Vintage Mustang Forums banner

1 - 13 of 13 Posts

·
Registered
Joined
·
201 Posts
Discussion Starter #1
I'm having trouble tuning the idle in on the 302 I know the 750 is not too big 'cause it runs great off idle but the idle is sporratic and won't seem to keep the adjustment.
Adjusting the idle screws have no effect. Is the rpm set too high bypassing the idle circuit? (700 in gear, 1000 in park) I notice that Edelbrock warns of idle tuning problems with a "fairly radical camshaft". Is cam lift .291, valve lift .467, dur. 280, .050 dur. 224, and lobe center is 108 considered "fairly radical"?

I'm going to get a vaccuum gauge as well. Can anyone run through the procedure for tuning with a vaccuum gauge again for me and what I should be looking for on the gauge?

The first order of business will be to check for vaccuum leaks. Although I don't think it is a vaccuum leak as I believe it is running rich at idle since the plugs are black. Is there any cleaner way of checking for vaccuum leaks other that spraying carbcleaner around the carb base and intake listening for surges? I thought I remember someone using propane?

Thanks
 

·
Registered
Joined
·
1,293 Posts

·
Registered
Joined
·
910 Posts
I had the same problem, it was a combination of float level and too much fuel pressure. Edelbrocks don't like more than 6 psi. IIRC. It pushes fuel past the needle and seats and then fuel drips down the venturies. An adjustable pressure regulator and a summit pressure guage fixed mine.
Kevin
 

·
Registered
Joined
·
201 Posts
Discussion Starter #4
Yes I have read that section. I'm just trying to figure out why the idle screws have no effect. It doesn't seem to say much about that topic there. Perhaps if I am pulling less that 7" hg and the metering rods are in the up position then fuel would be coming past the metering rods nullifying the effects of the idle screw adjustment right......?
 

·
Registered
Joined
·
910 Posts
I don't think at idle the metering rods would have any effect. IIRC that is an entirely different circuit.
I would also check for vaccum leaks. What is the size of your cam?
 

·
Registered
Joined
·
201 Posts
Discussion Starter #6
What is the size of your cam?
It's listed above:
lift .291, valve lift .467, dur. 280, .050 dur. 224, and lobe center is 108
 

·
Registered
Joined
·
910 Posts
Do you have a pressure gauge? I will bet your pressure is too high. That's my guess.
 

·
Incorporated Sell Out
Joined
·
17,130 Posts
Doesn't idle, plugs are black...sounds like its overcarbed to me ;)

It also sounds like your timing is too far advanced, when the car is warmed up and you put it into gear does it lurch any?
 

·
Registered
Joined
·
201 Posts
Discussion Starter #9
Initial timing is set at about 14 degrees. Total advance is about 36-38 degrees. I'm not running the vaccuum advance.

The car does not lurch when put in gear.
 

·
Gone but never forgetten
Joined
·
25,239 Posts
I would not consider that cam radical enough to effect idle very much.

I guess it's too late now, but here's an interesting article on carbs that mstngjoe turned me on to. This article convinced me REAL quick against getting a 750 Edelbrock, as it didn't perform any better than their 600 cfm:
http://www.jason.fletcher.net/tech/carbs/carbs.htm

I would agree with KEVIN69MACH1. You've probably got too much fuel pressure.
 

·
Registered
Joined
·
201 Posts
Discussion Starter #11
Interesting article, but I did have a 600cfm Edelbrock on the car before and the "butt dyno" showed a drastic increase in performance with the 750 installed.

I guess I'll check the fuel pressure too.
 

·
Registered
Joined
·
201 Posts
Discussion Starter #13
Yes I realize this and I'd never try to make a torque or HP guess on "butt dyno" data. I was just making the claim that the 750 performed better, and was noticeably stronger than the 600 in my case.
 
1 - 13 of 13 Posts
Top