The Stovebolt Site Forums The Shop Area Engine Shop Fuel problems?

Summers I drive my truck, but no long distances. In June I filled the tank, but I have been traveling in July, so it stood still for a month. It ran great in June. I came back at the end of July from the states, it started poorly, whereas COLD it has always started great. (It has not ever started well when warm, even the PO confirms that.)
I had bought a Pertronix pointless ignition, so I installed that, also in early August. Last week I drove it on a round trip of about 40 miles. It still starts poorly, cold or warm. Once started it idles fine. But when accelerating it kicks and balks. Once it is up to highway speed 50 mph it does just fine.
The modern plastic gas filter looks clean enough. The truck is an otherwise stock 53 3100. The spark advance looks to be working. I suppose I should suspect the accelerator pump, but the carb was rebuilt 4-5 years back and has been ok ever since. Would it dry out over one month in the summer? The coil was new about 5 years back, too.
My old MC would have problems after the first startup in the spring. I always parked it for the winter with a full tank, but in the spring that gas was not always so good. When the tank ran down to maybe a quarter, the bad gas would make the engine run just like the truck is doing now. It seemed like the worst of the gas would float at the top of the tank. The truck is maybe a quarter or less full now. But some of that gas might be remnants of the full tank that sat there all winter.
The bigger question is - if gas goes bad after a couple of months, than a lot of us ought to be having problems. I have heard that gas lasts longer in a tank that is full, but if we keep our tanks topped off then we never burn off the old gas. I don't put a lot of distance on my old truck, although I drive it pretty regularly in the summer. So the gas will be old. How do we best deal with the aging gas problems in vehicles that we don't drive such long distances?

I'm assuming you're running a stock 235 with a 1bbl carburetor. The similar problem that I've had with all my 235's was fuel pressure...that carb/motor combination likes about 4-5 lbs of fuel pressure...too much and you have the problems you describe.

Stock 216, 1bbl Rochester. Why would the fuel pressure suddenly change?
Karl

Hey organbuilder.A fuel stabilizer is a good product to use in in the off season,as unlead deteriates so quickly. I forsee a carb rebuild in your future. Also a tune up might not be a bad idea. If it has not had one recently. 1 barrel rodchester might be the problem? Can you get your hands on a carter w1 or yf. As my w1 carter cured alot of the starting and acceleration problems in my 216. Just a thought. thanks Floyd.4-6 pounds of fuel pressure to the carb, should be normal.

Organbuilder,

Do they make seasonal changes in your fuel in Sweden (most likely, yes)?

This might be clutching at straws but there is an article by Bob Adler in the most recent Vintage Truck magazine (Sept-Oct 2010) regarding the differences in volatility (vapor pressure) in gas formulations throughout the year (at different times and in different formulations in different geographic areas). Hard starting and poor running (and vapor lock at ambient temperatures - deadly, not only in fuel lines but also in fuel pumps and in carburetors) are some of the symptoms of using some formulations in the wrong season (symptoms that unfortunately could also be attributed to other factors). The author recommended not leaving full fuel-tanks in vehicles that will not be using that fuel in a 3-month period.

An extreme repercussion of wrong formulation for the season would be phase separation of alcohol and water from the gasoline, resulting in corrosion, diminished anti-knock properties, hard-starting, and poor combustion.

All of the above information might be meaningless in your situation; however, draining the gas and adding new gas is not a very difficult or expensive undertaking. Maybe even flush the fuel pump and empty the carburetor?

(As usual, Bob Adler has written an interesting and informative article in this issues' "Notes From The Corrosion Lab").

Personally, I'd be looking more at tuning - timing, carb, plugs, etc.

I don't buy into gas going bad in just a month or two as I've had cars on blocks for months with no gas problem. When I lived in Iowa (4 mi south of the MN border), my hot rods would sit for as long as 5 months with no problems at all during start up.

Just my .02, your mileage may vary.

Hi all, and thanks for the ideas. I am pretty overworked just now, and I haven't had much time to wrench. Tomorrow I head off on a longer working trip, so the fuel in the truck will get another month to fester.
I would guess that Floyd's ideas are not so far off, but the carb was rebuilt 5 years ago, and I should hope a carb rebuild would last longer than that. I am aware of the problems with the Rochester, and it has always had a little hiccup when accelerating, but lately it has been much better, no hesitation at all.
Yesterday I had a chance to pull the plugs, and they were well filled with carbon. Also the rotor seems a little worn. A tune-up is in the works. But not today. It still seems strange that it suddenly went from working great to working like horse-manure. And I still suspect that the fuel in the bottom of the tank has separated or otherwise gone bad. In any event, the solution will have to wait a few weeks.

Thanks for the help.

Karl

How much should the Pertronix uppgrade affect the timing?

Just read Wrenchbender's turbo diesel post. Could a restricted exhaust be causing my problems? Suppose something crawled up the tailpipe over the summer?

My experience is that although wear deteriorates the condition of things gradually, the performance yeilded deteriorates in more sudden jumps... The deterioration crosses a threshold of tolerance, and the result is a sudden noticable change in performance... Especially if multiple things cross their thresholds at the same time: carbonation on plugs/points/rotor, fuel filter contamination, vacuum, etc...

Keith

MacX is on the the money. Organbuilder, as you say a blind man knows when the sun is shining. Floyd.