manifold fitting and cap the fitting nipple.
Usually there's a PCV in that rear rocker cover hole. Like in my picture.

That is the PCV. Adding another pic that has an oil cap on the front. I put a new grommet out the valve cover for the PCV because it wasn’t very tightly seated. I shook the silver PCV and it rattled around so I figured it was good. Im willing to trash that silver thing and go with a “regular” looking PCV. Also, do I need a breather of some kind? My oil cap doesn’t look like any I’ve seen when trying to find info. Thanks.

Looks like a crankcase breather cap to me, going to l flow way more than a pcv valve. Yes you do need a breather cap of some kind.

More pics. Will pull that pcv valve and attach a pic in a second

Here’s the pcv next to oil filler cap.

Could the mechanical fuel pump be bad/torn diaphragm and that cause excessive amount of fuel to be delivered?

That’s a design I’ve never seen. Sure fooled me. I’d still disconnect it and then cap off the fitting in the manifold to see how it acts. Easy and reassuring all in one shot.

A torn or bad fuel pump diaphragm would cause fuel starvation and you’d have trouble keeping it running, if it even ran at all.

Still need to get an oil cap/breather combo?

The breather goes in the front hole. The cap you have there now won’t allow the crankcase to breath.
Any style PCV that fits properly in the rear hole is fine. Just needs to seal well at the gasket and be the proper size for a 250ci.

Never seen that funky PCV valve before. AS stated, need someplace to let air into the crankcase.

The deeper I get the more craziness I find.

That only means that you are on right track. It seems like you are having so much fun with this build.

Installed new pcv. Installed new oil cap breather. Any get it to start now. It’s been sitting about a week. I sprayed some carb cleaner in the carb. It started for a exonerated, sputtered then died. It went from extreme RPMs to not starting.

Carb cleaner isn’t the best choice. You’ll get better results with engine starting spray, or dribble a few tablespoons of gas down the throat of the carb just prior to cranking the engine.

You may need to reset the idle screw if you messed with it. The throttle screw can be adjusted in or out once you get the engine running. A Rochester B carb is very simple to adjust.

I'll try that. Does the PCV valve have anything to do with starting? I replaced that chrome looking one in the picture for a standard looking one. But got to thinking, when I picked up my Breather Oil Cap from Napa they may have just used the 1966 i6 info for the PCV and it's actually a 1975-1979 motor. When I looked up PCV for both motors, they were very different looking. Not sure if they have a different spring tension or really how the internals of a PCV work or are different for different vehicles.

Starting fluid can do major damage, sometimes they fire so good the piston keeps going down.
dripping gas into carb can flame back at you & fuel container you are dripping from. Have seen both of these things happen. I have been using spray choke cleaner all my professional life, never seen a issue.

Disconnect the PCV hose at the manifold and cap off the fitting in the manifold for now. An incorrect PCV will not affect the ability of the engine to start and idle. You should buy a PCV that is correct for the year of your engine.

Took off the intake/exhaust. See pics. Any concernes?

The pics are from back to front (and upside down). The first intake (last pic) looks wet, the other two lol dry.

Spark plugs.

Is it running yet?

No. Couldn’t get it started after I put on oil/breather cap and new pcv. So decided to replace intake/exhaust gasket, plugs and wires. Just pluggin away.