390 timing

[R.Smith]

I just put an edelbrock performer intake and holley 600cfm 4bbl on my 390. It's stuttering and stalling when I gag it at idle and at highway speed. The previous owner put what he called a "mild" cam in it and, after farting around with the timing, it looks like it runs best at around 20 degrees BTDC. I've checked all the vaccum lines and checked for carb leaks ect but, while it's running better, it still stutters when I gag it. Any suggestions?

Thanks
RS.

[DuckRyder]

Is the Holley new?

Whats the list number, or at least basic configuration (Side hung or center hung / vac or mechanical / double pumper or not / adjustable floats or not)

Any chance of narowing down "mild cam" one mans "mild" is another mans "unstreetable".

Checker the balancer agains true TDC?

And I assume you mean "GAS" not gag, most things don't respond well to gagging

[R.Smith]

It's a new carb. I think it's an 1850 model but I don't have the paper here so...don't hold me to that number. Vaccum operated, non adjustable float.

As for the cam, all I can say is the truck came from Cali so I assume it's street legal. It doesn't sound radical. All I know is that when I set the timing to 10-12 degrees BTDC it runs like the slang word for poop. When I say "gag" it, I mean stomp on the accelerator pedal.

[19674x4]

ide double check to make sure your dizzy is set right at TDC and the carb is set right. run it for a little bit and pull a plug and see what it looks like. if its black you are to rich, if its white your to lean, you want a milky brown color.

[DuckRyder]

That probably is an 1850, thats one of the most common ones, manual choke...

Assuming that the mixture is correctly set my first guess would be to change the secondary spring from black (no matter what Holley says, it will have a black sping) to something more appropriate like yellow or purple. Get the whole secondary spring kit and follow the instructions to change it. It is a pain in the rear end without the quick change kit, but once you get it right you'll never have to deal with it again.

[DuckRyder]

Oh one other thing, I'm not wanting to get in another big debate about it, but if it is a vac advance distributor, try moving the advance line from ported to manifold and vice versa and see if that helps or hurts.

All of this is after checking all of the usual suspects...

[fordman]

as already said i suppect 1 the correct dist insertation and bad timing chain a slipped balancer on the crank or the carb. but since it was just a swap thing i would look at insertation and carb problems before i considered anything else.

[rjewkes]

sounds like 20* btdc is about where vaccuum disapears(i may be mistaken) thus set to that point it loses the vaccuum leak. you may need to double check the gaskets on the intake. Those sometimes slip out slightly when you torque everything down. also i beleive the manifolds on a FE require distributor removal in rder to get the intake off.

And with a Ford you can be almost any degree off when the distributor get put in if not careful enough.

moving it to 20* BTDC your probably bringing it close to or slightly past true 0*.

What you might do before doing anything else is, verify the harmonic balancer has not slipped, then line the pointer up to the line/mark for TDC and see what is going on under the distributor cap. should be pointing at #1 plug wire position on the cap. speaking of wich, that to would maybe be the first thing to check is that all the plugs are connected to the correct wire.

having just two swapped wires will make it act up.

[BobbyFord]

Try this, assuming you have no vacuum leaks and firing order is correct. Disconnect vacuum line from distributor and plug it. Set initial timing at 15 degrees before TDC and let the centrifugal advance do it's thing. My '63 390 has been that way for 20 years because the vacuum came in too soon on the AFB that stuck on it. Just try it.

P.S. Don't even try this on a 360; not enough compression.

[montana_hiboy]

Where are you pulling vacuum from for your v/a, ported or manifold? if manifold you're pulling in all your vacuum advance at idle creating a flat spot off idle, a switch to ported will help that off idle stutter.

[slamons]

I had the same problem, same engine, edelbrock and new holley carb....After reseting float, adgesting power valve, and a lot of other stuff, I still had timing of a little over 20 Degrees. I messed with everything, Finally gave up, Runs good at 20 degrees, good vac, fairly good response.....I tried everything that fordman suggested also.....We must have an oddball.....

[R.Smith]

Thanks for all the input. The engine is running fairly well after farting around with the distributor some. It still backfires thru the carb occasionally when I accelerate too quickly. The plugs are a white gray with a hint of brown which could mean I'm running right on the edge of lean. Maybe the carb isn't keeping up with the modified cam as far as fuel mixture is concerned?

[mkpj1]

Accelerator pump. A failure is exactly what you describe.

Or....a valve is too tight, worn cam lobe. Intake valve is open at some point. Put another carb on and see what you get.

Here's a rebuild article thats pretty good.

http://www.hotrod.com/techarticles/600- ... index.html