Carburetor/drivability issues.

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1971 Mach 1, Grabber Blue w/Argent stripes. Original 2V 351C Auto, Tilt, rear defog, Black Comfortweave Interior. Under restoration. Original colors, 4V 351C, 4-Speed, Spoilers, Magnums, Ram Air. All Ford parts.
I need some help again.

The Setup: 71 351c 4v quench heads, mild cam, Holley 670 Ultra carb, 1/4 inch spacer gasket, original throttle cable, 4-speed.

The Problem: The car does not like to return to idle when driving.  Likes to hang at 1300 to 1500 at stop lights and between gears. When revving it tends to return to idle slow.  When warm and try to shut the car off it will knock and sputter then spew vapor out of the carb.  I often have to kill it with a clutch dump when it starts knocking.

Advice needed:  Should I start with carb return springs.  All I have is the original Ford throttle cable.  Are they different for 2v, 4v, auto or manual?  Need some help here as this makes it not friendly to drive and embarrassing to turn off in front of others.

kcmash

 
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I need some help again.

The Setup: 71 351c 4v quench heads, mild cam, Holley 670 Ultra carb, 1/4 inch spacer gasket, original throttle cable, 4-speed.

The Problem: The car does not like to return to idle when driving.  Likes to hang at 1300 to 1500 at stop lights and between gears. When revving it tends to return to idle slow.  When warm and try to shut the car off it will knock and sputter then spew vapor out of the carb.  I often have to kill it with a clutch dump when it starts knocking.

Advice needed:  Should I start with carb return springs.  All I have is the original Ford throttle cable.  Are they different for 2v, 4v, auto or manual?  Need some help here as this makes it not friendly to drive and embarrassing to turn off in front of others.

kcmash
 Kc, didn't we talk about this before? You have pretty much the same set-up as mine, except I have a 1" spacer that I custom made with a taper bore on all 4 bores because I found that the plates could interfere with the spacer and not close properly. First, I would double spring the return. I think I have a pic, if not I'll take one if needed. If that doesn't sort out the throttle return, perhaps there is a bent throttle shaft or other area it is catching. Look for the obvious first. As for knock and splutter on shutdown, that suggest timing is off or I think it could be a cam issue. That is not an area I have a lot of knowledge, so perhaps someone else can offer more help. Anyway start with the carb. In the pics, you can't see where the spring is hooked at the back end unfortunately. If you need more info, holla.

IMG_1729.1.JPG

IMG_1731.1.JPG

 
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1971 Mach 1, Grabber Blue w/Argent stripes. Original 2V 351C Auto, Tilt, rear defog, Black Comfortweave Interior. Under restoration. Original colors, 4V 351C, 4-Speed, Spoilers, Magnums, Ram Air. All Ford parts.
Stanglover,

I may have posted on this before, I cannot recall.  So thanks for reminding me.

Since last time I worked this problem I added the 1/4 inch spacer gasket which is a single plane opening to avoid throttle plate drag and not interfere with the RAM Air interface height.  I have also broke out the timing light and made sure the timing is correct.  That part is holding well.

I am very unimpressed with Holley's location for the fast idle adjustment screw.  That is just a dumb idea.  I seem to have that OK, but it is tough to get it to catch the first cold start, then it seems to hang on way too long, but I obviously have more to correct here.

I was thinking of the solenoid route as mentioned above.  My Ford solenoid will not fit, and I am unsure of the correct bracket/solenoid for my Holley so far.

So I will look at an additional spring to start things off.  If someone has more for me to try I am open to advice.

KCMASH

 
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I agree with Stanglover, just that one small spring is not enough.

I don't believe that '71s had the anti-diesel solenoid, but some have the anti stall dashpot, which that single 50 year old spring won't be able to close. Which brings up another possibility, the cable may be frayed or dirty and hanging up inside the housing.

 
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Don has a good idea there on the cable itself.  Trying disconnecting it at the carburetor and see if the engine returns to idle ok.  If it does then you know it's in the cable.  If it till does it then it is on the carb end.   

 
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Stanglover,

I may have posted on this before, I cannot recall.  So thanks for reminding me.

Since last time I worked this problem I added the 1/4 inch spacer gasket which is a single plane opening to avoid throttle plate drag and not interfere with the RAM Air interface height.  I have also broke out the timing light and made sure the timing is correct.  That part is holding well.

I am very unimpressed with Holley's location for the fast idle adjustment screw.  That is just a dumb idea.  I seem to have that OK, but it is tough to get it to catch the first cold start, then it seems to hang on way too long, but I obviously have more to correct here.

I was thinking of the solenoid route as mentioned above.  My Ford solenoid will not fit, and I am unsure of the correct bracket/solenoid for my Holley so far.

So I will look at an additional spring to start things off.  If someone has more for me to try I am open to advice.

KCMASH
 Hi kcmash,

So, good to know it's not a spacer issue. One thing off the list. I very much agree that the fast idle screw is in a dumb place, impossible to adjust on the car. I set mine (finally) to about 1200-1300 rpm., hot idle to 750-800 (manual trans). You might try adjusting the black cap position if your choke isn't coming off as quick as you want. I set mine for summer running, so at this time of year, it's a bit of a problem. As Don suggested, the actual cable could be ready for replacement. I actually have a spare in the "parts box". Kilgon also has a great suggestion to disconnect the cable and check the carb itself.

Timing, what is it set at now? It took me some time to find the "sweet spot" and eliminate spark knock and run-on. Then again, I did a lot of learning to recurve the factory Autolite dizzy. A different distributor might be a whole other story. But, first things first. Carb.

Going back to the carb, I also had modifications done to it by drilling a 3/32" hole in each primary plate. Much has been written on this, so I'm not going over it again right now, but that has proved to be what MY engine needed.

Plugs; correct plugs are essential. Ford call for Autolite 24's in the M code, but I found the 25's, spec'd for the Boss 351, run better at 1 stage hotter.

As for the Autolite 4300, the one I have that came (in the trunk) with the car when I bought it, does have that solenoid, but unfortunately there is no tag on the carb, so I can't really identify it as actually being off my engine. I'll never use it, but I have it.

Anyway, take your time, one thing at time, one change at a time.

I added a new pic with the bracket I made to hold the springs, which are too short to reach the normal bracket location.

IMG_1733.1.JPG

 
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1971 Mach 1, Grabber Blue w/Argent stripes. Original 2V 351C Auto, Tilt, rear defog, Black Comfortweave Interior. Under restoration. Original colors, 4V 351C, 4-Speed, Spoilers, Magnums, Ram Air. All Ford parts.
Springs make no difference. 

Possible Vacuum Advance problem?

Kcmash



I did unplug the Ram Air vacuum lines and plug the ports.  I then did the same with the vacuuadvance.  It seemed to drive a lot better with that combination.  So I need to know what to do with the Vacuum Advance now.

Kcmash 

 
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Well, that's one thing off the list!  The throttle seems to snap back to fully closed with out hesitation now. Vacuum leaks next I guess and maybe check the manifold to heads for leaks. Damn frustrating I know. Good luck.

 

boilermaster

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KCmash,

Sorry, I have been gone for quite some time.

Just a little food for thought; before you had the primaries drilled , did you first try opening the secondary butterflys to achieve a proper idle ?

That seems to be the standard procedure, perhaps the primaries are now at full bind CLOSED because of the secondarys being opened from a previous setting ?

Boilermaster

 

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