New to me 390, 1968 or 69..

PO says rebuilt with 900 miles, RV cam..

It has a new edelbrock manifold and 4bbl carburetor with electric choke...

This engine runs great-most of the time..Strong..

Every couple times I drive it, when I start up, warm engine, it barely idles, stumbles badly, and if I put it in gear (auto) it will not idle and cant be driven, stalls...

After sitting idling, revving, muttering unpleasant words, for 5 or 7 minutes, it seems to smoothe out.. And can be driven..

Usually, it diesels badly when I shut it off the time before this happens..

Fuel is fresh, I tried Seabreeze just to see..

ANY ideas? Similar experiences? I wonder about the electric choke?

 

The cold run issue is possibly the choke coming off too soon. I've owned a bunch of FEs and they do tend to be a bit cold natured. Does the manifold have the exhaust heat passages? Are the secondaries shutting correctly? And does it "diesel" only after you've driven it and opened the secondaries?

 

I wish it was just the choke coming off too soon.. Its like that in warm weather, with a warm engine as well..

Im not sure about the secondaries.. Thats interesting.. Ill look into that for sure, the dieseling-after opening the secs? Humm... Might be.. Worth checking as well..

Exhaust heat passages?? Tell me more about this?





Does the manifold have the exhaust heat passages? Are the secondaries shutting correctly? And does it "diesel" only after you've driven it and opened the secondaries?

 

The stock intake manifolds have a passage where the exhaust is forced into a heat passage underneath the carburetor. The heat serves to better vaporize the fuel while the engine is cold, thus quicker warm up and better drivability when cold. I don't know if your aftermarket manifold has this heat riser feature or not. THis is probably not your problem, anyway. Check those secondaries.

 

Ahh. Thats what I thought you were talking about...

This happens when its hot out.. Not the problem...

 

What is your timing set at?

 

Ive never checked the timing.. I can, but could timing cause an intermittant issue like that?

 

This may sound stupid, but are you having float sticking issues? Other thing I'm thinking is that you have a vacuum leak that is showing it's ugly intermittently.
When it's running ugly, can you tell if it is rich or lean? (smells badly of gas or alot of black or blue smoke out the exhaust)

Timing is a key player. FEs are yery picky with timing. Mine is at 8* and doesn't like much more than that and runs like a sloth with much less. Depending on your cam (sayin RV doesn't say anything, there are 100s of different 'RV' cams out there) can give you more leeway on your initial timing as well as the rest of the engine's build. I'd say 8*-10* is a safe starting point.

 

Thanks guys... Gives me something to work with... Float sticking was my initial thought, so it on the list, as well as the secondaries, choke, timing, and vac..

 

I will take a stab at this one... I would say it is a fuel issue, since you say it happens when it is warm you probably are suffering from vapor lock. It seems to happen more and more with ethanol based gasolines. Check your fuel lines and make sure the spacer is between the carb and intake. Possibly your fuel pump may also be heading south.

Hope this helps,
Paul

 

Drove it yesterday again.. Started great, drove to the store, came out.. Wouldnt hardly idle.. Died once, had to run it for about 5 minutes and then it started to run just fine..

While it was messing up, there was no noticeable exhaust, smelled normal, water vapor.. Fuel line was not hot to the touch...

Below are pics of the carb.. Metal fuel line is very close to the manifold.. ?

Thought I would replace the pump, and try moving the line? Thoughts?

 

If anything your motor sounds lean, my 390 will run very rough, diesel badly and run hot when it's lean.

Check for vacuum leaks, intake gaskets, carb gaskets and brake booster can all be problem sources.

Does yours run hot?

Also, I have heard that the factory intake bolts are too long to get proper torque before they bottom out. That would cause a massive vacuum leak.

Let us know what you find!

Sam

 

Hmmm... part of your problem is that shiney thing on top your intake...

On a tangent here.... is your mechanical advance in your distributor working and moving freely? Should be able to grab it by the rotor, twist it, and it should spring back freely.

Is that carb spacer a solid chunk of aluminum or is it hollow underneath? Is the posrt on the back of the carb plugged as well as one in the spacer (if applicable).

Your fuel line is fine, I don't see an issue there at all.

 

How about a piece of debris or a small "glob" of water drifting around one of the 2 float bowls? The tops are quickly and easily removed from these carbs to check.

 

I know! I have the stock aircleaner and valve covers... the PO took them off...

Have been swamped at work, but Ill get out there today or tomorrow and give a full report...