Car Bucking

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moparwedden

moparwedden

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Ok Last year I had some problems with my 72 440 duster, going and coming back from a show 3 hours away, the car starting bucking and surging on our main HWY, speed was between 65-75 MPH. Even quit and would start after awhile and even right away. got it home.

replaced my Fuel Regulator with a Mallory with return line, changed the vent line. Thought this fixed it but had not had the car on the main HWY since then. Been to the track a few times and all was ok.
Made a trip Friday night but took a secondary HWY and speeds were only 50MPH, no problems going there, 50miles one way.

Coming home decided to take Main HWY Speeds were the same as the first time it started acting up, and after 20 minutes it started to act up again so got off main HWY to drive on secondary one, all was fine for 10 minutes or so then slowly got worst to the point of having it stall which I finally pulled off into a parking lot. Started right up, Idles fine, left again and got some Ice to put in cool can but did make a difference, barely made it home,

Ok what's could this be?
 
At this point, my initial thought is that's it's rpm related. 50mph - good, 70mph - not so good. It does sound heat related, and while i'll disregard the track use being how it's short lived, i have a hard time seeing how the extra rpm on the highway is generating enough heat to cause any difference? Unless of course something is right on the edge?

I'll step on the limb and ask, how old and what shape is the coil in? Are you using a paper carb gasket vs a good insulating type? With your new fuel system, what pressure are you running? And are the floats set to a low or high setting on the site holes, if a Holley? Are you running a vacuum advance distributor? How do the spark plugs look after a episode like this? I'm honestly not sure if you're going lean or rich at this point.

Just grabbing at straws for now, but I hope one of us can get you going smoothly for good. :thumbrig:
 
Personally, I'd start with checking filters, then go on through the fuel supply details.

One thing good to note would be if it has a good pump shot after it dies, or if the fuel levels are low after it dies. (holley for levels and Eddie for pump shot)
Might tell you something important.
 
I had this same thing happen years ago...found out my fuel filter was clogged....that is where I would start.
 
Possible issues:
- Fuel filter
- Clogged sock in tank due to crud/rust in tank
- Cracked fuel line to top of tank from main fuel line
- Cracked fuel line into fuel pump

Vapor lock does not strike me as so likley since this is running and not stopped, unless that would be a side effect of the fuel system losing some pressure. But it is possible.

Good diagnostic note above IMO from Trailbeast BTW.....
 
nm9stheham said:
Possible issues:
- Fuel filter
- Clogged sock in tank due to crud/rust in tank
- Cracked fuel line to top of tank from main fuel line
- Cracked fuel line into fuel pump

Vapor lock does not strike me as so likley since this is running and not stopped, unless that would be a side effect of the fuel system losing some pressure. But it is possible.

Good diagnostic note above IMO from Trailbeast BTW.....
Click to expand...

I have ran in to it when the tank couldn't get enough air at a high rate of fuel consumption. First it would start running poor and then die but as soon as it sat a few minutes it would run again. Popped the fuel cap off, it sucked in a whoosh of air and ran fine afterwards.
 
Oklacarcollecto said:
I have ran in to it when the tank couldn't get enough air at a high rate of fuel consumption. First it would start running poor and then die but as soon as it sat a few minutes it would run again. Popped the fuel cap off, it sucked in a whoosh of air and ran fine afterwards.
Click to expand...


This could be a very good possibility.

OP, the next time it does it stop and jump out and open the gas cap and see if you hear that "whoosh" of air Bill speaks of.
 
Vent is new and was checked last year when I put a new one on, no blockage.
Checked gas cap last night after it had quit, no gush at all.
Fuel pressure set at 6.5-7lbs.
I use two carb gaskets with a metal one in-between.
All fuel lines are good.
Last year when I had this problem the first thing I checked was fuel filter and all was good, no crude in it.

It always started after being at a higher MPH for a while then it does not matter what mph I'm at, it just keeps getting worst. I kept it going by feathering the throttle and jabbing it.
I'll check the fuel cites to check the level of fuel, its a 850DP Holley.

I have not checked the sock yet, I'll check that tonight.
Not running vacuum dizzy
I'll also check plugs

Thanks guys hope this new info will help.
 
Black soot usually is either a rich condition or a weak spark, possibly too cold a plug.
 
There is a mixed signal there.
The plugs are black but the fuel bowls are low?
I guess the black plugs could be from trying to limp it home, but now I may switch to ign box also.
Probably a good idea to check the reluctor gap as well. (.008 with a non magnetic guage)
 
The other one is blocked off, I'm leaning towards fuel boil over, My fuel pump is a manual one, so maybe its getting too hot with the fender wells, it does get hot under there so maybe a electric fuel pump is in order. I think the plugs is probably from trying to keep it running and dumping lots of fuel down it.
 
msaund69 said:
Sounds more like an ignition module crapping out...
Click to expand...

I'm with him, I've had both a pickup coil in my distributor flake out and an ignition coil fail in this way, had to heat up, then starting cutting out. Good luck!
 
I once had a customer car with a similar problem, accompanied by rising engine temp. I found that the wire stiffener inside the lower radhose was missing. I surmised that as the waterpump impeller rpm went up, that hose would collapse and then the water temp would rise. Then it wouldnt run right, likely due to fuel perkolation. As soon as the rpm came down the hose would relax and all was fine. Took me a while to figure it out.
 
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