boss_frog

I've posted this on various board here and there, hoping to get an answer, so I hope nobody minds posting here.

I've been having problems with my 78 Monte Carlo stalling at speeds over about 50 MPH. It seems once the car shifts from 2nd to 3rd, I have to be real easy on the gas or it stalls. I've replaced the fuel filter, which did turn out to be part of the problem and I had the fuel pump checked. No problem there.

On the thermostat houseing, there are 3 vacuum ports. A top one, middle one, and bottom one and they're kind of staggered. I just noticed the middle one has no hose on it. I can't find any loose hoses anywhere and I also can't find a corresponding port anywhere else. There IS vacuum on that port. I can feel it fairly strongly. I'm thinking that might be messing up the vacuum advance on the distributor. If anyone has a 305 of this vintage, or knowledge of them, would you possibly be able to trace where that middle vacuum line is supposed to go so I can replace it? I don't know if that's the whole problem but it certainly can't be helping, assuming it's supposed to have a hose on it.

Thanks a million. I've been fighting this issue ever since I got a damn mouse out of the carburetor last week (with help from a lot of starting fluid and the car sat for 3 months.

Spectre

Sounds like the engine isnt getting the gaz needed to maintain the higher speeds.

I bet the carburator isnt functioning properly ..

wm_sorg

Check the accelerator pump in the carb. Also check for vaccum leaks.

oneloudchevy

If it is a vaccum leak there is an easy way to check. Take an oxy acetalene torch and turn on the oxygen only (dont lite it). With the engine warm and idling take the torch and run it all along the manifold and all the vaccum lines. If the engine speeds up you have a vaccum leak there.

boss_frog

Wouldn't that port on the thermostat housing that's sucking air constitute a vac leak? I'll still try the torch test. As for the accellerator pump, how do I test it?

Something I forgot to mention... When I first changed the fuel filter, it ran pretty good for about 45 miles. Then it went back to its previous behavior of stalling over 45 mph or so. I checked the filter again and it's fine.

One other thing. If I granny accellerate (0-60 in about 30 seconds) I can get it up to 60 mph or so without it stalling, but if I punch it, it stalls again and forces me to slow down to 45 or so to keep it running.

One other thing I just got to thinking about... I had to answer nature's call when I was changing fuel filter, so my brother actually put it back in and he overtightened the nut and stripped some of the inlet threads. It still had enough that we could tighten it good enough to seal with help of some teflon tape. I wonder if he might have knocked shavings down inside? Crap.

But I do want to find out if that one port is supposed to be open or not.

wm_sorg

A few things. You can use carb cleaner to test for leaks in a similar fashion the the acetalene. If there is any hose sucking air are you described you need to reconnect it.

Did you check to make sure the fuel filter is facing the right direction?

Is definetely sounds like the engine is starving for fuel. The check the accelerator pump remove the air cleaner and look down the front venturi. When you actuate the throttle linkage you should see a steady stream of fuel sprayed into the venturi. Try this at varying rates. The flow should be consistant. If there is spitting, etc your pump is shot or the jets are clogged.

Also the float level may be incorrect. If there is too little fuel in the bowl the engine will starve for fuel.

boss_frog

As for the filter, yes it's facing the right direction. I doubt the car would hardly run at all if it weren't. I'm one of those do it carefully once rather twice fast kind of guys.

Also, it's not a hose sucking air, its a port where a hose would connect. However, I can't find a lose end anywhere. I can't find a corresponding port anywhere either as if a hose were completely missing. The port that's open is the middle one on the thermo-housing.

I'm beginning to think maybe some shavings from the inlet might be clogging a duct internally somewhere. But I want to rule out everything else before I go ripping it out.

boss_frog

Okay, please bear with me here.

I tried the oxy on the vac hoses... no apparent leaks. I also tried around the carburetor.

The accelerator pump seems fine. the fuel flow is steady and doesn't sputter.

As for the float bowl, how do I adjust the fuel level? It's a Rochester 2GC carb.

Hope I'm not wearing out my welcome with all the questions...

What about the mixture? Should I try backing out the mixture screws half a turn or so to see if it helps? Another thing someone suggested at work was to screw them all the way in, then back out to where they are now.

wm_sorg

Close all open vaccum ports.

The mixture screws are mostly for the idle. Out is rich in is lean. Make sure the carb to intak bolts are tight. Unfortunately, the float level can not be adjusted w/o taking the carb apart.

You may want to consider taking the carb apart to check float and for clogged jets.

boss_frog

I guess I can try that. If I screw it up, I'm beginning to think messed up carb anyway.

THEGENERAL

sounds like you might need a new carb or a carb rebuild there