Does 10% ethanol = hesitation

I have a 74 with the original carter yf, everything has been recently tuned, carb rebuilt, new fuel tank and lines.

It runs perfectly for the first 20 to 25 minutes, then develops some miss or hestitation on acceleration after that. Last time it happened, I checked the choke and it was wide open.

Someone mentioned to me that it has something to do with the ethanol mix. The orginal owners manual calls for 91 octane, but I haven't found that near my home, only 87, 89 and 93 are avialable close by and they all have ethanol mix according to the label on the pumps.

Could the fuel have anything to do with it or have I missed something?

 

It might but up to 10% is not that much. Run some Lucas fuel system cleaner or thier octane booster through next tank and se if makes a differance.
My YJ has gotten real picky on fuel the last year or so, our Ram and XJ have no issues. :?

 

IIRC The octane rating had changed since you jeep was produced. 87 or 89 should be fine, but if you are worried you can always run 93. Its safer to run higher than reccomended octane that it is to run lower.

I'm not sure ethanol would give you a hesistation, but it will dissolve up some of the old crud in the fuel system, and deterioriate older rubberl ines.
I'd start with checking your fuel filter, and maybe other parts of the fuel system like the carb bowl for garbage.

 

forgot about the fuel filter, if you have not swapped it out I would.

 

Thanks!

I've replaced everything including the gas tank, sending unit, all the rubber gas lines, fuel filter. I cleaned the steel gas lines out with compressed air. The carb bowl has been clean since i did all that.

New coil, points, plugs, wireset, condenser, cap, rotor, vacuum lines, air filter, pcv.

The fuel pump is the only thing left that I can think of.

 

Doubt the fuel pump would cause it.
Are any of the fuel lines close to the exhaust?
If so it may be tring to vapor lock.

 

maybe its a timing isue, or a vacuum issue.

Are all your Vacuum prots properly connected/plugged on your carb. And unplugged timed vacuum port could cause similar problems.

 

Think of it this way. Ethanol is now 10% of you gas tank. 15 gallion tank now has 1.5 gallions of something you jeep was not meant to burn. In my case it caused hesitation. I am not for ethanol. BUY NO E GAS. Ethanol is add at the fuel yard. You should have a choice.

 

Ethanol can most certainly cause a flat spot or a stumble. If your engine was borderline lean before, that 10% would push it right over the edge and make it fall flat. Best thing to do is to run most of it out and refill with normal fuel. If it still does it, we can look elsewhere.

 

But why would it wait 20-25 mins to start doing it? :?
That makes no sense.
Wonder if the choke is sticking a little? Then it be a rich issue not lean.
What color smoke if any when it stumbles?

 

An engine takes a long time to get at full temp (not what the coolant temp reads) but rather, the oil, block, etc, (about 25 minutes really). Could be that when it gets up to temp completely is when it pushes it over the edge. The choke is also a reasonable assumption. If it's electric and has a broken circuit...it would still open, but would take a long time to go all the way open from manifold heat alone. So maybe it takes that long for the choke to open and then gets a lean stumble?

 

I understood the 20 to 30 running normal to be only once. Right after he fueled it. Which would still have reg gas. Drive it or Drain it in to the lawn mower. Get it out of you jeep before it eats you fuel hoses. Before it gums up your carb.