77 L48 stock. It is a weekend sometimes nice day driver. It has always started easily after sitting a while. Now it doesn't seem to start easily, takes several tries to get it to start, some gas pedal. Then when it does start it races rpm for a bit then dies. Try to "Save it" keep it going with some pedal but doesn't always work. Do that a few times then it starts and stays going. Later all day it starts easily once warm I assume.

Did it since it was in a shop to have a slow transmission fluid leak fixed. I thought they may have knocked off a vacuum line or something but everything looks like it is connected.

 

What is your skill level??? Point being...if I start describing "things" to you...will you know what to do and have the tools to do it???

DUB

 

Skill level is adequate. I don't have a lift in the garage but have every other tools needed.

 

Using your first though of a vacuum leak. Remove the hose from the fitting on the rear area of the intake and cap it off. This takes out all vacuum for you headlights,etc. See if that helps. If not. when it is running...and using a hose to your ear...listen for air sucking in at the PCV, and around the intake and at the base plate of the carb. Also see if you have a vacuum leak from the hole going to your power brake booster...if equipped.

On the passenger side of your transmission...you might have a tube that connects to the modulator valve at the transmission....this tube runs up the the same fitting that you unplugged the hose for your headlight vacuum. make sure it is connected and the hose(s) are good.

Once you get the engine hot/warm. It cranks and runs fine----right??? But really cold natured otherwise.


Is your choke working???? Or is it staying fully open. A fully open choke make a engine hard to crank...but not usually race.

May need more specific info what happens when you crank it and how long it takes to idle...and how well it idles when it is warm...and how it run when you drive it.

Does the engine have an EGR valve?

DUB
DUB

 

Finally got the time to check the problem out. Pulled the vac line to the brake booster first since I had problems with the pedal going low to the floor although not new. No change but very little vac felt at the line going to the brake booster.

Then noticed the choke plate was open and just hanging there dangling. The screw that connects the linkage to the choke plate backed out and the choke stayed open at all times. Fixed that by tightening the screw and securing the link and that fixed the problem of starting.

Back to the brake booster. The low brake pedal has been a problem long term. With foot on the brake and starting I can feel it pump up so it seems like some vac it getting there. It stops ok, not like trying to stop a freight train. Pedal is just low. I had it in to a shop and they changed the master cylinder and that did nothing. Pads are new. Is there supposed to be strong vac going in the booster. I know I should put a gauge on to quantify. Does it mean the booster is bad? I have read through some brake threads, DUB again very helpful. (Hijacking my own thread)

 

On your brake booster ? - Should there be strong vacuum to the booster? I don't have power brakes on my '72, so I checked the vacuum to the booster on my '98 Silverado. There is quite a bit of vacuum. You might try replacing the rubber hose that goes to the booster. They break down inside over time and that could be your problem. It could be partially plugged, and then some of that crap goes into the fitting on the carb base and plugs up your vacuum. Good luck.
Duane

 

I already changed the rubber hose a few weeks ago, no change. Little vac at the metal tube from the carb. Good idea about something clogging the tube, will remove that and see. The headlights work well so it must make vac.