Carburetor jetting for high elevation -Holley 4bbl

[92saturnsl2]

I own a 1985 Ford F-250 4x4 w/ 460 V8 and 4 speed trans. I rebuilt the Holley 4180C carburetor about a year and a half ago. I've put about 25k on the truck since that time.

Yesterday, I pulled the plugs and all look lean. Pretty grey/white with hardly any combustion deposits; very little carbon like I'm accustomed to seeing on a plug. I can post pics if anyone wants to see them.

Assuming the engine is lean, what should I do with jet size? Stock jet size for this carburetor is a Holley #62, which corresponds to a 0.061" orifice. To account for elevation here (around 6,000 feet above sea level), I went down three sizes as I was told one size for every 2,000 feet elevation. So I'm using #59 (0.058 orifice) at the moment.

Someone once told me that carbs were jetted quite lean from the factory in the 1980's due to tightening emissions regulations and that as emissions became more stringent, they did everything they could to keep carbs on the scene as long as possible (presumably to save money). So supposedly, many engines ran lean by design. Perhaps this is one of them..? Or could I have gone too lean by using a smaller jet to compensate for altitude?

Does anyone have experience sizing jets for Holley carbs? Is running lean even a bad thing? Is there any potential for adding power by richening the mixture? Any help, info, suggestions, etc. on the subject is welcome and greatly appreciated.

 

[Highline9]

get one of these http://www.summitracing.com/parts/inn-3795?seid=srese1&gclid=CPS5rKTA3cICFUto7AodPmYAMQ

 

[Chris142]

The performance carb would have #65 jets. I'd try #63's or 64's.

 

[Gokhan]

If engine is running OK, not hesitating, not pinging, and passing the emissions, don't bother.

My 1985 Corolla has a high-altitude compensation system, which bleeds more air into the carburetor above a certain elevation. It was kicking in prematurely at lower altitude than intended whenever I went to Las Vegas, which isn't considered high-altitude. It was a very annoying problem. The engine would run very poorly -- but only so in Vegas -- with a lot of hesitation at low throttle and even stall because of too lean mixture. One morning in the hotel parking lot, I removed the filters for the high-altitude compensation valve and tapped onto the bellows that sense the atmospheric pressure with a wrench. Guess what, the car ran fine in Vegas after that!

 

[The_Eric]

I agree with Chris- start with a 62-63 main. As for performance gains- I've found a lot of these 70's and 80's cars/trucks are pretty conservative on timing. I'd suggest bumping it up 2-4 degrees to start with. There will likely be no penalty as far as pinging/detonation goes, but a bump in power and fuel economy.

 

[spasm3]

Will this work for your application?

http://www.summitracing.com/parts/crn-99607-1/applications/year/1985/make/ford/model/f-250

I think if you have more timing advance,( quicker timing) but less total timing, you might get an nice improvement as The_Eric suggested.

 

[Vern_in_IL]

There is a propane enrichment setup that is to be used with this carb . with the air cleaner off it will get more air and has to be compensated for with the propane

 

[Ducked]

Originally Posted By: Vern_in_IL
There is a propane enrichment setup that is to be used with this carb . with the air cleaner off it will get more air and has to be compensated for with the propane


Seriously? You mean as OEM, from the manufacturer?

Come to think on't, why would anyone produce a setup to compensate for the removal of the air cleaner? The only people I know daft enough to permanently remove air cleaners are bikers, and not even that many of them.

I improvised a butane bleed as a choke substitute a while ago, and I'd guess it MIGHT be worth using something like that to get an idea of what the effect of richening the mixture would be,though maybe more trouble than just changing jets.

 

[Olas]

You shouldn't really touch the fuelling until you set the timing where you want it, if you don't have a strobe give it a few more degrees and go for a drive. Repeat until you hear pinging. Back it off just a hair and it's timed (assuming manifold vacuum, of course)

The spend somewhere between a couple hundred and a couple thousand here http://www.ebay.com/bhp/exhaust-gas-analyzer and play with the jetting till you get it how you like it.

NB plug colour is not an accurate indicator of stochiometry any longer since unleaded and ethanol produce different colours to what we would expect to see I the old days

 

[flanso]

If I recall from my days working at Carter Carburetor, a carb becomes 1% richer for each 1000 foot increase in altitude. So, in theory, your sea level calibrated carb became 6% richer at 6000 feet. Try reducing jet size by 6%. That 6% should be in the jet's annular area, 3.14r², where r equals the radius of the jet's orifice.

 

[punisher]

Agree with what Olas posted. Mainly, if it ain't broke.........don't fix it.
I have the same carb on an '84 Motorhome (460/C6). Those carbs are a balancing act as they tried for economy (lean), but the nitrous oxide emission went off the charts so the power valve really riches the fuel/air ratio even on moderate loads as compared to other carbs. 460s are just naturally prone to higher than normal nitrous oxide emissions, hence carb weren't leaned excessively, timing was retarded, and cam timing was wayyy retarded.

If everything else is to spec, timing etc, and it is running OK, call it a day. drive and concentrate on paying for gas. Just an opinion, I could be wrong.

Edited for worse than usual spelling.