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351 4V won't Idle anymore


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For those of you who don't know me, here is the back ground

351C -4V Quench heads, Ford Motorsport flat tappet cam, Holley 670 Ultra vacuum secondaries.  Less than 500 miles on engine and restoration.

About a month ago I had the car dialed in nicely.  Nice Idle and it was drive able enough for local commute, felt good on the highway and was fine at stops.  I was running BP ultimate gas in it.

It seems that the trigger event was when I had to put Phillips 66 premium(with ethanol) in it.  It has not been able to idle since.  I finally ran all of that gas out along with B12 Chemtool fuel system cleaner.  I pulled the idle mixture screws out and cleaned them along with blasting B12 through the idle holes.

Today I tried rolling the car out to re-adjust the idle mix screws with a vacuum gage, but I still could not get it to idle.  It seemed like every time I would get the idle down to about 1200, it would load up and die.  I took it for a drive and it did OK at speed. (Its a 4 speed.  I notice a stumble around the 2000-2300 RPM range when accelerating in second and third)  I am running the Quick Trip Red Handle Ethanol free premium now.

I am not a carburetor expert, so i need some help.

1)Do I need to completely tear the carb down and clean it up real good?

2) Is this condition indicative of a bad power valve?

3) The hesitation or stumbling at 2000-2300 has been evident for a little while.  Not sure what that could be.

Thanks for the help!

kcmash

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Since it seems it was a fuel change that triggered the no idle situation, it would probably be best to disassemble a clean out every passage hole. It could be a combination of things, sticky needle, clogged idle air bleeds, sticking or bad power valve. The very long shot is a bowel vent being blocked. You can test the power valve with a Mighty Vac and the small suction cup that comes with it. Or, if you like the taste of gas, you can just suck on the power valve and see if it shuts (not the best method). Long story made short, I recently mixed race fuel with pump gas and they did not like each other. The car started to run poorly with in a few miles. I disassembled the carb and the inside was covered with a dark grey substance. I found a needle that wasn't moving freely in the seat, and 3 of 4 high speed air bleeds were blocked completely. I used an ultra-sonic cleaner to get the carb clean, blew out the lines and replaced the tank. I hope you get it fixed easily. Chuck

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+1 on tearing it down. The ethanol may have started disintegrating the insides of the rubber hoses, if you haven't replaced them with fuel injection quality hoses, which are ethanol resistant. If you haven't already replaced them now would be a good time.

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“If you can't explain it simply, you don't understand it well enough.”

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OK I did a lot of work today and made a LOT of progress.

1) Pulled the carb to find a failed gasket underneath,  Proceeded to tear down the carb and clean it good anyway.

2) Put a new Holley gasket underneath and a new fuel filter in.

3) Started it up to backfiring and a lot of stumbling.

4) Re-set timing an d Idle.  My timing was about 10 degrees off.  Dialed that in and it really cleaned up a lot of the problems with idling, acceleration, power, everything.

5) Tried to dial the carb back in with a vacuum gage and had little response from it.  Vacuum is around 10 PSI.

So now it smells pretty rich.  I tried dialing it in a little more before dark, and could not get the rich smell out of the air.  Does that mean I have the carb jetted wrong?  It has 63s in the front metering block and 73s in the rear.  Does that sound correct?  What should I be at for a Cleveland?

I can't believe how much more drive able it is with the timing issue fixed.

kcmash

 

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Did you test the power valve? What is the Holley LIST number on the carb? Chuck

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List is 86670, it is a 4150 body.

No, I did not test the power valve. I did inspect it and it looked clean and moved easily, but I did not have the tools for a vacuum test.  Sounds like they move to fairly light vacuum level.

I was going to go for a drive this morning, but the rains came into town,

kcmash

 

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Make sure the floats are set correctly. Does engine idle speed and vacuum respond to changes in the mixture screws? 10 in/hg of vacuum seems very low unless you have an aggressive cam in the engine. What do the plugs look like? Chuck

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Engine is pretty insensitive to opening the metering jets.  If I close any one too far it starts to slow down and stall.

Now that the roads are dry I am going to go for another run.  I may need to set the curb idle a touch higher.  She sits closer to 600 than 800.  I prefer 8 to 9 hundred for curb idle.

kcmash

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Not sure if I can help or offer anything new that the more knowledgeable have already suggested, but you have pretty much the same motor as mine. You may have already read posts of mine about all the timing and carb issues I have been through and finally sorted out. Not all agree with the solutions that worked, but in a nut shell, here's what I have.  71 351C 4V , 4 speed. Cam is a Melling MTF 2 which is only slightly higher lift than stock. 17" Hg vacuum. Carb is the same 86670 (4150) with a silver secondary vacuum spring, 6.5 power valve. I think the jets are the 65 and 72 from factory. I increased the squirter from 31 to 35, which made a huge difference to stopping the bogging issue I had, The pump cam is as factory and pump is 30 ml. NOW here's what I had done by a tuning tech. He drilled a 3/32" hole in the front and center of each primary throttle plate, reset the transfer slots to "square", set the curb idle to 750-800 rpm, Floats are set so one can just see fuel at the threads of the plugs. Mixture screws are about 1 1/4 turns out (best vacuum). That's about it for the carb. I tried an 8.5 power valve according to the vacuum I have, but it was worse, went back to the 6.5. And yes, I did blow one when the motor backfired.

Distributor and timing; factory Motorcraft with a modified limit slot, i.e. 10L (.410") or equal to 20 degrees on the crank. cam springs are 1 heavy factory and 1 Mr.Gasket 925D (I think I have that number right!) Heavy spring is set just lose, no pretension, light spring is set with slight tension. The sparks are from a Pertronix Ignitor II and matching coil. Plugs are Autolite 25 set at .045 gap. Plug wires are 8mm spiral wound type. Initial timing I found best was 14 degrees for a total of 34 mechanical. The vacuum canister is adjustable and set for about 4 deg. on top. The retard side of the distributor has been totally removed along with the 3 port vacuum switch.

 On this engine, all the previous issues with rich gas smell, timing, idle and throttle response have been eliminated and now the car pulls like a train, and snaps like a whip.

TIP; IF your distributor has a 13L slot as well as the 15L that I think most were, you can rotate the shaft so the limit pin is in the 13L slot, then take a small piece of NYLON 1/8" tubing, warm it in hot water the stretch it over the post (pin). That will give you very close to the limit of a 10L slot. Quick way to lower your crank timing and increase the initial. Factory was 30 deg. crank, 6 deg. initial and that was for emissions, not performance.

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Edited by Stanglover

Geoff.

 I learn something new every day!

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  • 2 weeks later...

are you running vacuum advance?  Manifold or ported vacuum?  Do you have a choke on the carb, is it fully disengaging before you do your adjustments? Who is your favorite Playmate from 1981?

http://www.7173mustangs.com/gallery/1_01_07_15_8_53_18.png

 

"I love my Hookers!" and "Get some Strange" probably have a different connotation to non automotive enthusiasts!

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On 9/20/2020 at 4:59 PM, Tommyt said:

Stanglover I really enjoyed reading your post. Lot of good info there👍

Hmm, got you fooled eh!  I always say that I'm no expert at anything, but I do try to pass on what I have learned over the past 12 years of owning my current Mustang and from the guys on here that really do know what end is up. I also try to make reading at least somewhat interesting.

Thanks for the compliments  

Geoff.

 I learn something new every day!

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7 hours ago, Jeff73Mach1 said:

are you running vacuum advance?  Manifold or ported vacuum?  Do you have a choke on the carb, is it fully disengaging before you do your adjustments? Who is your favorite Playmate from 1981?

Ginger. No!  MaryAnne!  Ginger!  Maryanne!

Let me check your shorts!

http://midlifeharness.com

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Has to be Shannon Tweed

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73 conv. 460, D0VE large valve heads, Performer RPM manifold, Voodoo 227/233 cam, Holley 950 HP carb, C6 trans, 3.25 trak-loc.

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  • 2 months later...

I've been dealing with similar on my 300 page long "timing frustrations" thread. If you have a month of free time give it a read. LOL

I have the same thing. 11hg vacuum. Smells rich. etc. 4150 platform carb. 

This ethanol fuel is not good for sure. It ate up my fuel pump pretty quickly. Just replaced that. I didn't see you mention your fuel pressure. I need to do all the hoses as well.

If your timing was off and it was backfiring, you almost definitely blew a power valve. I idle at 1000 which drops to about 850 foot on the brake in drive. Hg drops to 9. So a 4.5 power valve it is. If it's blown, or way too high for your vacuum reading it will bleed fuel into the idle circuit.  

My base timing is up to 18 with no pinging, and this has helped also. I'm getting there, but it's taken a long time with a lot of good suggestions and help from the guys on here. 

Edited by Big Red Mach 1

Chris - BIG RED MACH 1

Born in '73 - Drive a '73

Former U.S. Army 63B10-H8

1st Infantry Division - The Big Red One

 

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