1986 460 idle issues

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Aug 4, 2009 | 11:16 PM

xirxious

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1986 460 idle issues

Hello! I just picked up a 1986 F250 pretty cheap and found out why. We have to pass emissions on it and I ended up failing the idle smog test. 400 PPM min and I was alost 800 in the hydrocrabon. Just way rich on idle. The carb appears to be the stock 1850. Is there a guide for all the adjustments and specs? I've heard it can be a bad power valve or a leaky carb. Normally you can get an exclusion, but you ned a visual check. Someone removed the smog pump and air tubes to the ex manifolds. I was hoping I can tune up the idle and re check it. I asked a couple shops and they wanted at least $120 with no guarentee that it would pass. After next year, the emissions requirements drop off. I honestly wouldn't mind spending the couple hundred if I KNEW it would help. This 'maybe, kinda, dunno' attitude makes me think it could be a waste. I've seen rebuilds for sale ~$130. The EGR in the back appears to be capped and theres no plugs on the EX manifold, but nothing leaks out. I've been searching for a basic 1850 tune up guide, but I keep getting other search engines offering to find them

Aug 5, 2009 | 07:30 AM

ctubutis

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From: Denver Metro Area, CO

So, the emissions controls have been disabled and now it doesn't pass the e-test.
And this surprises you?
In Colorado, it is the seller's responsibility to ensure the thing will pass.

Regardless, it can likely be made to pass the sniff test by leaning out the carb and creating
an intentional vacuum leak. The best way I know to do it is to put an exhaust gas analyzer
on the tailpipe and fiddle with the carb/vacuum/timing until it's within spec.

Aug 5, 2009 | 11:46 AM

ArdWrknTrk

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From: EXTREME southwest CT

If it's a 4180 emissions carb like mine the adjustment is easy with the right tool.
First you must remove the tamperproof plugs on the front of the base flange.
As shown here:
http://www.flemworld.com/Hto/CMod.html

The correct tool looks like a 3/32" allen wrench mounted on the end of a spring so you can get in there while the carb is mounted on the engine.
I think I paid about $10 and you should be able to find one at any real autoparts store.

...In is lean. Go in 1/8th turn increments and let it settle down.

Aug 5, 2009 | 12:26 PM

xirxious

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Thanks, I'll try that. I wasn't even aware it needed emissions. I was told 16 years and older did here, but it varies by counties. I lived most my life in Michigan where they have no emission requirements. Are there relatively inexpensive ex-gas analyzers?

Aug 5, 2009 | 12:30 PM

xirxious

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It appears someone already tried to tamper with those screws. I saw something was cracked off in that location, but i didn't know it was the idle screws behind it.

Aug 5, 2009 | 01:14 PM

ArdWrknTrk

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From: EXTREME southwest CT

To answer your question about adjustments, there are few because of federal regulations.
The link I posted may help but if you want the jetting specs and such look on pgs. 15 & 16 of this pdf. (the columns read all the way across both pages of their printed catalog)
http://www.holley.com/data/TechServi...%20Listing.pdf

You will find a reference number imprinted on the forward facing drivers side of the choke horn. (4180 is similar)

Hope this is helpful and welcome to the FTE forums xirxious

Aug 20, 2009 | 05:24 PM

xirxious

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I tried a couple things and failed again. It was only the idle so I went low tech and just turned up the idle out of the 'bad range' 500 rpm higher and it goes from 850 ppm HC to 32 PPM. This was a different station, its possible the other one had a bad probe? The truck was sitting for awhile when I got it. I ran some high test through it as well, disconnected the EGR and all was well. Its the last time it will ever need testing as 25 yrs or older (every 2 years a test is needed) do not need emissions tests any more.