Hello,

I got my truck back from a builder recently and am sorting stuff out.

The engine is a Ford Racing S347JR which is a Boss 302 block stroked out to 347 cu in with a pretty mild cam.

The carburetor is a Holley 0-80670 4150 670 CFM Street Avenger.

When I first drove it the engine stumbled badly when tipping in the throttle. So I did some reading and ordered a set of accelerator pump discharge nozzles. Holley recommends going up three sizes as a first cut so that is what I did (0.31 to 0.37). This helped a lot, but it was still far from great, it tipped in ok but seemed like it might now be a bit rich. I moved the Orange acclerator pump cam to screw position #1 (it came from the factory in position #2, which gives more fuel).

Now the engine actually runs pretty good. Not perfect but it is very driveable.

However, I am suffering a high idle speed. I backed off the idle adjust screw to the point that I removed it. I also disconnected the throttle linkage, in case some binding was preventing the throttle from closing completely. Even with that, when I started the engine it idles at around 1000 rpm if I would guess (I have a timing light and could measure it).

If I grab the throttle linkage with my hand I can turn it counter clockwise and get the idle speed down. So the throttle seems to not be completely closing.

I note that the two throttle springs are very weak. Could that be the issue? Are the external springs needed to completely close the throttle or is the spring on the throttle shaft all that is required?

Any input appreciated. Here's a pic of the work in progress:



Gustave

 

Seems to me that all the ford carburetors that I have dealt with have had an external spring somewhere along the linkage. Usually pulling from where the linkage hooks to the carburetor to a clip located toward the back of the intake manifold. I would think that it would have idled all the way down with the linkage disconnected though.

Paul

 

Sounds to me like it has a fast idle setting. Let it warm up, and whack the throttle, it should then return to the setting at which your idle screw is set at. If it does not check your choke/fast idle linkage.

 

From your description, it sounds like you do not have a return spring other than the one on the primary throttle shaft. If this is true, you have to have an additional throttle return spring to get the throttle to close all of the way.

 

I've never seen a holley carb without an external return spring..
I have one of those dual springs.. small one inside a bigger one.

 

I agree with you Sam I've never seen one without the dual return spring. That's what keeps it from sticking open at full throttle.

 

Just a wild stab, but have you tried changing the automatic choke setting? Does it act the same when fully warmed up?

 

Thanks folks for the input.

I did confirm today that the choke plate opens fully when the engine is warm.

It was idling a little lower today, for some reason.

I do have the dual external returns springs. What I am wondering is if those springs (and not just the spring on the throttle shaft) are required to get the throttle to close completely.

I ordered some like Sam showed and will try them. The ones that are on there now are very weak.




Gustave

 

mine pull from the back of the carb on the lower side of the linkage.

i am out of town all week, but can post pics next weekend if needed

Sam

 

I have a Holley carb on my 289. The return springs pull from the bottom of the throttle lever to the rear of the motor also.

 

One more thing that I have problems with this issue, is the secondary throttle plates
not being closed. This will have to be carefully examined. Either the small set screw
on the base or the linkage or the vacuum control I dont know, but I've had it happen
right out of the box. Or the choke fast speed idle hanging up most common. sam

 

I have seen this too. My prior carb had the secondary set screw set such that the secondarys didn't close all the way.

I never got it set right, and I knew I was buying a new carb anyhow

Sam