Holley Carburetor vs pump gas issue?

[dirtydrc]

Just had a new 390FE (stock, just an RV cam) installed in my 1972 F100, also brand new Holley 4 barrel carb. Always use 93 octane pump gas. It ran absolutely perfect for 250 miles. Then, all of a sudden it wouldn't stay running when I started it in the morning. I figured it was the first cool morning since I had it (55 degree). But it never got much better after it warmed up. Stumbles on acceleration from low RPM (like an accelerator pump issue). Brought it back to the shop that did the install. They said I should be adding Stabil and Marvel Mystery Oil every time I fuel up, because today's pump gas harms the carburetor since they started adding ethanol to the gasoline. I call :bs:. You mean to tell me Holley is making carbs for the street that aren't compatible with today's pump gas? What's everyone's thoughts on the fuel issue, and what might be the problem with the carb. FYI, it has new fuel tank and lines all the way to the carb.

[71Fe2O3]

It seems unlikely to me that the fuel is damaging your carburetor, especially over that short time period. It can be a problem for some small engines-I have rebuilt and replaced carburetors on chainsaws due to fuel problems, but I don't think that automobile engines or fuel systems are that sensitive.

The issues as I understand them are that because water is soluble in ethanol, water can separate out from fuel that sits in a carburetor bowl for a long time and can cause corrosion-I have seen this in some lawn mower carburetor bowls. Stabilizers can help prevent this from happening. Furthermore, ethanol itself may affect gaskets and seals, especially if it sits in the carburetor for a long time-this is probably what does in chainsaws with their delicate diaphragms, but it shouldn't affect an automobile carburetor-sites like this one would be full of reports of damaged carburetors and poorly running engines if this were true.

Fuel stabilizer may be help keep the gas from deteriorating if your truck sits unused for long periods. In my experience, these old trucks are not very picky about fuel-my snowplow truck starts right up and runs fine after sitting for months with unstabilized fuel, and my other one burns old chainsaw gas without any problems.

Search the web, especially the "bob is the oil guy" website, and you will find that some people swear by Marvel Mystery Oil and some think it is snake oil. I won't wade into that discussion, but I doubt that it or any other fuel additive will turn a poorly-running engine into a peak performer or compensate for mechanical problems.

The compression ratio of your engine should determine the octane rating of the fuel you use. Stock FE engines have relatively low compression ratios and run fine on 87 octane fuel. Higher octane fuel does not contain more energy or better additives than lower octane fuel-it merely contains a slightly different mix of hydrocarbons that prevent the fuel/air mix from combusting prematurely in high-compression engines. Using fuel with a higher octane rating than your engine requires will not make the engine run any better, but it will make your money go away faster.

I can't speak to the carburetor issue, and I don't understand why a knowledgeable mechanic would recommend fuel additives as a solution to a poorly running engine-your truck should be able to run fine on 87 octane fuel straight from the pump. The problem may be as simple as an adjustment.

[dirtydrc]

Just got this response from a technician at Holley: "The higher ethanol content will be harder on the rubber components. We sell a accelerator pump diagram that''s meant for alcohol that the higher content wont break down. The biggest problem with the ethanol is that that if it sits it separates and the sugars in the fuel will gum up everything that''s why a fuel stabilizer is recommended."..... not sure why they don't put that pump diaphragm in to start with...

[71Fe2O3]

There shouldn't be sugars in your fuel. Ethanol is an alcohol, not a sugar. So, sugars in the fuel gumming up your carburetor sounds most unlikely. I would expect that, even if you put sugar in your fuel, it would affect the combustion chamber as it caramelized due to the heat, but not the carburetor. Even gasoline without ethanol would leave deposits in the carburetor if it sat for a long time and evaporated away, and ethanol fuel may make the problem worse because it can contain water, but it would take a while, and shouldn't damage a new carburetor after 250 miles. You should only need fuel stabilizer if your truck sits unused for months, but I and likely many others do this without stabilizer without problems.

In many, if not most states in the U.S., all gasoline sold for passenger vehicle use contains ethanol, generally around 10%.
Where I live, I have only seen ethanol-free fuel sold in small quantities in stores that sell outdoor power equipment, and the price per gallon makes it prohibitive to use in an automobile. Problems with ethanol in fuel are most apparent in small, two-stroke engines, especially chainsaws, likely due to rubber fuel lines and carburetor diaphragms. Like it or not, ethanol in gasoline is a reality for most people, and many millions of gallons of it power our vehicles every day.

Ethanol contains less energy per gram than does gasoline, so, in comparison to ethanol-free gasoline will give your engine a little less power, and fuel economy will decrease a little. Engine management systems in modern vehicles compensate for this automatically, and I suspect that carburetors could be modified to deliver a little more fuel.

Its effects on gasket materials are well known, so you would expect that manufacturers of carburetors and other automotive parts exposed to gasoline would make their products ethanol-resistant, and that ethanol-resistance would be built-in, not optional.

If your fuel pump is old, fuel sitting in it may degrade the rubber diaphragm and cause some trouble.

[fastEdsel]

Your carb has an internal vacuum leak, been there, done that. Send away to Holley and purchase one of their new "blue gasket" carb kits. I fought this issue on my Edsel 361 for a long time. It turned out to be two things, a leaky vacuum advance on the distributor and the center gasket on the Holley 600. The car now takes off like a fuel injected car and pushes 20.5 MPG at 70 MPH. I also run premium fuel. Marvel Mystery Oil is a must in any engine so happy to hear you have that in your arsenal. I will try to find a label for the carb kit and write back.

[fastEdsel]

OK here is what I have. Holley Technical Support, 1801 Russellville Road, Bowling Green KY, 42101. Phone 270-781-9741 FAX 270-781-9772 www.holley.com.

The carb on my Edsel coincides with their kit for Holley Carburetor Model 4150/4150C. The instruction sheet is 199R8378. The gasket that is your trouble, in my opinion, is the "throttle body gasket." They vacuum leak right in the center in any direction to make life miserable. My carb was fairly new so I didn't think that was the problem so I was looking elsewhere. It had me about as confused as a goat on astroturf so, same as you, start chasing fuel additives, timing, spark plugs, hell I even changed the starter! But I learned about this newer carb kit from my parts man son so I ordered it. Nothing was leaking on the carb but I carefully took it all apart, cleaned it setting all the parts on clean paper towel then put it back together with the new blue gaskets. NO regrets! I bench set the idle mixture screws to 3/4 turn out and without a word of lie, as soon as I touched the starter, it started. Usually after a carb overhaul it has to crank for at least 30 seconds or longer but this thing lit immediately. On a personal note I actually hate Holley carbs. They have made my motoring life so miserable that I had no choice but learn how to diagnose and fix these damn things because it was a time in my life when that was all I could afford. I came to believe that ALL Holley carbs were as useless as nipples on slab bacon but set up and taken care of, driving in hot dry conditions and not too much in the fall or winter they will get you by. I did overhaul another 600 on my Son's '92 Boxer Mustang c/w 347 Stroker 302. That car actually scares me as that carb really comes to life, and 24.5 MPG at 75 MPH. Good luck with your project, keep us informed.

[basketcase0302]

I would run a can of sea foam through a tank full of ethanol free fuel and see what it does.
And yes, ethanol eats rubber like a redneck eating pork loin.
Never / never / never run ethanol in out older trucks. I won't let it touch my mowers / weed eaters / chainsaws or anything that I own that is carbureted or has rubber seals and/or gaskets in it. The accelerator pump on your Holley is also a prime suspect as they are known culprits for causing issues.