Discuss 1966 289 sputtering at 55-60mph after 13 miles on AllFordMustangs.com, the place for Mustang enthusiasts.
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Hey guys/gals. This is my first post and first project car (although im not completely mechanically deficient). I have a 1966 289 that is pretty much original. I bought it a few months ago and want to learn how everything works along the way so I dont mind replacing things as I go... needed or not.
The problem: It starts up perfect and Idles clean and flawlessly. Shifts smooth and drives beautifully round trip at speeds lower than 50mph (perfect for cruising) but when I take it on the back roads (my test strip) and run it 55-60mph for 13 miles or so, this happens to be a constant incline and i make sure to keep it between the 55-60mph speed and it sputters, sometimes it dies, and wont hold the higher speed. I let off the gas and if it doesn’t die, it will pick back up and will run smooth at the lower speeds as usual, but will sputter if I remain on the throttle.....
Upgrades: The previous owner had the carb rebuilt a couple years ago after running a long standing tank of gas through it.... Other than that he had done nothing mechanically. I have replaced the plugs (they were badly fouled), cables, and coil (I was thinking the problem might have been electrical??) and I was comfortable doing these things.
My next step is the fuel filter and anything else you guys recommend. I am getting it tuned up in a week also Thanks In advance for the help!!!
Sounds to me that the engine is running short on available fuel in relation to the throttle opening. This could be caused by a clogged fuel filter, an extremely low and incorrect float level setting in the carb, a fuel pump with insufficient output, a partially clogged or restricted fuel line (An internally collapsed fuel hose, a dented or kinked steel fuel line or hose) and a clogged fuel inlet sock that is on the fuel level sender assembly in the tank.
I've found that a very fine granular form of rust will develop inside of an old fuel tank that has been sitting. This form of rust is like a powder and will suspend itself in the fuel. This rust will gather and clog the fuel line inlet filter, (Sock), until there is enough built up to cause fuel starvation. The finer rust will pass through the sock and start clogging the filter, further restricting flow.
The more time that the car is running, the worse the clog can get, as the fine granules accumulate. Sometimes the granules will stick to the filtering surface and sometimes they will fall off when the engine is shut down, only to reattach the next time the engine is run. This can cause an intermittant supply of fuel and a reoccuring engine performance problem. This may be why it takes a little time before the engine starts to act up.
Sometimes you can remove the tank and try to flush out most of the rust with mineral spirits, but usually the only real remedy is to replace the tank. I've been through the rust in the tank issue where I was continually replacing filters. I'd remove the filter and give the inlet end a couple of taps on the work bench only to find a small pile of mud like rust coming out. This left me wondering when this was going to stop. After all, for the price of about 10 filters, I could buy a new tank. If you were to figure in the cost for labor, it would be even fewer filters.
Thanks for the responce, and I think you are exaclty correct. I pulled the fuel filer/pump and replaced them with new ones. The new in line filter has a glass housing and as soon as I started it up you could see the rust from the tank clogging the filter and starving the engine..... So I pulled the tank and got a replacement but couldent believe the rust that was built up on the fuel sending unit when I popped it out!! I will post a few pictures when I get a chance.
I will flush the line from the tank but is there any chance that it is rusted as well? Should I just replace it while im working on it?
That's the worst that I've seen a sender in my 40 years of turning wrenches. If the rust is that bad on there, the rest of the fuel system must be in about the same condition.
The only real way to remedy this is to replace the tank, sender and lines. Prebent lines are readily available. The parts including the tank don't cost that much. A new tank with a drain plug, (Highly Recommended) can be had for a little over $100.
Get the best quality sender that you can. Original equipment, if you can find it, is best, but I recommend that whichever sender you buy have the larger 3/8" fuel line inlet. The prebent fuel lines need to be 3/8" also since you're running a V8 and especially if you have performance plans for it. The 66 Shelbys with their HIPO 289s used 3/8". You'll get better fuel delivery and they cost about the same as the smaller 5/16" lines. The smaller lines are fine for a six cylinder, but in my opinion, marginal for a V8.
The regular steel fuel line has an outer zinc plating, but no plating on the inside. The line can look good on the outside, because of the zinc, but can be almost rusted through inside. There's no easy way of knowing until rust starts showing up in the filter or the line starts leaking. I'd say that a change out would be due after 46 years. The steel brake lines are plated the same way and will rust on the inside, too. Something else to consider.
Today's gasoline contains alcohol. Alcohol attracts moisture and so does brake fluid, for that matter. The moisture is eventually going to start the rust process all over again on the new lines. The remedy is to get everything made in stainless. It's all available, even the sender and the fuel tank. If you can afford it.