225 Dart chugging past 70...

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Aaron65

Aaron65

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My Dart has been running great, so my wife and I hit the road and drove 150 miles yesterday, and on the way home, as soon as I past 70 mph, it started chugging and losing power. As soon as I slowed down to 65-70, it ran fine.

Later on, after it had cooled off, we took it out on the freeway again. Same deal. So today I messed with it. Here's what I did.

1. Check fuel pressure. ~ 6psi, even when I revved up the engine.
2. Changed fuel pump for a spare, just to rule out volume. No change.
3. Blew main line back to tank. Heard bubbling.
4. Changed my Mopar electronic distributor back to points. No change.
5. Threw on a Carter BBS I have rebuilt in the garage (I run a Holley 1945). No change.

Now, I'm down to thinking that the sock in the tank's plugged up or the coil's breaking down. I didn't try the coil because I got to the point where I was sick of looking at the thing. I don't think it's vapor lock, because it's never done that before, even on hot days, and it did it when it was not even hot.

Anything I'm missing (pun intended)? :)
 
The engine's original...runs perfectly up to 70.

I set the lash last summer at .012/.022 (a bit loose is better than tight).
 
What kind of ignition system are you running? Can you make the problem happen at a lower road speed by driving in 2nd gear?
 
I've been running a Mopar Orange Box, but swapped back to my points distributor today to rule that out. That's as far into electrical as I've gotten.

I have revved it up in first a bit and it seemed to be fine. I think I ran it up to 40 or so in second and it was OK there, too.
 
Revving while sitting still it will not use anywhere near the same amount of fuel as running to a given RPM under load, and the wind resistance at 70 mph put a moderately heavy load on the engine and requires a fair amount of fuel. Revving and seeing fuel pressure @ 6 psi is not replicating the situation that you had under load at 70+ mph.

So, if it acts like it is running out of gas, it probably is. Your symptoms point to that. Time to get into the tank, and also check the fuel line all the way. Someone here or on /6.org reported finding a bug stuck up in the fuel line at one time.... Since you changed the carb as well as not reporting any problems under hard acceleration, that tends to rule out the power valve.
 
That brings up another question...

Anyone know if there's a reproduction tank for a '65 Dart wagon? I had my Corvair's tank cleaned and sealed a few years back and for what it cost I could have just bought a new one.
 
That's a good deal. Unfortunately, the sender is something like 55 dollars. Anybody have a preference for a brand of sender, or are they all junk? :)
 
Mine is a normal parts store brand one and it hasn't failed me yet
 
I ran the car out of gas this spring. It feels exactly like it did when it started running out.
 
Oh, ok. Then scratch the muffler.
In that case, I would suspect a loss of fuel. Since you have done your due diligence, I would suspect a restriction in fuel delivery, or the pump is sucking air, or, you maxed out the mainjets.
Since delivery is easy to test, I would start there. And if you dump the fuel from the pump into a clear jug through a clear hose, you can check for air entrainment at the same time.
Alternatively, It might be possible to run it up to speed, and when it craps out,chop the throttle and pull over. Pop the top of the carb off and check the fuel level.Choose your test location carefully.
 
Yup, definitely a fuel supply problem. Running the car out of gas probably put a bunch of silt in the strainer at the bottom of the fuel pickup pipe.

If you're replacing the tank, the Spectra Premium brand you can get from RockAuto is fine. But perhaps the tank just needs cleaned out and a new strainer installed.

Sender: Chrysler P/N 4051 004
Strainer: GM P/N 5651 705 (NLA from Chrysler)
Gasket: Chrysler P/N 6031 475
Sender grounding clip: Chrysler P/N 2258 862
 
Get ready to laugh at my expense. It's time to remember to keep it simple...the plastic fuel filter before the carb was plugged. Granted, it had to reach that state somehow, and that somehow was likely running the tank dry because my gas gauge doesn't work. For now, however, it will exceed the legal speed limit with no bucking bronco impersonations. Thank you all for your help. There are no guarantees I won't have to drop the tank anyway, but it's working for now. :)
 
Glad it was an easy fix.

You'll have to drop the tank to clean it. The way I cleaned out gas tanks involved putting about 1-2 lbs of 1/2" to 3/4" diameter gravel (not smooth) and a pint of gas in the tank. Seal tank and shake like crazy turning tank around to expose interior surfaces to shaking gravel. Time tank and contents are shaken > 5 but < 10 minutes. Yields about 1-2 lbs of environmentally hazardous gravel and a gas tank that has a lot less rust in it. Not tested on tanks with LaBrea tar pit-like goo in the bottom.
 
White vinegar will clean a tank, be it will also flash rust fast.
I use it on motorcycle tanks.
 
my MAzda pickup did just what you explained, same bad plastic filter but mine was right in front of the tank, would idle all day but once you got on it, it would bog bad. Changed filter and bingo, until I got it on the smog check dyno and it wouid start to drop RPM's on the dyno wheels. Weak fuel pump! all fixed now. Do yourself a favor and change out the headpipe on that 6. The pipe after the manifold to the muffler necks down to about 1.5 inches at the nasty production line weld, get a muffler shop to replace it with a mandrel 2.25, ala Super six. itll really uncork that 6.
 
pishta said:
my MAzda pickup did just what you explained, same bad plastic filter but mine was right in front of the tank, would idle all day but once you got on it, it would bog bad. Changed filter and bingo, until I got it on the smog check dyno and it wouid start to drop RPM's on the dyno wheels. Weak fuel pump! all fixed now. Do yourself a favor and change out the headpipe on that 6. The pipe after the manifold to the muffler necks down to about 1.5 inches at the nasty production line weld, get a muffler shop to replace it with a mandrel 2.25, ala Super six. itll really uncork that 6.
Click to expand...

It already has a 2.25 system all the way back, and I didn't even ask for it! The muffler shop used 2.25 pipe.
 
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