Boy, does my son's slant run crappy!

-
'74 Sport

'74 Sport

Well-Known Member
Joined
Oct 23, 2004
Messages
1,482
Reaction score
70
Location
Troy, TX
Aaron came home from college over the weekend to leave his slanted '74 Dart Sport with me to diagnose and hopefully fix. He has been complaining for several weeks about how badly it has been running.

I got a good dose of it this morning on my way to work. It fired right up, idled fine through a short warm-up period, and had quick throttle response - so far, so good. I backed it out of the driveway, eased down the street to the stop sign, made the turn and drove four or five blocks to the next stop at a leisurely pace.

Then it started...
I slowed down to get over a rough RR crossing and for the next acceleration it began sputtering. I eased off the throttle for the length of the block to the stop sign, and it idled OK while stopped. I made my turn, and for the remainder of my 10-mile trip to work, it sputtered each time I pushed the throttle. The best way I can describe it is that it acts like a 4 HP Evinrude boat motor - it literally "sputters".

It is a "Super Six" with a Carter BBD 2-bbl and MOPAR electronic ignition. Just before Aaron's semester at A&M began, we had to have it worked on for carburetor problems. At that time, it would start but only run if you kept pressure on the throttle. Otherwise, it would bog down and die. It turned out that one of the brass tubes in a venturi had fallen out and wasn't siphoning fuel as it should - the carb was running too lean.

This time, it does not act the same way - it idles fine with no bogging. Are we looking at a carburetion issue, or could it be ignition? Or something else?

Any ideas are welcome,
Jerry
 
If you believe it to be running lean, check the fuel pressure and the filter. If you believe it is running too rich check the float. Moisture can affect old wires caps and rotors so check them, and be sure the distributor isn't loose and timing has gone out of adjustment. Other probs I have had in the past with poor drivability are EGR valves, leaking vacuum lines, bent distributor shafts, and timing chain issues. If it has been running bad for weeks it is it is going to be a basic issue with any luck. It may just need a tune up.
 
First grab the carb and try to wiggle it. It may be lifting with the throttle if its loose. Start it , let it run to warm and verify choke fully open. Cup your hands down over the air horn. Just an easy way to check for vacuum leaks.
If the engine dies ( smothers it ), cool. If the rpm picks up you have a mixture problem. Visualy inspect evey vacuum hose, pcv valve, egr valve.
Hurry back :)
 
The fact this happens when your starting up and just after coming to a halt tells me it's got something to to with the fuel level in the bowl. Gas is still sloshing around in there for quite a while after you stop. I would check the needle and seat,plus the float and it's level.
 
some good points have been made from vacume problems to carb problems...could be ignition problems or something....but I would start with a couple easy things.

to me it sounds like it could be a couple things.

since when first started it runs good and then gets worse.....that makes me think choke!....sounds like the choke is on at start and runs good and once warmed up,the choke should be off to let it keep running good....it does not sound like the choke is all the way closed because it would probably be stalling.

But it does sound like the choke is not opening all the way ,as said before...verify that your choke is working properly (that is where I would start).

I also would not rule out a fuel pump,there cheap and easy enough to replace if it came down to it.
I have had them give me similar problems before.

And I would check your fuel filter.....I have had this happen multiple times!

Start the car up and it runs great.....the longer it runs and the more fuel that the pump draws through the filter.....if you have a worn out paper filter or dirt inside or something it will eventually pull it to the fuel feed hole from fuel pressure and it will limit fuel flow and cause the problems you have.

if thats the case,there cheap and easy to replace and I would check this by disconnecting the fuel line right before the filter to relieve and pressure in the filter and then reconnect it....start the car back up and see if it runs good again,if so than you have a bad filter.

or if you don't mind the extra work,pop the filter off and wipe off the inlet and try blowing through it....if air does not flow out the other side freely and easily,your filter is plugged.

pretty basic stuff but worth mentioning none the less!
 
I had a similar problem with my 69 cuda slant six car. As it turned out the tank sock had gone bad and trash was filling up my filter shutting it down. I replaced both of them and drove on...... Make sure that there are no restrictions in the fuel lines and that the pump is good...
 
I had alot of issues with a lazy choke that would stick and cause poor running conditions.
Fixed it with a new choke assy.

A poor carb will give you alot of guff, also may want to put some new tune up parts on it if not already.
 
Hey Jerry, I am with Joe Gilmore. If you get the gas level in the tank less than 1/4 you can take off the pickup without spilling any gas. Check the sock, the pickup itself and get an eyeful of the inside of the tank with a flashlight (rubber coated one). If you got that peppery crap in the tank it will do strange things to your car. It starts to clog up the sock and the pump then the filter. Try to think outside the box here. If the car is running good on the start and after awhile it starts to run crappy its a fuel delivery issue. A great way to figure this out without taking anything apart is to start and just idle the car. Most likely it will have no symptoms while at idle. Let the car cool down even waiting an extra day if needed and do the same thing again only this time mash that gas alot on and off. If its a fuel delivery issue the car will sputter, bog, and die out after awhile. Starting the car right away will be hard and you most likely will have to pump the heck out of the gas pedal to get gas back to the carb (kind of like you ran out of gas). After the car starts it will seem fine until the next cycle like the first. Sounds kind of goofy but it will save you stalling out or bogging down in traffic. I think you will find problems in the carb but if there is any reddish brown crud in the bowl its from a rusty tank and it is screwing with all the stuff on the way to the carb. Might even be clogging up in the line like mine was. I replaced the tank, pickup, pump, line, and carb so I have no more issues. When I pulled the stuff the line had some restriction and the carb was crudded up some but it was the pump that was really bad. Look for that reddish brown crap in the filter. If its there you know what you gotta do bud. Good luck!!
Chas.
 
My 63 Valiant did this and ran good till it got warmed up then it just barley made it home, It was my coil as soon as it got hot it would brake down.
The very same thing happened to my truck 83 318 I changed the ecu and coil and it fixed the problem

Weird that the coil and ecu was fine till it got hot.
 
Check the 4" rubber fuel line at the gas tank. It connects the gas tank to the hard fuel line. Maybe cracked or dry rot and sucking air.
 
When it sputters,is there any smoke from the tailpipe?Is it overheating?When it sputters,does it backfire?(through the tailpipe or carb)Does the exaust smell really rich or anything like that?Me myself,I would check the ignition system first.Check the condition of your distributor cap,rotor,plug and plug wires.Also check the condition of the spark plugs.Check for the obvious first like loose wires to the distributor,cracked or leaking vacuum lines and hoses,loose parts,etc.Check your timing with the a timing light.Another thing I want to mention,I had this happen to one of my cars,ran fine until it got warm,then it started sputtering and backfiring.Turned out to be a bad Ignition Module so you may want to check your module.Also get the ignition coil checked also.Most places can test them but with some research online,you can test them out with a multimeter set to "ohms" and measure the resistance on the coils secondary and primary windings to check the resistance.If all is good with the ignition,check that your choke is open when the vehicle is warm and not stuck closed.Check your fuel pressure also and the float level inside the carb,it may also be getting too much fuel.Hope this all helps =)
 
Yes,I forgot to ask if it had an EGR valve.Sometimes when these get stuck open or closed,they can reak havoc because they recirculate exaust gas into the intake when open but they should not open at wide open throttle(when vacuum is at its lowest in a engine in good condition) or at idle.Good luck !
 
I'm going to do some additional troubleshooting and I'll let you guys know what's going on. I appreciate all the suggestions - gives me more things to double-check or confirm.

So far...

No EGR
No overheating
No backfiring
Not sure about unusual smell - I don't know what it normally smells like
New rotor and cap
Tried new ECU - had no effect (is grounded properly)
Choke closed when cool - open when hot
Carb is bolted down tight
All vacuum lines are intact

I'll be back.....
 
Try the spark plugs... that's all that was wrong with mine and it had the same symptoms as yours. 6 new ones and it runs great now!
Keep us posted.
 
Well, I guess the mechanic I took the car to for a quick look knew his stuff. He said it sounded like it was missing - and it was. I checked all of the plug wires with an inline ignition tester and the number 3 wire wasn't getting fire to the plug. I replaced the crimped-on tip inside the boot and it fixed the firing problem.

However, the Carter BBD on this slant six has another issue. One of the two brass tubes in the venturi cover had fallen out a few weeks ago, and a mechanic buddy tapped it back in as well as he could when he found the problem. Well, it fell out again. The engine will only continue running if you stay on the accelerator - it won't idle on its own. I've got another carb coming in a few days, so this should hopefully fix all the recently developed problems.

I'll let you know how it goes,
Jerry
 
The venturi bleed tubes dropping out is a common prblem with many brands of carbs. Peck the tube back down in its hole. Use keen center punch beside the tube to stake the tube in place. The center punch mark beside the tube distorts the potmetal casting and the roundness of that hole. Hope this makes sense. If you'll look closely at the casting you'll see thats how the factory did it.
 
Are you saying to center punch it before, or after, you tap the tube back in? Afterwards might distort the diameter (and the cross-sectional area) of the tube. Would it be enough to even matter? I don't know how sensitive these circuits are to change.
 
'74 Sport said:
Are you saying to center punch it before, or after, you tap the tube back in? Afterwards might distort the diameter (and the cross-sectional area) of the tube. Would it be enough to even matter? I don't know how sensitive these circuits are to change.
Click to expand...

Seat the tube down into the casting first. The stake doesn't really colapse the tube it just close enough to distort the roundness of the hole and make it bite the tube. Check the tube for straight and centered in the throttle bores. If you need to shift t tube a little , you can.
 
Man, what a difference it makes when all cylinders are firing and the carburetor is working as it should!

Fixed a plug wire, installed a rebuilt (not reman) carb, did a little quick tuning, and the test drive went great. I still want to set the valve lash, check the timing, replace the rubber fuel lines, tweak the idle settings, and replace the air filter.

What should I expect the vacuum reading to be? Right now, it stays at a steady 15 in. at 750 rpm idle.
 
Mine has 19in at 750 tapped from the #6 runner. Timing set at 11* BTDC. From what I've read, 17-19 is about normal depending on how the timing and carb mixture are set.
 
Frank, I'm going to set the valve lash, idle mix, and freshen up a few parts before I take another reading. I was also told to move the test point somewhere else other than the #6 intake runner. I've got a port on the carb I will use for the next test.

The good news is the Dartster is alive again!
 
The rebuilt replacement BBD I installed was running great - for about a week. It was running good at curb idle, at part throttle stop sign to stop sign, and at highway speed. It would sit and idle all day long if I wanted it to. All I needed to do to get it finely tweaked was to set the valve lash and a final idle mix adjustment. Until Friday...

After work, I cranked it up and let it warm a bit while I visited with a co-worker in the parking lot. I left the office, made several slow approaches to intersections, a couple of stops at some stop lights, cruised down the highway at 70 mph, took the off ramp, slowed down to make the turn onto a residential street - then it happened again, just like the old carb had been doing when all this started - it bogged and died.

I dropped into neutral and it cranked right up; back into drive and made it a few hundred feet and slowed to cross a RR track; it bogged and died as I rolled over the tracks. Cranked right back up; made it a few blocks farther to my street; made the turn and it die rounding the corner. It started again and I made it into my driveway and killed it.

It fires right up and runs as long as I keep a little pressure on the accelerator. As soon as I let the rpm drop, it bogs and dies. This is the very same symptoms as the old carb exhibited, so I suspected this one may have dropped a main idle tube like the other had done. I pulled to carb apart and found both tubes intact, so that is not the problem.

Now, I am completely stumped!

Here is one observation that may mean something or not...
When I pulled the top off the carb, there wasn't any leakage at the seal between the carb halves. I was expecting the bowl to be full of fuel and it would pour out. When the top came off, there was only a tiny bit of fuel in the bowl. The floats were sitting on the floor of the bowl. If the bowl is full when the engine is running and the fuel pump is doing as it should be, and the needle valve is functioning properly, and the float is set correctly, then where did the fuel go after the car sat overnight?
 
Jerry
If I read right you purchased a reman carb. This type of thing has happen more than once to me. These carbs just die. I went thru 6 of them once and finally gave up and went to a new 4 bbl. BTW SS Dan has NOS ones that I have bought and they have been great.( it was cheaper than a reman).

Did you ever change the fuel lines in the front and back at the tank?

It is possible that you leaked the fuel back or boiled it off over night. Check the temp of the carb after you stop. Or leave the hood up over night and check it then. Are you having to crank a lot to start the next morning?
Frank
 
You must log in or register to reply here.
-

Back
Top